Is the (main) problem with the stars in this image the focus?

[LowGravitas]

Taken with a modified Canon 600D/T3i and an SMC Takumar 200mm F4 lens with an M42 adaptor.

Are the bizarre pentagonal halos of the stars a focus problem or an intrinsic lens flaw, by the looks of it?

Edited October 24, 2020 by LowGravitas

[Budgie1]

Is this a single sub or has it been stacked?

You have quite a few pin-point stars in there, as well as the bloated ones, so focus doesn't seem to be the issue.

Was there dew around when you took the image as it could be a build up of dew on the lens? If the image is stacked then check the subs and see if some later ones have this issue, which may indicate dew.

(You may want to change the text colour in the post as it's come out brown or dark grey and I had to swipe over it to see what it said. )

[LowGravitas]

Oh sorry. This is a stack. I don't think dew is the issue, because the stars seem bad in this sub from the start of the session.

 

Edited October 24, 2020 by LowGravitas

[Seelive]

To me it appears to be a lens issue, the 'flares' appear to be roughly concentric with the field centre. If you get the chance, try stopping the lens down a stop or two and see if that makes any significant change.

[LowGravitas]

Thanks for your input. I did stop it down to f 5.6. I've seen many astro photos taken with this lens with Canon DSLRs at that focal ratio, and none have stars that look anything like this.

Maybe mine is defective.

[happy-kat]

Have you tried another lens on your modified camera body on an area of sky with bright stars.

I have an old takumar lens and rather than the blue channel having chromatic aberration it is the red channel. Maybe you could carefully adjust focus allowing for this. 

[LowGravitas]

I haven't yet, but I will when the clouds clear again.

[happy-kat]

Is your camera full or part modified, my memory is thinking something about with one if the shims on the sensor are out focus might be a problem.

[LowGravitas]

Its hot mirror was removed by Juan from Cheap Astrophotography. 

Edited October 24, 2020 by LowGravitas

[happy-kat]

I think wait to try another of your lenses on it first to see what goes on then

[Chefgage]

2 hours ago, LowGravitas said:

Oh sorry. This is a stack. I don't think dew is the issue, because the stars seem bad in this sub from the start of the session.

 

I get the same with my canon 75mm to 300mm lens (it's the EF 4-5.6 version). This got a lot worse when I modified the camera (lots of red halos). The issue goes away when a telescope is used instead of the lens. From what I have read it's common with cheaper lenses.

[LowGravitas]

I really hope that's not the case, as I can't afford a telescope. I've seem images taken with modified DSLRs and this lens at the same f stop with stars that look nothing like mine. So I don't know why the problem would apply to me and not to them.

[ollypenrice]

It looks like a miscollimated lens to me, at first sight.

Olly

[LowGravitas]

14 minutes ago, ollypenrice said:

It looks like a miscollimated lens to me, at first sight.

Olly

Could the adapter be the issue? It causing the lens to no sit perfectly flush with the camera body? It's just a cheap thing off Amazon.

[rnobleeddy]

I saw issues like this, but not as pronounced, using a few cheaper lenses with an astromodded camera. 

I never really figured out exactly why but it doesn't happen with a scope, it got better as I stopped down and it was worse on a camera with a full astromod compared to a stock camera.

The lens I was using had a red dot indicating the infinity IR focal position and that was quite a long way from standard infinity focus. I guessed I was getting some aberration on the red end which was exacerbated by the mod (although I was using a CLS CCD filter as well). 

 

Edited October 25, 2020 by rnobleeddy

[LowGravitas]

1 hour ago, rnobleeddy said:

I saw issues like this, but not as pronounced, using a few cheaper lenses with an astromodded camera. 

I never really figured out exactly why but it doesn't happen with a scope, it got better as I stopped down and it was worse on a camera with a full astromod compared to a stock camera.

The lens I was using had a red dot indicating the infinity IR focal position and that was quite a long way from standard infinity focus. I guessed I was getting some aberration on the red end which was exacerbated by the mod (although I was using a CLS CCD filter as well). 

 

I've seem images taken with modified DSLRs and this lens at the same f stop with stars that look nothing like mine. So I don't know why the problem would apply to me and not to them.

[ollypenrice]

19 hours ago, Chefgage said:

I get the same with my canon 75mm to 300mm lens (it's the EF 4-5.6 version). This got a lot worse when I modified the camera (lots of red halos). The issue goes away when a telescope is used instead of the lens. From what I have read it's common with cheaper lenses.

In support of this observation the 'shuttlecock' artifacts are predominantly red, suggesting that the lens is not controlling those newly active deep red wavelengths. Note that the shuttlecocks are all orientated as if racing away from a roughly central point, strongly suggesting an origin in the lens.

Origin

[LowGravitas]

2 minutes ago, ollypenrice said:

In support of this observation the 'shuttlecock' artifacts are predominantly red, suggesting that the lens is not controlling those newly active deep red wavelengths. Note that the shuttlecocks are all orientated as if racing away from a roughly central point, strongly suggesting an origin in the lens.

Origin

I echo the above sentiment. I've seem images taken with modified DSLRs and this lens and the stars don't look like mine.  Here is a review of the lens showing an image taken with it and a modded Canon DSLR, for example:

http://www.nightofmanywords.com/articles/budget-lenses-for-astrophotography

 

So, I don't know why the problem would apply only to me.

[happy-kat]

I think there may have been careful use of focus to not focus on what would be perfect focus but just off focus so chromatic aberration was not at it's strongest. You'll have to fiddle and experiment.

[LowGravitas]

9 minutes ago, happy-kat said:

I think there may have been careful use of focus to not focus on what would be perfect focus but just off focus so chromatic aberration was not at it's strongest. You'll have to fiddle and experiment.

I suppose I will. I also found this thread, where a user says that an M42 adaptor with a flange that presses the auto pin (such as mine) causes the lens to sit tilted on the camera:

Anyone know if that's right? Might it have any bearing on my problem?

[rnobleeddy]

1 hour ago, LowGravitas said:

I suppose I will. I also found this thread, where a user says that an M42 adaptor with a flange that presses the auto pin (such as mine) causes the lens to sit tilted on the camera:

Anyone know if that's right? Might it have any bearing on my problem?

 

4 hours ago, LowGravitas said:

I've seem images taken with modified DSLRs and this lens at the same f stop with stars that look nothing like mine. So I don't know why the problem would apply to me and not to them.

This does look worse than others I've seen, but have you see other people with the same lens posting pictures? Do you know that lens is good for this kind of photography? 

Next thing I'd do is try a different lens. Or adapter. I rate https://www.amazon.co.uk/Pixco-Confirm-Adapter-Camera-M42-EOS/dp/B079BGLP4P?th=1 a lot more highly than the one I got for £3 on eBay, but they produced the same results.

[LowGravitas]

10 minutes ago, rnobleeddy said:

 

This does look worse than others I've seen, but have you see other people with the same lens posting pictures? Do you know that lens is good for this kind of photography? 

Next thing I'd do is try a different lens. Or adapter. I rate https://www.amazon.co.uk/Pixco-Confirm-Adapter-Camera-M42-EOS/dp/B079BGLP4P?th=1 a lot more highly than the one I got for £3 on eBay, but they produced the same results.

Yeah, here's a review of the lens showing a pic taken with it:

http://www.nightofmanywords.com/articles/budget-lenses-for-astrophotography

And images on astrobin:

https://www.astrobin.com/search/?q=smc+takumar+200mm

A video extolling it's virtues:

https://www.youtube.com/watch?v=z6TuOa3mCFY

None have stars like mine.

Edited October 25, 2020 by LowGravitas

[rnobleeddy]

4 minutes ago, LowGravitas said:

Yeah, here's a review of the lens showing a pic taken with it:

http://www.nightofmanywords.com/articles/budget-lenses-for-astrophotography

And images on astrobin:

https://www.astrobin.com/search/?q=smc+takumar+200mm

None have stars like mine.

Then you're going to need to try changing one thing at a time.

[happy-kat]

I would start with testing any other lens you may have. 

[LowGravitas]

Taking a close look at my lens, I noticed what looks like a chip or aberration near the centre of one of the elements behind the objective. Look problematic?