Posts Made By: Jason Lane

That's a nice pic. Jim are you able to rotate your camera on the mount? Rotating it 45 degrees clockwise would have framed all four of those stars pretty good.

-Jason

when in reality there are very few 1/4 wave 8: and larger optical systems

That claim is incorrect.

-Jason

Hi John,

You'll want to learn how to swap those out, because the 1-13 with the split image type is best for daytime photography. For night-time I think you have the best one in there. I use 1-11 screen, which isn't quite as bright as yours but I've gotten used to it.

I've tried the Beattie Intescreen that the others suggest, but I didn't like it for whatever reason.

-Jason

The requirements for a telescope design are different for visual vs. photographic. For example, a telescope designed for photography must be able to achieve good focus across the entire field of view in a flat image plane. This is to ensure the stars are sharp and in focus across the entire film frame (I talk film because all the photographic designs were of course designed for use with large photographic plates or film). For a visual scope, this is not as stringent a requirement because the eye tends to accomodate for slight changes in focus. Another requirement is that off-axis, a photographic scope should provide nice, round images of stars (whether or not they are in perfect focus). This is partly because odd-shaped stars are ugly looking, but also for professional fields like astrometry it is easier to pinpoint the exact location of a star in the image if they are round blobs (the actual position is in the center of the blob) versus streaks (astigmatism) or shaped like a comet (coma). In a visual scope, this isn't as important because you can either refocus for best shape or it's just not as noticeable. These are just a couple of examples of requirements driving the design.

This is why there are many different telescope designs. Some will be optimized for visual and some are optimized for photography. Some are a compromise of the two, meaning they are not best at either but are good at both. For example, the RC design and the Schmidt Camera are examples of scopes designed for photography. The Newtonian and the Schiefspiegler are good examples of visual scopes. Finally, the Schmidt-Cassegrain (as Celestron and Meade have designed theirs) would be an example of a scope designed as a compromise, giving generally good performance either as a visual or as a photographic telescope. The SCT is interesting because it is robust enough that you could design one that would be a killer visual scope, or you could design one that would be a killer photographic scope.

Hopefully I haven't confused the issue too much. I'd recommend you getting a copy of "Telescope Optics" by Rutten and van Venrooij. This is a very good reference that talks about just these issues.

-Jason

If that's an APO, then I'm going to start calling my Fiat Spyder a Ferrari. What, they're both red and Italian!

-Jason

Rob,

If you're a tinkering type, look for "Nye Damping Grease" on the web. Most commonly used damping grease in the industry (damping = nice buttery smooth action when you turn a knob, focuser, volume control, etc.). When you run across them, look for a heavy or very heavy. This stuff works well down to low temperatures, and is a lot cheaper than a new focuser. Simply tear down the old one, clean the old grease out, and replace it with this stuff.

-Jason

Barnesite polish is once again being made. Do a Google search and you'll stumble across it.

Cheers,
Jason

Hey Herbert,

How bout one of them retractable phone cord thingies? It has 4 wires so you could double up pairs of wires to accommodate current. Radio Shack?

-Jason

Hey Bill,

I've got a question for ya..why would you use aluminum alt bearings vs. the Teflon pads that most people use in dobs? Seems like Teflon would be even lighter than the composite bearings.

Cheers,
Jason

Another favorite from that night...

Lunar Eclipse Rising Through The Clouds
27 October 2004, 7:30 PM
Olympus OM-1 on LX90 @ f/10 (Cassegrain Focus)
Fuji Provia 400F Color Slide Film
2s exposure

Enjoy,
Jason