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Posts Made By: Jarad Schiffer

June 20, 2005 05:44 PM Forum: Telescope Making

Focuser height/ eyepiece focal length?

Posted By Jarad Schiffer

You can look up the specs on all the Televue eyepieces here:
http://www.televue.com/engine/page.asp?ID=144
If you have at least one of them, you can measure the focuser position on that one and compare it to the focuser position on your other eyepieces to get the rest of them.

Jarad

June 22, 2005 07:31 PM Forum: Equipment Talk

low power of for my 12.5" f4.7

Posted By Jarad Schiffer

Are you using a paracorr? If not, the 27 pan is about as low as you want to go. If the 2" size isn't an issue, get that one. If you have other scopes with a 1.25" focuser, get the 24 pan so you can use it in them, too.

If you have a paracorr, that makes your effective f-ratio f5.4. In this case, I would consider jumping to the 35 pan (or 31 nagler if you can afford it, or 30 Pentax XW). All of these will give you quite a bit more true field than the 27 pan without excessive exit pupil at f5.4.

Jarad

June 27, 2005 02:05 PM Forum: Telescope Making

Who Has A Cellular Mirror?

Posted By Jarad Schiffer

I had an 18" one by Stabilite. Worked great - it was a Zambuto, so it had an excellent figure. Almost no cool-down time, especially with a fan blowing into the open center of the mirror (it was a radial spoke design instead of a post design, with an opening in the center of the back plate that I had a fan blowing right into). Sold it because of kids - couldn't fit into the car with them, so I got a 14.5" scope that I could fit with them.

Jarad

July 1, 2005 03:21 PM Forum: Politics

Vacancy on Supreme Court

Posted By Jarad Schiffer

Depends on Bush - he can pick someone who is reasonably moderate to replace a moderate, and have an easy confirmation, or he can pick someone certain to draw fire, and have a long fight. Given his general behavior for the past 5 years, I am betting on a far-right candidate, probably one of the 7 who are already being fought over, just so he can have it as an issue to distract from other things.

Jarad

July 15, 2005 07:35 PM Forum: Equipment Talk

Question about Coma.......

Posted By Jarad Schiffer

There were some threads about these two on CN a while ago. Several people reported that the Lumicon unit adds some spherical abberation. This was okay for photographic use, but made it undesirable for visual use, unless you have a slightly overcorrected primary (someone reported about some scopes that were intentionally made with a bit of overcorrection so they could be used with the LCC).

Jarad

July 28, 2005 02:20 PM Forum: Equipment Talk

Big Dob Mirrors

Posted By Jarad Schiffer

Of the ones you mention, I would recommend Pegasus. John Hall is an excellent mirror maker (he trained Carl Zambuto), and a nice guy to work with.

I have heard good things about Woden, although on smaller sizes than you are considering. No personal experience.

Kennedy as other have mentioned is building quite a reputation as well.

Jarad

July 29, 2005 02:06 PM Forum: Reflectors

Truss Dob Manufacturers and Apeture Fever

Posted By Jarad Schiffer

I'll throw in Portaball, although it's a little different than the others you mentioned. Starstructure seems to be focusing more on the larger scopes according to some posts in another forum, but I think he still offers some in the sizes you want.

Jarad

August 3, 2005 02:50 PM Forum: Equipment Talk

Fast Scope - Bad Scope?

Posted By Jarad Schiffer

As Charles pointed out, at f4.5 you will want a paracorr. You will also need to use high-quality eyepieces (TV pan's or naglers, Pentax XL's or XW's, Meade 4000 UWA's, etc. Jury still out on the Meade 5000 series. Most plossls are okay also). Avoid the cheaper widefields like Konig's, Meade 4000 SWA's, 1RPD's, etc. They will have astigmatism that will be far worse than the coma, and the paracorr won't fix that.

But with good eyepieces and a paracorr, a fast newt can give outstanding images.

Jarad

August 4, 2005 09:05 PM Forum: Eyepieces

EP Recommendation for Fast Scope

Posted By Jarad Schiffer

If it's undriven, I would get a 7 or 5 nagler instead of the 6 radian - the extra FOV means less nudging, nice for a dob.

At f4.5, I would consider a paracorr. If you get one, you might consider the 27 pan or 35 pan as the lowest power one.

Also, the 13 nagler T6 could be subbed for the 12 T4 (lighter, smaller, cheaper, but less ER). That's just a matter of taste, both are excellent EP's.

Jarad


August 31, 2005 01:57 PM Forum: Equipment Talk

Why an equatorial platform?

Posted By Jarad Schiffer

Well, a full Servocat system costs about $2000 (including the DSC's), there are a lot of platforms for less than that. Brian Reed's have been mentioned, and are among the cheapest, but there are several others in the $500-$1000 range as well (Johnsonian, Astrosystems, etc.), not to mention lots of do-it-yourself guides.

Other reasons to pick a platform over GOTO are to get true equatorial tracking for photography (no field rotation), or to use with multiple scopes.

Jarad