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4" f/9 or 4" f/6 with quark?

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#1 NorthernlatAK

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Posted 23 May 2019 - 06:01 PM

I'm considering getting into ha solar and was wondering if anyone has done side by side comparisons with same aperture, different f ratio scopes. Preferably a test with the same quark. How much of a difference will there be in contrast and how slow can you go with a 4" before it's too dim? You guys and gals have given me the ha bug and I thirst for your ha wisdom.

#2 Spikey131

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Posted 23 May 2019 - 07:22 PM

I have not. But I did make aperture masks to make my 80mm f/6 a 60mm f/8 and 40mm f/12.

I did not see any significant improvement in surface detail, contrast or proms.

#3 MalVeauX

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Posted 23 May 2019 - 08:29 PM

Heya,

 

I've used 80mm F5 and 80mm F7.5 with the same scope. It's not terribly different visually, not enough for me to worry about. The surface contrast is slightly better in the longer focal-ratio situation, but visually, it's not nearly as noticeable as the difference isn't profound. Also, you would be hard pressed to ever get the focal-ratio too long, visually, and get a dim image. I've used F10 scopes with my Quark with binoviewers and 20mm eyepieces and still had plenty of brightness. You don't need to worry about it being dim. If you use a really long focal-ratio (heck, use a F15 if you want) and it will still be bright, and if you want it really bright, use longer focal length eyepieces (25mm~32mm).

 

Very best,



#4 NorthernlatAK

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Posted 23 May 2019 - 09:00 PM

Thanks for that response, that's exactly what I was wondering. So it seems I can get a cheap long achromat and still get decent results. This will widen my search to keep the cost down. I probably won't have a setup for at least a few months but now I know what to look for. My only other concern is with a long f ratio will I need tracking with a smaller fov? Or is manual tracking doable? I'm used to manual tracking with my 8" f/6 dob.

#5 MalVeauX

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Posted 23 May 2019 - 09:16 PM

Heya,

 

You'll want tracking for anything longer than maybe 600mm I would think. The 4.2x telecentric amplifier in the Quark will put your focal length quite long. A 600mm scope will be 2520mm with the Quark, with a 32mm eyepiece, you're at around 78x magnification. That's going to show a lot already. But it will be moving out of the FOV. You will be able to keep up with it at a lower magnification. But, longer than that, as you creep into the 750~1,000mm+ focal length ranges on the base scope, it will quickly become very difficult to stay on target manually unless it's one of your passions to manually track things at high magnifications. Ultimately you will not want high magnification with solar anyways, very often, unless seeing is really good (which it won't be unless you're in a location with excellent seeing to begin with due to geographic location). You'll likely not want to venture too far from 100x magnification in general, unless seeing is exceptional. Daytime seeing is significantly worse than nighttime.

 

That said, you can see a lot on the sun with an 80mm aperture. Any typical 80~102mm achromat will do a fine job and can be used manually with a long focal length eyepiece (32mm~40mm) and throw up a bright image no problem.

 

Very best,



#6 NorthernlatAK

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Posted 23 May 2019 - 10:19 PM

I have a wl baader filter for my 8" and seeing allows me to go to roughly 100× like you said. Rarely more. Alaskan skies are quite turbulent but magic unicorn dust does rarely gets sprinkled for steady skies at times. I'll probably start manual then upgrade when I can afford it. Your pics, Marty, are mostly what inspired me to start this solar expenditure, so I'll blame you mostly for my empty wallet! Love your work and thanx for sharing your knowledge with us!

#7 ValeryD

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Posted 23 May 2019 - 10:54 PM

NorthernlatAK,

 

better to use longer F/D.   You will get three advantages:

 

1. The bandwidth will be somewhat tighter (can easily note this for dark filaments and mottling).

2. The Field of View (FOV) will be more uniform in brightness/contrast.  This is very important.

3, For the same magnification you will need longer FL eyepieces,  say 40-42mm instead of 30-32mm - this means your eyes will be in more confortable position with longer eye relief.

 

I always use my Quark with final F/40-45.

 

Hope this helps.

 

 

Valery



#8 NorthernlatAK

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Posted 23 May 2019 - 11:14 PM

Love your work as well Valery, your pics always have tons of contrast and sharp detail. My gut was telling me f/10ish but wanted to confirm. Once I have a few $ I'll look for a 4" f/10. I don't think seeing will allow me to go much bigger in aperture.
One last question. Is there differences/advantages in using a mak vs a refractor of similar f/ratio and aperture?

#9 ValeryD

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Posted 24 May 2019 - 01:32 AM

Love your work as well Valery, your pics always have tons of contrast and sharp detail. My gut was telling me f/10ish but wanted to confirm. Once I have a few $ I'll look for a 4" f/10. I don't think seeing will allow me to go much bigger in aperture.
One last question. Is there differences/advantages in using a mak vs a refractor of similar f/ratio and aperture?

 Don't be  misleaded about total absense of a seeing.  This is a common misconception.  In a warm season the earth atmosphere has two periods of relatively equilibrium condition - early morning and just before the sunset.  The morningperiod is very prone to a period of a good seeing.

Also, during early fall or middle spring a good seeing can occur even during a whole day.

 

Better to use a refractor. 

 

And don't forget to use at least 1.25" UV/IR  better Baader 35nm H-a filter on the nose of a 1.25" star-diagonal - to protect the Quark's blocking filter.

 

Hope this helps. 

 

 

Valery


Edited by ValeryD, 24 May 2019 - 01:35 AM.


#10 NorthernlatAK

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Posted 24 May 2019 - 02:28 AM

Don't be misleaded about total absense of a seeing. This is a common misconception. In a warm season the earth atmosphere has two periods of relatively equilibrium condition - early morning and just before the sunset. The morningperiod is very prone to a period of a good seeing.
Also, during early fall or middle spring a good seeing can occur even during a whole day.

Better to use a refractor.

And don't forget to use at least 1.25" UV/IR better Baader 35nm H-a filter on the nose of a 1.25" star-diagonal - to protect the Quark's blocking filter.

Hope this helps.


Valery

Ive noticed some good seeing at those times and almost never observe around noon. At my location evening is surprisingly good at times and at my latitude we get about 3 hrs in the morning and evening of decent seeing due to the shallow inclined path. We get no true darkness from end of April until August. We do get a brief period in spring and fall of good seeing. As I write this a photographer friend is donating a tripod towards my ha setup! Understood with the uv/ir block. Thanks again for the help.


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