Issues Imaging with Mirrorless Camera

[Northernlight]

Hi All,  I have a few years experience imaging with a traditional scope setup (Frac, newt etc) using a dedicated astro cameras, but recently i wanted to try a portable rig using my mirrorless camera.   So i shot 150 images using my camera with a 16-80 F4 lens which has a constant F4 aperture though the zoom range. My images were shot at 80mm Focal length,  but after stacking i noticed a central ring artefact, so went backed and check my individual images, and sure enough there was a ring artefact in the uncalibrated images.

I can't make any sense of it, as i wasn't using any filters, and the lens had no obstruction, so i didn't expect to see such an artefact appearing.  So i'm struggling to figure out the cause of the ring.  Would be grateful for any suggestions to the cause of the ring from other mirrorless camera users.

Many thanks in advance,

Rich.

[Elp]

Are you using a Sony by any chance?

[michael8554]

Hi Rich

I couldn't see what you described so I stretched your image:

 

I can see vignetting, which as an experienced imager I'm sure you're aware of.

More concerning are the vertical lines all over the image.

Michael

[Northernlight]

I did wonder about the vignetting, but the odd thing is that it didn’t show up in the flats as they only had a tiny bit of vignetting on the extreme corners.  I took the images at the max 80mm focal length, but I’m wondering if I took the flats at the shortest focal length 18mm which might account for the issues.

 

[andrew s]

Mirrorless cameras have built in lens correction including vignetting so it may be due to that. Not sure if it's done in all formats or if you can turn it off.

Regards Andrew 

[Northernlight]

5 hours ago, michael8554 said:

Hi Rich

I couldn't see what you described so I stretched your image:

 

I can see vignetting, which as an experienced imager I'm sure you're aware of.

More concerning are the vertical lines all over the image.

Michael

All I can only assume that the vertical lines are some issue with calibration. I’ll check the unprocessed images to see if they appear. It could also be an issue with the bias files I created.

I’ll check tonight

[Elp]

16 hours ago, Elp said:

Are you using a Sony by any chance?

Camera?

[Northernlight]

It’s a Fuji x-s10, but the line issue is sorted as I just forgot to click cfa option for calibration settings in PixInsight as I was just used to mono processing.

I still however haven’t figured out the issue of the ring appearing in my image, as I don’t see any such artefact appearing in my flats, so no way I can correct it in my image. I can only assume it might be something to do with using a zoom lens rather than a prime lens, but at the same time i don’t see similar artefacts when doing long exposure daytime photography.

[Elp]

I'm also guessing you're using native Fuji lenses and not a lens adaptor which can introduce internal reflections (from what I've read there aren't really any out there which don't internal reflect).

It could be the lens construction, I specifically only use manual primes as they tend to focus to infinity better. 

The reason I ask about camera model is because I recently got a Sony A7s, and upon trial I had a similar issue where from midpoint to outer edge I got a red/green ring pattern which didn't calibrate out. There's an option in camera for lens compensation and I've turned it off but haven't trialled it since. But with Sony cameras there's an apparent issue with these rings as well as the sensor being a half half design, as a lot of cameras out there use Sony sensors I wouldn't be surprised if the issues translate to different manufacturer bodies. Daytime photography is fine, but I can see the issue immediately at night when imaging 15-30s per image.

Edited June 17, 2023 by Elp

[Northernlight]

I'm using a Fuji X-s10 and the native fuji lenses (16-80mm) Prime zoom, e.g. constant F4 throughout the range. I can test the theory about the lens design, as i can test one of my other lenses which is a 13mm F1.4 Prime

I hope were wrong, otherwise it's screws my whole portable rig setup as i cant afford to buy any more lenses at the moment, but might have to consider saving for a small 80mm triplet instead of using lenses.

[Northernlight]

27 minutes ago, Elp said:

I'm also guessing you're using native Fuji lenses and not a lens adaptor which can introduce internal reflections (from what I've read there aren't really any out there which don't internal reflect).

It could be the lens construction, I specifically only use manual primes as they tend to focus to infinity better. 

The reason I ask about camera model is because I recently got a Sony A7s, and upon trial I had a similar issue where from midpoint to outer edge I got a red/green ring pattern which didn't calibrate out. There's an option in camera for lens compensation and I've turned it off but haven't trialled it since. But with Sony cameras there's an apparent issue with these rings as well as the sensor being a half half design, as a lot of cameras out there use Sony sensors I wouldn't be surprised if the issues translate to different manufacturer bodies. Daytime photography is fine, but I can see the issue immediately at night when imaging 15-30s per image.

Elp, have you got any examples of the similar issues you faced.

[Elp]

Will post this afternoon, I've got a similar feeling with my Sony, I wanted the FF FOV and it's smaller than my Canon but I'll likely still keep it due to its video capability. Regarding lenses the best for AP is generally the Samyang 135mm F2, it's as good if not better than a lot of refractors or any other scope I've used, I've also achieved results with vintage Asahi Takumars with a little more post processing around star halo bloat.

[Northernlight]

I also have a Fuji 70-300mm zoom, i'm also going to test that as well.  will be interesting to see if the results will be as we suspect e..g. my prime doesn't show similar circular artefacts, but i expect my 70-300mm fuji to show similar artefacts as the 16-80mm lens.  The annoying thing is that both of my Fuji lenses were not cheap, they were around £750 each, so it would be a shame if they can't be used for Astro, as i was hoping to use the long 300mm focal length of my longer lens which is is equivalent to 450mm on full frame.

I'm also going to try stopping down my 16-80mm lens to F5.6, just to see what happens - whilst not ideal at F5.6 it will give me a good idea of what's going on with the lens.

Unfortunately it looks like i'm clouded out for the next week, so will be a while before i can test again. - No i remember why i got out of imaging nearly 2 years ago 🤔 - Imaging is a constant battle, that i dont seem to win very often lol.

 

[900SL]

Are you using a lens hood and do you have any off axis light sources like street lights etc?

[Northernlight]

no lens hood, and no stray street lights as taken in my back garden.   The only way i can really test is to try my 13mm Prime lens to see how that differs from the zoom lenses.

Will be interesting to test the same lens but without it being zoomed to see if i get the same effect. e.g. at the 16mm focal length vs the zoomed 80mm focal length.

[Elp]

3 hours ago, Northernlight said:

lenses

From my experience I'd guess 80 percent maybe of lenses just can't handle astro imaging, they're not designed for it so one cannot expect it. You can get results (as I've imaged with compact cameras with built in lens), but reading up on reviews you tend to hear the same models being recommended. I now generally steer clear from lenses which do not have ED lenses in their construction, and their MTF graphs need to show good sharpness across the frame (most suffer from bad coma, CA and loca away from centre). A lot depends on how fussy you want to be with the result.

Edited June 17, 2023 by Elp

[Elp]

This is the issue I had last time, image is previewed with a histogram stretch so you can clearly see the issue. After this was taken I looked it up and found that there was a lens compensation option switched on in the camera, but I was also using a Canon EF adapted Samyang 135mm so wouldn't rule out internal reflections in this image, was also using an lextreme filter up front which can also cause issues, I'm erring on it being a camera issue as it also happened when I did short test shots with my Takumar 50mm (again with a lens adaptor but no filter):

 

Another issue with my camera is apparently its sensor is half half rather than one whole sensor (don't know what genius came up with this idea), there's some residual green glow on the one side which also doesn't calibrate out, synthetic flats also don't work well with this. The bit on the bottom left corner is mostly a stacking artifact as the fence was coming into view, but the red tint is still there.

So my next port of call, try with the lens compensation off, and use a native E mount lens, but I may also try with the same optical setup to see if the issue changes.

Edited June 17, 2023 by Elp

[Northernlight]

I’ll try my 13mm prime and let you know how I get on,  but if my current lenses are no good I’ll have to reconsider and come up with plan B.

 

[happy-kat]

Do you have a different camera you could try with the lens as a comparison. Good luck in your testing 

Edited June 17, 2023 by happy-kat

[Northernlight]

Unfortunately not. I suspect the issue is the type of lens im using, as when I look at YouTube to see what everyone else is using, they are all using prime lenses. In the test shots I took with my zoom lens, it also had significant coma.

I just don’t want to spend £400 on the samyang 135mm prime lens, as i thing I’d rather put it towards a 80mm triplet.