Is this Star Bloat ?

[WolfieGlos]

I recently purchased a ZWO 585mc for planetary imaging - and to try for some DSO as well after good reviews.

Due to ongoing cloud cover and being part way through a mosaic with the DSLR, I haven't taken apart my imaging train to try it on my main scope. So feeling a test session with the recent Full Moon, I hooked up the 585mc to my Evostar 72ED with 1x FF with a nose piece, and tried imaging some clusters. I wasn't bothered about tilt, it was more just a test to see how it performed. I intended to then capture the Moon, but clouds stopped that.....

Anyway, the blue rings to the stars are quite obvious, but the star sizes seem excessively large. This was 75 x 30s subs at gain 252 on NGC 659, using a ZWO 1.25" IR/UV Cut Filter.

No star reduction, just stacked+processed in Siril. Original stacked file also included.

 

result_2252s.fit

[ONIKKINEN]

Looks like chromatic aberration, yeah. Bright stars are larger on the blue channel than the red and green channels, which is seen as star bloat.

Probably just the 72ED to blame and not something to do with the camera itself i would say.

[WolfieGlos]

Thanks Onikkinen.

Perhaps I should have bought an Astronomik L3 UV/IR filter if pairing with the 72ED then.

I need to buy a 2" filter to use it with my Canon 200mm f2.8 lens which I intend to try it with (gives a really nice FOV - https://astronomy.tools/calculators/field_of_view/?fov[]=334||9791||1|1|45&messier=31 ), so perhaps I'll try an L2 to start and see how it goes. This would then also work if I try and pair it with my 102ED, which I doubt would require an L3.

[ollypenrice]

The bloat is also quite magenta, so green is low - for whatever reason.

Olly

[gorann]

Quite a nice image but is not this (blue bloating) what you would theoretically expect from a doublet compared to a triplet apo?

Edited November 8, 2023 by gorann

[Adam J]

On 06/11/2023 at 00:10, WolfieGlos said:

I recently purchased a ZWO 585mc for planetary imaging - and to try for some DSO as well after good reviews.

Due to ongoing cloud cover and being part way through a mosaic with the DSLR, I haven't taken apart my imaging train to try it on my main scope. So feeling a test session with the recent Full Moon, I hooked up the 585mc to my Evostar 72ED with 1x FF with a nose piece, and tried imaging some clusters. I wasn't bothered about tilt, it was more just a test to see how it performed. I intended to then capture the Moon, but clouds stopped that.....

Anyway, the blue rings to the stars are quite obvious, but the star sizes seem excessively large. This was 75 x 30s subs at gain 252 on NGC 659, using a ZWO 1.25" IR/UV Cut Filter.

No star reduction, just stacked+processed in Siril. Original stacked file also included.

 

result_2252s.fit 94.93 MB · 4 downloads

Yes that is star bloat as a result f chromatic aberration, not unexpected on your 72ED. There are better options than the ZWO UV/IR filter you are using, the astronomic L3 being one good option as it will cut more blue out. The 1.25 inch version will work fine just use the filter adaptor that came with the camera. 

Adam 

Edited November 11, 2023 by Adam J

[Adam J]

2 minutes ago, Adam J said:

Yes that is star bloat as a result f chromatic aberration, not unexpected on your 72ED. There are better options than the ZWO UV/IR filter you are using, the astronomic L3 being one good option as it will cut more blue out. 

Adam 

 

On 06/11/2023 at 13:15, WolfieGlos said:

Thanks Onikkinen.

Perhaps I should have bought an Astronomik L3 UV/IR filter if pairing with the 72ED then.

I need to buy a 2" filter to use it with my Canon 200mm f2.8 lens which I intend to try it with (gives a really nice FOV - https://astronomy.tools/calculators/field_of_view/?fov[]=334||9791||1|1|45&messier=31 ), so perhaps I'll try an L2 to start and see how it goes. This would then also work if I try and pair it with my 102ED, which I doubt would require an L3.

No the L2 is the same spec as the ZWO one and will change nothing. 

[WolfieGlos]

Sorry, I should have been a bit clearer about what I meant!

The large stars in the top left and right looked bloated to me, and that was my concern. I commented on the blue halo's suggesting that whilst I've noticed them, I wasn't concerned because it is a doublet - perhaps I wasn't clear about that. I was thinking more along the lines of whether the UV/IR cut was not doing it's job on the larger, bloated looking stars.

I don't intend to pair the camera with the 72ED for imaging, it was just convenient at the time for a test session to see how the camera worked because a) I didn't want to dismantle my 102ED imaging train and b) I didn't have an adapter to use it with a camera lens.

[Adam J]

1 hour ago, WolfieGlos said:

Sorry, I should have been a bit clearer about what I meant!

The large stars in the top left and right looked bloated to me, and that was my concern. I commented on the blue halo's suggesting that whilst I've noticed them, I wasn't concerned because it is a doublet - perhaps I wasn't clear about that. I was thinking more along the lines of whether the UV/IR cut was not doing it's job on the larger, bloated looking stars.

I don't intend to pair the camera with the 72ED for imaging, it was just convenient at the time for a test session to see how the camera worked because a) I didn't want to dismantle my 102ED imaging train and b) I didn't have an adapter to use it with a camera lens.

So I would actually say the top right is suffering from a tiny amount of tilt.