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EAA More detail on galaxies: Monochrome or extra 1" of aperture

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#1 jkelly

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Posted 23 March 2023 - 08:06 AM

I realize this is a flawed question.

What would provide more detail in my EAA images.

Switching to a 533MM and shooting monochrome or getting a new scope with an extra inch of aperture (3") and keep using 533MC.


 

#2 alphatripleplus

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Posted 23 March 2023 - 08:18 AM

Exactly what do you mean by detail?

 

If you mean the ability to resolve close stars or see see more structure in nebulosity, that depends on seeing and the image scale (in arcsecs/pixel) for a given camera/scope focal length combo. If on the other hand, you mean sensitivity, i.e. showing fainter stars in a given exposure, that will depend on aperture and mono vs colour camera. Please clarify.


 

#3 Tfer

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Posted 23 March 2023 - 08:30 AM

You can always make up for mono vs color with extra time.

There’s no substitute for aperture when it comes to resolution.
 

#4 jkelly

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Posted 23 March 2023 - 08:51 AM

Exactly what do you mean by detail?

 

If you mean the ability to resolve close stars or see see more structure in nebulosity, that depends on seeing and the image scale (in arcsecs/pixel) for a given camera/scope focal length combo. If on the other hand, you mean sensitivity, i.e. showing fainter stars in a given exposure, that will depend on aperture and mono vs colour camera. Please clarify.

 

The ability to resolve close stars or see more structure in nebulosity. And thank you for the answer!

 


Edited by jkelly, 23 March 2023 - 08:52 AM.

 

#5 PeterAB

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Posted 23 March 2023 - 09:08 AM

Hi,

 

I assume you are using your 50ED with the flattener now.  

 

My other assumption is that by detail you are looking for more resolution of details in galaxies.   This is different from simple light gathering.   For example two arms of a galaxy clearly separated, vs blurred together appearing as one.

 

An 80mm telescope would be the way go for more resolution.    I would go for a modest focal ratio in the f7 range.   A Skywatcher 80ED would work.

 

Two benefits.   The increase in aperture will increase optical resolution.    The increase in focal length will improve pixel scale and be a much better match for your asi533. 

 

You are now under resolved and under sampled for even fair seeing conditions.     This is fine for some objects like large nebulae.    Not so good for galaxies.    A new telescope would help both these issues. 

 

A new camera with much smaller pixels to match the 50ED will not fix optical resolution.

 

I use https://astronomy.to...pe_capabilities to estimate optical resolution and https://astronomy.tools/calculators/telescope_capabilities to match the camera to the telescope and seeing conditions.

 

 

Peter


Edited by PeterAB, 23 March 2023 - 09:13 AM.

 

#6 nicknacknock

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Posted 23 March 2023 - 09:15 AM

Invest $369 in the Astro-Tech 80ED. The AZ GTi can handle it in EQ mod. Bigger light bucket, better sampling and resolution. Fairly light scope, truly wonderful focuser. Classic f7 ED optics.

 

I was doing EAA at some point with a 90mm Borg FL with heavy Kasai focuser - no problem at all with the GTI.

Attached Thumbnails

  • Borg.jpg

 

#7 jonnybravo0311

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Posted 23 March 2023 - 09:39 AM

Invest $369 in the Astro-Tech 80ED. The AZ GTi can handle it in EQ mod. Bigger light bucket, better sampling and resolution. Fairly light scope, truly wonderful focuser. Classic f7 ED optics.

 

I was doing EAA at some point with a 90mm Borg FL with heavy Kasai focuser - no problem at all with the GTI.

I'm pretty sure that's the first time I've ever heard an 80mm 'frac referred to as a "light bucket" :p


 

#8 nicknacknock

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Posted 23 March 2023 - 09:40 AM

In terms of 80mm  Vs 50mm and for EAA, it is a bigger light bucket lol.gif lol.gif lol.gif

 

Buckets come in all sizes and shapes tongue2.gif


 

#9 jkelly

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Posted 23 March 2023 - 10:17 AM

Astro-Tech 80ED.ordered !

TY!


 

#10 Mark Lovik

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Posted 23 March 2023 - 11:07 AM

Sounds like you are on a good path.  The 50mm scope is a good way to start, but there are often 2 different issues when shifting over to looking at smaller objects (examples can be things like: globular clusters, galaxies, planetary nebula)

 

Scope resolution and Seeing Limited Resolution

For larger aperture scopes (think 6-20 inches of aperture here) - seeing dominates resolution to the point that different sized scopes have an insignificant difference in their effective resolution.  So bigger scopes are useful because they are faster.  Total resolution is the sum of the squares of OTA resolution and seeing.

 

Using standard 2" seeing - aperture has an impact in the resolution for small scopes. 

  • 50mm scope -   resolution is 2.28". This larger than the seeing limited resolution (3.03" combined)
  • 80mm scope - resolution (daws) is 1.45".  This is a bit smaller than the seeing limited resolution (2.47" combined)

Pixel Scale (fitting a cameras)

  • If you have the better system resolution with a bigger scope - under sampling will still degrade the resolution of what you can see in the sky
  • Using linear Nyquist criteria - you want to target a pixel scale around 1.24" for critical sampling for your 80mm scope.  About 1.52" is the best the 50mm scope can handle.

EDIT: Ugh ... calculated 2.5" seeing.  This is now corrected to 2.0" seeing


Edited by Mark Lovik, 23 March 2023 - 10:36 PM.

 

#11 Relativist

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Posted 23 March 2023 - 02:24 PM

Astro-Tech 80ED.ordered !

TY!

Congrats.

 

Aperture and dithering will help. Consider a 6" f/4 newt.


 

#12 ex-Bubblehead

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Posted 23 March 2023 - 06:31 PM

Congrats.

Aperture and dithering will help. Consider a 6" f/4 newt.


If I did my math right, he would get a similar jump in view going from a 50mm to 80mm as going from 6" to 10"...might as well skip the 6" and jump right to a 10"! Might need a bigger mount. But if you are getting a bigger mount anyway, might as well skip the 10" and go to a 16"...
 

#13 Mark Lovik

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Posted 23 March 2023 - 10:48 PM

Resolution differences are seeing limited - square root of sum of squares.  So going from 50-80mm is a much larger resolution jump when compared to a 6" to 10" jump

 

2" seeing is similar to scope resolution in the 2-3 inch range.  So scope resolution has a larger impact on the total.  Around a 22% resolution change.

  • 50mm - 3.03" seeing limited resolution
  • 80mm - 2.47" seeing limited resolution    

2" seeing really dominates in the 6" to 10" range  -- under 5% difference

  • 6"   -  2.14" seeing limited resolution
  • 10" -  2.05" seeing limited resolution

 

Going for a speed difference ... different set of calculations


Edited by Mark Lovik, 23 March 2023 - 10:50 PM.

 

#14 nicknacknock

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Posted 23 March 2023 - 11:04 PM

Astro-Tech 80ED.ordered !

TY!

Was just browsing the classifieds and saw your SW50ED now has a new owner. Congrats on the quick swap of scopes!

 

You will need to have about 5 pounds of counterweights for the AT80ED so plan acccordingly. Also, at f7 it is a bit slow, so consider a 0.80x reducer / flattener.

 

If you have a solar white light filter, it would pair great with as is and with a 2x barlow for imaging full disks and sunspots. Plus of course for traditional night time viewing. 80mm is a very versatile aperture!


 

#15 ex-Bubblehead

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Posted 24 March 2023 - 08:30 AM

Resolution differences are seeing limited - square root of sum of squares. So going from 50-80mm is a much larger resolution jump when compared to a 6" to 10" jump

2" seeing is similar to scope resolution in the 2-3 inch range. So scope resolution has a larger impact on the total. Around a 22% resolution change.

  • 50mm - 3.03" seeing limited resolution
  • 80mm - 2.47" seeing limited resolution
2" seeing really dominates in the 6" to 10" range -- under 5% difference
  • 6" - 2.14" seeing limited resolution
  • 10" - 2.05" seeing limited resolution

Going for a speed difference ... different set of calculations

Heh, it was a tongue in cheek post though using the wrong metric as you pointed out...I was just ratioing the square of the diameters which, looking back, should have been the radius, anyway.

But the point still stands: if upgrading from a 50mm, might as well just go to 16". Buy once, cry once!
 

#16 BrentKnight

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Posted 24 March 2023 - 08:43 AM

Heh, it was a tongue in cheek post though using the wrong metric as you pointed out...I was just ratioing the square of the diameters which, looking back, should have been the radius, anyway.

But the point still stands: if upgrading from a 50mm, might as well just go to 16". Buy once, cry once!

I've gotta believe going to a 16" is more like buy once, cry every time you need to tote it out...


 

#17 jkelly

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Posted 24 March 2023 - 10:25 AM

Was just browsing the classifieds and saw your SW50ED now has a new owner. Congrats on the quick swap of scopes!

 

You will need to have about 5 pounds of counterweights for the AT80ED so plan acccordingly. Also, at f7 it is a bit slow, so consider a 0.80x reducer / flattener.

 

If you have a solar white light filter, it would pair great with as is and with a 2x barlow for imaging full disks and sunspots. Plus of course for traditional night time viewing. 80mm is a very versatile aperture!

Thanks.
Yeah, I was pretty fortunate there was a buyer right away so for a -$150 I switched over to the AT 80 and flattener. I also can add an electronic focus in the future which was pretty difficult to do with the helical focus on the evoguide. I do have 4.4 pounds of counter weights. Hopefully that will work.
Looking forward to next week. 


Edited by jkelly, 24 March 2023 - 10:29 AM.

 

#18 MarMax

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Posted 24 March 2023 - 11:53 AM

Astro-Tech 80ED.ordered !

TY!

I think you've made an excellent choice and congratulations on the swap! I also saw your add for the 50mm.


 

#19 jkelly

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Posted 10 April 2023 - 09:28 PM

First light with the AT80ED and TS-Optics .08 Flattener/Reducer.

Lots to work on...waiting on Bahtinov mask for focus

55 minutes screen capture from ASIair.

 

M1

 

IMG_1395_sm.jpg

 

A little better with some post processing:

 

https://www.cloudyni...mage/176778-m1/


Edited by jkelly, 11 April 2023 - 06:54 AM.

 

#20 alphatripleplus

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Posted 11 April 2023 - 06:55 AM

As we seem to have moved on from the original topic - more detail on galaxies - this topic has run its course.  lock.gif


 


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