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EP Confusion

Started by eyork, 02/10/2004 04:54PM
Posted 02/10/2004 04:54PM Opening Post
I've been doing some research and have read all the cool stuff that some eye pieces do and I am thoroughly confused. It seems that TV is the most popular high end.

2 Questions:

** Of these the Naglers and Radians seem to be "The Cat's Meow". What's the difference?

** At some point going wider(where eye relief isn't as critical) do I switch over to the TV Plossl's to save cash, or do these EP's have some other allure then eye relief.

As backgound info - I have an 8" f5 reflector, usually plenty of light pollution, and like deep sky with the occasional planetary viewing.

Thanks,
Another Ed
Posted 02/10/2004 06:34PM #1
Naglers are fully corrected to help eliminate coma and they have an 82° FOV with a flat field.
Radians have a 60° FOV and are also well corrected. The Radians can have reflections and some have said false color at times. They have a 20mm eyerelief which is good for glasses.
The Radian is a good EP, but it is no match for a Nagler.
TV Plossls have a 52° FOV with good correction and a nice flat field. They are good all around EPs. Again, they are no match for a Nagler.
You should go to a star party and look through a few EPs and I think you will rapidly understand the difference.
;^)
Floyd

[SIZE="Large"][/SIZE][COLOR="Blue"][/COLOR] Floyd Blue grin
Amateur Imager
Posted 02/10/2004 06:36PM #2
Naglers have an 82 degree AFOV. Radians have a 60 degree AFOV, and fixed eye relief of 20mm.

Well, a TV 32mm Plossl has a 27mm field stop, 22mm eye relief and a 50 degree AFOV, and the equivalent focal length Nagler (31mm Type 5) has a 42mm Field stop, 19mm ER and 82 deg AFOV. So you not only a get a wider AFOV, you get a huge (well corrected) True FOV for the same magnification. That is the allure, IMO.

Mark
Posted 02/10/2004 06:51PM #3
>It seems that TV is the most popular high end.

TV is in that spot because they have the widest variety of premium ep's, introduce new products every year, and market vigorously. They're also very good, but some less prolific brands (e.g. Pentax) are also worth consideration.

>the Naglers and Radians seem to be "The Cat's Meow".
>What's the difference?

Radians have a 60 degree apparent field-of-view (AFOV) and 20mm of eye relief. Naglers have an 82 deg. AFOV and shorter eye relief - 12mm in the type 6's, variable in other types.

Besides eye relief, you pay a lot for that wide field-of-view, especially since the TV ep's are very well corrected across the field. Less expensive wide-field ep's tend to show increasingly distorted or blurry stars as you go away from the center, especially with fast scopes like your f5. Of course, in a fast Newtonian, you will see some coma in the outer field, even with the best eyepieces, unless you buy another pricey TV accessory, the Paracorr.

Other factors that affect eyepiece price are the quality of the polish and coatings, the accuracy of the lens surfaces, and the mechanics.

TV plossls and UO Abbe orthos are excellent moderately priced eypieces, but both AFOV and eye relief (in short focal lengths) are small.

Many dob users prefer a wide AFOV, and will trade off some optical quality to get it, if they don't want to spend on Naglers. What works best is a matter of personal preference. If you can, borrow different eyepieces and try them in your scope. If that's not an option, Buy a few different types, and sell the ones that don't work for you. You can buy and sell used on Astromart and pretty well break even.

David