Posts Made By: Gary DuBose

Debbie,

I have heard that these are great. I'm ordering a 5" f15. Two reviews are on Cloudy Nights. Both have great things to say about the scopes that we're considering. I'm hoping that this will be a great scope for doubles.

I've done a good deal of questioning on these forums about D&G, and I've not heard anything negative about them.

Gary

I've never looked through an APO, but I own an f10 achromat. On very bright objects, such as 1st magnitude stars, Venus, Jupiter, etc., the scope will show a small "violet haze" around the edge of the object. This supposedly reduces contrast on planetary detail. It can also make seeing a faint companion of a bright double star more difficult. I don't have a minus-violet filter, but I sometimes use a yellow filter to remove this haze. This can help when viewing the companion of Rigil, or other such doubles with large magnitude contrast.

The shorter the focal length, the more severe the chromatic abberation. Very long focal lengths (f15 or f16) do not suffer as much from this problem. As I've said before on this forum, I think that the short focal length refractors (almost all Chinese) that are now saturating the market are a bad idea, and are giving achromats a worse reputation than they deserve.

Apos (Takahashi, Astro-Physics, TMB, etc) use either an additional lens element, fluorite glass, or ED glass (or a combination of these) to virtually eliminate this false color, even at short focal ratios, while preserving the crisp, high-contrast images that good refractors can give. This seems to be especially important for those who do CCD photography, thus some are willing to pay very high prices for these.

Gary

Ted,

In high school and college, I owned a 6" f8 Criterion Dynamax that I stupidly sold when I bought a C8. This was a nice scope that I didn't really make good use of, because of my limited knowledge at the time. I agree that 6" f8 scopes are top-notch.

Gary

I can't comment on the C5, but I would say that the f10 version of the C102 will give good planetary views. I have had one of these for almost a year, and have been pleased. I have split double stars down to about 1.5" separation (I believe it was 57 Cancri.) The major cloud belts on Jupiter show up very well, and the Great Red Spot is visible. There will be some false color ("violet haze") around very bright stars, Venus, and Jupiter, but it is within the acceptable range in my opinion.

You can get a C102 for less than $500 delivered, or maybe even cheaper if you buy something used. At the risk of starting another argument, I would strongly advise the f10 version. In a 4" scope, its still small enough to be easily portable.

Gary

For about the same money, you would think that Meade could make a decent 4.5" f6 or f8, without the internal barlow. Scopes this size are still plenty small enough, would be easier to collimate, and would probably perform better. Manufacturers these days always seem to want to make something exotic, when plain vanilla would work better.

Gary

You did not put this on your list, but I can recommend the f10 version of the Celestron 102. I have been using a C102HD for about a year, and have been very pleased. When used with a 2" 40mm eyepiece, it gives great wide-field views, but is still good for high magnification (I routinely use 200X on double stars) without image breakdown. The false color only begins to show up on very bright objects. I would expect the false color to be much more objectionable on the faster ones that you mentioned.

Gary

I am able to use up to 200X on planets and double stars with my C102 (4", f10) and have been very pleased with the views. As these are available pretty cheap (less than $500 new, around $200-300 used), you should be able to get something nice with a $1500 budget. You might find a used fluorite version of the C102 that Vixen produced for a while, a different model of Vixen refractor, some model of 4" TV, or maybe even pick up a used Tak FS102 for this price. (OTA's for new Tak FS102's can be had for less than $2000.)

Good luck with your choice, but whichever you choose, I would second Victor's advice about a longer focal ratio, especially if you do not get an APO. Good achromats f10 and longer tend to be much better for planets than the fast models. With low-power 2" eyepieces, you can still get pretty good wide-field views. (I use a 2" U.O. Konig 40mm with mine.)

Gary

Gamma Virginis has closed to less than 1" separation now. It will be very difficult for the next several years. Its orbit is on this site: http://www.dibonsmith.com/vir_g.gif

Search the Double Star forum if you're interested in more info. A couple of the guys with larger scopes got it last year. It would take very high magnification on a large, high-quality scope in perfect seeing.

Gary

I know a guy here in S.C. that has a 29" scope made from a Coulter mirror that he bought back in the 80's. I looked through it once when it was new, and got the best view of M13 I've ever had. I really can't evaluate the optical performance, but to the best of my knowledge, he still has the scope. It was built as a big dob that he could roll out of a shed. Definitely not portable.

Gary

An astronomy book that I would recommend to everyone is "The Perfect Machine," by Ronald Florence. It is a comprehensive history of the development and construction of the 200" telescope at Palomar. It gives details on all the pitfalls that occurred in constructing the mirror, plus insights into the personalities of Hale and Hubble, among others. Originally published in 1994, I picked up a used copy off Amazon last year that was inexpensive.

Gary