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Posts Made By: Tim Libert

March 1, 2003 09:52 PM Forum: Equipment Talk

Best Contrast Eyepieces

Posted By Tim Libert

It probably depends on what you are using them with Some optics complement the total "train" better than others. However, some factors that influence diffusion are: the number of lens to air surfaces; and, the effect of the coating on each of these surfaces. So in general less lens elements and/or superior coatings help make high contrast. Also lens surface quality. I put this in a seperate category as some manufactures produce such a fine glass finish (leitz ans some zeiss to name a few) that they don't use normal coatings as they can't get the same quality surface. So what does it all mean. The old standby ortho has few glass to air surfaces and if produced by a quality manufacture and/or with good coatings will have great contrast. Personally My opinion is that Erfles produce the best contrast even though they have one extra interface, however, I primairly use them with long focal length scopes. Erfles tend to have coma distortion at the edges although the newer designs have overcome this. Vernon Scope (Brandon) EP are high quailty Erfles and have super conrtast qualities. There are gives and gets to every design and it would take a book to get into everything to consider. My $.02

March 1, 2003 10:05 PM Forum: Telescope Making

Looking for Advice and Parts to build an APO.

Posted By Tim Libert

Texas Nautical will sell TAK objectives by themselves.

March 2, 2003 10:10 AM Forum: Equipment Talk

CarlZeiss APO-TESSAR 110mm 1200mm F/11 lens

Posted By Tim Libert

William, I have made several scopes from old large fromat, aerial and process lenses. You can make very good scopes depending on what you want to use them for. The Zeiss Tessar is one of the best lenses to use for this. I'm sure you are familiar with Zeiss quality, you can't ask for better. The challenges you will encounter will be associated with the conjugate focal plane. This might mean that you would have a long travel distance for focus between points. These lenses also have more curvature and thus edge of field abberations can be noticed when the conjugate focal plane is extended. With this all said the lens you mention is a very long focal length, for such a lens, and this will minimize the fore-mentioned problems. While that is a rare and beautifull lens I'm sure, and well worth $1500, If you want to spend in that price range I'm sure you could find a high quality 4" objective primairly suited for a telescope. I believe you could get a TAK FS replacment 4" for that price range. either way you would end up with a fantastic scope. Tim

March 2, 2003 10:33 AM Forum: Telescope Making

Mirror Cell - # of points

Posted By Tim Libert

Tim, From an engineering point of view: In theory a object will only rest on three points. With that said, the mind-set behind more points is that the glass will deflect under it's own weight to fing more points at which to rest. At every point of contact stress will incure and will influence deflection. with more points added, less stress at each point and thus less deflection at each point. So now you have to play a balancing act. the more points you can rest on the better, however, you don't want your glass deflecting (bending) to acheive rest on these points. So build a mount (cell) that has three solid points of contact. From each of the three branch out with a somewhat flexable moment arm to more points. and so on and so on. This will allow the cell to conform to the glass shape and provide the three point rest. If you do this right, more is always better. Tim

March 3, 2003 10:33 AM Forum: Equipment Talk

What is this eyepiece?

Posted By Tim Libert

I've seen them...., I had one... Got it from a surplus store in West Lafayette, IN in about 1985. The salesman there told me it was off a tank gun sight WWII era. I never took mine apart but it performed like an erfle in my estimation. Great views as I remember. Wish I still had it. You don't want to sell that one do you? smile(LOL) Thanks, Tim

March 6, 2003 08:29 PM Forum: Religion

...and Politics

Posted By Tim Libert

Hey Joe, (isn't that a song or something ) Yes, Bush did use the same anwser, but, for a reason (I believe). The questions of the reporters, though many good, tended to draw away from the issue. It's like asking if abortion is ok in a rape case. The issue is wheather abortion is murder. If that is true than a rape shouldn't change that. Circumstances sourounding his decision concerning support from other countries, the peoples opnion, the cost...none of them change the fact that he feels this is his job, as President, to protect the American people.

March 7, 2003 05:48 AM Forum: Deep Sky Observing

Viewing in the reagon of black holes

Posted By Tim Libert

Hey Jim, I think I'll lay out in my driveway tonight and see if I will be transported to New Jearsy.... smile

August 12, 2003 03:06 AM Forum: Equipment Talk

Finder scope question

Posted By Tim Libert

Yes. The larger the objective the more light you can gather. Now in pratice the differance between 30mm and 50mm (about 78% more light) I think that will astound you providing it is the same quality. Given the light polution problem you will want to get a "high contrast" scope or good quality with good coatings. Antaries Canada makes a nice scope for not to much $. TAL (Inties) Russia makes a real nice finder scope. Of course TAK is probably the best, however, big $.


May 2, 2015 08:34 PM Forum: Equipment Talk

SCT Reducer/Corrector question

Posted By Tim Libert

I have almost certainly eliminated the corrector as the problem. I tried it on another scope and it checked out fine (no change whatsoever in the star test pattern). Same result while rotating the reducer. I believe that my problem is with my main tube. I think that the optics might be "tilted" (not concentric with the tube/not perpendicular to the threaded rear attachment/rear of the scope). I plan on verifying that the center (visual) tube is concentric with the outside walls. Then when verified/fixed I will check that the primary mirror is perpendicular to the center and outside tubes. When that is completed I will need to install the corrector plate parallel to the axis of the primary mirror. Then I can collimate the secondary. Anyone see any problem with this logic? Thanks