Eyepiece / Barlow for C8 and 80/400

[Guest]

Hello!

I think I need your advice.

My telescopes are an old C8, and an 80/400 refractor, using the following eyepieces:

Plössl 32mm (gives 65x / 12.5x)

Plössl 20mm (gives 100x / 20x)

Radian 12mm (gives 167x / 33x)

I'm very happy with these eyepieces, thus I don't feel like changing them.

But I'm lacking a high-power configuration (Eyepiece and/or Barlow), for planetary observation (at 200-250x with the C8 and about 100x with the 80/400) - and collimation use (400x needed for the C8).

For which eyepiece/barlow combination would you go?

Just to make things more difficult, three other pieces of information: (1) My budget is.. rather limited. I want to buy used and am willing to wait and save money, still, please no Ethos/Nagler/... suggestions please :-) (2) some month ago, I tested a 9mm TMB-type planetary eyepiece, and wasn't really satisfied (internal reflections). (3) I read the Radians don't really barlow well

Have a great day!

Raphael

[John]

The ST80's don't take high magnfications well because of the chromatic abberation they produce - they are much better used for low / medium power / wide field observing, in my opinion.

For the C8 I'd be thinking about an 8mm for 250x which is around the max useful magnification most of the time.

The Vixen NPL plossls are well thought of and cost £30 for the 8mm.

[E621Keith]

Have you considered a Baader Hyperion Zoom. It's around £130 used and can replace a whole set of eyepiece.

[Guest]

Thank you John and Keith for you feedback. Well, the Zoom covers a range of focal length down to 8mm -- that won't be enough for collimating the C8 properly (following Thierry Legault - The collimation).

John, I agree that 80/400 refractors aren't made for planetary observation; but with a magnification of 80 - 100x, my 80/400 (Vixen) does still deliver quite a good view without too much CA.

So, when going for the Vixen Plössl, I should probably go for a 8mm, and 5mm, giving (250x / 50x) and (400x / 80x) -- the 400x are certainly just used for collimation, not for observation.

Would you suggest to go for a Plössl instead of an orthoscopic eyepiece? For the ~5mm eyepiece, I don't worry about the f.o.v. (as just used for collimation and planets), but the ~8mm eyepiece delivers 50x in the refractor, which is not enough for planets, but with an ortho I might also not be able to enjoy DSOs... what do you say?

[E621Keith]

5mm on a C8 delivers 406x magnification which is very high for UK, however I don't know the condition where you are so your sky may or may not supports it.

Personally I will opt for the baader zoom and a good barlow. At the 8mm setting, you C8 will give a magnification of 254x which is very close to the seeing limit. When seeing allows or when collimating, I'd barlow the zoom for higher magnifications.

If you are set on fixed focal length eyepieces, I'd pick ortho over plossl, because plossl at short focal length will have very little eye relief. Quality will vary for both designs, but orthos are generally better made.