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Selecting my first telescope for Imaging


Lrlinnell
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I have been using my Canon DSLR 5D Mark III with a 100-400 L Lens mounted on a Orion Atlas-Pro AZ-EQ-G mount  for astrophotography of stuff like Orion nebula and Andromeda galaxy but now it is time to purchase a scope.

I had been thinking of refractor APO Triplet but it seems that a lot of people are having good luck with Newtonian scopes like the Orion 8" f/3.9 Newtonian Astrograph. I would be doing strictly astrophotography, guided, BackyardEOS and PHD. Any thoughts on what might be a good scope?

I would start with the scope, Canon camera body, mount. Then add guide scope. Then replace the Canon body with CCD. That is the plan anyway.

 

Thanks, Lloyd

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An 8" f/3.9 Orion is going to need a big mount and at f/3.9 will need you to check collimation each time and the use of a coma corrector. The APO is I suspect the "easy" option, the new WO GT-71 should be good although there is also the ES FCD-100 APO (80mm and others) as well. Depends on the size of the APO that you are considering. Refractor will need a flatener either immediatly or at some time.

People use both refractor and reflector so if you are aware of the nature of each you will get the results. Person I know uses a 10" reflector but they have a permanent set up. I tend to play with a refractor - but I like refractors for visual, and a good refractor crosses over easily into imaging.

I suspect the mount requirement could be the deciding factor, as said the 8" reflector would need a big mount to supply the stability. If you transport the imaging set up to places the the refractor likely holds the advantage for size.

Your equipment details have just appeared, didn't come up while writing the previous. The Orion Atlas should be able to handle the 8". One odd question: Do you like star images with spikes? Just a reflector tends to produce spikes and people can either not care or some dislike them.

Edited by ronin
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Since your camera has a full frame sensor, you may want to check which scopes can actually illuminate the whole chip. Not all scopes can do this. Depending on when you intend to replace the Canon with a CCD (which most likely will have a smaller chip), this should be part of your decision making process.

As ronin noted, if you go for a fast (f-ratio smaller than 4 - 5, imo) newtonian, collimation becomes critical, and you may end up spending more time getting your scope right than doing any AP.

If you have reasonably dark skies, the f-ratio of the scope is of less importance, and you might consider a slower newtonian or an apochromatic refractor. (F-ratio by itself is of no importance, only at a fixed focal length.)

Another thing to consider is intended use. Will you be doing mostly planetary or galaxy imaging, or going for extended deep space objects. For small targets you need more focal length than general dso's.

You may want to check this field of view calculator:

http://astronomy.tools/calculators/field_of_view/

Then there is of course the small matter of your budget ...

 

Good luck

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Thank you both for your knowledgeable comments. Based on the fact that I have to transport the scope to a dark-site I will go with the refractor for the faster set-up. About to pull the trigger on an Orion EON 130mm Triplet Apochromatic (130mm aperture, f/7.0, 910mm focal length. Using the FOV calculator that Brown Dwarf pointed me to, this looks like it would be fine for Andromeda Galaxy, Orion Nebula, Triangulum Galaxy, etc. Any knowledge about whether this scope call fill my full-frame sensor in the Canon 5D Mark III?

Thanks, Lloyd

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You want consider not going to a dark site every night.

Many people in cites do obtain good results, starting with the really bright objects, developing their own workflows, and progressing onwards.

 

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4 hours ago, Lrlinnell said:

Thank you both for your knowledgeable comments. Based on the fact that I have to transport the scope to a dark-site I will go with the refractor for the faster set-up. About to pull the trigger on an Orion EON 130mm Triplet Apochromatic (130mm aperture, f/7.0, 910mm focal length. Using the FOV calculator that Brown Dwarf pointed me to, this looks like it would be fine for Andromeda Galaxy, Orion Nebula, Triangulum Galaxy, etc. Any knowledge about whether this scope call fill my full-frame sensor in the Canon 5D Mark III?

Thanks, Lloyd

Visit astrobin.com and search for your camera model. You find images taken with your camera model. Then check which scopes were used.

Since you plan to get a ccd, and these tend to have smaller chips, you can also decide to live with vignetting. Flat frames will correct some of the vignetting, and the rest can be cropped from the final image. An alternative is to buy a cheap (2nd hand?) canon camera body with APS-C sensor. As Andy pointed out, scopes that can cover a full frame sensor, and deliver decent quality, can be expensive. Unfortunately, not all scopes advertised as being full frame, are.

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You can just fit the Andromeda galaxy onto a full frame chip at 530mm focal length.

M31%20outer%20halo%20web%20FIN2-M.jpg

I ended up doing it as a 2 panel instead, though, to have more breathing space than seen here.

Have you considered looking for a second hand Takahashi FSQ106N fluorite quadruplet? They are very good value in Europe and probably even better in the USA. Tak buyers are notoriously fashion conscious and like the latest. Persoanlly I like the old 106N best because they are less fussy on focus during cooldown. They will (and very easily) cover your chip and they are fast at F5. As others have said, not much will cover full frame.

Olly

 

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1 hour ago, ollypenrice said:

You can just fit the Andromeda galaxy onto a full frame chip at 530mm focal length.

M31%20outer%20halo%20web%20FIN2-M.jpg

I ended up doing it as a 2 panel instead, though, to have more breathing space than seen here.

Have you considered looking for a second hand Takahashi FSQ106N fluorite quadruplet? They are very good value in Europe and probably even better in the USA. Tak buyers are notoriously fashion conscious and like the latest. Persoanlly I like the old 106N best because they are less fussy on focus during cooldown. They will (and very easily) cover your chip and they are fast at F5. As others have said, not much will cover full frame.

Olly

 

Out of curiosity, and assuming an extensive evaluation of many different refractors whilst preparing to take 'customers', did you keep a list of which which do did actually cover a full frame sensor?

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