Posts Made By: Kurt King

My original question was meant to learn if this eyepiece can handle a fast light cone, say F/4 or 5. MOST eyepieces will do very well with the longer F ratios out there, the SCT's, Cass.-Maks, and long refractors. Kurt(Curtis) King

Machined concave metal molds, machined to desired R are needed to hold the flat glass that is placed in them. An oven with a thermostat and controller that can be programed to raise the temperature slowly over time are the necessary equipment. The program used to slump my 19"(I'll have pictures Monday nite and hope you guys can give some assistance)took the temp up to 1180 deg. F and holds that temp. for 6hrs. The time from start up until it could be safely removed was 20 hrs. The machined mold helps in the process by getting to temp also and keeping the glass from cooling too fast. This produces a fine anneal. Just one way its done that I have seen and has worked well for years.

Floyd, You just gotta get the 26mm Nagler t5. That is just the ticket to fill that gap. By the way, I couldn't stop lusting after a 20mm T2 so I got one from an Astromart ad.Should be here Wednesday. Go for the 26mm.

Herb, sorry but what is wrong with his purchase approach?

"I am looking to create the best quality mirror possible." With that being the most important point and money(as with your 8" mirror) not being an issue, then quartz or another ultra low expansion material is really the best. The ability to test immediately after a figuring session and being able to rely on the results as accurate(due to no surface changes) is a big plus with the ultra low expansion materials. Just a personal opinion formed from working large, thin mirrors of Pyrex, plate, and quartz. Hope all goes well with your first mirror. You'll have a great time regardless of the material chosen and will learn a lot and that's what first mirrors are for.

I visited the gentleman's website that details grinding with steel washers. It was a quite lengthy article with a lot of pictures. Very interesting and an innovative way of grinding but different doesn't mean better and I could not discern any advantage in his method over conventional ceramic tiles. Just a different way of achieving the same end. Any claim to speed of or effectiveness in grinding time would be hard to verify. Too many variables such as substrate chosen, experience, work ethic, tool preparation, etc. A well written, interesting technique though. Wish I could find it again.

Alan,
Glass Fab gets my vote. havehad many dealings with them over the years. I'll recommend them. Interesting though, that while i have never doubted their material or delivery, I usually find them a bit pricey.

Hello Paul, BK-7 is much closer to plate glass in it grinding/polishing properties than Pyrex and I would rate the thermal expansion figures more comparable to
plate than Pyrex as well. These thoughts are from personal experience with all 3.

Hello Phil,
I have a 19" plate glass mirror, which is 1" thick. It is polished and slightly overcorrected. If I ever get the truss ota together, I'll finish figuring it, No problems have been encountered, the blank was slumped and has a 100% support cell. The final figuring will be done in the cell

Good day Ido, I can see you having some similar prblems I had when using an 11" F/5 primary for a Cass. May I first say though that the odds of coring a hole thru your primary(full thickness??) are not good, regardless of the method used. My 11" hole was cored than glued in before grinding/polishing. Another potential problem you will find is that the F/5 of your Newt. is slow for a cass. This will mean a longer than usual tube, and one of a cassegrains nice features is a short tube. A longer F ratio primary means not only a longer tube but the secondary is going to need a higher magnifying power to get that long light cone back thru the primary. A larger secondary can be placed closer to the primary but it would make for an usually larger than normal secondary and thats not too good either. Please note that there is an elegant solution to your situation in your message inbox. All the best on your project.