focal reducers for visual

[earth titan]

Well the obsy is nearing completion. Deciding on the main scope for visual work has led me to thinking about mounting my f10 sct for visual.

Brilliant for planets as is, but not so good for DSOs. Would a focal reducer work for visual?

[ollypenrice]

Not really. If you only have 1.25 inch EPs then yes, you can widen your field with a reducer. However, the way to maximise the FOV in an SCT is to use a 2 inch back, diagonal and an ultra wide EP like the Nagler or Ethos. There are cheaper options of course. What happens if you use the large widefield EPs is that you end up limited by the baffle tube so you can't further widen the FOV with a reducer. All you do is reduce the magnification. Given the cost of the reducer I think you'd be far better going for the 2 inch EP option.

Olly

[earth titan]

Not really. If you only have 1.25 inch EPs then yes, you can widen your field with a reducer. However, the way to maximise the FOV in an SCT is to use a 2 inch back, diagonal and an ultra wide EP like the Nagler or Ethos. There are cheaper options of course. What happens if you use the large widefield EPs is that you end up limited by the baffle tube so you can't further widen the FOV with a reducer. All you do is reduce the magnification. Given the cost of the reducer I think you'd be far better going for the 2 inch EP option.

Olly

I see.

If I understand you correctly what you are saying is use the 2" EPs effectively as focal reducers. I use a 2" diagonal on the rear and have a couple of 2" EPs - so effectively I end up with the same magnification as if I had a focal reducer and 1.25" EPs.

I think i know what I mean... ish

I'm guessing adding one of these or similar:

http://www.telescopehouse.com/acatalog/Meade_F6_3_Focal_Reducer__566.html

Won't allow me to use my 2" diagonal?

[ollypenrice]

If you have a 2 inch back and some 2 inch widefield EPs, as you do, you would gain no additional FOV with a reducer because the extra field would simply be cropped by the baffle tube. You'd reduce magnification without increasing the FOV so there would be no point.

The widest FOV possible in an SCT is to be had using a long FL ultra wide EP like the 31 Nagler.

Olly

[earth titan]

Cheers. Nice and concise as always Olly.

[Stu]

Quite correct as always Olly.

That is the approach I use with my f20 mak. I have a 28mm UWAN and 31t5 nagler which I use when I want the widest field, not that it ever gets much above 0.6°!

Compare that with 3.6° in the Astrotech

Stu

[earth titan]

Would this be about the same performance as an 8" newt then?

[Mr Spock]

My 42mm LVW gives x56 and 1.28° - right on the maximum limit for my C9.25, the limiting factor being the baffle tube diameter.

If I had a f4 Newt the same size, I could use the 31mm Nagler to give x30 and 2.7°. I wouldn't recommend an eyepiece longer than 32mm at short focal lengths due to an oversized exit pupil. Still, that's more than twice the field.

Any scope is a compromise of uses; there's isn't really a scope that can do everything.

[earth titan]

Any scope is a compromise of uses; there's isn't really a scope that can do everything.

Totally agree. Good to know I can probably leave the sct in place, for deep sky stuff.

[Davey-T]

Hi Tom

I have 31 T5 Nagler and it works well with 10" SCT as Olly says, also have Altair Astro 2" visual back which works well .

I have 6.3 F/R but only use it for imaging

Davey-T