Macro varon test and confusion

[Davids]

I'm testing out a Macro Varon lens and, while I'm very pleased with the results, I'm a little confused.

The following image was taken with the lens extended ~102 mm away from my fuji xt-1. For a larger version, click https://www.flickr.com/photos/150316026 ... res/rJHq4T




The lens has a focal length of 85.1 mm, so I expected the magnification to be around 1.2 x. I took an image of a ruler using the same settings as above and this is what was in focus.


My camera's sensor is 23.6 mm long, so the lens appears to be focusing at ~0.5x. Why is this given the distance from lens to sensor?

Thanks!

[rjlittlefield]

The following image was taken with the lens extended ~102 mm away from my fuji xt-1.
...
My camera's sensor is 23.6 mm long, so the lens appears to be focusing at ~0.5x. Why is this given the distance from lens to sensor?

At http://www.schneiderkreuznach.com/filea ... 4.5-85.pdf , the table on page 2/2 says that 0.5X happens when the "flange-to-image" distance is 106 mm.

How does that compare with whatever you're measuring as 102 mm?

--Rik

[Davids]

Rik - Thanks! That answers my question.

[rjlittlefield]

Excellent.

So then, to add a bit of theory that I'm guessing you were missing...

The formula that magnification = extension/focal_length only applies when the "extension" is measured as the additional extension beyond infinity focus.

It is a specialization of the more general formula that added_magnification = added_extension/focal_length, working from a base of infinity focus where magnification = 0.

But the Macro Varon is a "short barrel" lens that requires some extension just to reach infinity focus in the first place.

Working backward, that base extension would be about 106-85.1*0.5 = 63.45 mm. From that you can reproduce most of the other numbers in the PDF to within a mm. The 2X number is several mm off. If that's not a measurement error, then I'm guessing it's due to a side effect of the beta adjustment.

--Rik

[Charles Krebs]

Davids,

The careful test results I have seen with this lens indicate that it really makes a significant difference if the "beta ring" is not set for the proper magnification. So a careful measurement of actual magnification (and then beta ring setting) is a very good idea with this lens.

[Davids]

Once again, thank you both for the input! Here's a second go with the lens. This is a seed pod of Carolina Cranesbill at around 1.1x. You can see a larger version here: https://flic.kr/p/TgupUJ