9 replies to this topic

[YossiZ]

Hi all,

I recently recieved a new WO GT71 f/5.9 refractor (for both night and day use), a Daystar Quark Chromo filter and a UV/IR cut filter. I intend to use it both for visual solar Ha and for imaging with my ASI290MM and x0.5 reducer (between the Quark and the camera).

I am still waiting for an opportunity for first light. In the meantime, I re-read some suggestions that I saw and want to be prepared. I understand that f/24.8 is a little less then recommended, so I started to think about aperture mask.

A few questions for the experienced observers:
1. Is the lose of resolution really worth the added contrast?
1. If so, will masking to 60mm (yielding f/7 and therefore f/29.3) be good enough?
3. How do you suggest to prepare the mask? Will a 3D printed disc with 60mm hole that can be inserted into the OTA do the trick?

Thank you!

Edited by YossiZ, 26 January 2022 - 03:01 PM.

[betacygni]

I’m only visual with my quark, so my experiences only apply to that realm:

1) I have done many experiments with aperture masks, f ratios, and different scopes. For visual I think the longer focal ratio is overblown, and in fact sometimes worse at longer focal lengths. In side by side comparisons between same apertures, at f5 vs f11, the f5 is better. Yes there is slightly more contrast at the longer focal length, but nothing “new” is seen at f11 that can’t be seen at f5. Rather the image is much dimmer, and the magnification much higher, often becoming seeing limited. I much prefer the slightly less contrast, but brighter/more steady image of shorter focal ratio scopes. For imaging though I could see the opposite being true, but again no first hand experience there. I’m still playing around with an f8.2 that I really like, but it’s more aperture and image scale, still need to experiment, but I think that has more to do with it than f ratio.

2) I’ve noticed the contrast gain starting at around f8-f9. Though don’t recall if I’ve used an f7, for sure an f5, f6, and f8.2 though.

3) I had a 3D dust cover (over dew shield type) made with smaller aperture for testing, it deformed under heat of the sun and would no longer fit. Don’t know if 3D printing can use more heat resistant materials, but what I had didn’t work . I’d say just use home materials like tape and thin cardboard, easy to test out to see if you like the change, then maybe make a more permanent solution after.

Edited by betacygni, 26 January 2022 - 03:27 PM.

[hamers]

I think you should also consider impact on exposure time. A smaller aperture may give slightly higher contrast due to increased effective f/number, but it will also mean a longer exposure time, which means less ability to freeze in seeing. 

Edited by hamers, 26 January 2022 - 05:27 PM.

[hopskipson]

The beauty of the Quark is that you can use it on different size telescopes.  I've used it on an ST80 at F/5 but find the image is way too bright.  I think the sweet spot for most seeing conditions is a 100mm F/7 scope for imaging and 120mm at F/10 for visual.  If you have excellent seeing conditions then that is a different story.

 

With mica spaced etalons like the Quark, the bandpass is dependent on the F-ratio.  The more narrow the bandpass the less photosphere light leaks through.  This is why the image gets dimmer and more features can be seen on the disk.  I've used the Quark at F/30 - F/50 and the difference is night and day.

[YossiZ]

Thank you for the information.

I will start with f/25 with and without the binoviewer and then try f/30 as well.

[YossiZ]

I just had my first light.

I did not have time to tweak the quark, make masks or anything like that.

Nethertheless, it was fantastic to see some proms, ARs, filaments and plages.

 

The hand-held S20 images shows mostly proms.

 

 

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[MalVeauX]

Hi all,

I recently recieved a new WO GT71 f/5.9 refractor (for both night and day use), a Daystar Quark Chromo filter and a UV/IR cut filter. I intend to use it both for visual solar Ha and for imaging with my ASI290MM and x0.5 reducer (between the Quark and the camera).

I am still waiting for an opportunity for first light. In the meantime, I re-read some suggestions that I saw and want to be prepared. I understand that f/24.8 is a little less then recommended, so I started to think about aperture mask.

A few questions for the experienced observers:
1. Is the lose of resolution really worth the added contrast?
1. If so, will masking to 60mm (yielding f/7 and therefore f/29.3) be good enough?
3. How do you suggest to prepare the mask? Will a 3D printed disc with 60mm hole that can be inserted into the OTA do the trick?

Thank you!

Hi,

 

1) Really depends, a lot goes into the contrast bit including the weather conditions of the air you're shooting through (high moisture, etc). You can get decent contrast even at F21 (nearly 0.9A) for imaging, if you can process it (visually it will work but it will not be great for surface visual, but works perfectly fine at the limb). I would argue that the resolution difference is negligible because unless your seeing is excellent, you won't be realizing a resolution difference anyways. You would need better than 2 arc-second seeing sustained to benefit the larger aperture over 60mm for example in HA wavelength to bother worrying about the 71mm aperture of your native scope. If you mask it, make sure its a very smooth circle. The beauty is you can try both and see what works best for your expectation and conditions since a mask is reversible.

 

2) It will be ok. F30 is the minimum, not the ideal. F40~F50 is more ideal. You'll just have to see what you think of your results (heavily depends on your filter's quality and properties like finesse, etc). I wouldn't stress it too much. A 42mm mask would be more ideal for the filter performance (F10), but you may not like the resolution if you have better seeing conditions and sampling will be mismatched to your tiny pixels even with a reducer.

 

3) Absolutely, works great. I use lots of these, it gets you a smooth circle and you can make lots of different masks.

 

Very best,

[Siderius]

You're off to a good start with your phone pictures! I started with handheld afocal, too, though not through a quark (much, yet). Most would advise a dedicated astronomy camera to capture batches of frames to process and stack. But new phones are very capable cameras in their own right. A phone holder is all it takes to put one to work.

 

Once the phone is positioned, you can systematically study exposure and focus to tease out the most detail from an exposure. And with your hands free, you can do a lot of handwaving during outreach ;^)

 

[YossiZ]

You're off to a good start with your phone pictures! I started with handheld afocal, too, though not through a quark (much, yet). Most would advise a dedicated astronomy camera to capture batches of frames to process and stack. But new phones are very capable cameras in their own right. A phone holder is all it takes to put one to work.

 

Once the phone is positioned, you can systematically study exposure and focus to tease out the most detail from an exposure. And with your hands free, you can do a lot of handwaving during outreach ;^)

 

 

Thank you, and nice phone-imaging rig.

 

After I'll gain some visual experience, I will try imaging with my ASI290MM and 0.5x focal reducer.

[YossiZ]

I just finished my best visual session so far. The amount and varity of sunspots, filaments, plage regions and proms is amazing, but there were two other factors as well.

1. High clouds / haze made a very stable and contrast view. I tried 50 and 60mm masks, but it was not necessary under those conditions.

2. I started observing right after plugging in the quark. The view started as WL with all the sunspots, and gradually more and more Ha detail was added: first the brightest proms, then darkest filaments, then more and more limb and surface details and finally the Sun at its full glory. I think I will do the same every time from now on.

Some images:
The system and the great weather conditions:


The 3D printed mask (I know, black is not ideal):


A lousy hand-held phone image of an insanely high detached prom:

Edited by YossiZ, 31 March 2022 - 12:24 PM.