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Posts Made By: Doug Summers

August 16, 2002 04:33 PM Forum: Telescope Making

22" F4.0 truss dob design thoughts/questions

Posted By Doug Summers

I've been dreaming about an ultralight 22" design that falls somewhere between a Greg Babcock design (look at his 24" ultralight) and an Obsession (which I currently own an 18" model of). I wonder why innovative design thoughts aren't gaining ground (why don't mirror cells pivot (tailgait) for easy cleaning of the primary mirror), and why aren't the altitude bearings attached directly to the mirror cell (eliminating most of the primary box/rocker assembly height). Does anyone know of a person/company that's on the leading edge of new ultralight large dob designs where the box assembly isn't the end-all design goal and feet-on-the-ground viewing is king? I'd love to find that company or forum to support. Maybe if a few of us were more forceful in driving design considerations, we'd have more choices. Large dob designs seem to be in a rut and in need of some creative engineering to get to the next breakthrough. Anyone want to offer an opinion of who's leading the pack in new design thoughts for the big ones? I'm stuck between capitulating for a smaller commercial scope than I want (due to the boxy designs), and making my own scope (which may be problematic while I work through issues to "get it right"). Ideas?

August 29, 2002 09:48 PM Forum: Telescope Making

Need 4.5 inch secondary; can't find vendor

Posted By Doug Summers

I'm looking for a 4.5" secondary for a 22" f3.7 primary but can't find one. I must be doing something wrong, because it seems no vendor sells this size. Does anyone have any ideas on where I can get large secondary optics? Thanks.

September 2, 2002 07:51 PM Forum: Telescope Making

PLOP cell designs

Posted By Doug Summers

I've been looking at PLOP cell designs vs. standard commercially available designs. Now that I'm convinced that PLOP designs are the only way to go, I'd like to find a shop that makes them. Anyone know of a good machine shop that's familiar with ATM work and PLOP cell designs in particular? Thanks!

October 7, 2002 07:49 PM Forum: Telescope Making

Mirror Vendors - who's got best quality for $$

Posted By Doug Summers

Hi All,

I'm interested in procuring a large (22") fast (f3.7) mirror for an ATM project. I don't want to make the mirror myself, so I'm going commercial for it. I've looked at most everyone, and I'm noticing a price "pecking" order of (lowest to highest) Swayze, Nova, Pegasus, Galaxy, Intermountain Optics, and Torus. The order isn't necessarily important, but quality is to me. Is anyone aware of actual independent testing done on these vendors' products? I'm weary of all the bickering over wavefront quality claims...especially since they are so hard to verify (outside of a star test which is often seeing limited and incorporates total system error). The price difference between Nova (Ronchi) and Torus (interferometry) is $2K (which is 56% markup). I don't mind paying for quality, but I don't know how to verify it and level the playing field. I'd like to get a fine optic and expect to pay a fair price. Ideas, opinions, and/or comments?


February 24, 2003 08:56 AM Forum: Telescope Making

fringe analysis software

Posted By Doug Summers

Hello all, I'm looking to find software or a company to have an interferogram analyzed. The cheapest fringe analysis software I could find is about $1500 (too much). I tried a couple of web demos, but I couldn't get them to calculate the WFE. Does anyone know of someone that can perform fringe analysis given a digital image of the interferogram? Thanks!

March 7, 2003 01:12 AM Forum: Telescope Making

foucault testing with a digital camera

Posted By Doug Summers

Hi all,

I'm trying to use foucault1-2 image analysis software, but I've run into trouble getting enough light back to fully illuminate the pupil through ROC. Either side is ok, but at focus produces a very small image. It's a 22" f3.745 mirror, and I've tried small and jumbo LEDs to try & get a larger return spot. It's not the LED, and I am able to get images. The perplexing thing is that at ROC, I don't get a clean flip, and I see quite a bit of extinction from both sides when moving the KE. Am I doing something wrong?

October 8, 2002 03:53 PM Forum: Telescope Making

Mirror Vendors - who's got best quality for $$

Posted By Doug Summers

Thanks Ed (and everyone),

I think you're right; Vaughn seems very responsive (he is even willing to do interferometric tests for a fair price). I've also had very good response from Pegasus. I suspect that both these vendors produce excellent optics; a coin toss is probably required to finalize the decision! To be fair, the other companies are probably also good; I just didn't get the same responsiveness on my particular optic out of the other vendors. I'm not a fan of the divergent quality claims however, I think the industry should try and rally around a single number (strehl?). Vaughn quotes SURFACE RMS while Pegasus quotes WAVEFRONT RMS. This is very confusing (and probably gets Intermountain some business from time to time when it's really a wash). In any case, I don't think it's intentional; probably just convenient.

Thanks for venturing an opinion.