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Share your star crops made with Canon EF 70–200mm f/2.8L IS II

Equipment Collimation Help Needed
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Viktoryia Lazarava avatar
Viktoryia Lazarava avatar

Hello, everyone!

I’ve recently bought a used Canon EF 70-200mm f/2.8L IS II lens and while I have no issues with it in everyday photography, I’ve been disappointed with how it performs with astro. Stars even in the center of the frame have a noticeable asymmetric, pear-like shape and I have to stop down the lens considerably to get decent looking stars. I wat to determine whether my lens has an optical issue or whether what I'm seeing is normal for this lens. Could anyone who owns this lens share 100% center and corner crops of a rich star field (or a RAW file) taken at 200 mm, especially at f/2.8? I'd really like to compare my results with another.

lens defect.jpg

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Tony Gondola avatar
Tony Gondola avatar

Funny, it looks more like star trailing than aberration. Was this test just done on a tripod with no tracking? If so, I would try a set with a much shorter exposure time, just a few sec. and see what you get.

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andrea tasselli avatar
andrea tasselli avatar

How exactly the trailing is going to disappear when closing down the diaphragm, prey?

Tony Gondola avatar
Tony Gondola avatar

I was just thinking that the apparent over exposure might be making the slight trailing easier to see. Probably not the case but there’s a lot of ways to check.

sharkmelley avatar
sharkmelley avatar

Astrophotography is a very tough test for a lens, especially a zoom lens used wide open. On-axis stars (i.e. stars in the centre of the image) should be radially symmetrical, so pear-shaped stars definitely indicate some kind of lens issue which may or may not be within manufacturer’s tolerances.

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Arun H avatar
Arun H avatar

Viktoryia Lazarava · Jul 19, 2026 at 12:31 PM

Hello, everyone!

I’ve recently bought a used Canon EF 70-200mm f/2.8L IS II lens and while I have no issues with it in everyday photography, I’ve been disappointed with how it performs with astro. Stars even in the center of the frame have a noticeable asymmetric, pear-like shape and I have to stop down the lens considerably to get decent looking stars. I wat to determine whether my lens has an optical issue or whether what I'm seeing is normal for this lens. Could anyone who owns this lens share 100% center and corner crops of a rich star field (or a RAW file) taken at 200 mm, especially at f/2.8? I'd really like to compare my results with another.

lens defect.jpg

It has been a very long time (maybe 8 years) since I last used a Canon 70-200 f/2.8L IS II lens for astronomy. I cannot easily find my images with this lens but can say what you have shared seem similar to mine. Even in the center, the stars were not perfectly round. The lens had other issues that made it unsuitable for astrophotography You can get a little bit of zoom creep if the lens is vertical which makes flat fielding near impossible. It is impossible to fully correct with flats at intermediate zooms. These issues are why I migrated to a prime lens (Canon 400mm f/5.6L) which was much better, and then eventually to dedicated scopes.

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Simon_W avatar
Simon_W avatar

I’ve used both the 70-200mm f/2.8 IS Lii zoom and the 200mm f/2.8 prime. There are certainly good copies of the zoom out there, rendering sharp, round star images into the corners of the image. For both the zoom and the prime, using liveview focus at high magnification was essential if I wanted decent star images. Even then, the prime is quite difficult to bring into optimum focus because of chromatic aberration. Even using RGB filters and FocusMax via RoboFocus with the prime doesn’t guarantee small star images, and the focal position is very sensitive to temperature changes. Both are very good lenses, but they do need careful setup to achieve their full potential- but then, what f/2.8 system doesn’t?

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Arun H avatar
Arun H avatar

I was finally able to find an actual image I took with this lens; this was in 2018. This was taken at 142mm f/l and f/3.2 from my data. No flats, and I used a different stretching program than PixInsight. I believe all I did was apply profile corrections in Adobe Lightroom, converted to TIFF and used Deep Sky Stacker at the time.

NAPelican_cropped.jpg

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Simon_W avatar
Simon_W avatar

I have one image taken with the zoom at 70 mm, 43×10s subs (tracked, of C2023 A3 Tsuchinshan-ATLAS). Thin, rapidly-moving clouds and Bortle 9 light pollution caused the gradients, but I think the star images can be judged well.

https://www.astrobin.com/lsx2s3/B/

Processing in Deep Sky Stacker and MaximDL to calibrate the subs, perform the stacking and reduce gradients (I’ll rework the image one day in PixInsight) . Star profiles were not adjusted.

Clear skies,

Simon

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Viktoryia Lazarava avatar
Viktoryia Lazarava avatar

Simon_W · Jul 21, 2026, 06:19 AM

I have one image taken with the zoom at 70 mm, 43×10s subs (tracked, of C2023 A3 Tsuchinshan-ATLAS). Thin, rapidly-moving clouds and Bortle 9 light pollution caused the gradients, but I think the star images can be judged well.

https://www.astrobin.com/lsx2s3/B/

Processing in Deep Sky Stacker and MaximDL to calibrate the subs, perform the stacking and reduce gradients (I’ll rework the image one day in PixInsight) . Star profiles were not adjusted.

Clear skies,

Simon

Hi, Simon!

Thanks for sharing the stacked image. May I ask you to attach a single raw frame just the way it came out of the camera? It’s hard to inspect star shapes on a stacked and stretched image.

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