Posts Made By: dan hilts

It could be the astigmatism is in your eye, not the scope. Your eye will cause more trouble at low power views with a wider exit pupil from the scope. To eliminate your eye as a problem, make sure the lens and focuser are well aligned and then look at the star image at high power. There will be the usual color problems but any astigmatism in the image will show up as out of round images that change orientation as you go from inside focus to outside focus.

good luck,

dan

If it is only a question of plate versus pyrex it can be done. Fused silica will complicate the issue, (density 2.21 - 2.23) because it is so close to pyrex. I have tried to determine glass types this way but it is very difficult to get definitive results as there is some variation in the glass densities from one batch to the next and from one supplier to the next.

have fun,
dan

Unless the mirror is absolutely filthy, DON'T clean it. A little dust and even some smudges will look much, much, worse than they are. Live with it for a while until you have had the chance to learn good collimation and have a pretty good idea how your scope functions. It probably isn't hurting the views as much as you imagine.

When you can finally no longer stand it, clean it then. I like to soak the mirror for 15 minutes in a solution of room temperature distilled water, a little pure alcohol and a drop or two of liquid detergent. Then use fresh cotton swaps to wipe the stubborn dirt loose, no scrubbing (one gentle wipe each, do not reuse). Rinse the clean mirror with fresh distilled water and the drops should run right off when the mirror is stood on edge to dry. Use the corner of a clean tissue to soak up any stubborn droplets. That should do it for a few more years depending on how dirty your viewing site is.

That's the basic process in a nutshell. Bottom line, clean as little as possible. That's the real trick.

good luck,
dan

A friend of mine here in Toronto had the same experience. His Meade camera is acting up and now only provides a half frame of image. He has received a return authorization from Meade for his DSI Pro and they will provide a replacement for $189 + $10 shipping. Shipping by UPS only and that will add another $35 or so for brokerage fees to get it into Canada.

This is becoming normal service policy for a lot of companies. Our youngster had one of the early Kodak Easy-Shoot cameras. When it needed service, the service depot wanted more to look at it for an estimate than Walmart was selling new units for. If you have ever tried to have a cell phone or PDA serviced you quickly realize that this stuff is meant to be disposable.

clear skies,
dan

Hi Bob,

I asked this very same question not so long ago. The AFOV formula gives a reasonable approximation only if there is no distortion in the eyepiece. In eyepieces that have some distortion, there can be errors generated because the magnification changes across the field of view. This is particularily noticable in the wider view eyepieces. Magnification tends to increase towards the edge of the field so the true field of view defined by the field stop is smaller than the AFOV.

hope this helps,
dan

Hi Steve,

Have you looked at Antares? (not the telescope people)

http://www.antaresoptics.com/SecEM.php

dan

That's a good looking little scope. I'm glad you won your bet!

clear skies,
dan

Enrique,

I think you won't really appreciate the differences of a short scope until you try it. Don't under estimate the value of a wide-field view.

I was out last night panning the skies with a hand-held 80mm F5 using a 24mm Pan. You can't do that with a long focal length. The views are really different than one gets through a long focal length scope. More like a binocular view only more flexible. Everything is framed much better, relative sizes of objects becomes obvious, and the position of one object with respect to another is much easier to see. There were some objects, like M26, that I have easily spotted with the short tube but have been elusive when I searched using my F12.5 refractor. There's lots to see with the shorty including M11, M26, M27, M33, M31-32-110, double cluster, Auriga clusters, and everything else in between. The Teapot was too low in the wash from the city lights last night but in the summer it is a great place to wander around.

I took the short scope out because transparency was forecasted to be good but there was turbulence and seeing wasn't expected to be good. There was also some wind gusting and my long refractor can get the shakes under those conditions. It was a good night for the short scope and I enjoyed it thoroughly rather than fighting with the big scope for less-than-satifying viewing.

Under better conditions, I would have had both scopes out and stayed all night.

clear skies,
dan

You didn't mention what type of mount you are using. If the mount is a design where the scope sits high above the pivot point, like an AZ-3 or similar mounts, then you will have a balance problem. The weight of the scope is at a changing distance from the centre of gravity depending on where the scope is pointed. When aimed horizontal, the weight is centered above the pivot. When aimed toward the zenith, the weight of the scope is way off to the side. With these mounts, the balance point keeps changing.

dan

Big heavy glass will need big strong tubes and at those F ratios, tubes would be long even if folded. You would need to take great care to ensure tube currents don't destroy the image.

I did work out the spot diagrams for a 4"F25 once and was tempted to build one. At this aperature and F ratio, all visible light shows up inside the airy disk and the field is free from abberations over a very large diameter. However, this changes quickly as the aperature increases.

The suggestion to get a Meade 178 ED is a good one. It would be easier to recoup any investment when it was time to sell.

have fun,
dan