Posts Made By: Jim Nelson

Actually, I think part of your problem is too little magnification. Saturn's colors are subtle, and will get washed out if the image is too bright. With a 15mm eyepiece, I think you're getting around 133x with your 8 inch scope. That's not pushing an 8inch scope too much, and the image brightness will be quite high. I think if you get your magnification up to about 200x, colors will be easier to see - but the image probably won't be as sharp and clear.

With my 6inch scope at 171x, Saturn looks pale golden with tan banding, and the two main divisions of the ring seem to be different shades. These colors are subtle, but not hard to see. (...but never as colorful as the more colorful images you'll see posted around here).

On the other hand, I seem to see pale color better than some people, but if the Orion nebula has that blue/green look to you instead of just grey, then you probably have pretty good color sensitivity.

Your formula applies equally well to 2 inch and 1.25 inch eyepieces. It should be stated that your formula is technically only roughly correct, but is usually within a few % of the true value (most eyepieces have some degree of curvature or distortion of the field that renders your calculation not quite right...that said, it's what I use).

What really determines the field of view is the "field stop diameter", as explained in more detail by Clyde. If you have a 32mm Plossl with 50 degree apparent field, it's going to have the same field stop regardless of the barrel size. But you'll notice that 1.25 inch 40mm Plossls typically have about a 42degree apparent field of view, instead of the usual 50-52. That's because the 1.25inch barrel itself is acting as the field stop. You can get a 50 degree field in a 40mm Plossl, but you have to increase the barrel size.

Maybe that clears things up. Not my clearest explanation ever, but I gave it a shot.

After boosting the contrast on the "spokes", they appear radially arranged to me, which seems unlikely if the cause was dirt. I've included what I got after toying with the contrast and inverting the light/dark scale.

http://www.tmboptical.com/itemsRecord.asp?item_id=21&cat_id=4&

It's small, light and 12mm of eye relief vs. big, heavy and 17mm of eye relief. Optical differences are subtle in all comparisons I've read.

I'd be a little leary of buying something that appears in the same ad as the "Beer Bottle Telescope". :S You'd think Apogee might try a little harder to give itself a respectable sheen.

First - brands to get...

Most "name-brand" Plossls are in the same league or even better than the Meade Plossls. Orion's are a good deal, but with the recent price decrease the Meades are a good deal too (they were overpriced for a while). If you want a small step up in quality, Orion's Ultrascopics, Celestron's Ultimas, and Tele Vue's Plossls are the usual recommendations for very high quality at a moderate price. The difference may not be dramatic between these and the Meades, but side-by-side tests do show a difference. These are in the $75-$110 range. University Optics Orthoscopics are also available at an even lower price, and are favorites of many planetary observers.

Second, what focal length to get...

A barlow isn't a bad idea for a next eyepiece. Celestron's Ultima or Orion's Shorty-Plus are very good units at a modest price (although some people report that their magnification factor is actually more like 2.3x or 2.4x; hmmm). With a little planning, a barlow will save you money, and allows you to use longer focal length eyepieces for higher powers. If you don't know already, Plossls of less than about 10mm focal length (depending on personal preference) get uncomfortable to use (tiny little eyelens, have to get very close to it.)

Here's my personal suggestion:

Get a 2x Barlow, and a 15-17mm Plossl.

This will give you:

26mm: 48x, 96x w/barlow
16mm: 78x, 156x w/barlow

It's an idea. The 78x and 96x are a little close, but all in all this is a pretty nice range. About 150x is a good high power for the ETX90. You could push it higher - the optics on those things are usually pretty darn good, so it can probably handle 180-200x or more, but personally I think that 150x will be more generally useful (I rarely go over 200x with my 6-inch scope).

Not quite as succinct as I was planning, hope it's useful

"Many people complain about the "window" or "lens" of these finders being too dark or too heavily coated to allow the user to see "through" the finder. They miss the point [...etc.]"

You know, I was wondering if I was some sort of oddball in how I used red-dot finders, because I never felt like I looked "through" them at all, but used both eyes, but I had often read complaints about how much they dimmed the view. I only in the last few days have purchased one of my very own (and for only $169, it came attached to an Orion Starblast, what a deal!). I'll try the single eye/looking through method, just to see what people are complaining about...

The University Optics 24mm Konig (60 degree field) would really do the job for you, I think. Helix (check out the sponsor page) sells these over the internet.

Looks a little like what Galileo saw!

http://www.library.wisc.edu/libraries/SpecialCollections/hsi350/galimg1.html