Guillotine / Drop Shutter and Exposure

[Richard K.]

I've now seen a few of the drop type gravity fed shutters on You-Tube etc. They seem to be a cheap reasonably reliable alternative for large shutterless lenses. My question is - how do they avoid uneven exposure from top to bottom of the neg due to acceleration of the slot due to gravity? Or are the prints burned?

The only thing I can think of is that the slot reaches terminal velocity due to friction before it starts crossing the lens path. But it seems that a higher starting point would have been required to reach terminal velocity?

Can someone confirm that the negs are evenly exposed?

Also, anyone know where to get *this shutter, or is it home-made?

* http://www.youtube.com/watch?v=8odb2oeBrJA

[Steven Tribe]

There was an extensive thread a few months back. Starting point was a "new" drop shutter. Suggest you search using "guillotine".

[Robert Hughes]

My question is - how do they avoid uneven exposure from top to bottom of the neg due to acceleration of the slot due to gravity? Or are the prints burned?

Since the drop/guillotine shutter is at the lens, rather than at the film focal plane, the question is moot. Any part of the lens that is exposed transmits light to the entire sheet of film.

For my DYI 8x10 box camera I built a spring-driven two blade guillotine shutter based on the Minox shutter (but bigger and only one speed: 1/30 sec). I don't use it though because I found a "Galli style" sheet of black foamcore with a 1/2" wide slit cut through the middle works just as well.

[BetterSense]

Since the drop/guillotine shutter is at the lens, rather than at the film focal plane, the question is moot. Any part of the lens that is exposed transmits light to the entire sheet of film.

That pretty much explains it. It's a bit weird to think about but the proof is in the working.

[Mark Barendt]

Since the drop/guillotine shutter is at the lens, rather than at the film focal plane, the question is moot. Any part of the lens that is exposed transmits light to the entire sheet of film.

I doubt this explanation. If it were true vignetting would not happen.

My guess it that the distance across the lens is so short that it doesn't matter a lot.

[Robert Hughes]

I doubt this explanation. If it were true vignetting would not happen.

What would vignetting have to do with it? I don't see the relevance.

I'm seeing some bogus optics talk here. Experts, please chime in.

[Paul Fitzgerald]

"Any part of the lens that is exposed transmits light to the entire sheet of film."

"What would vignetting have to do with it?"

If any part of the lens exposed covers the whole plate, how could vignetting ever happen?

As far as uneven exposure from a drop shutter goes, it does not because there is NO comparison to a focal plane shutter.

A 1/4" slit in a focal plane exposes 1/4" of film, a 1/4" slit with a drop shutter exposes 1 inch or more at the film plane. You would need to do a film test or use a shutter speed tester to gauge exposure from each slit AT EACH EXTENSION LENGTH, the lens extension changes the 'swipe' size. Drop shutters do work BUT were replaced for lots of reasons.

[JRFrench]

This could be easily tested by holding a slit in front of a view camera and looking at the image on the glass.

[jp]

I'm wondering if a slit shutter on the front would increase DOF. That would not be desirable if using a portrait lens or if you are otherwise going for shallow DOF. It doesn't matter where the aperture is based on some of the soft focus designs where the aperture is at the front for a combination iris/lens shade.

[Arne Croell]

Since the drop/guillotine shutter is at the lens, rather than at the film focal plane, the question is moot. Any part of the lens that is exposed transmits light to the entire sheet of film.

That would be correct if the shutter would be close to the aperture stop plane like a leaf shutter. But in front of the lens it is not that close. It is also not near a field stop plane like a focal plane shutter, where a variable speed would have a visible effect. It is somewhere in between, so it acts a bit as aperture stop and a bit as field stop at the same time.