JOGS International Gem Show April 7-18 Tucson Expo Center
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 Post subject: Re: NA - R - DOF
PostPosted: Mon May 02, 2011 10:17 pm 
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Joined: Tue Jan 02, 2007 8:20 pm
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There is also such a thing as too much zooming. When designing zoom optics the designers
usually have to make compromises and trade offs. The more zoom , the more compromises.

The things that get traded away are things like distortion, flatness of field , color rendition accuracy as well as other optical characteristics like coma and numerous other things which is why there are not that many good optical designers floating around out there.

Computers and software have allowed all sorts of optimization. But if I look at my own
(albeit ancient )history of love affairs with microscopes and cameras in the stereo microscope department it goes like this. In 1974 I looked through a Wild M5 (old model) and realized I was seeing stuff that I couldn't see through other stereos. This was a four position mag changer turret (where many of these compromises don't have to be made because the intermediate lenses are fixed) The next scope I really like was an AO Cycloptic with an APO objective. Again a barrel changer step mag stereo. Then I had ocassion to look through some Zeiss stereos that worked like the Cycloptic. All these scopes had a great view.

I have never had a zoom camera lens that I liked though I am sure there are plenty of good ones out there by now. But when I was buying them there was not much in zooms that made me want to get out the money.

All the stereos I use now are zoom of course. I have an example of the Zeiss SV11 which is 11 to one. I think this may be too much zoom. I haven't decided yet.
But I had a previous SV11 and had no compunction about selling it and was not particularly tempted to keep it.

The SV11 started a numbers race in zoom ratios. Then Olympus went to 10 to one and
12 to one. Now Leica has upped the ante. But until I get a chance to look through one of these critters I would be quite skeptical. I am also skeptical of outlandish claims of high NA and resolving power (listed in lp/mm) which are hard to believe given the working distances of stereos.

The Zoom ratio is one of those numbers that the marketing jerks like to get their hands on , like gigaHertz and megapixels and horsepower. There were huge increases in the zoom range of lenses for video cameras and some of these design lessons may be able to be transferred successfully.

But Leica have a couple of design ideas I wouldn't touch with a ten foot pole. Like two different optical paths one with high res and one with higher depth of field. I forget the gimmick name they have for it.

I would not be in too big a rush to have one of these. Get an ApoZoom and be happy.

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 Post subject: Re: NA - R - DOF
PostPosted: Tue May 03, 2011 2:38 am 
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Joined: Thu Dec 13, 2007 3:42 pm
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Location: the Netherlands
Sell/swap me one of your apozoom objectives and I'll be happy! :D

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