Visual capabilities of an Astrograph

[ozzy21]

Dear all,

I have a big experience mainly with Dobs. I would like to start doing some astrophotography. I was looking at this https://uk.telescope.com/Telescopes/Orion-8-f39-Newtonian-Astrograph-Reflector-Telescope/rc/1306/p/109883.uts. What I would like to ask, is apart from astrophotography what are the capabilitites those scopes (this or other astrographs in general) have for visual usage. I understand that they are made for photography but do they have a handicap for Visual usage?

Thanks,

Fotis

[AstroMuni]

I dont think there would be a handicap for visual usage as astrophotography puts higher demands on the optics than visual observation. If you are used to Dobs then this one would need a good mount (EQ or AZ). The other option could be that your present dobs mounts maybe capable of taking this scope on.

[vlaiv]

Couple of things come to mind:

1. Astrographs are usually fast systems - that will put some strain on eyepieces and "demand" expensive ones for good / to the edge correction. Otherwise, if you can live with only central part of the view being sharp - you can use regular ones as well

2. They will be slightly less performant than their visual counter parts if mirrors are used. This is due to central obstruction which both blocks some light and also robs you of some planetary contrast (but helps with finest frequencies - which are usually killed by seeing). It is not unusual for astrograph to have 40-50% central obstruction (by diameter).

3. They will be somewhat more difficult to collimate - faster optics requires greater precision of alignment.

4. Some astrographs are corrected with "distance to sensor" in mind. This means that you need to put eyepiece into exact position which varies with eyepiece - similarly to visual coma corrector that needs system to adjust for each eyepiece.  It would be best to avoid astrographs with built in correctors that are distance sensitive - it is very hard to find variable eyepiece distance adapter that you can fit on such scope. If you use fast newtonian then you should consider visual coma corrector like one of these:

https://www.firstlightoptics.com/coma-correctors/explore-scientific-hr-coma-corrector.html

or

https://www.firstlightoptics.com/coma-correctors/tv_paracorr_2.html

both of which have system for adjusting eyepiece distance together with coma corrector - so it's all in one package that works good.

Probably the main reason you would want to use such scope for visual is that you want it to double as imaging scope as well? You'll most likely need coma corrector in that case anyway (for imaging), so factor it in the price.

Other reason could be that you want very wide field larger aperture scope. In that case, you'll want to enjoy pretty stars to the edge - so again, CC is recommended.

[Highburymark]

7 hours ago, ozzy21 said:

Dear all,

I have a big experience mainly with Dobs. I would like to start doing some astrophotography. I was looking at this https://uk.telescope.com/Telescopes/Orion-8-f39-Newtonian-Astrograph-Reflector-Telescope/rc/1306/p/109883.uts. What I would like to ask, is apart from astrophotography what are the capabilitites those scopes (this or other astrographs in general) have for visual usage. I understand that they are made for photography but do they have a handicap for Visual usage?

Thanks,

Fotis

When I bought my F/3.3 Tak Epsilon, I was mildly surprised to see that the manual contained instructions for visual use. I cannot imagine what the view would be like through a high power eyepiece. Maybe I should try it.

[JeremyS]

2 minutes ago, Highburymark said:

I cannot imagine what the view would be like through a high power eyepiece. Maybe I should try it.

Go in Mark - would be interesting to hear! Maybe try the epsilon Lyrae challenge (lowest power to split eps 1 and eps 2)

🙂

 

[vlaiv]

3 minutes ago, Highburymark said:

When I bought my F/3.3 Tak Epsilon, I was mildly surprised to see that the manual contained instructions for visual use. I cannot imagine what the view would be like through a high power eyepiece. Maybe I should try it.

From what I can see - they only quote their own line of eyepieces - probably because you can use those without the need for adjustment. Ideally, every eyepiece out there should have focus point at eyepiece shoulder. That would make every barlow work at prescribed magnification and every eyepiece would be par focal.

In reality this is not the case, and eyepieces often require refocusing. I don't own any Tak eyepieces but it might well be that they were careful enough to put focal plane at eyepiece shoulders?