Less diameter / diaphragm for more contrast? (Quark + APO)

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LucaR
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Less diameter / diaphragm for more contrast? (Quark + APO)

Post by LucaR »

Hi!

I've a Daystar Quark Combo and a setup APO+telecentric barlow+camera that allows me to get the full disc. However, it seems I'm too low in F/D and I dont get as much contrast as I should with my Quark - its obvious when I compare with pictures from other Quark's owners.

However I dont want to increase my focal lenth (by switching for a bigger barlow), in order to keep that full disc on frame. So I wonder if I can just shorten the diameter of my refractor by puting a disc with a hole in front of it? Would it work or am I believing in Santa Claus? :-)

Thanks!

My precise optical path is: APO 102mm f/5.3 - UV/IR-cut filter - Telecentric 3x barlow - Daystar Quark Combo - Asi2600mm.


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Re: Less diameter / diaphragm for more contrast? (Quark + APO)

Post by rsfoto »

Hi,

Stopping down will not bring you more contrast. Contrast in this case has something to do with the adjustment of the etalon eg. to be in band or not ...

IMHO

Stopping down will define if you under- or oversample as far as I have learned here.
Last edited by rsfoto on Tue Aug 09, 2022 2:44 pm, edited 1 time in total.


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Re: Less diameter / diaphragm for more contrast? (Quark + APO)

Post by marktownley »

Try it, a 50/60mm aperture mask.

I would also consider 2x binning with that camera to get a better sampling rate.


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Re: Less diameter / diaphragm for more contrast? (Quark + APO)

Post by LucaR »

marktownley wrote: Tue Aug 09, 2022 6:24 am Try it, a 50/60mm aperture mask.

I would also consider 2x binning with that camera to get a better sampling rate.
Thanks! I will give a try to see if it works. Its not as if it were something expansive or hard to do :-)


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Re: Less diameter / diaphragm for more contrast? (Quark + APO)

Post by OlegLviv »

Asi2600mm ohhh this camera not for sun.....yes big matrix and 26mp but rolling shutter and less fps....and f5.6 you never have good contrast...


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Re: Less diameter / diaphragm for more contrast? (Quark + APO)

Post by LucaR »

OlegLviv wrote: Wed Aug 10, 2022 1:18 pm Asi2600mm ohhh this camera not for sun.....yes big matrix and 26mp but rolling shutter and less fps....and f5.6 you never have good contrast...
Yeah I know :-) I use it because it gives me full disc scale with my setup, so I try to get the best I can from it :-) Slow FPS is not such a big deal: at this scale, we dont see much movement on sun surface in term of a few minutes. When I want to get closer, I use a faster Zwo 178mm. And yes f5.6 even with barlow 3x is not enought, that's what I try to improve here. Rolling shutter well... there is nothing I can do about it :-)


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Re: Less diameter / diaphragm for more contrast? (Quark + APO)

Post by LucaR »

OK so!

I tried to put that... thing... very amateurish... in front of my lense :-)

20220810_134135 (2).jpg
20220810_134135 (2).jpg (467.28 KiB) Viewed 1625 times

( I'll definitivly call it my "Black hole sun" :-D )

The hole has a 70mm diameter.

And it gave me this (best I can do with it):

Soleil 220810 - Avec diaphragme 70cm.jpg
Soleil 220810 - Avec diaphragme 70cm.jpg (6.05 MiB) Viewed 1625 times

Seconds after I immediatly took an other image without it, in order to compare. Best I could do with this other image is:

Soleil 220810 - Sans diaphragmre.jpg
Soleil 220810 - Sans diaphragmre.jpg (8.38 MiB) Viewed 1625 times

Seems good! As expected: clearly better contrast, but lesser definition:

Comp.jpg
Comp.jpg (864.2 KiB) Viewed 1625 times

Prominences are by far better in the non-diaphragmed photo:
Comp2.jpg
Comp2.jpg (449.18 KiB) Viewed 1625 times

So I combined both images with a mask: most of the disc is from the diaphragmed one, circumpherence and prominences are from the other:

Image


So ya... it works!

I might give a try to a 50mm hole later, but at some point I'll probably loose too much details to keep this interesting.


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Re: Less diameter / diaphragm for more contrast? (Quark + APO)

Post by OlegLviv »

Nice Testing! 70mm better 102mm


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Re: Less diameter / diaphragm for more contrast? (Quark + APO)

Post by marktownley »

Stopping down for contrast is definitely better.


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