Adequate Eyepieces for my telescopes???

[AlexxxAA]

Hi everyone. It's been a while since I've posted anything. I got into photography for a good while, but now I want to go back to the good basics and concentrate on observing.

I've been trying to figure out what wide-field eyepieces are the limits for my telescopes... What is the determining factor that gives the limit for an eyepiece in a telescope? Is it the Focal Length? Or the f/ratio?

I own: 8" f/4 Newtonian, 800mm Focal Length.

80mm f/6.8 Zenithstar ED II, 545mm Focal Length.

90mm f/13.8 Meade ETX, 1250mm Focal Length.

What is the widest eyepiece I can purchase for each telescope?

And on another note, what is the difference in the "apparent field of view" of the newer eyepieces? Some EP's have 40 degrees, 60 degrees, 82 degrees... Etc...

Do those degree values change the actual magnification of the view? Or is it just something to do with image quality?

Thanks to everyone in advance

[Adrian]

And on another note, what is the difference in the "apparent field of view" of the newer eyepieces? Some EP's have 40 degrees, 60 degrees, 82 degrees... Etc...

Do those degree values change the actual magnification of the view? Or is it just something to do with image quality?

Thanks to everyone in advance

It's like the size of the window you are looking through... If you have 2 eyepieces of the same focal length (so same magnification), one 40 degree and one 60 degree, with the wider one it is like you are standing closer to the window - it all looks the same, but you can see a wider area.

once you get to 70 degrees and above you have to look around the view to see the edges like you have your head pressed up against a window in a spaceship.

I'll let someone else tackle the rest

[E621Keith]

It's like the size of the window you are looking through... If you have 2 eyepieces of the same focal length (so same magnification), one 40 degree and one 60 degree, with the wider one it is like you are standing closer to the window - it all looks the same, but you can see a wider area.

From my understanding, the magnification should be the same, but the eyepiece with the bigger AFOV will be like looking through a bigger window.

Your Mak and APO should be relatively easy to cater for, but your F4 Newtonian is a different story. I reckon you will need Televue's eyepiece, because most other designs begins to deteriorate at F5-F6. I think only TV test theirs down to F4.

[Moonshane]

there are a number of factors that will affect the answer to your question:

Exit pupil - usually try and stick with eyepieces that give max of 5-6mm. Exit pupil = eyepiece focal length (e.g. 20mm) divided by focal ratio (e.g. f4.) so in that case 5mm

Max magnification - work on 1.5x aperture in mm as a guide.

Cost - what's your budget? this is often the one that matters most

Focuser - will it take both 1.25" and 2" eyepieces?

Weight - will a heavy eyepiece upset your balance and will it irritate you having to rebalance when changing eyepieces?

Eye relief - do you wear glasses (specatcles) to observe? Some widefield eyepieces have short eye relief.

Focal ratio - as mentioned the lower this is the better quality is generally needed.

basically, any apparent field of view will work in any scope, it's the above factors that matter.

Answers to these will help you guage what will be best for you.

[carldr]

Sorry to hijack the thread! Regarding exit pupil, is there a minimum I should be considering?

[Moonshane]

some say about 0.5mm but I sometimes use less than this on double stars.

[carldr]

Ah right, so I shouldn't be worried about an exit pupil of, say, 1mm?

[Mr Spock]

I would recommend a 22mm T4 Nagler. Great at f4, long eye relief, easy to use and over 2.25° field of view with your scope.

[John]

Ah right, so I shouldn't be worried about an exit pupil of, say, 1mm?

Why not start another thread on this - otherwise you will hijack the thread

I agree with Mr Spock - the 22mm T4 Nagler would be a superb choice.

[AlexxxAA]

Hhhmmmm i see thanks so much for the help guys. I'm starting to understand a little clearer.

So for sure I should be considering two separate eyepieces: one wide field for the smaller scopes, and one not so wide for my f/4...

My budget is, I guess, not so bad... About $150-$200 US...

Is the Nagler a different design? I already own one of the stock 25mm eyepieces that came with a celestron I used to own, and it works fine with my f/4... Will the 22mm Nagler actually be a wider field of view in comparison?

[AlexxxAA]

And in terms of actual magnification and widest field of view, it does have to do with the Focal Length right? In essence, my zenith star with 545mm FL should give me the widest field of view with a decent lens of about 32mm???

[Mr Spock]

Is the Nagler a different design? I already own one of the stock 25mm eyepieces that came with a celestron I used to own, and it works fine with my f/4... Will the 22mm Nagler actually be a wider field of view in comparison?

Your 25mm Celestron is a Plössl. It has a field of view of 50°. This will give you x32 and an actual field of 1.56°. The Nagler will give you x36 and an actual field of 2.26°. So yes, a much wider field of view.

[John]

And in terms of actual magnification and widest field of view, it does have to do with the Focal Length right? In essence, my zenith star with 545mm FL should give me the widest field of view with a decent lens of about 32mm???

Yes thats correct. Put a 31mm Nagler in the Zenithstar and you would get a whopping 4.6 degrees of true field.

[AlexxxAA]

Wow thanks guys!!! Lol I know what I'm asking for Christmas then!

[AlexxxAA]

Hi guys. Thanks for all the help... Just wanted to let you guys know that I ended up getting a 2.5mm 82degree type 6 Nagler mostly for planetary viewing, and a 20mm Explore Scientific 68degree waterproof

I was told that this 20mm should easily outperform the view of my 25mm plossel.

Hope you guys approve! Thanks for all the help