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Telescope for Narrow Band Astrophotography?

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#1 Alan Brunelle

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Posted 21 September 2020 - 02:01 PM

I am sure that this topic has come up before, but after failing to get results on my search, I thought that I would post this question.

 

If I want to do exclusively narrow band astrophotography and want a dedicated refractor to do so, would it make sense to avoid the multi-element corrected (and expensive) APO telescopes and get a single element telescope instead?  After all, I would not be asking this rig to focus photons of widely dispersed wavelengths onto a single spot.  Also, I am assuming that a single element refractor would lose less light to absorbtion and be more efficient.  Are there any high quality such scopes out there for this purpose, or is this now entering the domain of amateur telescope (lens grinding) building?  Not looking to settle for a 50mm f15 single element cheapo rig.

 

Thanks,

Alan



#2 wrnchhead

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Posted 21 September 2020 - 02:07 PM

https://www.cloudyni...for-dso-imaging

https://www.cloudyni...ting-narrowband

https://www.cloudyni...tro-photography

https://www.cloudyni...-for-narrowband

 

Tons of opinions on that. I see people I have learned from and respect on both sides of the discussion. 


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#3 Alan Brunelle

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Posted 21 September 2020 - 02:10 PM

Thanks!



#4 Narrowbandpaul

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Posted 21 September 2020 - 02:21 PM

I’d be looking more for an ED doublet at least. Chromatic aberration is not the only thing to worry about. Spherical aberration exists too. Think about a reducer/flattener. You should be able to get an 80-100mm down to around f/5 which will give a nice FOV for some of the extended nebulae.

#5 Alan Brunelle

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Posted 21 September 2020 - 02:31 PM

Much appreciated.  What I learned from perusing the links sent by Vanguard is that the question I pose at the end of my first post is probably answered by a simple "no". 

 

There likely is no decent single (really doublet) element telescopes out there that are not department store quality.  That is one that is got a reasonable focal length and can be properly accessorized (such as field flatteners, focusers, etc.).   In fact I raised the question because I could not find such a scope on the typical gear sites, except for maybe a Takahashi achromat 80mm at f10.  But not the aperature or f.l. I would want for deep sky.


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#6 MikiSJ

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Posted 21 September 2020 - 02:56 PM

In my experience, I could not fault my APM/TMB 152/1200 but that was a top of the line ($$$$$) triplet apochromat. I did not use a field flattener as the FOV was quite flat, especially using it with a QSI532 CCD camera.



#7 GrafikDihzahyn

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Posted 22 September 2020 - 12:21 PM

I agree with a doublet when going with NB. I chose a triplet APO because I was also interested in LRGB. 

 

If I was going strictly NB on a budget, I'd look at a 50-70mm ~ f/6-7 with a flattener/reducer, 1.25" NB filters, and choose a camera based on the image scale you'd prefer, but a ASI1600 or similar would be perfect.

 

Take a look at William Optics Zenith Star lineup, or Stellarvue Access one (these may only be used now, but occasionally SV puts a few new models up for sale).



#8 terry59

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Posted 22 September 2020 - 06:52 PM

I agree with a doublet when going with NB. I chose a triplet APO because I was also interested in LRGB. 

 

If I was going strictly NB on a budget, I'd look at a 50-70mm ~ f/6-7 with a flattener/reducer, 1.25" NB filters, and choose a camera based on the image scale you'd prefer, but a ASI1600 or similar would be perfect.

 

Take a look at William Optics Zenith Star lineup, or Stellarvue Access one (these may only be used now, but occasionally SV puts a few new models up for sale).

A doublet will still have larger spot sizes than a triplet

 

smile.gif



#9 GrafikDihzahyn

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Posted 23 September 2020 - 09:13 AM

A doublet will still have larger spot sizes than a triplet

 

smile.gif

And narrowband will have much smaller FWHM. As long as you're taking pixel scale into consideration I don't see the issue.. 



#10 terry59

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Posted 23 September 2020 - 12:06 PM

And narrowband will have much smaller FWHM. As long as you're taking pixel scale into consideration I don't see the issue.. 

Compared to a triplet the star spot sizes will be larger. If that's not an issue great

 

smile.gif



#11 GrafikDihzahyn

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Posted 23 September 2020 - 12:38 PM

Compared to a triplet the star spot sizes will be larger. If that's not an issue great

 

smile.gif

You're speaking semantics, which the OP clarified they don't care about.. smh

 

As long as one is staying within the correct pixel scale, and using a SINGLE WAVELENGTH by way of narrowband filters, then doublet/triplet really doesn't matter. Save the money for a better camera, mount, or some quality NB filters.

 

If we were talking about OSC or even LRGB, then sure, triplet all the way, or a quality petzval design, but we're not. 

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