Help me sort out what eyepieces to get for my SCT

[blinky]

I have a problem - my eyepieces I currently have were sourced when I had a nice 12inch F5 Dobsonian - I sold that and now my visual scope is my 8 inch Meade SCT and they are too high magnification or in the case of the 35mm 2inch ED eyepiece, they dont fit!

I have a 2 inch visual back, the F6.3 reducer, a 1.25 inch visual back and a 1.25 inch diagonal.  I’m just wondering what to sell/keep and what to buy....  I’m looking for something high powered for planets, a medium a low and a ‘as low as you can go’/finder type eyepiece.  

I don’t particularly want to connect and disconnect the reducer and faf about with it at night but also dont want to spend a lot of money as I’m mainly an imager and this is really only for the odd occasion or to show friends the night sky.

So, what if I keep the Nagler as a high power eyepiece but use it mainly with the F6.3 reducer so make it more useful as a standard high power eyepiece? So when using the eyepiece it would be: F6.3 reducer, 1.25” Visual Back, then 1.25” Diagonal....  This setup would give 140x magnification

What about lower magnifications though?  I do have an eyepiece marked 70Degree FOV thats 20mm, so I suppose with the same setup as above with reducer in place, this gives 63 times magnification.

So do they should like decent magnifications for medium and low power?  I also have a BST 8mm EP, which with the reducer gives, 157, so on good nights that could possibly be used as a higher power eyepiece, if I want to leave the reducer in place?  I also have 7 and 5mm Celestron XCel eyepieces, so again, on exceptional nights could use them with the reducer....

What about lowest power though?  I do have the 35mm ED eyepiece in 2” fitting, maybe all I should purchase is a 2” Diagonal - would F6.3 reducer, 2” Visual Back, 2” Diagonal, 35mm ED eyepiece work?  Would give me 36X magnification.

So assuming the above sounds ok to you visual guys, all I would need to purchase is a 2” diagonal!

[johninderby]

Have a look at these results from the Televue eyepiece calculator for the Meade 8” SCT. Will give you an idea of the mags various focal length eyoeces will give.

[Mr Spock]

Get your self a 2" diagonal. The 35mm would be fine for low power use.

Get rid of the focal reducer. They have a very limited aperture which restricts wide field viewing. They also add extra lenses to the optical train which reduces contrast.

For higher powers you will need something around 10 or 11mm. The 8mm is fine as a top limit; the 7 and 5 will only be useful for double stars. You might get away with the 7mm on the moon in really good seeing.

For looking at galaxies and other nebulous objects you may want something around 20-22mm.

[blinky]

Ok, found a2” SCT diagonal for a good price, I have the 70 degree 20mm eyepiece so thats covered.  I suppose I really need something around the 12mm size then if I’m to loose the reducer, as the 9mm Nagler is too much power for general use.

[Louis D]

3 hours ago, blinky said:

would F6.3 reducer, 2” Visual Back, 2” Diagonal, 35mm ED eyepiece work?

Nope.  You'll get all sorts of vignetting.  A 32mm Plossl is about the max when using a reducer.

[Don Pensack]

3 hours ago, Mr Spock said:

Get your self a 2" diagonal. The 35mm would be fine for low power use.

Get rid of the focal reducer. They have a very limited aperture which restricts wide field viewing. They also add extra lenses to the optical train which reduces contrast.

For higher powers you will need something around 10 or 11mm. The 8mm is fine as a top limit; the 7 and 5 will only be useful for double stars. You might get away with the 7mm on the moon in really good seeing.

For looking at galaxies and other nebulous objects you may want something around 20-22mm.

When I used the reducer, I stuck to eyepieces that worked with the reducer, i.e. eyepieces with field stops < 30mm.  The field delivered was wide, and I saw no restriction of the field of view.

In fact, the unvignetted field was a bit larger than that accomplished with 2" eyepieces at f/10.  The clear aperture of the lens was LARGER than the clear aperture of the rear baffle on the scope.

I also saw no noticeable loss in contrast, but I did see a substantial improvement in field flatness and the quality of the star images in the outer 50% of the field with the focal reducer/corrector in place, compared to f/10.

I did use one of the earlier made-in-Japan Celestron f/6.3 reducers, however.  Maybe they were better, optically?

 

[Louis D]

I read on CN where someone resorted to using a Starizona reducer to get decent images at the edges with their SCT after trying many standard reducer/correctors.  Perhaps you got really lucky visually?

[Don Pensack]

3 hours ago, Louis D said:

I read on CN where someone resorted to using a Starizona reducer to get decent images at the edges with their SCT after trying many standard reducer/correctors.  Perhaps you got really lucky visually?

Mine was Japanese-made, 1993, not the current Chinese-made unit talked about in the linked thread.

I don't know if there is a difference or not.  Mine had 4 elements.

Edited August 9, 2020 by Don Pensack

[Louis D]

4 hours ago, Don Pensack said:

Mine was Japanese-made, 1993, not the current Chinese-made unit talked about in the linked thread.

I don't know if there is a difference or not.  Mine had 4 elements.

Like the original smoothie Meade Super Plossls and 8-24mm zoom, the older, Japanese made items are better apparently.