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Coathanger CR 399

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Posts Made By: Mike Hosea

September 14, 2003 08:10 AM Forum: Equipment Talk

Astonished & Disappointed - Please Comment

Posted By Mike Hosea
If you don't see the point in seeing what the eyes can see versus astrophotography, then I'd have to say there are a lot of people who feel something like that. Heck, I feel something like that when looking at those targets. However, when viewing Jupiter, Saturn, the moon, open and globular clusters, I find that astrophotography is no substitute for real-time visual observation. Clusters take on a jewel-like appearance that have about the same relationship to photography as fireworks. Jupiter is constantly changing, and lighting conditions on the moon are both crucial and take many years to duplicate precisely. Saturn is spectacular. Galaxies and Nebulae do sometimes present a lot of detail in a 24" scope, but some are more impressive than others visually. Color, however, tends to be elusive except for hints of pink in the Orion nebula.
--
Mike

September 16, 2003 07:22 AM Forum: Telescope Making

Collimation and secondary alignment

Posted By Mike Hosea
Floyd,

Here's a diagram drawn to scale. Note how the on-axis light cone strikes the secondary closer to the lower-left edge. Incidentally, I created this figure in Cabri Geometry II Plus.
--
Mike

September 19, 2003 12:04 AM Forum: Telescope Making

Holes in mirror coating?

Posted By Mike Hosea
I don't know the particulars of the "Diamond Brite" coating, but it is normal for SiO2 overcoated aluminum, and yes, brand new. You want a very thin coating. A thick one will distort the figure.
--
Mike

September 20, 2003 09:00 PM Forum: Equipment Talk

Equipment Review websites...trustworthy??

Posted By Mike Hosea
Just check the author and decide for yourself on a review by review basis. You may not see any "slam" reviews, though, as it is fairly simple for a manufacturer to make legal threats, and these have to be taken seriously by a small operation. I remember a scathing review of a Nisur mount that was quite negative (and I knew the reviewer from many electronic discussions), and Nisur threatened it off the site. That was well before there were sponsors.
--
Mike

September 21, 2003 12:46 AM Forum: Telescope Making

Front Aperature Calculations

Posted By Mike Hosea
The Newt number (9.3") is undoubtably the correct one. Just 0.48" of clearance isn't going to allow much of an entrance angle before vignetting from the cage/tube occurs.
--
Mike

September 21, 2003 10:33 PM Forum: Equipment Talk

Exit Pupil Question?

Posted By Mike Hosea

October 5, 2003 08:25 AM Forum: Equipment Talk

UO Orthos Overated?

Posted By Mike Hosea
They are good for the money, you know, bang for the buck. Tak orthos are significantly better, IMO, but they cost more ($141 new) are 0.96" (need an adapter), and except for the 4mm and 2.8mm HI orthos, for some reason or another they don't get the respect they deserve on the used market, probably due just to sheer ignorance.
--
Mike

October 6, 2003 02:31 AM Forum: Equipment Talk

Lunar viewing

Posted By Mike Hosea
What sorts of features are you trying to observe on the lunar sufrace? Craterlets and rilles near the lunar terminator do not benefit from filters because they are extremely high contrast objects. Instead, maximize the useful magnification. Filters may be helpful when tracing out ejecta patterns and otherwise determining other variations in surface composition, generally features observed under high illumination, but the benefits are somewhat limited compared, say, to viewing low-contrast, colored features on Mars or Jupiter.

"Moon" filters are optional equipment. IMO, they are most helpful when you want to do lunar observing and DSO observing in the same night. Many experienced lunar observers never use them. One way of avoiding the need when not in a star party situation is to do your lunar observing with a white light on.
--
Mike

October 7, 2003 12:03 AM Forum: Equipment Talk

Buy Tele Vue 20mm T2 or spend more on T6?

Posted By Mike Hosea
I don't understand the question. Do you mean Type 5, as in 20mm Nagler Type 5? The Type 6 Naglers are all 13mm and shorter. Apples and oranges.
--
Mike

October 7, 2003 09:19 PM Forum: Telescope Making

Secondary size for 10" reflector?

Posted By Mike Hosea
Well, a very important differentiating factor is the distance from the secondary to the focal plane. The 10" f/5 Teleport performs just fine with the 1.83" secondary, but it uses a low-profile focuser to keep the distance form secondary to focal plane short. If you want a conventional focuser, the distance will be greater, so you will tend to want the next larger secondary size, particularly for DSO observing. If you haven't experimented with the SEC program (available for download from the S&T site), I recommend that you do.
--
Mike

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