Posts Made By: Alan French

People with an interest in Mid-Atlantic Star Party might find this article of interest....

http://www.thepilot.com/stories/20060914/news/local/20060914starparty.html

We enjoyed our visit to MASP several years ago.

Clear skies, Alan

Keep in mind that orthoscopic really means an eyepiece that is without distortion, and there are a number of variations that carry the label "Orthoscopic."

Clear skies, Alan

I think a 90 to 100mm or so APO would be a perfect second scope. It would allow you to get low power, wide field views, and be nice and portable. Add a white solar filter and/or an H-alpha filter and you've got some new abilities.

I often use my 90mm for birding, setting up on the back deck or water's edge somewhere and enjoying some fantastic close-up views of my feathered friends.

Clear skies, Alan

Golly gee, if you are on a budget, you sure don't need 10 eyepieces/barlows etc. You could get away pretty easily with three, and four or five would handle pretty much anything.

Please don't ask how many we have here. Of course, the two of us have a total of about 70 years to accumulate such things.

You only need 10 eyepieces for one telescope if you have a binoviewer.

Clear skies, Alan

The Moon is a very nice test for lateral color, which is common in many eyepieces.

Clear skies, Alan

Thanks for taking the time to write this up!

Clear skies, Alan

For the same level of color correction, you'd need to go to f/20 on the 8". That's getting a bit on the long side, and would be very tough to mount properly in a straight through version.

Clear skies, Alan

jess tauber said:

Was just reading the latest discussion in the Refractors section (6 inch F/15=....) and remembered something I'd asked about in this or some other forum but don't remember getting an answer to.

If one has a dome-shaped observatory roof, why couldn't you use some sort of mechanism to incorporate your refractor cell right into the roof and still allow it to orient as needed? For instance, if it ran on curved rails (two sets of rails orthogonal to each other, one of which rotated about its ends at the 'equator' of the dome. The two sets of rails ought to give some stability.

Has anyone ever seen a setup like this for very long FL refractors, sans 'tube'?

Jess Tauber

Keeping to collimated would be murder. Feeding a long refractor with a flat would likely be much easier.

Clear skies, Alan

I am not sure why this should be confusing. Fluorite is fluorite, or CaF2. Fluorite occurs naturally, but optical fluorite is often grown in the lab.

Glasses with abnormal dispersion characteristics similar to fluorite are fluor-crown glasses (Ohara FPL51, 52, 53; Schott FK54, 56; Lzos OK4).

All of these are ED (Extra-low Dispersion) materials.

As we've been discussing, the folks selling optics don't make it easy. I note that Zeiss has binoculars with "Fluoride (FL) Glass Lenses." I suspect that most of us would find it clear that Zeiss is not talking about fluorite. Calling fluor-crown glasses fluorite would be incorrect.

Clear skies, Alan

I have no idea how familiar you are with telescopes, so I'll just assume they are new to you.

The diagram shows the scope set up for solar projecting - that is, for using the telescope to project the image of the Sun onto the white screen. For visual use, the eyepiece holder (#23) should be angled upward and an eyepiece placed in it. You may have several eyepieces. The one with the highest number on it (possibly 25) should be the one to start with.

The number on the eyepiece is the eyepiece's focal length. Somewhere on the tube of the telescope, perhaps near the focuser, it should have the telescope's focal length. My guess is around 900mm.

The magnification is the telescope focal length divided by the eyepiece focal length. So for my example, 900/25 = 36, so it would be 36 power or a mafnification of 36. Low powers provide the widest view and often appear sharper than higher powers.

As Herbert suggested, try the telescope on a distant object during the day. Some telescopes like this have a draw tube which slides inside the focuser. If that is pushed all the way in you may not be able to move the eyepiece far enough outward to focus on a distant object (or a celestial one). If you remove or don't have the diagonal (#23), you may need to slide the draw tube out even farther.

Good luck!

Clear skies, Alan