Posts Made By: Roland Christen

Marj and I were on a service trip, to work on several mounts and scopes and to update software for these remote observatories. The morning started out with the hike up the mountain from our room down below. The first day required a few rest stops on the way up, but by the third day we were champs and were scrambling all over the mountain top.

That is very very good!

Rolando

This next photo shows the sun almost on the horizon, but because of atmospheric refraction, it is already set and just below the horizon. It is therefore slightly north of true west because of the angle of the setting sun at our 42 degree latitude.

Rolando

This next photo shows the sun almost on the horizon, but because of atmospheric refraction, it is already set and just below the horizon. It is therefore slightly north of true west because of the angle of the setting sun at our 42 degree latitude.

Rolando

Thank you for your post. Interesting comparisons.

Roland Christen

Close-up of crater taken with 130 GT scope and Barlow set to 4x.

Rolando

Post a picture of what you have.

Rolando

Niiiice!

Rolando

Be careful! The two galaxies at left are about to crash.

Rolando

There is no way for you to know which glass is used. FPL51 and FPL53 are both clear colorless glasses. The only way for anyone to know which was used is to measure the radii of all surfaces and the actual focal length and backing out the type of glass used. Without that knowledge, you will have to simply accept the advertised glass type.

Having said that, I have seen ordinary crown glass mirrors being advertised as low expansion quartz. Again it is hard for an amateur to verify this kind of thing without the inherent knowledge that past amateur telescope makers have known. We who are in the business of making telescopes will know pretty much whether a particular telescope has quartz mirrors just by looking at the price for the complete telescope. Even in Asia (China) an unfinished raw quartz blank costs as much as some of these advertised telescopes that have all other components plus labor added, complete with tubes, focusers, secondaries, ground and polished surfaces and high reflectivity coatings.

How can you tell a quartz mirror from an inexpensive crown glass? Simple. Aim the scope at a bright star and run the focus out so you can see the donut. Now place your warm hand in one spot on the outer part of the mirror back for about 1-2 minutes. Take a picture of the result with your CCD camera. On a crown glass mirror you will see a bump where your hand was. With a quartz mirror you will likely see nothing. The image is not distorted with quartz. This does not take high powers to see. 80 to 150x is all you need to see the distortion caused by expansion of the glass in that spot which you heated. You will also not have any cooldown issues with quartz - the figure you see at sundown is the one you get hours later.

Rolando