Obtaining parfocality on a zoom lems (Wild Makrozoom)

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Scarodactyl
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Obtaining parfocality on a zoom lems (Wild Makrozoom)

Post by Scarodactyl »

I suspect this is kind of a basic question, so bear with me. A while back I got my hands on an extra Wild Makrozoom zoom lens/objective, not attached to the usual macroscope setup. I have tried mounting it directly to my camera with empty spacers. I can always get a decent image at max mag, but it seems like there is no distance where it is at all close to parfocal, with the lower mags ending up being a couple feet longer than the highest. This is in contrast to the one that is on my M420, which is nearly parfocal across the whole range with a ~4in working distance. So I kind of assume the head must be doing something to wrangle this thing into parfocality, but what? It does have a 1.25x magnification factor. Is this something I am likely to be able to replicate with a tube lens or something?

enricosavazzi
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Re: Obtaining parfocality on a zoom lems (Wild Makrozoom)

Post by enricosavazzi »

Scarodactyl wrote:I suspect this is kind of a basic question, so bear with me. A while back I got my hands on an extra Wild Makrozoom zoom lens/objective, not attached to the usual macroscope setup. I have tried mounting it directly to my camera with empty spacers. I can always get a decent image at max mag, but it seems like there is no distance where it is at all close to parfocal, with the lower mags ending up being a couple feet longer than the highest. This is in contrast to the one that is on my M420, which is nearly parfocal across the whole range with a ~4in working distance. So I kind of assume the head must be doing something to wrangle this thing into parfocality, but what? It does have a 1.25x magnification factor. Is this something I am likely to be able to replicate with a tube lens or something?
Yes, the head has a "tube lens" close to the objective mount. I do not know what are the properties of this optic. I also do not know if it is a tube lens in a proper sense or just a "relay lens" to increase magnification, and whether the objective is in fact infinity corrected.
--ES

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Scarodactyl
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Post by Scarodactyl »

From what I can tell it is finite, but I'm not an expert so i could be wrong. I've stuck it on an AO infinite head, though, which did kind of work, but if I remember right it wasn't parfocal either. Neither was the weird industrial mount this makrozoom came on (as a side note, I tried the coax illuminator that came with it and it has an odd red filter on it. Wonder what those rigs were meant for, and who made them).
As a side note, I really appreciate the information you have on your site! It has been a lot of help in building my system, which is getting close to complete.

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Scarodactyl
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Post by Scarodactyl »

Just as a quick update, I tried a really informal test of holding a random surplus lens of unknown purpose and specs (but which appears to have a moderate magnifying effect) in between the camera and the lens, and it did have a dramatic effect on the working distance. The random spacing I chose didn't make it parfocal but the 0.63x working distance went from feet to inches. So I guess it does need some sort of lens to get that parfocality just so, though probably not a proper tube lens per se.

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