Posts Made By: Jarad Schiffer

Yes, pretty much ALL optical defects lower resolution. Spherical abberation, zones, coma, etc. all have adverse effects. Turned down edge is a particularly nasty one in reflectors.

And a 4" apo, assuming good optical quality, should outperform other scopes of the same aperture (with the possible exception of an unobstructed reflector). The apo has no obstruction, no coma, no spherical abberation, so produces the most resolution possible for 4" of aperture. Even a perfect reflector at least has a central obstruction, which slightly lowers the resolution, and may also have coma (depending on the f-ratio). If the other scope also has optical defects (Spherical, truned down edge, astigmatism, etc.) then of course they will lose out, but then so would a poorly made APO with the same defects.....

Jarad

I would recommend running an insulated wire through the center of the truss. You can have a connector sticking out near each end. I would worry about shorts and giving myself little zaps running it through a bare aluminum pole, unless you put some kind of insulating wrap around the rest of the pole except where the connection are.

If you want to use the spiders to carry the current to the secondary mirror, just make sure that the rest of the spider is painted to it isn't going to short either (or use one of the Protostar units - their spiders are coated with something non-conductive to prevent this problem).

Jarad

You didn't mention how wide your edge mask is. This will change the numbers slightly (making the diameter a bit smaller and the f-ratio a bit larger - for example, if you have a 1/4" edge mask, it becomes a 7.5" f7.46). This will make the 100% illumination zone a bit bigger than you calculated. I would stick the with 1.83". As for edge defects, rather than getting a larger secondary and masking it, just get a higher quality 1.83" secondary.

Jarad

Yeah, if you can store your scope outside, that will eliminate most of the cooldown issue. But if you keep it inside, then it's a real issue. It can also be a problem if you live somewhere where the temperature drops quickly after sunset, since then even storing it outside won't help...

Jarad

It could be done, but you will have to take the weight of the secondary into account. Call up Bryan Greer at Protostar and ask him if his spiders will be adequate to handle the weight of your secondary (I assume you have weighed it...). You might also want to consider a 4-vane curve (like Rick's design mentioned earlier in this forum) or one of the double-C designs (these are a bit sturdier than the single C type or 3-vane, although they obviously have a bit more total diffraction).

Jarad

ALso check out the San Diego Astronomy Association: www.sdaa.org

They have a nice site in Tierra Del Sol, about an hour drive from San Diego. But since that is the RTMC weekend, a lot of them may be there instead.

Jarad

I did this on my 18" Starmaster, It lasted a few years, then I sold it (it was still on when I sold it). Didn't make a big difference, of course, but it did cover up a few shiny scratches in the original paint. I used the protostar paper because I had some extra from the piece I ordered to flock the UTA and a few other things - some of the other options people have mentioned would probably be cheaper unless you happen to have some around.

Jarad

This is a big issue for me, too. To me, the two most important factors are distance from home and dark skies (I am ignoring seeing because I am going to assume for the moment that the seeing won't be significantly different anyplace within a few hours drive). Obviously, less distance is better, and darker skies are better. Unfortunately for most of us who live in or near big cities, these two are inversely related (i.e. the darker the skies, the further we have to drive to get there).

For short sessions, I am only willing to drive about 10 minutes or so - to the nearest park with a decent sized field without too many lights in my face.

For all night sessions, I am willing to drive about 2 hours, which can get me to several fairly decent sites in the North Georgia mountains. Seeing is about the same as in Atlanta, but the skies are much darker.

For a weekend or more, I am willing to drive 5-6 hours or so, which could get me to places like Chiefland, etc. That's pretty much the only time where seeing becomes an issue, since it takes several hours drive to go far enough for really significant differences in average seeing (I am ignoring "local" seeing like heat off of streets, parking lots, nearby houses, etc.).

Now, ideally I would love to have a dark site with great seeing within 10 minutes of my house, but since my house location is also controlled by minor issues like my job, my kids' school, etc., that won't be happening anytime soon....

Jarad

At f8, I would get a 41 Panoptic if price and weight are no object. If weight is an object, then the 40mm Pentax XL. If price is an object, a 40mm GSO superwide.

Jarad

I saw that 24" scope at RTMC in 1996, I think. The owner had unfortunately parked next to Steve Swayze's 40" dob, and there was a long line at the 40" and nobody looking through the 24". My wife and I went over to the 24", and the owner (whose name I have unfortunately forgotten) spent over an hour giving us a tour of his favorite objects. It was a great scope (and a nice guy!). We never got over to the 40", we were enjoying the 24 too much....

Jarad