Posts Made By: Alex McConahay

Is nobody going to mention the "oldest" scopes on the field?

Ken Graun and Alan Binder from Arizona had hand crafted three replica Galilean scopes. They were the hit of the Merit Award telescopes. How Galileo ever discovered anything is beyond me.

Alex

Way to go, Darrell.

It is a great feeling to get one of these things finished. It's fun to just look at it knowing you did it. It is even more fun to look through it.

Many years of enjoyment are ahead of you.

Alex

Alan,

Actually, nothing happened besides what Canon said was going to happen in the first place. They announced some while ago that they were going to make a limited run of Astro specialized 20D's called the 20Da. They did that. Then their run was over. It was never meant to be a forever offering.

Now, one very interesting development was a by-product of RTMC. Every year the RTMC people award an honor to whoever has made a great innovation in amateur astronomy. This year, the award went to Canon. A rep from Canon came to receive the award. He was very impressed with all that happens at RTMC. Apparently he did not realize that their camera had such an impact on such a bunch of enthusiasts.

So, maybe we will hear more from Canon in the future. In the meanwhile, as they said they would do after making a limited number of 20 Da's, Canon has stopped production.

Alex

A car battery with a solar panel (as at most RV places) should handle those minimum requirements.

Alex

Light pollution does not limit magnification. Seeing limits it (to that 150-200 power you are talking about). But you can have bad seeing in the darkest of deserts or mountaintops. Seeing is the steadiness of the air. It does not change depending on whether it is light or dark at your observing site. As a matter of fact, seeing is a problem in solar observing, also.

Now, there are those who say that the larger the aperture, the more problem you can have with seeing. I don't buy that.

The big reason to limit yourself to four or six inches in a city (in my mind) is that the really big aperture telescopes excel at seeing dark sky objects--dim, dark fuzzy things. Well, you aren't going to get them in the big city. SO, you are stuck carrying around a lot of aperture that you really cannot use. You will spend your time on the moon and planets and bright doubles, globulars, and such. Since you don't need the extra aperture, you skip it by getting something small and portable--which shows the kinds of objects you are looking at as well as anything. (Oversimplified, of course.)

Alex

Well, you gotta watch out here. In the first place, there are diferent uses of the terms "magnitudes."

When we talk of magnitude of the star, we are talking about the total amount of light coming from a point source. That is, all the light is coming from a single point. This is pretty easy to compare.

However, when talking about deep space objects, we are talking about the total amount of light coming from an area. To compare these magnitudes, one must take into account the size of the area. And this is much more difficult.

Another similar concept is "surface brightness." Surface brightness is, well, the brightness (or amount of light) coming from a given area. When you add up all the surface brightnesses, you get a "magnitude" for an deep space object. When you are talking about "point sources" such as stars, there is only one area to add up--the point of the star--but you still get a magnitude.

At any rate, compare a tungsten filament to a flourescent bulb. The tungsten filament is much brighter--puts out more photons (has a higher surface brightness--more light per unit of area) than any one small part of the flourescent tube. However, the Flourescent Tube is much, much larger. As a result, the the Flourescent bulb can put out as much overall brightness as a tungsten filament, even though the tungsten filament has a much brighter surface area.

OK, back to the stars. M42 may have more total light output than a sixth magnitude star-- But it is spread out over a larger distance. Therefore, no one part of it shows through.

M33, for instance, has a pretty bright overall magnitude, but it is so large, that it appears rather dim (has a low surface brightness).
In addition to this little explanation, remember that various measures of magnitude depend on visual, photographic, wavelength of light, and so forth. The eye is more sensitive to some colors, etc. So, there is no one "magnitude" for a celestial object.

Alex

No, it's not washers, although I suppose that would work. There are machined pieces called radius blocks. Basically a shallow "v" that cradle the scope. You can also get a "W" shaped piece of aluminum to do the job.

ANd yes, they are plenty stable. They sell the 9.25 on a CG-5 mount with such an arrangement.

Alex

The Pronto is probably a better telescope than Messier had. However, if Messier had a 10 incher, we would now be trying to do a Marathon of a couple of thousand objects in one night.

Alex

My Meade 10" Starfinder is eleven years old and still shows no sign of deterioration.
I don't know if that is typical.

Alex

Okay folks--for those who may be thinking about this problem.

I called Tele-vue. David helped me out (isn't Tele-Vue Great!)

In order to work right, Para-Corrs need a specific distance (55mm) from the para-corr to the field stop/film plane/chip, etc. That is why they made the "tunable top" on the newer models. You can move it in and out to accommodate the different positions of the field stops/etc. in your eyepieces.

The old Para-Corr's (top screwed off and left a T-adapter) were meant to be used attached directly to the camera adapter. This gives the correct distance.

Well, I was attaching my camera through a camera adapter to the Para-corr's eyepiece holder. SO, the distance was way off. Hence my bad coma.

ON the other hand, my scope would not reach focus (not enough travel) if I connected the camera directly to the Para-corr's t-threads. Therefore, I had no choice if I wanted to use the Para-Corr at all. (The coma was so bad, I decided to remove the para-corr entirely and just suffer the regular coma from the 4.5 mirror.

Now, I forget whether it was lack of infocus or lack of outfocus travel that hung me up last weekend. Hopefully, it is lack of out travel--in which case I merely have to add a spacer. If it lack of intravel, I to either move either the mirror or the focuser. (or maybe just change collimation screw position if it is just a bit!).

I'll see what I have to do this weekend, and try it all over again.

Alex