Posts Made By: David Brodeur

February 11, 2004 02:51 AM Forum: Equipment Talk

EP Confusion

Posted By David Brodeur

>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



May 12, 2004 08:08 PM Forum: Equipment Talk

refractor diagonal comments?

Posted By David Brodeur

you need to make sure that the filter uses glass that is flat and uniform to optical standards. Many filters use ordinary float glass and cause image degradation when used away from the focal plane (e.g. on a diagonal). Check the recent S&T article about color correction filters. The only filters they mention as not degrading the image were the Baaders. Elsewhere, Astronomik has been mentioned as making good optical quality filters. Not sure if either of them make a 2" minus violet filter.

David

February 13, 2005 02:12 AM Forum: Equipment Talk

Expanding GM-8 load capacity?

Posted By David Brodeur

To increase the load capacity of the mount, you'd need thicker shafts and larger bearings for increased rigidity, plus beefier worms, wheels, gears, and motors for smooth tracking. And yes, a heavier tripod. Losmandy has already done this for you; it's called a G11. wink

David