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DSLR Astrophotography

Using A Canon 300mm Lens for Astrophotography

|Nebulae|9 Comments

If you watched my video about Comet 46P Wirtanen, you may have noticed that my imaging gear included a Canon EF 300mm F/4L USM Lens. This may have seemed a little odd to those that are used to seeing me use a telescope for astrophotography, but a camera lens like this can be a great way to capture deep sky images.

Over the years, a lot of people have asked me why they should invest in a new telescope when they already own a high-quality telephoto camera lens with a comparable focal length. After all, a prime lens like the Canon EF 300mm F/4L isn’t cheap, and its got some seriously impressive optics.

So, if you’ve already got a lens like this in your kit, you should definitely try using it for astrophotography before investing in a new telescope.

Canon 300mm F/4L Lens for Astrophotography

Make no mistake, a telescope designed for deep sky astrophotography has many advantages in terms of deep sky astrophotography. Specialized features such as a robust dual speed focuser, light baffles, and the ability to easily accommodate astronomy cameras and autoguiding systems to name a few.

But if you’ve been into photography for a while, there’s a good chance you’ll already own some camera lenses that are perfect for astrophotography. The secret is, to leverage the tracking abilities of an equatorial mount that allows you to capture long exposure images of the night sky without star trailing.

In this post, I’ll show you how I managed to capture an impressive portrait of the Orion Nebula using a 300mm camera lens from my backyard in the city. I’ll discuss the filter I recommend, the camera settings I use, and the share the process of capturing long exposure images on a tracking mount.

Canon 300mm Prime Lens

My Canon EF 300mm F/4L USM Lens

Canon 300mm F/4L (Non IS)

The camera lens I am using is a first generation Canon EF 300mm F/4L (Non-IS). This is an old L-series lens from Canon that does not include Image Stabilization, but does include the ring type USM autofocus motor. Features like IS and autofocus won’t work for astrophotography, so older prime (non-zoom) lenses like this are a great value in the used market.

It’s quite useful to have prime lenses at different focal lengths in your astrophotography kit. You’ll be able to capture a wide variety of targets from large open star clusters to emission and reflection nebulae like Orion. (See my review of the Rokinon 135mm F/2 for even wider deep sky images).

Video: Deep Sky Astrophotography with a 300mm Camera Lens

I purchased my 300mm F/4L used, and drove a fair distance to meet the seller. The lens was originally intended for bird photography, which I still enjoy today with a 1.4 extender attached for more reach. The native focal length of 300mm and widest aperture are a better configuration for astrophotography purposes. 

The 1.4 x Canon teleconverter introduces chromatic aberration, and I lose a full stop of light (F/5.6).  This is not usually an issue in my daytime photography images, but it’s out of the question when photographing stars.

Using the Canon 300mm F/4L lens on a crop-sensor DSLR (APS-C) camera like my Rebel T3i will effectively create a narrower field of view than a full-frame camera does. This creates an equivalent focal length of 480mm with the crop factor applied (1.6X), which is important to consider when framing up an astrophotography target.

Using a simple FOV (field of view) calculator, you can get a preview of the expected image scale of your target. As you can see, the Canon 300mm F/4L and Canon EOS 600D combo frame the Orion Nebula and Running Man nicely.

camera lens FOV

The Field of View using a 300mm Camera Lens and APS-C Sensor DSLR

Most of the astrophotography telescopes I recommend for beginners hover around the 400mm to 700mm focal length mark, so this camera lens is quite comparable. Also, the Canon EF 300mm F/4L Non IS contains two UD (Ultra low dispersion) lens elements similar to the construction of an apochromatic refractor.

The rather fast optics of this lens (F/4) is advantageous for night photography, as its widest aperture will allow plenty of signal (light) to be collected in each shot. For comparison, my Sky-Watcher Esprit 100 APO has an F-Ratio of F/5.5.

When it comes to acquiring astrophotography data for a healthy signal to noise ratio, a camera lens with a fast aperture is recommended. This is why camera lenses like the Rokinon F/2.8 and Canon F/1.8 are excellent choices for astrophotography.

Focusing the lens

Finding a precise focus using a camera lens is much more difficult than it is with a telescope. Rather than using a smooth dual-speed micro focuser, you have the challenging task of using the rather sensitive focusing ring on the lens (in manual mode of course).

It’s best to point the camera towards a bright object (not a star) to find the initial focus. The Moon, or a distant streetlight will do. Once you have it dialed in using the lenses widest aperture (F/4), you can then aim the lens at a bright star in the night sky using your cameras highest ISO setting. 

From here, it’s a matter of trial and error until you find the sweet spot. Once you’ve found it, be very careful not to bump it out of focus when slewing to your target. You can always fine tune the focusing ring on your deep sky target using short test exposures after.

The Camera: Canon EOS Rebel T3i 

This Rebel T3i (600D) camera has been “modified” for astrophotography, which isn’t nearly as complicated or technical as it sounds. I’ve basically removed an internal filter that blocks certain wavelengths of light from being recorded on the sensor (I didn’t modify this 600D myself, it was done by a professional).

The stock internal IR cut filter found in DSLR cameras like the Canon Rebel T3i creates “normal” looking daytime images, but can hold your astro images back. If you own a DSLR camera that you want to use for astrophotography, look into getting it modded. I waited almost 4 years before making this upgrade, and it significantly improved my astrophotography images.

This modification will better showcase the rich areas of hydrogen gas in the Orion Nebula. For certain deep sky targets (such as the California Nebula) a full-spectrum modified DSLR is essential for a respectable image.

Canon EOS Rebel T3i DSLR

My Full Spectrum Modified Canon EOS Rebel T3i 

The Orion Nebula isn’t one of them! A stock DSLR camera can capture exquisite images of this reflection/emission nebula with beginner-level equipment.

To photograph Messier 42, I’ll shoot a series of 1.5-minute exposures at ISO 400. The images will collect a healthy amount of signal (or light) on this nebula and the surrounding area. With the temperature hovering around zero on the night of acquisition, I benefited from a cool camera sensor that didn’t produce nearly as much noise as I experience in the summer.

Covering the sensor is an Optolong L-Pro filter. This broad spectrum filter is an excellent choice if you are looking to produce natural looking astrophotography images in the city. Light pollution is a big problem for many amateur astrophotographers, and filters like the L-Pro can make your life easier.

This filter clips-into the camera body, and fits neatly underneath the camera lens. Being able to use this filter with either a camera lens or telescope attached is a real bonus. I have also used this filter underneath the Rokinon 14mm F/2.8 lens for some wide angle shots of the night sky from home. 

The Camera Mount: iOptron SkyGuider Pro

The iOptron SkyGuider Pro is the perfect solution for those looking to get started in astrophotography with a DSLR camera and lens. It’s a highly portable, non-nonsense astrophotography mount that allows you to start tracking the movement of the night sky for long exposure imaging.

With the counterweight attached, it can handle heavier lenses like this 300mm F/4L, and even a small telescope like the William Optics Z61.

For this mount to be effective, it must be accurately polar aligned. In the northern hemisphere, we have the advantage of being able to use the north star, Polaris, to help us align with the polar axis of the Earth.

iOptron SkyGuider Pro

The iOptron SkyGuider Pro Camera Mount

To start tracking, its a simple as turning the SkyGuider on, with the mode set to 1X sidereal rate. After that, the camera mount slowly matches the apparent rotation of the night sky, and my long exposure images record pin-point stars without trailing.

The SkyGuider pro includes an illuminated reticle that you can use as a guide to align the mount. This make it really easy to get your alignment just right – which is critically important for astrophotography. Polar alignment and balance will make the biggest impact on your images.

The farther off you are in either area (balance and polar alignment), the shorter your exposure times will need to be. With a sound polar alignment and a careful balance, unguided exposures of 3 minutes or more are no problem on the iOptron SkyGuider Pro mount.

Locating Objects with the SkyGuider Pro

To locate and frame a deep sky target using this mount, it must be done manually (no GoTo functionality). For bright targets like the Orion Nebula, this is extremely easy, as I can line up the target using the viewfinder on my DSLR camera. For faint targets, or when using a narrowband filter, you may need to take a number of test exposures to get it framed just right.

I personally have the SGP mounted to a lightweight carbon fiber tripod. This is a highly portable configuration, but it’s likely a little too flimsy for folks that want a rock-solid platform. Consider using a more robust aluminium tripod with this mount.

The Target: Orion Nebula

The bright moon certainly isn’t helping me capture the faint dusty details surrounding Orion. Luckily, M42 is such a bright deep sky object that it can be enjoyed in less than perfect conditions. I’ve photographed this target so many times, and it never gets old.

It’s a spectacular target to test new equipment on, because you are bound to get a rather impressive image no matter which approach you take. The light pollution filter used (Optolong L-Pro) did a great job of reducing the unwanted artificial light present in my backyard, allowing the natural star colors to shine through.

To create my final image, I’ve stacked the individual exposures together using a free software called DeepSkyStackerThe resulting was then brought into into Adobe Photoshop for further processing. If you want to learn how I process my astrophotography images, have a look at some of the image processing tutorials I’ve shared in the past.

Orion Nebula 300mm Camera Lens

The Orion Nebula captured using a Canon EF 300mm F/4L Lens (Click for larger version)

Image Details

  • ISO Setting: 400
  • Exposure Length: 90-seconds
  • Number of Exposures: 117
  • Total Overall Exposure: 2 Hours, 49 Minutes
  • Support Files: 15 Darks, 15 Flats, 15 Bias
  • Image Processing: DeepSyStacker, Adobe Photoshop

The Bottom Line

As you can see in my image above, the stars are sharp and free of chromatic aberration (color fringing). This is a testament to the high quality optics of the 300mm F/4L lens, and an important factor to consider when choosing a camera lens for astrophotography.

Capturing sharp, accurately colored stars is the ultimate challenge for optical equipment, and the Canon EF 300mm F/4L passes with flying colors. The field is also extremely flat, another trait of only the best camera lenses. 

A prime telephoto camera lens like the Canon EF 300mm F/4L is a great way to capture deep sky astrophotography images, as long as you’ve got a way to track the night sky for each shot. The wide field of view is very forgiving, meaning autoguiding isn’t necessary for a successful long exposure image.

Whether you’re using a camera lens, telescope, or a pair of binoculars. I hope you’re able to get out and appreciate the impossibly beautiful history of our universe that shines above our heads this season.

Until next time, clear skies.

Helpful Resources:

Astrophotography Cameras – What’s the Best Choice for Beginners?

Examples using a Canon EF 300mm F/L Non IS for astro imaging (Cloudy Nights)

How to Make a Bahtinov Mask for Your Camera Lens (Deep Sky Watch)


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Astrophotography with a DSLR Camera and Small Telescope

|Telescopes|18 Comments

This week, I returned to my roots and enjoyed some deep sky astrophotography using a DSLR camera and small telescope. Don’t get me wrong, dedicated astronomy cameras and heavy duty mounts are great, but my latest imaging session in the backyard was a breath of fresh air.

In this post, I’ll share my early results with a new compact refractor telescope, the William Optics Zenithstar 73 APO.  I’ve managed to collect some exposure time on a number of deep sky objects using a crop-sensor (modified) DSLR.

My experiences with the Z73 have reminded me how much I enjoy deep sky imaging through a wide field refractor with a DSLR. This is where my astrophotography journey began, and it has not lost its appeal over time. Not one bit.


Returning to my roots…

The cooler nights of fall have allowed me to begin using my DSLR camera again for astrophotography. The overnight low has dropped to about 8-10 degrees C, a welcome relief from the scorching, humid nights of summer.

These conditions not only make the longer nights more pleasant outside, but they offer up better conditions for photography as well. There is less moisture in the air and the electronics in my DSLR are able to function properly without becoming dangerously hot.

The temperature of the sensor in my Canon EOS Rebel T3i has been hovering around 25 degrees C during my imaging sessions, which is still warm enough to produce a quite a bit of noise. A 5-minute exposure at ISO 1600 is a lot to ask of a camera designed for daytime photography.

But enough about my old DSLR for now, let’s get to the fun part. (My new telescope). To stay up to date with my latest endeavours in deep sky astrophotography, please subscribe to my email newsletter.

DSLR camera and telescope

The William Optics Zenithstar 73 APO

The William Optics Zenithstar 73 is a compact doublet APO refractor designed specifically for astrophotography. Owners of full frame DSLR cameras will appreciate its 45mm diameter illumination circle for edge-to-edge images.

After picking up the Z73 from the William Optics booth at NEAF, I am finally using this premium refractor for astrophotography at home in the backyard. A series of rained out camping trips and even a clouded-out star party put a lid on my summer plans to use this portable APO under dark skies.

This compact and lightweight apochromatic doublet refractor has a lot going for it, including an ultra-wide field of view and high-end Ohara FPL-53 objective lens construction. I was fortunate enough to receive a complete package that includes the dedicated Flat73 field flattener, 50mm Guide Scope and more.

When asked which color I prefer, I had to keep the tradition of white and gold alive to match the Z61 APO and FLT 132 refractors. This “big brother” to the Z61 uses a new mounting ring and guide ring design, that match the gold Vixen-style dovetail bar.

Z73 Guide Scope Rings

After taking the Zenithstar 73 out of the neatly packaged soft carry case, the first thing I did was separate the guide scope rings a notch to provide a more balanced hold of the 50mm guide scope. I removed the Rotolock (which is an added accessory from the standard package) to thread the dedicated field flattener in for astrophotography.

A great place to thread a 48mm filter (such as the Baader Moon and Skyglow filter pictured below), is on the Flat73. Then, you can attach the field flattener to the telescope with the filter inside.


I must say, I was spoiled with a totally complete package that included all accessories. These are additional items to consider when calculating the overall price of the package. The accessories for the Zenithstar 73 include:

Optional accessories:

  • Soft carry case
  • Flat73 1:1 Full frame flattener
  • 2” Rotolock with M63 threads
  • 50mm F/4 Rotolock Guiding scope
  • 48mm T mount for Nikon or Canon

What’s nice is, William Optics outlines everything you’ll need for a deep sky astrophotography system – and you can order it all together. You don’t need to go searching for field flatteners or guide scope rings that will fit your telescope. Astrophotography is the number one priority behind everything William Optics makes.

FPL-53 flourite glass

William Optics Zenithstar 73 APO Specs

Glass Type:FPL-53
Focal Length:430mm
Weight:5.5 Lbs
Retracted Length:310mm
Focuser:2.5" Rack and Pinion
Dew Shield:Integrated
Mount:Vixen-Style Dovetail


The Zenithstar 73 APO is available at Ontario Telescope


Deep Sky Images from a City Backyard

The timing of the full moon and ever-present glow of my urban sky meant narrowband filters were the obvious choice. Even with a color DSLR camera, astrophotography can be enjoyed a great deal more with a simple clip-in ha filter.

The primary DSLR I use for deep sky astrophotography is an old Canon EOS Rebel T3i that has had the full spectrum modification performed. To compare it with a dedicated astronomy camera or CCD, you could consider it to be an un-cooled one-shot-color camera.

DSLR Ha filter

An Astronomik 12nm ha filter was snapped into the body of my APS-C sensor Canon T3i for the following images. With the Flat73 field flattener in place, it should come as no surprise that the stars in my image were recorded as pinpoints top the very edges of the image.

Sadr Region in Cygnus (Butterfly Nebula)

The Butterfly Nebula (IC 1318) is a rich emission nebula region in the constellation Cygnus. It is part of a much larger complex of gas and dust residing in the Sadr region. The photo below shows off the wide field of view and crisp stars you can expect when using an entry-level DSLR with the Z73.

Butterfly Nebula in Ha

I captured roughly 2 hours worth of exposure time in Ha using my Canon T3i through the Z73. The images are free of star-trailing and elongated stars thanks to the accurate tracking of my Sky-Watcher HEQ Pro Synscan mount.

This mount is a twin to the Orion Sirius EQ-G GoTo, which I often recommend to beginners as a robust, astrophotography-worthy mount for a setup like the one shown on this post. With a sound polar alignment routine, this equatorial mount can consistently provide sharp images of 5-minutes or much more. (The longest I’ve shot was 10)

The iOptron CEM60 center-balanced mount I used for the past 12 months has been returned to its rightful owner after a generous extended loan from Ontario Telescope. Luckily, the 5.5-pound William Optics Zenithstar 73 is nowhere near the limits of the HEQ5’s payload capacity.

GoTo Telescope Mount

The Heart Nebula in Cassiopeia

Next up is a rather dynamic looking nebula in Cassiopeia known as the Heart Nebula. As you can see, this massive target fits within a single field of view using the Zenithstar 73 with a crop-sensor DSLR camera. The F/5.9 aperture of the Z73 provides a healthy balance between light gathering ability and sharpness.

Heart Nebula in Ha

Both the Butterfly Nebula and Heart nebula images were produced using 5-minute image exposures at ISO 1600. Astro Photography Tool was used to automate the image captures, with PHD2 guiding helping to accurately guide my HEQ5 mount during each sub.

Dithering between each image and stacking multiple light frames helped to improve the overall signal to noise ratio in the images. The individual light frames were very noisy, but using dark frames in the stacking process (DeepSkyStacker) can really help to correct this.

Why I love a DSLR Camera and Telescope Setup Like This

For the type of astrophotography I’m most interested in these days, it’s hard to beat the photography opportunities available at the 400-500mm focal length. At 430mm and F/5.9, the Zenithstar 73 fits the profile of the ultimate wide field APO for deep sky.

I’ve repeatedly mentioned how much I love to use APO refractor telescopes, and I believe that they offer a better user experience and more consistent astrophotography results than any other telescope type.

Sky Watcher HEQ GoTo Mount

Telescopes that offer a longer focal length (of 1000mm or more) are great for small DSO’s and galaxies, but deep sky objects that cover a large area of sky such as the Heart Nebula are impossible to photograph with a DSLR without creating a mosaic.

One of the advantages of having a wide field of view is the ability to capture multiple deep sky objects in a single shot. It allows you to get creative with the framing of your target next to a star cluster or some interesting nearby nebulosity.

The photo opportunities are endless, and I you may find a lifetime of ideas before feeling the need for a telescope with an increased focal length.

Image Processing Narrowband Images from a DSLR

Here is a look at the individual light frames using the Canon T3i through the Zenithstar 73. The images have a red cast because of the strong narrowband filter that was used (h-alpha). I have registered and stacked the images just as I would with a color image in DeepSkyStacker.

light frames

Reviewing my RAW images in Adobe Bridge


For the Heart Nebula, I’ve got about 5 hours of total integrated exposure time. This is two nights worth of shots that I’ve separated into their own tabs in DSS. I captured matching dark frames of the same temperature, and also bias and flat frames to help produce the highest quality stacked image possible.

Extracting the Red Channel from an RGB image

The trick after that is – to extract the red channel with the strongest signal in Photoshop. Have a look at the difference in the image quality of the red channel alone vs. the full RGB image with weak Green and Blue channels.

channels in Photoshop

Notice the difference in signal from the red channel to blue when using a 12nm h-alpha filter

I copied the red channel channel out to a new image canvas, and processed it using many of the same techniques as a traditional deep sky image such as minimizing stars, a curves stretch and a bit of noise reduction. This greyscale image can then be added to existing color data, or become a part of a complete narrowband project that include SII and OIII.

For now, I’ll just enjoy the black and white image in good old Hydrogen Alpha.

Final Thoughts

It felt great to use my DSLR camera for some astrophotography again. I began my journey many years ago with a camera and telescope like this. If you are a beginner thats thinking about taking the plunge into deep sky astrophotography – I think you should go for it – and a setup like this is likely the best way to get started.

Next, I’ll shoot some broadband color images using a full frame DSLR with the Zenithstar 73 to really take advantage of the fully illuminated image circle. The Sky-Watcher HEQ5 has proven to be a reliabe GoTo mount over the years and continues to deliver incredible results for me. I look forward to more sessions like this in the coming weeks as the longer, cooler nights usher in the new deep sky targets of Fall.

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A New Ritchey-Chrétien Telescope for Astrophotography

|Telescopes|12 Comments

I’ve been given the unique opportunity to review a new Ritchey-Chrétien Telescope, the iOptron Photron RC6. This telescope has a longer focal length than any of my refractors, which I plan on putting to good use. The impressive 1370mm focal length means that this stocky red Ritchey-Chrétien is a perfect choice for astrophotography during galaxy season. I’m looking forward to some large, high-resolution images of galaxies such as M101, the Pinwheel Galaxy.

With this added “reach” also comes an increased demand for focus and tracking accuracy. Added challenges include a strong need for an effective plate-solving solution, as locating deep sky objects at this magnification can be very time-consuming. These issues are not nearly as apparent when dealing with wide-field refractors, and one of the countless reasons I recommend them to beginners.

Although the iOptron RC6 telescope presents a new learning curve, it also means that I’ll be photographing a deeper view of space than ever before.

iOptron Photron RC6

The iOptron Photron RC6 Telescope 

Until now, I’ve only photographed galaxies through wide-field imaging telescopes such as refractors and Newtonian reflectors. A Ritchey-Chrétien telescope is a much better fit for smaller deep-sky targets, including many of the galaxies up for grabs at this time of year. The increased magnification means that smaller galaxies will appear in higher resolution, and take up more real estate in the frame.

Deep Sky Astrophotography with the iOptron Photron RC6 (Video)

The Ritchey-Chrétien Telescope Design

The iOptron Photron RC6 is a Ritchey-Chrétien telescope, the first of its kind to ever grace my backyard. By design, an “RC” telescope uses hyperbolic primary and secondary mirrors. Compared to a traditional Newtonian reflector design, this RC6 is said to offer a coma and chromatic aberration free results. Quite an impressive feat for a modest 6-inch diameter telescope with a conveniently stocky design. Mounting the tube to my equatorial mount is quick and easy, as the stubby design of the RC6 is compact and easy to manage.

Ritchey Chretien Telescope Design

What is an RC Telescope? Discussion on Quora

The Ritchey-Chrétien design is known for its great imaging performance, which is why you’ll find this design used in large professional telescopes including the Hubble Space Telescope. The RCT sitting in my backyard is just a few meters smaller than the HST, but the little iOptron Photron has the heart of a champion.

The Photron includes a 2″ dual-speed Crayford focuser. This is a nice touch for a telescope that will need to execute precision adjustments when in use for deep sky astrophotography. The design of the fixed primary mirror is said to eliminate the image shift that other telescope designs can suffer from. I have not experienced this phenomenon myself (or I didn’t notice), but perhaps any readers that have used a Newtonian reflector can weigh-in on this subject in the comments.

iOptron Photron RC6 Specifications:

  • Aperture: 150mm
  • Focal Length: 1370mm
  • Focal Ratio: F/9
  • Focuser: 2″ Dual-Speed Crayford
  • Dovetail Bar: Vixen-Style
  • Tube Weight: 18 lbs

The iOptron Photron RC6 was built for astrophotography. Its steel tube includes internal knife-edge baffles that reduce the stray light entering the objective of the scope. In a long exposure photo, the smallest amount of stray light can become quite bright, and it reduces the overall contrast of your image. Light baffles are present in most of the astrophotography telescopes I have used, but its a nice feature nonetheless. I’ll take all the help I can get when it comes to reducing the negative effects of light pollution from home.

Knife edge light baffles

The Knife Edge Light Baffles on the Photron RC6

Similar variations of this particular Ritchey-Chrétien model exist, each with its own particular flair. Previously I have seen a lot of fantastic images taken using the Astro Tech RC6, or ATRC6. Browsing equipment photos of this version of the telescope being used for deep-sky astrophotography was helpful when trying to determine the correct back focus for my camera.

Compared to a Newtonian Reflector

I’ve spent a number of astrophotography imaging sessions using an Orion 8″ F/4 Newtonian reflector telescope. Unlike this RC, the reflector required constant collimation adjustments, and a coma corrector to produce a flat imaging field. A coma corrector is an essential added expense for anyone looking to take pictures with a “Newt”. In the case of my Orion 8″ astrograph, the Baader MPCC II (coma corrector) cost nearly as much as the OTA itself.

Compared to Refractor

A small apochromatic refractor telescope such as the William Optics Z61 is much easier to use than an RCT. The compact size and forgiving wide field of view make the entire deep sky astrophotography experience less labor intensive. The drawbacks of a small apochromatic refractor telescope are their high price tag, and short focal lengths. As convenient and versatile as they may be, a Ritchey-Chrétien telescope is a better choice for capturing small targets such as galaxies.

backyard astrophotography

Setting up for a night of astrophotography with the RC6

First Impressions of the iOptron Photron RC6

I received an early demo model of the RC6 in late 2017, and am only just now getting chance to use it. The vibrant red finish of this telescope is hard to ignore. This was evident with the audience at NEAF 2018, where iOptron displayed several sizes of the Photron RC in matching red on the show floor. This is my first iOptron telescope, and I have high expectations based on the tremendous experiences I’ve had with their reliable astrophotography mounts.

Related Post: iOptron CEM60 First Impressions

The included dovetail bar comes in matching anodized red paint, which I promptly marked up after securing it into the base of my mount. Speaking of mounting the telescope, I had a bit of tough time properly balancing the load, particularly with a guide scope attached. Luckily, the RC6 includes not only a finder scope base on the left-hand side but drilled holes to easily add another finder/guide scope base on the right side.

iOptron RC6

The RC6 with a guide scope and finder scope mounted

This option proved to be the perfect solution to my balancing issues. I mounted an old finder scope to the newly installed base to for better balance, and a useful way to align the RC6. I’ve accumulated a number of telescope accessories from previous ‘scopes over the years, which is handy in situations like this. The finder scope I’m using was an Orion 9 x 50 Achromat I ordered years ago. Having a few extra accessories including finder scope brackets and bases can be a lifesaver in a crunch.

I’ll be adjusting the focus of the telescope manually during my astrophotography sessions on the RC6. iOptron does offer an electronic focuser built exclusively for their Ritchey-Chrétien telescopes, which will set you back about $200 USD. This is a nice available upgrade, which would certainly come in handy when fine-tuning the focus on a distant galaxy.

If you’re looking to install an aftermarket focus motor to your telescope, be sure to check out my experiences using this model from Pegasus Astro.

Guiding the RC6 on the iOptron CEM60

The iOptron CEM60 mount is more than capable of giving the RC6 a smooth ride. The telescope and all imaging accessories fall well below the maximum payload capacity of the mount, meaning any minor balance issues are unlikely to affect autoguiding. The auto guiding telescope I am using is a new StarField 50mm F/3.4 model, from Ontario Telescope and Accessories. This has replaced my old Altair guide scope but continues to house the reliable and no-nonsense Altair GPCAM2 AR0130 mono guide camera.

Autoguiding RC6

I’ll have much more information about the Starfield line of products including the reducer/flattener in the near future.

As I touched on earlier, a deeper view into space puts a stronger demand on tracking accuracy. The 1370mm focal length of the RC6 will not forgive a rough ride through a 3-4 minute long exposure, so I’ll be paying close attention to the graph in PHD2 guiding. As always, a precise polar alignment of the mount early on will save headaches later. Those of you that own a QHY PoleMaster already understand the importance of this step. (I’ll get one this year, I promise!)

Finding Focus with the iOptron RC6

I was happy to see that iOptron made the effort to include the necessary accessories needed to reach focus for astrophotography. The RC6 includes three focuser extension rings for a variety of back focus applications. For my Canon DSLR camera, I found focus using the 1″ and 2″ extension tubes as seen in the image below.

Astrophotography telescope

To reach focus on the iOptron Photrom RC6 with a DSLR, use the 1″ + 2″ extension tubes.

If you’re having trouble reaching focus with RC6 and your particular camera, try setting up during the day (that’s what I did). This year, our Canadian winter lasted well into the spring. The sky was cloudy for weeks on end, meaning I didn’t have a single star to focus on. Instead, I used a distant street light to find focus. At a focal ratio of F/9, this telescope produces a dim view through the eyepiece. You’ll need to use a bright object if your focusing at night.

Once you have found focus on your test subject, you can mark the location on the focuser, take a photo of it, or simply keep it locked in. The idea is to have a benchmark to use when you’re ready to start imaging with the RC6 on a clear night. You’ll have to tweak the focus on a real star of course, but you should be close. Without knowing the correct back focus of a new telescope with your camera, it can take hours to find the right combination of extension tubes. The iOptron RC6 has a long focal length and a slow focal ratio (F9), making this process more difficult than it is with a fast little refractor.

Which Camera to use with a Ritchey-Chrétien Telescope?

When it comes to choosing the “right” camera to use for a particular telescope, understanding pixel scale is essential. This involves the correlation between the size of the imaging chip (camera sensor), and the telescopes focal length. Most planetariums and imaging software programs will calculate the most common camera chip sizes for you, or you can do the math for yourself. Richard Wright shared an excellent article on pixel scale for astrophotography in this Sky and Telescope article.

To be quite honest, I haven’t spent too much time obsessing over exact pixel scale details in the past. I know that my wide field refractor will capture the entire Soul Nebula with my Canon DSLR and that the ED102 frames the Cone Nebula and friends up nicely with the 183M. This is a result of my trial-and-error approach to astrophotography I somehow crave, but I understand why this isn’t for everybody.

Based on the sound advice from my good friend Steve Mallia at Ontario Telescope, I have decided to use my APS-C sensor Canon EOS T3i (600D) with the iOptron RC6. Because a longer focal length shrinks the area of sky you see, the larger imaging chip in this DSLR is a better fit with the focal length of the Photron. Combining this telescope with a camera that houses a small imaging chip such as the Altair Hypercam 183M would make for an extremely restricted field of view.


The iOptron Photron RC6 Includes:

  • The Optical Tube Assembly
  • A 2″ Dual-speed Crayford focuser
  • 2 X 25mm, 1X 50mm focus extension tubes
  • 1.25″ accessory adapter
  • Vixen dovetail bar

Early Deep Sky Astrophotography Results (First Light)

I decided on the stunning Pinwheel Galaxy (M101) as my first deep-sky target with the RC6. The size and magnitude of M101 make this spiral galaxy a good fit for my full-frame DSLR camera. Historically, April and May are a great time of year to capture some serious light on this deep-sky target. The Pinwheel is one of many fine galaxies up for grabs during “galaxy season“. Unfortunately, my test image was captured under an 82% illuminated moon, on a night that also suffered from poor seeing and transparency.

The following photo was made using 70 x 4-minute exposures. (4 Hours, 40 Minutes). The images were integrated with support frames including dark, bias and flat frames in DeepSkyStacker. The final stacked image was brought into Adobe Photoshop for final image processing, using the techniques outlined in this Photoshop tutorial.

The Pinwheel Galaxy in Ursa Major

M101 – The Pinwheel Galaxy with the iOptron RC6

Image Quality

I looked closely at my individual light frames produced by the iOptron RC6. What I looked for was a flat field of view, sharp stars, and an increased resolution in my subject. I was thrilled to capture M101 in great detail than ever before, thanks to the increased aperture and focal length of the telescope. The image was captured during a nearly full moon, which made processing the image a challenge.

single image sub

A single 3-minute exposure @ ISO 1600

Removing some harsh gradients in the final image was the biggest obstacle. I used a Photoshop technique that includes applying a synthetic flat frame and setting the blending mode to subtract. This can be a helpful strategy to use when the Gradient Xterminator plugin does not produce the results you’re looking for. As always, adding more overall exposure time and improving the signal-to-noise ratio would improve the quality of this image immensely.

A Baader Moon and Skyglow filter helped reduce the effects of light pollution in my images and made a big difference in terms of overall contrast. I mounted the 2″ round version of the filter to nosepiece of the camera. The 2″ round mounted version offers the flexibility to shoot using a variety of dedicated astronomy cameras and DSLR’s. Of all the light pollution filters I have used for astrophotography from the backyard, this particular Baader model is one of my favorites.

baader moon and skyglow filter

Baader Moon and Skyglow Filter

Final Thoughts

The iOptron Photron RC6 telescope was a pleasure to use, and provided the deep sky results I was looking for. The optical quality of the Ritchey-Chrétien design produced flat, coma and chromatic free results as advertised. Surprisingly, this F/9 focal ratio did not reduce the amount of light collected in my image subs the way I expected. 3-minute exposures at ISO 1600 were well exposed, likely due to the increased 150mm aperture of the telescope.

Take a look at the dramatic difference in magnification between the following two images of the Pinwheel Galaxy. The version on the left was captured using a crop-sensor DSLR with an 80mm refractor telescope, while the version on the right used the new iOptron Photron RC6.  As you can see, an RCT is a much better fit if you want to collect close-ups of smaller DSO’s like the Pinwheel Galaxy.


Those of you that shoot with a DSLR camera should have no issues in terms of pixel scale with the RC6. An APS-C sized sensor is a great match with the focal length of this telescope. My image of the Pinwheel Galaxy should give you a good idea of the field of view you can expect to see through the Photron. At just 18lbs, the iOptron RC6 requires a modest equatorial mount for accurate and smooth tracking. The iOptron CEM60 is overkill for this OTA, and I think an Orion Sirius EQ-G or similar mount would be more than enough to carry a complete imaging payload.

The RC6 fills a noticeable void in my arsenal of optical instruments. Having a no-nonsense telescope that excels in high magnification targets such as small galaxies has given me a more complete set of tools for capturing deep sky objects of all sizes. Next up, I’ll focus on capturing some of the smaller galaxies I have traditionally avoided due to lack of reach.

The iOptron Photron 6″ Ritchey-Chrétien telescope is available at Ontario Telescope and Accessories.

Astrophotography by Trevor Jones

Related Posts:

The Best Astrophotography Telescopes for Beginners

Recommended Filters for Deep Sky Astrophotography

The iOptron Company | History, Timeline, and Top Products


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Summer in the AstroBackyard

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This is one summer that I will never forget.  The addition of my new telescope, the growth of AstroBackyard and the explosion of my YouTube channel has given me an astronomical boost in motivation and passion for astrophotography.  This has not come without hard work, it has been extremely busy in terms of both astrophotography and my day job.  The common sacrifice between the two has been sleep, of course.  The battle between day and night is a struggle astrophotographers know all too well.  I take comfort in the fact that the winter season will have many cloudy nights that will force me to catch up on my sleep, and maintain a healthier lifestyle balance.

How hard did you go this summer? Did you opt for sleep instead of imaging time?  Let me know on Facebook

Astrophotographers are not normal!

I recently created a short “trailer” for the AstroBackyard YouTube Channel:


AstroBackyard on YouTube

We have a burning desire to capture the wonders of the night sky each and every night.  We check the weather constantly and plan most social activities during the full moon, or during stretches of bad weather.  A stretch of clear nights surrounding the new moon means getting less than 4 hours of sleep during the week. For me, my health takes priority over all, so this is an issue that I am still trying to properly address. A more permanent deep-sky equipment setup and a dedicated observatory will help me optimize my setup time. These dreams are on my radar, and will become a reality in the not so distant future.  Which leads me to my next point;

The social following from this blog and my youtube channel have added another level of pressure to regularly produce quality astronomical images. This is a huge motivator for me, and a challenge I am honored to have in my life.  The AstroBackyard following has already grown much faster than I anticipated. I have big plans for the future of this venture.  

New Photo: The Trifid Nebula

Deep-Sky Nebula in Sagittarius

Tridi Nebula - DSLR astrophotography

M20 – The Trifid Nebula

Messier 20 is one of my all-time very deep-sky objects.  I remember one of the very first times I saw an image of the Trifid Nebula in a book called: The Practical Astronomer by Will Gater.  The dynamic color combination of blues and pinks had me looking into astrophotography equipment so I could capture it for myself.  I realized that dream in April of 2013, and have continued to soak camera time on it ever since.  The image above was achieved by shooting over 3 separate nights in early August.  Complete photo details below:

M20 – The Trifid Nebula

Photographed on: August 2, 3, 8, 2016

Total Exposure Time: 2 Hours, 54 Minutes (58 x 3 Minute Subs @ ISO 1600)
Mount: Sky-Watcher HEQ-5 Pro
Camera: Stock Canon Xsi
Telescope: Explore Scientific ED102 CF

Guided with PHD Guiding
Stacked in Deep Sky Stacker
Processed in Adobe Photoshop CC


Autoguiding telescope package

I documented my night under the stars for my third and final installment on the Trifid Nebula in video form.  The video discusses the specifications of my new Explore Scientific ED 102 CF, the Field-Flattener I use, and some simple tips for backyard astrophotography.  Thank you to the (now over) 1000 subscribers to the AstroBackyard YouTube Channel!

New Photo: The Summer Triangle

Wide-Field Image with Tracking and Autoguiding

Milky way stars from backyard

The Milky Way including stars in the “Summer Triangle”

This was a very exciting experiment was finally actualized the night of August 2nd, 2016.  I have always loved wide field camera lens astrophotography. Whether it’s a constellation full of stars with hints of nebulosity through a 14mm lens, or a complete portrait of the North America Nebula shot with a 200mm; camera lens astrophotography is responsible for some of the greatest images ever taken.

I mainly shoot deep-sky astrophotography through my 102mm Apo Refractor, with a focal length of 702mm. This is a great distance to photograph many deep-sky objects. It fits the entire object in the frame, yet is close enough to reveal some solid detail.  However, this is far too “deep” for a number of large nebulous regions and star clusters.  In instances like this, a camera lens anywhere from 50mm – 300mm will execute your plan better than any telescope.  That’s great news for anyone who already owns a lens or two!

Here’s the catch. You need 2 things to produce long exposure astrophotography images with no star trails:

1. A tracking mount

A German equatorial mount will allow you to capture a much longer exposure without star trails. Your camera can then pick up deep-sky objects such as nebulae and galaxies.

2. External camera control

You will need to take exposures longer than the 30-second maximum your DSLR will take on its own. (Without holding the shutter button down!) A camera remote or laptop comtrol will allow you to choose exposure length, and automate the process.  Autoguiding will create an even better image.  However, you may be able to get away with 1-2 minute exposures without it – depending on your mount.

An astrotrac or iOptron sky tracker was meant for moments like this. Not only to they simplify the polar alignment process and accurately track the sky, but they are MUCH lighter and more transportable than a full-blown GEM. If I ever plan on diving into travel astrophotography (I do!) I will certainly invest in one of these ingenious devices.

Back to my Experiment…

Mounting a Canon DSLR to a telescope with a Gorilla Pod

I have everything needed to execute a coveted wide field camera lens astrophoto, but I rarely opt for this method over shooting deep-sky through the telescope. Not to mention I must find a way to securely fasten my DSLR and lens to my astrophotography rig while maintaining a proper balance, and a functioning auto guiding system.  I used a small gorilla pod meant for a GoPro and wrapped it around my telescope.  This kept my existing alignment and guiding from an earlier deep-sky session.


The bendable legs of this sturdy little tripod firmly grapple onto my scope, so much so that I can leave the camera running in this position for hours with confidence.  I should mention, that this photo was acquired during the night of new moon. I can count on one hand the number of clear new moon nights I have experienced. I have had many clear nights leading up to and following my favorite day of the month, but to bask in the glory of our night sky on a summer new moon? That’s the stuff I live for.


I used BackyardEOS to automate my imaging session:


Camera: Canon EOS 7D
Mode: Bulb
ISO: 800
Exposure: 120 seconds
Dithering: Enabled

I ended up taking about 15 x 120-second exposures at ISO 800.  I also shot a few dark frames after my session, so I could stack the images into Deep Sky Stacker for a better SNR (Signal to noise ratio)

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I often tweet during my imaging sessions:

AstroBackyard on Twitter

Results from the 2016 Perseid Meteor Shower

The weather was a bit iffy the week of the Perseid Meteor Shower (August 8-12).  The skies were clear the night before the peak (August 10th) so I took a shot at capturing some decent meteors on that night.  When thundershowers are in the forecast, I am weary of setting up my astrophotography equipment, even if the conditions are currently clear!

I piggybacked my Canon 7D onto my telescope using a gorilla pod as per my previous session so that I could have a wide-field eye on the sky.  I pointed my wide-angle camera lens (Canon EF 17-40mm f/4L) towards the constellation Perseus over my house.  This arrangement worked extremely well.  I was able to capture sharp images that revealed an impressive amount of detail of this area of the sky by taking 2-minute exposures.


Perseid meteor photo from my backyard

Perseid Meteor photographed from my backyard the Night of August 10th-11th


What’s Next?

I have realized that my current DSLR camera is holding back my astrophotography.  Despite the fact that my Canon Rebel Xsi is modified for astrophotography, I think I would be better off with a newer unmodified, stock Canon camera.  I have my eye on a used Canon T3i camera.  This will give me much better noise performance, increased ISO capabilities, and a higher resolution than my ancient 450D’s 12.2 megapixels.  Yes, a full-frame Canon 6D would really take my images to the next level, but that is a much bigger investment than the reasonable cost of a used Canon T3i DSLR.  (Under $500!)  I can then modify this camera for astrophotography myself using the tutorial by Gary Honis. 

I would like to thank you all for the continued support of this blog for the AstroBackyard YouTube channel.  Please follow me on Facebook for the latest news about my on-going astrophotography journey.  I wish you all the best in your own efforts and hope that I have inspired you to keep going.

AstroBackyard on Facebook

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