Darlot lens help..

[Glen Seelenbrandt]

I just recently began working with large format gear after many years of both smaller format and alternative photo processes. Recently was able to purchase a very nice looking Darlot lens. I was hoping for some help in both identifying the lens and gathering some information about lens functionality and coverage. The lens' physical measurements are 125mm by 66mm (or 4.9in x2.6 in) without lens hood. Would also love some info on how to measure focal distance. Is it from ground glass to rear element? or to lens board? Other info: I am shooting a Graflex Super Graphic. Any help in the learning process would be greatly appreciated.

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[Two23]

Often, the physical length of a Petzval (minus hood) is its focal length. I'm betting this was made for quarter plate. Might barely cover 4x5 w/o movements if you aren't too picky about the outer third of the image.

A quick way to measure FL is to stand next to a white wall, shine a light through the lens, and focus the the light until it becomes a tight dot. Measure from center of lens to the wall, and that's pretty close. Closer would be to just stick it on the camera (make temp lensboard out of cardboard), focus on something at infinity (>100 ft. away), and measure.



Kent in SD

[Glen Seelenbrandt]

Thanks Kent! I did make a cardboard lensboard and it seems like I have some fairly round and dark corners. When you say w/o movements, do you mean with the lens dialed all the way back? Hard to tell what happens when I turn the knob..should I expect less or more dark edge as I extend the lens?

Thanks!

Glen

[Steven Tribe]

The movement of the knob doesn't introduce camera movements, it is just a focussing device from the days when cameras (or in your case, magic lanterns) did not have precise mechanical adjustments. Movements mean introduction of an image on the GG which is not central or symmetrical to the lens axis. The easiest example is the correction for making tall buildings have parallel sides all the way up to the top. This reduces the size of the OK image on the GG.

Normally, the focal length is measured from the Waterhouse stop slot to the GG image when focussing on infinity. Another way to do it is to measure the width/height of a fixed object like a window frame on the GG and find out the same width it has with a lens of known focal length seen from the same position. Their apparent length on the ground glass is exactly in proportion to their effective focal lengths.

Darlot is a bit of a teaser with their non-photographic lenses as they made them exactly like their photographic lenses unlike most other makers. Fortunately, Darlot came after the Waterhouse revolution so no WHS means Projection use. Apart from "gem" lenses made for mass CdV production.