Using a Canon EF 75-300mm Lens for Astrophotography

The Canon EF 75-300mm F/4-5.6 III lens is a budget telephoto zoom lens (4x) that can be used for astrophotography. This lens is often bundled as a kit with an entry-level Canon EOS Rebel DSLR camera.

In my experience, the Canon EF 75-300mm F/4-5.6 III lens does an impressive job at capturing the night sky, considering the price. A refractor telescope with a comparable focal length of 275mm (and well-corrected optics) can cost up to $1000 or more.

The Canon EF 75-300mm F/4-5.6 III is a surprisingly good lens for astrophotography considering the price. With the right approach, it can produce sharp, flat images of deep space objects in the night sky. 

It does not meet the standards of a Canon L-series prime lens (such as the Canon EF 300mm F/4L, but that does mean that it isn’t a great beginner lens. There are a number of variations to this lens (such as a USM version).

The version I have is the ‘III’ version (non-USM), which came out in 1999. This lens is considered to be a “very low-grade consumer lens“, but it might be the best one you’ve got at the moment. 

Below, is an image I captured using the Canon EF 75-300mm lens (at F/6.3) on a Canon EOS Rebel T7 DSLR camera.

The Witch Head Nebula. Canon EF 75-300mm Lens (130mm at F/6.3).

This lens has a rather slow r-ratio compared to other, more expensive prime Canon EF lenses. It includes an autofocus feature (AF), which can be turned on or off on the side of the lens. 

For astrophotography purposes, the manual focus method should be used. The manual focusing ring of the Canon EF 75-300mm F/4-5.6 III is a little loose, and a stiffer focusing

This lens is considered to be “reasonably sharp for the price“. In my experience, the images of my deep-space objects were impressively sharp when the lens was stopped down to F/6.3.

In the photo below, you’ll notice some lens flaring on the bright star Rigel. In my tests, these artifacts were not excessive unless it was a very bright star like Rigel. 

Lens flaring on the bright star Rigel.

There are many ways to deal with issues such as lens flaring during the image processing stage of the astrophotography process. To learn how I edit my deep-sky photos of galaxies and nebulae, consider purchasing my Premium Astrophotography Image Processing Guide.

My final image of the Witch Head Nebula includes 90 x 2-minute exposures (3 hours total) at ISO 6400. The images were stacked using dark frames in DeepSkyStacker, and processed in Adobe Photoshop. 

Before and After processing my image of the Witch Head Nebula. 

Canon EF 75-300mm Lens for Astrophotography

Over the years, I have used a number of camera lenses for astrophotography from the Canon EF 50mm F/1.8 (nifty fifty) to the Canon EF 24-105mm F/4L. Each lens has its own characteristics and performance varies. 

In the following video, I discuss the challenges of photographing a deep-space object like the Witch Head Nebula using the Canon EF 75-300mm F/4-5.6 III lens.

In my experiences using this lens, it can be a little frustrating to use at times. Because this is a zoom telephoto lens, it allows you to adjust the focal length anywhere from 75mm, all the way to 300mm.

For an astrophotography project, you need the focal length to stay fixed at a specific focal length for a long period of time (even multiple nights). This is not a problem for a prime lens or astronomical telescope, of course, but retaining a fixed focal length on the Canon EF 75-300mm F/4-5.6 III can be tricky. 

Once you have chosen a focal length to photograph your deep-space object, it is very easy to accidentally knock the lens out of position. If this has occurred, it will be nearly impossible to return to your original focal range position.

The best way to hold your focal range setting is to use a piece of electrical tape. You simply need to wrap a piece of tape around the barrel of the lens at the base where the focal range markers are located. 

You may also want to tape the focus ring down once you have received critical focus on a bright star. However, you will likely want to confirm you are still in focus with the help of a Bahtinov mask as the temperature changes throughout the night. 

Astrophotography Uses

Most experts will not recommend the Canon EF 75-300mm F/4-5.6 lens for night sky photography. This lens is not particularly fast, or sharp. However, I believe that with the right settings, I can be a viable option for beginners looking to add some ‘reach’ to their camera kit.

Although this lens has a maximum focal length of 300mm, I would suggest using it in the mid-range of 100mm-150mm. This provides enough focal length for deep-space imaging, with the benefit of being more forgiving in terms of tracking.

Speaking of tracking, a star tracker must be used with this lens (even at the minimum focal length of 75mm) for a long exposure image free of star trails. I use a Sky-Watcher Star Adventurer tracking mount to take photos of deep-space objects with my telephoto camera lenses.

The Canon 75-300mm lens and Rebel T7 mounted to a portable star tracker.

Because this lens is so lightweight, you may find that the ball head attachment on your star tracker is more than capable of securing your camera in place for long-exposure astrophotography. When the lens is mounted to an entry-level DSLR camera body such as the EOS Rebel T7, you may even find it difficult to achieve balance on your star tracker using the counterweight kit. 

The extending front focuser design is not ideal and can create challenges in the field, especially if you have a dew heater band wrapped around the objective of the lens. 

The Canon EF 75-300 F/4-5.6 does not include a lens shield, which would make taking flat frames easier, as well as help to block stray light from entering the lens. 

Canon EF 75-300mm F/4-5.6 III Lens Specs

Who This Lens is For

If you own a Canon DSLR camera, the 75-300mm is an affordable way to add a telephoto zoom lens to your kit. It costs less than $200 USD and can present many new and interesting projects.

The Canon EF 75-300mm lens includes the Canon EF mount, meaning that it can only be used with Canon EF mount camera bodies. This includes full-frame DSLR camera bodies such as the Canon EOS 6D.

Canon EOS RF mount camera bodies (such as the Canon EOS Ra) will not accept this camera lens without an adapter. 

If you own a DSLR camera with a kit lens such as the Canon EF 18-55mm F/3.5-5.6 and are looking for an affordable option to shoot at longer focal lengths, the 75-300 is a respectable choice.

If you are looking for premium glass and fast optics, this is not the lens for you. 

Pros / Cons

Pros:

• Affordable
• Various Focal Lengths Available
• Lightweight and Compact
• Compatible with Canon EF Mount Cameras
• Relatively Sharp, Flat Images

Cons:

• Difficult to Focus
• Focal Length does not lock
• Mild Color Fringing and Flaring
• Poor quality stars at F/4

If you would like to process my image captured with this lens, you can do so here: Data shot using the Canon EF 75-300mm F/4-5.6 III lens. 

Related Posts:

• 7 Astrophotography Tips for Beginners (No Telescope Needed)
• Using a Sigma 24mm F/1.4 for Astrophotography
• Rokinon 14mm F/2.8 Review (Astrophotography)