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Field of View... what would you do?

astrophotography
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#1 Richoff

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Posted 01 December 2019 - 04:59 PM

So, here I sit with a quite nice 92mm f6 scope with Field Flattener (the manufacturer says the FF bumps the focal length up to 565mm).

My quest is to attain a wider FOV for those larger DS objects... which of course got me thinking about the shorter scopes (72ish mm)

                                                                                                                                     ^dangerous^

What would you folks do, given the same circumstances?... Find a premium short/fast scope, or for a little more $, look in to a full frame sensor camera? (I currently own a ASI071 aps-c).

I suppose another option would be to source a reducer for my 92mm, yes? (manufacturer doesn't make them)

More thinking says, hmmm, why don't I try putting together mosaics with SGP... looks outside to see clouds again :(  clear sky's are becoming more rare in my 'hood.

 

PS - there's also that RASA8, Chuck got one... I want one too! ;)

 

Cheers



#2 aeajr

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Posted 01 December 2019 - 06:25 PM

So, here I sit with a quite nice 92mm f6 scope with Field Flattener (the manufacturer says the FF bumps the focal length up to 565mm).

My quest is to attain a wider FOV for those larger DS objects... which of course got me thinking about the shorter scopes (72ish mm)

                                                                                                                                     ^dangerous^

What would you folks do, given the same circumstances?... Find a premium short/fast scope, or for a little more $, look in to a full frame sensor camera? (I currently own a ASI071 aps-c).

I suppose another option would be to source a reducer for my 92mm, yes? (manufacturer doesn't make them)

More thinking says, hmmm, why don't I try putting together mosaics with SGP... looks outside to see clouds again frown.gif  clear sky's are becoming more rare in my 'hood.

 

PS - there's also that RASA8, Chuck got one... I want one too! wink.gif

 

Cheers

You already have a short, wide field scope.   Now the question is whether it can take 2" eyepieces or not.

 

Assuming it can take 2" eyepieces, with a focal length of 565 mm, if you put in a 38 mm 70 degree eyepiece you will have 14.8X and 4.7 degree field of view.  That is a binocular like field of view.   

 

How wide are you trying to achieve?

 

 

If you only have a 1.25" focuser and can't upgrade to a 2", then your best bet is a 32 mm Plossl eyepiece for low power and wide view.

 

That would give you 17.6X and 2.8 degrees which is still pretty wide for a telescope.

 

So, how wide are you trying to go?

 

Understanding Telescope Eyepieces- There are recommendations, based on budget, but the meat of the article is about understanding the issues when selecting eyepieces.
https://telescopicwa...cope-eyepieces/


Edited by aeajr, 01 December 2019 - 06:26 PM.


#3 Richoff

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Posted 01 December 2019 - 06:50 PM

My thrust of my question(s) were to be taken in the context of AP exclusively.

Thanks for the info/links tho... always welcome. smile.gif

Cheers



#4 aeajr

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Posted 01 December 2019 - 07:04 PM

Suggest you request a moderator move this to the AP forums. 



#5 caseyfinn

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Posted 01 December 2019 - 11:48 PM

Definitely a Rasa 8. F2 is so much fun!



#6 jerahian

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Posted 02 December 2019 - 12:25 AM

For that wide field itch, I've been recently thinking about the William Optics SpaceCat 51 or RedCat 51.  I've been seeing some fantastic images coming out of those sharp little scopes.  They are f/4.9 though, in case you were indeed looking for a much faster scope than your f/6.  I think it would go quite nicely with your APS-C size sensor of your ASI071MC.

 

Ara



#7 AhBok

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Posted 02 December 2019 - 12:32 AM

I use the ASI071MC Pro with an 8”F4 newt and image at 866mm. I wanted wider fields for some objects so learned how to do mosaics. The modern tools have made mosaics cheap and easy. They are a lot of fun to do and you simply add panels until you get the size you want.
  • dawziecat likes this

#8 Hesiod

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Posted 02 December 2019 - 07:17 AM

If are looking into "premium" fast refractors could give a look to the VSD 100/380.

I have purchased the fl55ss+reducer kit (roughly 230mm at f/4 or 310mm at f/6) as my travel rig and am very pleased by its performances with an aps-c sized dslr

Edited by Hesiod, 02 December 2019 - 07:21 AM.


#9 dawziecat

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Posted 02 December 2019 - 09:47 AM

I second mosaics, as Randy has already suggested.

BTW, SGP makes mosaicing pretty easy with their marvelous Framing and Mosaic Tool. (I don't know about other acquisition software.) 

The downside to mosaics is that it increases the amount of acquisition time required. 

BTW, no matter how wide your FOV, you'll still likely want to do a mosaic from time to time. I use a full frame CCD and a TAK FSQ reduced to f/3.6 (5.1 x 3.4 degree FOV)and STILL want to do mosaics! 


Edited by dawziecat, 02 December 2019 - 09:47 AM.


#10 richorn

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Posted 02 December 2019 - 01:10 PM

Is there a reason you haven’t considered a ff/reducer for your existing setup instead of just the FF?



#11 Richoff

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Posted 02 December 2019 - 01:31 PM

Is there a reason you haven’t considered a ff/reducer for your existing setup instead of just the FF?

The manufacturer (CFF) doesn't sell one afaik, I will look into it further tho



#12 APshooter

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Posted 02 December 2019 - 03:45 PM

I bought the Rasa to fight back against cloud events, all too common in the Midwest. Wide and fast. If you do go with a larger chipped camera you'd have to verify the imaging circle well be large enough to cover the chip.

#13 bobzeq25

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Posted 02 December 2019 - 04:07 PM

I first bought a shorter telescope.  Stellarvue SV70T.  336 mm with reducer.  That worked well for a couple of years.

 

I recently got a C8 RASA, 400mm.  Am getting it to work well, but it's not trivial.  The big thing is that the tiniest amount of tilt ruins your image at F2.  Another is that spacing is critical, using filters not very easy.

 

I think I'll like it eventually, but it's not trivial, as the SV70T was.  First night out I was practically giggling, got a fine image.



#14 Stelios

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Posted 02 December 2019 - 10:15 PM

So, here I sit with a quite nice 92mm f6 scope with Field Flattener (the manufacturer says the FF bumps the focal length up to 565mm).

My quest is to attain a wider FOV for those larger DS objects... which of course got me thinking about the shorter scopes (72ish mm)

                                                                                                                                     ^dangerous^

What would you folks do, given the same circumstances?... Find a premium short/fast scope, or for a little more $, look in to a full frame sensor camera? (I currently own a ASI071 aps-c).

I suppose another option would be to source a reducer for my 92mm, yes? (manufacturer doesn't make them)

More thinking says, hmmm, why don't I try putting together mosaics with SGP... looks outside to see clouds again frown.gif  clear sky's are becoming more rare in my 'hood.

 

PS - there's also that RASA8, Chuck got one... I want one too! wink.gif

 

Cheers

The full-frame camera is a gamble, because you may be unable to get flat field at the corners with a flattener (and especially a reducer/flattener).

 

Me, I went for the 336mm (70mm scope with 0.8x reducer). Of course when I got it the clouds rolled in...



#15 TxStars

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Posted 02 December 2019 - 10:22 PM

Just get a Tak Baby-Q with reducer  ...   lol



#16 WadeH237

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Posted 02 December 2019 - 11:17 PM

For wide field work, I like a short focal length scope.

 

The thing about large sensor cameras is that the drive up your costs everywhere.  The camera is more expensive.  The large imaging circle that it requires will drive up the cost of a telescope to properly cover and illuminate it.  The cost of narrow band filters to cover a large sensor can be more than the camera itself, unless you go one shot color.  The issue with one shot color is that most of the nice wide field targets also lend themselves well to narrow band imaging.  If you want to do HaOIIIRGB (and a big one to cover a large sensor is expensive), you can get a tri-band filter, but it's not realistic to do Hubble palette with a one-shot-color.

 

For my wide field work (which I actually don't do that often), I use an 80mm refractor with a reducer/flattener running at F/4.8.  That puts me at 384mm focal length.  There are decent small refractors that can get you down to 250mm focal length.



#17 Richoff

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Posted 03 December 2019 - 06:44 AM

Just get a Tak Baby-Q with reducer  ...   lol

Yeh, that's "Premier" alright! waytogo.gif



#18 terry59

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Posted 03 December 2019 - 07:59 AM

Just get a Tak Baby-Q with reducer  ...   lol

I've watched a lot of experienced people struggle to get a flat field with the reduced FSQ85, especially (but not exclusively) with a full frame camera, right here on CN


Edited by terry59, 03 December 2019 - 07:59 AM.



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