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Posts Made By: Bob Chester

March 7, 2005 11:06 PM Forum: Birding Optics and Photos

Pelicans on Ice

Posted By Bob Chester

Of course, the eagles do a little people spotting too. smile

If I were a fish or a furry little critter, I'd be scared. 8O

March 21, 2005 09:46 PM Forum: Equipment Talk

Curved Spiders

Posted By Bob Chester

First, the long answer:
Dick Suiter and William Zmek did a very nice article on spider diffraction in ATM Journal issue #11. If you can get your hands on a copy, it's a good read. If not contact me via a-marts' private message.
Suiter's analysis showed that a true semi-circle spider most evenly distributes the diffraction over the entire field. Only one spider maker I know of makes this design and since I don't see them listed as a sponser they shall remain nameless. I tried to make one and it came out too 'springy' and thus a poor support. I did talk to someone at Novak when I ordered my last 2 spiders (curved of course) and asked if they had tried the design. They responed that they had the same stability issues I had, so they stuck with thier old design.

Now the short response,, I hope.
All 3 of my newts have Novak curved vane spiders.
My 10" was built that way so I have no comparison to make.
My 4-1/4" went from a single stalk to a 2 vane curved. Huge improvement but unfair comparison.
My 6" went from a Novak 4 vane straight to a 2 vane curved. Nine years straight and 2 years curved. As Paul mentioned, without a side by side comparison I think it would be impossible to to rate planetary performance. My best views with that scope were with the straight vane spider, but that was due to seeing conditions and not spider diffraction.

with a spikeless preference,

March 27, 2005 07:40 PM Forum: Equipment Talk


Posted By Bob Chester

I own the older version of the Vixen, the GA-3, and am very happy with it. Got it used for a very good price. The rotatable and x-y adjustable reticle make capturing a guide star a breeze and the ability to use an eyepiece with comfortable eye relief is a plus.
Bare in mind I have no experience with any others.

April 2, 2005 01:57 PM Forum: Equipment Talk

Focuser Upgrade for Orion 80ED

Posted By Bob Chester

Starlight intruments makes thier feather touch for refractor upgrades. Moonlight also makes decent focusers and thier web site has them pictured on some Orion scopes. If you only need a micro focuser option then you might check out Mecury Systems Support.

April 6, 2005 06:06 PM Forum: Equipment Talk

Diffractions rings sharp extra focal, fuzzy intra?

Posted By Bob Chester

That would be a sign of over correction. However, I have seen atmospheric turbulence cause the same results. Another cause could be the cooling of the glass. It is said that mirror makers used to leave the mirror slightly under corrected so that they would perform better under cooling conditions.
The star test is a very sensitive test and can tell you a lot but requires ideal conditions. Star test often and get to 'know' your mirror. Don't let the knowledge that your mirror may be less than perfect (none are) discourage you from enjoying the views it provides.

Try this free star testing software from Aberrator.


April 12, 2005 06:12 PM Forum: Equipment Talk

mount polar finder for southern hemisphere

Posted By Bob Chester

The Vixen® polar-axis finder scope has a reticle for both N & S hemispheres.
I have no experience with it.
The model for the GP & GP-DX 'might' fit the SVP.
It can be purchased here:

Info on it's usage is on page 3 of this pdf file.

The Orion® unit is cheaper but I've never seen the reticle and can't find any info on thier site. Is it N hemisphere only?


April 14, 2005 05:24 PM Forum: Eyepieces

EPs which need LEAST amount of focuser in-travel

Posted By Bob Chester

I can't entirely answer your question but maybe I can get you started.
The E.Ps that require the least amount of IN travel will have the field stop the furthest down the barrel, below the collar. Tele-Vue® is the only maker I know that provides this information and the link is here:

Dimension (F) is how far above or below the collar the field stop is.
You may be in trouble since most makers try to keep the field stop near the collar.
If your T6 Naglers come to focus, then all T-V plössls , 1-1/4" Pans and all Radians should also come to focus.

Hope this helps.

April 23, 2005 02:37 PM Forum: Beginning Astronomy?

CG 5 Go-To Mount Head

Posted By Bob Chester

Nope, I have one of those cases (great case for 10 bucks) and I have a CG-4 gem. To get the cg-4 to fit I would have to remove the motors and the counterweight shaft. There would be no room for a cw or any foam on the top or bottom to protect the mount.

May 18, 2005 08:24 PM Forum: Telescope Making

My first mirror!

Posted By Bob Chester

Dive right in, I'm sure you will be just fine. The only advice I have for you at this point is to do a really good cleaning between grits. This includes changing clothes. A stay grain of #80 grit can cause nightmares. Patience is king - examine the surface with a lupe or magnifier to insure uniform smoothness before moving to the next grit.
And most importantly---- have fun.

May 20, 2005 01:36 AM Forum: Telescope Making

Can you crack the code?

Posted By Bob Chester

I too suspect that they are test readings of deviation from optimum. If the numbers were .003 -.007 etc. I'd be much more comfortable in saying so.
This is a mass produced factory mirror - perhaps they set up their test apparatus for a +1 and -1 tolerance level and if all readings fit within these tolerances they pass inspection. Then you don't need an experienced optician to preform the test.
Just a thought.