X1D Mediumformat and Macro

Have questions about the equipment used for macro- or micro- photography? Post those questions in this forum.

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rjlittlefield
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Post by rjlittlefield »

ChrisR wrote:I believe the 247mm TL came from taking a known objective which covers a particular sensor size then, basically enlarging the image by using a longer FL tube lens. When you increase M that way, the image diameter on the sensor follows.
I'm guessing you meant 267 mm tube lens, in which case that number came from me as follows...

Mitutoyo M Plan Apo objectives are designed to be used with 200 mm tube lens.

With all infinite objectives, the actual magnification is just proportional to the tube length FL, when focused as intended.

So then for the Mitutoyo 7.5X, we have:

actual magnification = (nominal magnification / 200) * tube lens FL
10.0 = (7.5/200) * tube lens FL
tubelensFL = 10 / (7.5/200) = 266.66...
gmfotografie wrote:or can i use also a 250mm but with not exact 10x magnification ?
Yes.

If you then want exact 10X magnification, you can add a short extension behind the 250 mm lens. This drags the objective slightly away from its design point, but at 7.5X NA 0.21 that effect will not be visible.

In my tube lens tests on full frame, I used that technique of adjusting the rear extension for the Raynox DCR-150 tests, so as to get exactly the same magnification and FOV for all the tube lenses. The Raynox DCR-150 is nominally 208 mm FL, so focusing it exactly at infinity would have given nominal 10.4X magnification. In that "perfect" configuration, the corresponding slightly smaller FOV than the other lenses would have put their corners outside the frame of the Raynox, making it impossible to compare the same details on subject. So I opted to de-tune the Raynox configuration slightly, to permit direct comparison. It handily outperformed the other lenses anyway, in terms of corner quality.

--Rik

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