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How effective is a 0.5x Reducer with a Quark?

Posted: Sat Jan 09, 2021 9:02 pm
by SimonM
With Quark, I have a small 178 camera for cropped views. My interest is getting a very wide view. Probably best not to use a colour camera with a bigger sensor?

How effective is a 0.5x Reducer placed after the Quark:

Objective —> UV/IR cut —> 2” diagonal —> Quark (with 4.3x Barlow) —> Reducer —> EP/ camera?

Quark Specifications (page 13):

1. Integrated 12mm blocking filter;

2. 20mm clear etalon aperture;

3. Passes full solar disk for focal lengths under ~450mm;

4. Suggested EPs are 25, 32 and 40mm EP.

I have 25mm and 40mm 1.25” Plössyl EPs.

Also a 36mm 2” (with a 1.25” alternative) and wide 72 degree FOV EP.

Also 5mm - 24mm EPs.

Need to evaluate Quark across field - going to use my colour 294 and DSLR (wrong choices, but all I have).

The big unknown, is effect of a 0.5x reducer. Would a cheap 0.5x Reducer help here, or just be a waste of money?

An EP like my 36mm, that has both 1.25” and 2” barrel, will be limited by Quark field stop and not the 1.25” barrel? So, no value in using a 2” EP holder with Quark?


Re: How effective is a 0.5x Reducer with a Quark?

Posted: Sat Jan 09, 2021 10:13 pm
by SimonM
I think I found the answer. (reading other threads), a “cheap” 0.5x reducer is probably a complete waste of time e.g. lucky to get anything useful out (and in focus). To aid my understanding, is the size of the blocking filter also the maximum available useful sensor size?

Re: How effective is a 0.5x Reducer with a Quark?

Posted: Sat Jan 09, 2021 10:27 pm
by rsfoto
Instructions state a “whole disc” requires 450mm FL or less, my scope is 550mm.
Hi Simon,

I just looked into the DayStar page and there it says
Full disk viewing possible on refractors up to ~450mm focal length refractors
" viewing ", not imaging and as far as I understand a Quark with a 4.3X telecentric makes your native focal length 4.3X bigger and a common rule for the disc size in mm for imaging is about the focal length in mm / 109.

So your 550 mm native focal length telescope with 4.3X gives you a focal length of 1650 mm which equals to a full Sun disc of about 15.1 mm and adding a 0.5X reducer then your disc is about 7.55 mm ...

Re: How effective is a 0.5x Reducer with a Quark?

Posted: Sun Jan 10, 2021 1:07 am
by SimonM
Thanks Rainer

I updated the list of specs (see above).

With an EP of 40mm I will see as wide a FOV as the Quark can show. About the same from the 36mm for normal use with a scope.

I think the issue here will not be how low a magnification can be used, but what are the limitations of the Quark e.g. the Etalon aperture or the blocking filter size.

My 36mm EP with SCT has a FOV of 72 degrees using a 2” EP barrel and a 31mm field stop, but put it in a 1.25” and it drops to 58 degrees. With the Quark I think it will be further restricted to much less. Similarly the 40mm plössyl is restricted by being 1.25”. So I’m expecting far less than a FOV calculator implies.

The focal length / 109 disc size would be correct for imaging, but may be limited by the size of one of the apertures in the scope e.g. 12mm.

Although it is not ideal, I can use my colour camera with a diagonal of 23mm, to see what can be achieved. My 178 is not a big sensor, but ideal for detail if conditions permit it.

A 0.5x Reducer can change the FOV, but it is also up against practical limits of the Quark. 0.5x in a spec is just a guide e.g. varying the spacing to an EP might reduce the effectiveness. The quality of cheap versions also means it may not be worth the effort (and expense).


Re: How effective is a 0.5x Reducer with a Quark?

Posted: Sun Jan 10, 2021 8:34 am
by marktownley
My advice Simon, evaluate the Quark using the mono camera with 2x2 binning.

On terms of eyepieces, Daystars advice of 25-40mm plossls is the best. Personally I don't like using a 40mm plossl, I find it too much like looking through a drinking straw, I use a 32mm and 25mm the most, I think my preference is the 25mm. I'm hoping astroboot reopens soon, they have a 25mm 58deg Skywatcher WA plossl for £25 which could be interesting.

In terms of constraints with eyepieces, the Quarks 21mm etalons aperture is key here, so, eyepieces with a field stop larger than this will suffer vignetting. This may not be an issue when viewing a full disk where the sun is surrounded by sky, but, for closer views the vignetting can be annoying.

I don't like or use 0.5x reducers, if I want a larger fov I use a larger chip, if the seeing doesn't allow I sample it at a smaller aperture that supports the seeing.


Re: How effective is a 0.5x Reducer with a Quark?

Posted: Mon Jan 11, 2021 3:12 pm
by RodAstro
Hi Simon

As Mark says use a mono camera
Your QHY5 mono camera has a large chip for a guide camera and that with a 0.5 reducer will see most of the etalon so for evaluating the etalons field illumination it should work fine. It wont be the best for imaging as the QHY5 suffers greatly horizontal lines when Ha imaging but it will give you a good idea of how well the quark works.
Also for field illumination testing you need to take an image with a long focal length scope of the central part of the sun where the suns illumination is even.
If you already haven't done so learn lucky imaging using Firecapture, Autostakkert and ImPPG with the QHY5 for best evaluations.

Quarks are not good for full disk images of the sun as they work best at f30 so you end up with a scope around 30mm aperture and that limits resolution.
But for looking at zoomed in detail and imaging this detail they are very good (when you have a good one) and are easy to use.
They also work very well with binocular heads especially for viewing chromosphere detail. The telecentric beam after the quark gives you more scope for things like bino heads and camera tilters so you don't need as much in focus to use them.

Cheers Rod