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Posts Made By: Jarad Schiffer

May 2, 2005 05:32 PM Forum: Telescope Making

Mirror Cell Advice Request

Posted By Jarad Schiffer

Well, first I wouldn't use a 9-point cell. It turns out that a properly designed 6-point cell will actually work better than the "classic" 9-point design. You might want to download a copy of PLOP to help you design the proper support points.

For attachment, I do recommend using silicone glue. I would put the dabs of glue on the support points, with some spacers on either side (a few toothpicks may work well) and set the mirror on top. Give it plenty of time to cure before you remove the spacers.

For some ideas on how to make the cell, go to either the Mag1 website or the Zambuto Yahoo group and look forpictures of the Portaball mirror cell - it's a very sleek design with a built-in fan.

Jarad

May 4, 2005 01:34 PM Forum: Eyepieces

Biggest true field for a 2" ep

Posted By Jarad Schiffer

Any of the following will be very close:
41 Pan
40 Pentax XL or XW (XW a bit closer than XL)
55mm Plossl (watch for exit pupil issues)
40mm erfle variants (GSO, Konig, etc.)
40mm SWA

In a fast scope, I would stick to the Pentaxes and Panoptics - the others will have astigmatism.

In a slower scope, the erfles, SWA, or even the plossl may be cheaper alternatives.

Jarad

May 4, 2005 01:44 PM Forum: Telescope Making

Now The Fun Begins!!

Posted By Jarad Schiffer

I had a Stabilite 18" mirror in a Starmaster scope for several years. It was a sweet mirror. Cool down was very fast. Mine had a central hole in the back plate, and I placed a fan blowing right into that hole, which made cool down even faster (<15 minutes even for a large temp drop). You can also place the mirror clips over the back plate so there is nothing on the edges of the front place. It should also be less sensitive to cell supports since the back plate can flex a tiny bit without transmitting it to the front plate (but mine had an 18 point cell anyway).

Enjoy the scope!

Jarad

May 18, 2005 01:24 PM Forum: Telescope Making

Can you crack the code?

Posted By Jarad Schiffer

Sounds like zonal readings from a focoult test to me. The 7.36 is probably the radius of the outermost zone.

Jarad

June 1, 2005 02:07 PM Forum: Eyepieces

Why no more Pretorias?

Posted By Jarad Schiffer

I think it is simple economics. A paracorr costs about $300 new. Some of that is barrel, cell, etc., so there would be some savings by incorporating it into an eyepiece, lets say it would add $100 to cost of an existing eyepiece to make it coma correcting as well. Lets say an average scope owner uses 5 eyepieces. That means getting 5 coma correcting eyepieces will cost an extra $500, vs. an extra $300 for the paracorr plus 5 normal eyepieces. If you want more eyepieces, it gets worse. If you have a second scope that doesn't have coma (say a small refractor to complement your large dob), now you need a complete second set of eyepieces for that scope.

What I would like to see (and it may becoming soon) is a focuser with a built-in paracorr for large dobs. That would save some weight, money, and fiddling in the dark.

Jarad

June 2, 2005 07:23 PM Forum: Equipment Talk

Wide-field Complement to my C9.25

Posted By Jarad Schiffer

My only concern with the NP101 is weight on the mount. Might be fine, might be pushing the mount a bit depending on which mount you are using.

The Borg 101 is a very lightweight scope, and a bit cheaper than the TV NP101. Probably not quite as good color correction, but if the weight is an issue it might be worth considering.

Jarad

June 7, 2005 01:17 PM Forum: Eyepieces

Meade 32mm SWA

Posted By Jarad Schiffer

They are fine for slow scopes (say f6 or slower). They suffer from edge astigmatism in fast scopes (say f5 or faster).

Jarad

June 9, 2005 01:13 PM Forum: Refractors

Taks

Posted By Jarad Schiffer

You can buy nice adapter plates like the one Herb linked to. For a small light scope, if you have access to a hacksaw (or better yet a mitre saw or table saw) and a drill press, you can make your own. Go to a hardware store, and buy a strip of aluminum (1" or 1.5" wide, 1/4" thick). Measure how far apart the tube rings are on your scope(s), and cut a piece of aluminum an inch longer than that. Now drill two holes 1/2" from each end - those will hold the rube rings. Now drill some holes to match the mounting holes on the mount. Add a few nuts, bolts, and lock washers and you are now done for about $20. It's not as pretty as the professional ones, and does not have a sliding dovetail to adjust the balance (you can slide the scope in the tube rings for that), but it's cheap....

Jarad

June 11, 2005 09:11 PM Forum: Eyepieces

Orion Stratus eyepiece review! What's the catch?

Posted By Jarad Schiffer

There is a review of the 5mm on the CLoudy Nights Eyepieces forum. In short, it performed quite well in an f4.5 dob out to about 85% of the FOV, but became somewhat soft near the edge. Strangely, this happened at all f-ratios tested (even slow scopes), so seems to be something different than the usual astigmatism in fast scopes. Performance was deemed somewhat short of Panoptic/nagler level, but very good for the price, and a significant step up from most of the cheaper widefields available in the fast scope.

Jarad

June 15, 2005 07:54 PM Forum: Equipment Talk

Secondary size for a 12" f/ 4.7

Posted By Jarad Schiffer

Assuming you use a 14" diameter tube, and a 1.6" tall focuser with 0.25" extra in-fcous, the 2.14" secondary will give you a 1.252" 75% illumination zone (1.278 degrees). The 41 panoptic has a 46mm field stop (1.81"), and will have about 60% illumination at the edge. The 2.6" secondary will boost that to 70% at the edge. This also assumes you use a secondary holder with no lip over the secondary.

Given that you have the 41 panoptic, and presumably like to see wide-field stuff, I would go with the 2.6" myself, especially if you use a wider tube, taller focuser, or a secondary holder with a shroud which will shrink the actual available secondary area. If you really want to focus on planets, you can use the smaller one, but in that case I would consider a longer f-ratio too.

Jarad