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Using a Canon EF 24-105mm Lens for Astrophotography

Canon 24-105 lens for astrophotography

Do you already own a Canon EF 24-105mm F/4L  lens and want to use it for astrophotography purposes? If so, you’re in luck. I’ve tested this very lens for some wide field deep sky images from my backyard. I love testing new camera lenses at different focal lengths, and playing with new ways to frame objects in the night sky.

The subject for this imaging session is the constellation Taurus. At this lenses widest field of view (24mm), I was able to include a number of interesting subjects in a single image. With enough exposure time, you can expect to collect light on a number of interesting deep sky objects including the Pleiades star cluster, NGC 1796, the California Nebula and more. 

The Canon EF 24-105mm F/4L USM IS lens is an excellent choice for astrophotography. The unique focal lengths offered create interesting photo opportunities not available with a traditional wide-angle lens. And because it’s a L series lens by Canon, you can be sure that the image quality and performance of the 24-105mm meet the demanding aspects of astrophotography such as focus and star quality.

Using the Canon EF 24-105mm Lens for Astrophotography

I should start out by saying the example image featured on this page was captured at the camera’s widest focal length and lowest magnification. 24mm offers a unique field of view compared to a more traditional wide angle shot of 18mm or wider. Wide angle lenses such as the Rokinon 14mm F/2.8 are fantastic for capturing a large swath of the Milky Way, but a narrower filed of view is better at isolating specific regions of the sky. 

Because this is a zoom lens, I could also try shooting the same are at 105mm for an even tighter view, or anywhere in between. The tough part about using heavier zoom lenses like the Canon EF 24-105mm is that when the lens is pointed upward, gravity works against you. This means that any magnification other than its widest 24mm will result in the zoom slowly “falling” back to 24mm.

To deal with this issue, you can tape the lens to the desired focal length. I’ve done this before with this very lens, and it worked extremely well. It’s easiest to tape the lens at either its minimum or maximum focal lengths rather than at a stage in between the two.

Horsehead Nebula and Orion

New framing opportunities available thanks to the unique field of view at 105mm (Orion)

Canon EF 24-105mm F/4L IS USM

The lens is an EF mount style Canon telephoto-zoom lens that was introduced in 2005. This an L series lens, which Canon considers to be their professional line of DSLR lenses. I’ve been adding to my collection of L series lenses for several years, purchasing a used model 24-105mm in 2017.

This is the first version of the 24-105mm, not the popular “II” version that is said to have improved the Image Stabilization function. This camera lens is widely used by amateur photographers, largely due to the fact that is was included as a kit in the Canon EOS 5D Mk II, 5D Mk III and EOS  6D packages. 

The lens itself it weather-sealed to protect it from dust and water, although it is not completely waterproof. It uses 77mm filters on the objective and contains a single Super-UD glass element in the lens design. When you compare this lens to an apochromatic refractor telescope, the obvious advantages are its wide field of view and impressive fixed aperture of F/4.

This lens offers some serious benefits for amateur astrophotography purposes, especially if you are looking for a mid-range focal length to create future imaging projects. If you are using a full-frame DSLR camera, the maximum magnification of 105mm is likely to be a bigger seller point for you as this presents some unique framing opportunities (think Rho Ophiuchus).

On an APS-C camera body, the 24-105mm focal length becomes 38-168mm due to a crop factor of 1.6X. This version of the lens is best suited for photography, rather than video work, as the image stabilizer motor is rather loud and is recorded along with your audio. (I found this one out the hard way!)

DSLR camera and lens

Using a Crop-Sensor DSLR Camera

A crop sensor DSLR camera such as the Canon EOS Rebel T3i (600D) used in my image creates a narrower field of view than a full-frame camera does with this lens. A full-frame DSLR such as the Canon EOS 6D would produce images at a true native focal length of 24mm with this lens. 

The crop factor (1.6X) applies an extra bit of magnification with any lens attached, for better or for worse. In situations where an ultra-wide field of view is important such as a Milky Way nightscape or Meteor shower, a full-frame DSLR is best. 

For creative shots that feature a selected region of sky such as this, perhaps an APS-C sensor is a better choice. In the end, it doesn’t really matter all that much. The key is that you understand the field of view you can expect to capture with a particular lens. In this case, the focal length will actually be 38mm (24mm x 1.6), which is what I was going for. I purposely chose to use my crop-frame DSLR with this lens for this photo.

The fact that this camera is also modified for astrophotography was considered, as neither of my full-frame DSLR’s have been modified. The California nebula will show up in my images thanks to this upgrade, as a DSLR that has had its stock IR cut filter removed will allow emission nebula objects to be recorded.

Related Post: Choosing a Camera for Astrophotography

Light Pollution Filter

If you’ve spent any time browsing my website, you’ll know that I do the majority of my deep sky imaging in a Bortle Class 8 city sky. This necessitates the use of light pollution filters for 95% of the broadband color images I take. 

The filter used for the image on this page is the Optolong L-Pro broad-spectrum filter. This filter specializes in preserving the natural star colors in the night sky while reducing as much artificial light and sky glow as possible. It clips into the camera body to fit securely underneath my camera lens. 

When shooting star clusters with a DSLR camera in the city, it’s often better to shoot shorter exposures with a mild light pollution filter. This will help to reduce the harsh effects of color degradation associated with light pollution filters.

Ideally, you’d shoot under dark skies without the use of a filter at all, but the L-Pro has been the best option I’ve seen from the city thus far. 

My individual images are quite conservative at ISO 400, and 1-minute in length. The fast F/4 speed of the Canon EF 24-105mm lens helps to collect a healthy amount of signal, even if a lot of noise comes with it. The signal to noise ratio is the holy grail of capturing great data from the city, so take every advantage you can get.

The cold temperature I experienced the night this photo was taken (-3 degrees Celsius) helped to reduce the amount of thermal sensor noise present in my shots. Dark frames were applied in post processing to subtract as much noise as possible.

Related Post: How to Take Dark Frames

Tips For Focusing the Camera Lens

The process of focusing the Canon EF 24-105mm F/4L is as simple as pointing the camera towards a bright light. I used a streetlight from across the street to find my initial focus position. It’s nice to know that this glaring artificial light has some sort of use for my backyard astrophotography.

Focusing the lens is a straight forward process at 24mm, and even offers a little forgiveness at an aperture of F/4. Faster lenses that can open up to F/1.8 are beneficial for astrophotography, but often result in a challenging focus routine. There is very little room for error when shooting the night sky at F/2.8 or below.

The recommended camera settings for focusing your lens at night include your widest aperture (f-stop) and a high ISO setting (I use ISO 6400 on my Canon EOS Rebel T3i). Set the exposure length to “bulb mode” (one exposure passed 30″)  so the camera is collecting the absolute maximum amount of light possible.

Use your DSLR cameras “live view” mode, which is essentially a live video of view your camera sees. As long as you’ve used the settings above, you should see the brightest stars in the night sky on the live view screen. 

I used the bright red star, Aldebaran to focus the lens. Using 10X magnification in live view mode, the star was very close to perfect focus based on the rough position achieved using the streetlamp. To really nail the focus, simple move the focus ring slowly in and out while zoomed in on the star. You can also take short 5-second test exposures and compare the images against each other if you want to get it bang-on.

At this point, I usually shoot one full test image at my desired exposure length. Then, I zoom in to the image on the DSLR display screen and inspect the sharpness of my shot. This is also a great time to check the accuracy of your polar alignment. Shots that are 2-minutes in length or shorter should not show any star trailing at this focal length.

 

Subaru (Pleiades)

Here is a photo of the Pleiades using this lens at its maximum magnification, 105mm

Tracking the Night Sky

Unless the type of images you’re into includes star-trailing, you’re going to need a star tracker for astrophotography. Fortunately, smaller deep sky imaging setups like a DSLR and the 24-105mm lens don’t require a robust German equatorial mount like you would for a telescope.

I use the iOptron SkyTracker Pro to move with the apparent rotation of the night sky and capture crisp images with sharp stars. This lightweight camera mount (2.5 lbs) easily fastens to your existing photography tripod for tracked images. 

Polar alignment and balance are the keys to a successful image when using a star tracker like this. Once the mount has been accurately aligned with the rotational axis of the Earth, you can expect to collect long exposure images of up to 2-minutes or longer depending on the focal length of your camera lens. Higher magnifications are less forgiving to alignment, as the increased magnification will highlight even the slightest error in your setup routine. 

I prefer to use a ball-head mount so I can point the camera in any sort of upward direction I wish. Once I have framed the object(s) up the way I want, I let the mount do it’s thing and run a sequence of long exposure images using a remote shutter release cable.

Camera Control with a Remote Shutter

A remote shutter release cable like this one creates an enjoyable way to automate your imaging sequence. Rather than connecting the camera to a computer and running it with external software, this lightweight cable takes up very little space and does it’s job effectively.

A typical imaging sequence will include about 60-100 exposure of 1-minute or more, with a 5-second delay between shots. The cable reduces the chances of camera shake or jarring the cameras focus as you no longer need to touch the DSLR camera body whatsoever. 

For my imaging sessions in the backyard, I usually leave the SkyTracker Pro and camera running for hours on its own while I catch up on other things in the house. Be sure to set a large number of shots to go off continuously, as you don’t want the sequence to finish shooting because you have lost track of time. I use this device to capture a set of dark frames after each shoot as well. 

Camera Settings Used:

  • Mode: Manual
  • Exposure: 1-Minute
  • ISO: 400
  • White Balance: Daylight
  • F-Ratio: F/4
  • Filter: Optolong L-Pro 

The constellation Taurus

The Taurus region of the night sky at 24mm – Click the image for a larger view

As you may have noticed, some clouds crept into the photo. In the end, it wasn’t a great night to test the lens as my clear sky time was extremely limited. The photo above includes 10 x 1-minute exposures at ISO 400 using the Canon EF 24-105mm lens on a Canon EOS Rebel T3i. 

The larger version of the image shows the impressive star colors found in the image. If you look closely, you should be able to make out the California nebula near the upper left of the frame.

The Bottom Line

I have to admit, astrophotography was not my primary intended purpose for the Canon EF 24-105mm lens when I purchased it. I bought it to fill the void of not having a high-quality telephoto-zoom camera lens for general daytime photography purposes.

However, I have since discovered that the both its minimum and maximum magnifications have opened up some incredible astrophotography opportunities to shoot the night sky in new ways. At 24mm, the view is humbly more targeted towards a specific area of the night sky than a traditional wide angle of 18mm. At 105mm, the lens is perfect for large targets such as the North America Nebula, or to highlight the beauty of the Sagittarius star cloud in the Milky Way.

The creative framing opportunities available would be squandered if the lens showed any signs of color fringing or chromatic aberration. Thankfully, this is a Canon L series lens. The red stripe indicates that you can count of these lenses to live up to the scrutiny of the amateur astrophotographers keen eye. 

Related: Example astrophotography images captured using the Canon EF 24-105 F/4L on Astrobin

The stars are sharp, colorful and flat to the edges of the field in my crop-sensor DSLR. I am able to use the Canon EF 24-105mm F/4L with a wide variety of clip-in light-pollution and narrowband filters. All in all, it’s been a fantastic addition to my gear, and a lens I am sure that will get plenty of use in the future.

Related Posts:

Deep Sky Astrophotography with a 300mm Camera Lens

The Best Camera Lens for Astrophotography (That you probably already own)

Milky Way Photography using a Rokinon 14mm F/2.8 Lens