Navigating the eyepiece jungle

[mytola]

Being quite a newbie in the eyepiece jungle, I would greatly appreciate some advice, and I'm going to use the summer months to find out what I need for the coming dark season. I've got an old Celestar C8 that I plan to use for more stationary visual, and hopefuly I'll have a new WO GTF-81 within a month or so for imaging on my NEQ6 and portable visual (planning to use a photo tripod for this right now). In the future I'll probably be tempted to invest in a bigger fast dob for visual, so I need to think about that when buying eyepieces.

The eyepieces I already have is only the 25mm SMA that came with the C8, and a 9mm orthoscopic one, so it's room for a lot of improvemet. I'm thinking I should probably start with getting something in between what I have now, so something around 15-20mm and perhaps something 30mm +. Or should I replace what I have with something better? I can't justify using the same amount of money on eyepieces this year as I've used on the gtf-81, but I don't want to buy something that I will want to replace within a year or two either...Maybe I should just buy ONE quite good one that I'm sure is a stayer...

Solar system is nice, but I'm really most into DSOs and star fields. Any advice would be greatly appreciated!

[jerryTheC]

If your scope supports using 2" eyepieces, then they're really good for low power, wide field views.

[mytola]

It seems my C8 has a 1.25 visual back only, so I'll need a bigger one if I want 2" eyepieces. I'll need a 2" diagonal anyway...have to check if one exists that has both a normal 2" connection and a c8 thread...

[Dunkster]

Check the thread on the end of the OTA... I'm not sure about older models, but some of the current models still ship with a 1.25" visual back despite the 2" thread on the back of the cell. It should be obvious to look at, but a rule across the cell thread or cell end of the visual back should confirm.

[Dunkster]

Regarding diagonal... you can get SCT threaded 2" diagonals (I bought one for my C6 for extra security) and it keeps the diagonal close to the OTA (minimising the FL) but if you're getting a 2" inch diagonal with your other scope(s) you could just use that with a 2" vb for flexibility. I think all Celestron SCTs use a 2" thread, besides the 11 and 14 which are 3.25"! Baader do a really nice click lock vb if you decide to head in that direction.

[Capricorn]

Stick to the 1.25" eyepieces, you have a bigger choice and to get a 2" on means additional cost and a more (geverally) expensive eyepiece.

With the scopes you have, will get and are considering it will be difficult.

I will drop back on the old favourite of the BST options, they do 5mm, 8mm, 12mm, 15mm, 18mm and 25mm at £47.

The 25 and 15 should be good on the C8 and a later dob, you will need shorter for the GTF-81, perhaps the 5mm they do.

Means 3 eye[pieces but can be acquired over time.

The Celestron X-Cels are an alternative at £69,

[jerryTheC]

It's not an either/or decision - you can still use 1.25" eyepieces in a 2" diagonal, with an adapter (that often comes with the diagonal).

For shorter focal length, higher magnification eyepieces, you're only looking at the central part of the image formed by the telescope, so 1.25" eyepieces are fine, and there's no point or optical advantage in making a 2" version (though some eyepieces will fit both 1.25" and 2" holders, which can be a bit more convenient if you're using them with other 2" ones).

However, for wide true field eyepieces - either low mag wide ones, or medium mag ultrawides, you need to see more of the image created by the telescope - and in these cases, the 1.25" barrel size becomes a limiting factor, while a 2" barrel allows you to see a much bigger area - and that's where the 2" eyepieces come into their own - you get wider views that aren't physically (optically) possible in a 1.25" design. Yes, this usually (but not always) means that they tend to be more expensive - but just about everyone that has the option to use 2" low power eyepieces prefers them (not all scopes - especially smaller SCTs and MCTs, and probably smaller newtonians, too) can take full advantage of 2" eyepieces, since other factors can (and often do) prevent the scope from forming an image wide enough)

[mytola]

I appreciate the input by everyone, It seems my reducer to the C8 has 2" threads, and I think I'll have to get a 2" vb and diagonal. They're not that much more expensive, and all I've seen seem to have 1.25 adapter anyway.

I've played around with a telescope simulator to see how different focal lengths and apparent field of the eyepieces affect the true fov. Is there any advantage gained from using a lower focal length eyepiece with greater apparent fov compared to just getting a a greater fl one with a narrow fov?

[jerryTheC]

Is there any advantage gained from using a lower focal length eyepiece with greater apparent fov compared to just getting a a greater fl one with a narrow fov?

You'll see a similar area, but enlarged more, in the wider-but-shorter eyepiece. I think Televue called this a 'majesty factor' in their adverts . The wider view tends to give a more immersive experience - there's less in the way between you and the stars - although some people don't get on with ultrawide views. The bigger magnification will also darken the sky background and dim extended objects a bit.

Personally, I like the ultrawide views - at least up to 82 degrees, which is about as much as I can see at once - I might like the even wider ones too, but haven't had a chance to try that out - but I usually use an old Meade 2" 40mm SWA eyepiece - around 68 degrees or so - for finding things in the first place. That way I can definitely take in the whole area easily, with no chance of missing things at the edges, which might happen with a 30mm or 26mm ultrawide.

On the 2" diagonal - you don't have to go with a 2" visual back and refractor style diagonal, you can also get 2" diagonals that screw directly onto the SCT thread. (and also ones that come with an exchangeable SCT thread attachment and a 2" nosepiece).

[E621Keith]

I appreciate the input by everyone, It seems my reducer to the C8 has 2" threads, and I think I'll have to get a 2" vb and diagonal. They're not that much more expensive, and all I've seen seem to have 1.25 adapter anyway.

I've played around with a telescope simulator to see how different focal lengths and apparent field of the eyepieces affect the true fov. Is there any advantage gained from using a lower focal length eyepiece with greater apparent fov compared to just getting a a greater fl one with a narrow fov?

Telescope simulator doesn't really work. They give you a hint of what is possible but does not prepare you for actually looking through the real eyepiece. Shorter FL wider FOV eyepiece is useful for reducing sky glow compare to a longer FL narrower FOV eyepiece.

[Dunkster]

I've found Stellarium invaluable in helping me decide which FL and aFOV I'd like to try next

With a nice wide/long EP you should be able to eek out about 1.3 degrees FOV out of the C8 (before resorting to a focal reducer). Most things will fit in that FOV, for the rest you can use the frac

[mytola]

It seems what I really want is a bunch of Naglers... But with the pricing I could get an 18mm and a 30mm Explore Scientific with the same specs for the price of one 31mm Nagler...are the Naglers really that good?

Im starting to think this hobby is going to be my ruin

[jerryTheC]

Yes, the Naglers really are that good - especially in faster scopes - but SCTs are less demanding, and the ES eyepieces seem to be well regarded, though I haven't seen one myself...

You could always do what I did, and keep an eye out for used bargains