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Sculptor Galaxy (NGC 253)

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Posts Made By: Jarad Schiffer

September 7, 2005 02:21 PM Forum: Telescope Making

thin plate mirrors

Posted By Jarad Schiffer
One thing to be very careful of with a thin mirror is to not grind astigmatism into it during polishing. I think you will need to do short sessions to avoid distortions from friction heating.

One the cell, I would consider gluing it to the cell and skipping edge supports. The thinner the mirror is, the better this works, since there is more issue with potato-chipping with edge supports of any kind, and less with lateral sagging (front-to-back) with glued supports. Just make sure you make the cell out of material with similar expansion characteristics to the mirror, with enough of a silicone blob to have some give to accomodate what little differential expansion there is, and not out of something that will warp over time (i.e. not wood).

Jarad

September 16, 2005 02:50 PM Forum: Telescope Making

18 inch f-4.8 secondary

Posted By Jarad Schiffer
I had a 3.1" secondary on my 18" f4.1 Starmaster, so it should be fine on a f4.8. Just don't use a huge UTA diameter.

Jarad

September 19, 2005 12:49 PM Forum: Eyepieces

Nag 26 or Pan 35

Posted By Jarad Schiffer
If you plan on using a paracorr, I would get the 35 pan. If you don't I would get either the 26 nagler or the 27 pan (based on budget).

Jarad

September 27, 2005 07:15 PM Forum: Eyepieces

What's causing my spike?

Posted By Jarad Schiffer
Also, if you had a slight smear on the glasses, that can cause a spike like you are describing. Especially if it was partially cleaned by wiping with something, which will smear the grease into lots of tiny parallel lines, and act like a diffraction grate.

Jarad

November 8, 2005 09:18 PM Forum: Eyepieces

Re: Safety undercuts

Posted By Jarad Schiffer
I would actually like to see them make the safety groove angled like the WO diagonal insert is - so that the setscrew pulls the eyepiece in. I had a diagonal with a normal safety undercut, and it was a real pain because when I got a new scope, the edge of the groove was right where the setscrew was, and it wouldn't sit flush. So I replaced it with a WO diagonal, and the reverse-cone shape of the barrel means that no matter where the setscrew hits on it, it pulls the diagonal in securely. And since it is an angle, loosening the setscrew lets is slide out smoothly without catching. I think that would be great on eyepieces, and would work equally well with setscrews or retaining rings.

Jarad

November 17, 2005 07:33 PM Forum: Equipment Talk

Travel scope for a trip to Africa...

Posted By Jarad Schiffer
A couple of questions first:
1 - Do you want to use the scope as a telephoto lens for a camera as well? If so, then I would concentrate on refractors.
2 - What price range are you looking at? I mean this both from a point of what you can afford, and what you want to risk during the trip.

If you don't feel comfortable schlepping an expensive scope around and risking damage or theft, then look at something like an ST-80 (useable as a telephoto lens as well) or a Starblast (which takes care of the mount issue as well).

If you can afford $1000-$2000, you might want to consider a Borg. The ED-101 would be a nice sized aperture, useable with a camera or as a daytime spotter if you want, breaks down very compactly, and only weighs about 6 lbs. You could downsize to the 77mm if you want to save a bit of weight, or the 100 achro or 77 achro to save money.

If you don't want to use it as a spotter or telephoto lens and want some more aperture, one of the UTI scopes might be a good choice (6" or 8"). These also have the mount built in.

Jarad

December 21, 2005 03:14 PM Forum: Reflectors

Opinions Wanted!

Posted By Jarad Schiffer
Well, I don't know about that particular scope, but I can give you some more general answers. For tracking platforms, I have an astrosystems one for my 14.5" portaball. I like it a lot. It is very simple to set up - just place it down facing roughly north, put the top on, and set the scope on it. It tracks accurately enough for visual use, even at high powers.

Also, I find that a medium dob makes a very good complement to a small refractor. I have a 4" refractor, and I usually take both the dob and the refractor with me to dark sites. The wide fields of the refractor give a nice contrast to the higher power views in the dob - look at the whole veil in the refractor, then zoom in on a section in the dob, etc.

Jarad

February 21, 2006 04:03 PM Forum: Eyepieces

18mm Radian vs. 19mm Panoptic?

Posted By Jarad Schiffer
I had the chance to compare an 18 radian and a 19 panoptic a few years ago at the WSP. The 19 does have a slightly wider TFOV, but I found the 18 to be slightly but noticeable sharper, especially on planets.

So if your intended use for the eyepiece is primarily for widefield objects, I would get the 19 pan. If you plan to study smaller objects (planets or globulars or small galaxies), I would take the radian.

And of course, if you wear glasses, I would take the radian.

Jarad

October 29, 2007 12:31 PM Forum: Telescope Making

Webbed Back mirror blanks

Posted By Jarad Schiffer
I anm not sure these really offer much advantage over a normal blank. Look at how thick the front face it - the 20" one is 3.8" total thickness, with 2.2" deep ribs. That means the front face is 1.6" thick - the same as a normal solid blank. So it weighs more than a normal 1.6" thick blank, and will probably cool at either about the same or even slightly slower rate.

In order to be worthwhile, a cellular design has to allow you to use a thinner front plate than you would be able to otherwise (like 1/2" - 3/4" or so). These are like taking a normal blank and adding more glass to the back.

Jarad

June 6, 2008 06:43 PM Forum: Eyepieces

6.5mm Ethos

Posted By Jarad Schiffer
Linton Rohr said:
I think a 5mm version would be welcome around Christmas time. wink

No, that's the wrong direction. A 25mm Ethos is what we need next (same TFOV as the 31mm nagler). Then an 18, so you can 25, 18, 13, 8 and have lowest to highest powers at 100 degrees AFOV. A 2x barlow or powermate will take care of anything higher, but we need those lower power ones. grin

Jarad

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