Slip on focal plane shutter

[Ron Lee]

I would but I'm in Europe for the moment and to send it back would cost me more than I would like to pay for the proof. But no amount of testing can remove the basic physical limitation of the construction (inclination sensitive beside all the other imprecision sources also those mentioned by RichSBV).
GPS,
I'm not sure that you know of what you speak when you say "the basic physical limitation of the construction" when you haven't seen the unit and you know nothing of the tolerances in the constructions. I will load the holder with two sheets and shoot completely vertical, the other I will tilt to the max (aprox. 45 degrees) and scan both film together with no corrections whatsoever, then would this convince you? Frankly I am not trying to convince you, but others whose confidence that you have destroyed in the unit with your split hair jargon non- sense. I just don't know why I bother! I heard the cry several times for a shutter that could be mounted on the lens that works, not for the profit but for the humanity of man was it built. You should know that we are all united is some way one to another for no man is an island. Look me in the eye and tell me that I know not of what I speak.

[IanG]

You can get Thornton Pickard shutters for bout $16 / £10, they are extremely easy to restore, even if you have to make a new blind

And they'll most likely be more reliable. They aren't heavy, they are small and compact.

Ian

[Jim Michael]

It doesn't really matter whether the speed changes with tilt, as long as the change is consistent and can be documented as part of a calibration process. I think a more useful analysis might be performed by taking some electronic measurements of the shutter speed variation with tilt. There's a pretty easy to build shutter tester you can make with a few easily obtainable components, one example at http://www.hrtranslations.com/photo/.../shutter2.html

[Turner Reich]

It doesn't really matter whether the speed changes with tilt, as long as the change is consistent and can be documented as part of a calibration process. I think a more useful analysis might be performed by taking some electronic measurements of the shutter speed variation with tilt. There's a pretty easy to build shutter tester you can make with a few easily obtainable components, one example at http://www.hrtranslations.com/photo/.../shutter2.html

That's what I'm saying but build one into the shutter with a on-board readout.

[RichSBV]

I have been using quite successfully for about 4 years now a speed graphic focal plane shutter on the front of my Deardorff, behind my lenses. The concept of the stick is valid with the exception being that what is moving at the end of the stick is a point and what is moving at the film plane with a slot shutter is a slot and the size of the slot varies with the focal length, being larger the longer the focal length. I believe the change in the slot size at the film plane compensates for the change in the speed of travel...

Arthur,

Thanks for that thought. I wish I would have had it years ago when I looked into making such a shutter. I'll have to put some more thinking into this to see if I may still invest the time into it now.

As for accuracy claims though, it still presents a problem of the original slit distance from the lens, front or rear. It can still only be accurate for any lens at a specified distance from the lens (most probably the nodal point). If, for example, you front mount and then screw on a filter, you move the slit further away from the lens. This would change the effective speed at the film plane. Maybe we need a math person to clear it all up?

I think it's great that this shutter exists and there is interest in it, but some reality checks may be in order...

[Ron Lee]

Arthur,

Thanks for that thought. I wish I would have had it years ago when I looked into making such a shutter. I'll have to put some more thinking into this to see if I may still invest the time into it now.

As for accuracy claims though, it still presents a problem of the original slit distance from the lens, front or rear. It can still only be accurate for any lens at a specified distance from the lens (most probably the nodal point). If, for example, you front mount and then screw on a filter, you move the slit further away from the lens. This would change the effective speed at the film plane. Maybe we need a math person to clear it all up?

I think it's great that this shutter exists and there is interest in it, but some reality checks may be in order...

The actual shutter distance from the lens of my unit is sitting at 2mm . Not unlike Jim Galli's shutter, my theory is almost identical to his and what about using your lens cap, do they work? I don't know much about what goes on between the lens and film other than the stick demo and I can deal with that. Do a simple test; cut a thin slot in a dark piece of stiff paper and slowly pass it across the front of your lens when you are focused on a scene and you can actually watch what is happening to your film. The light is dim at first then gets brighter then fades with the subject being displayed at all times. Hope this helps.

[Ron Lee]

Hope i'm not talking to myself! Back with the shutter test with the electronic testor and here are the results. I had little time to go through all the speeds. Vertical= 1/20th, 26degree tilt=1/17th, and last 45degree tilt=1/10. I might add that at the vertical position the shutter drops without touching the envelope that I could tell. Here are the actual numbers respectively, 0.049987, 0.05953, 0.09878. these are elapsed times.

[Gordon Moat]

I have seen many images of Guillotine shutters in old photography publications. They were somewhat proven around a century ago. The only accuracy I would wonder about today would be their usability with transparency films, since those are more exposure critical.

I did look into making a Guillotine shutter, though I ended up finding a large diameter Wollensak shutter that solved my exposure needs. While that only has four shutter speeds, and no flash sync, it works reliably and packs small into my main 4x5 bag.

I think the shutter you have is a great idea, and I wish you luck with selling a few. I have no doubt that some people will find these quite useful. Don't get too bent out of shape with the negative comments, since I doubt any of those guys even use brass lenses without shutters.

Ciao!

Gordon Moat Photography

[Arthur Nichols]

As far as the question of varying exposure depending on the focal length: I honstly do not have the math skills to work this out. I would suspect that setting aside all other considerations like tilt angle and so on, that a slot of a given size would always give the same exposure regardless of the distance from the shutter to the film plane. With my admittedly limited understanding: I think that the speed of the slot as it moves across the film plane does vary with the distance from the shutter to the film plane but is always compensated for by the fact that the further away from the film plane the shutter is the larger the area of film that gets wiped.
To recap: the longer the distance from film plane, the faster the traverse of the slot across film but by a larger area.

[Mark Sawyer]

A couple years ago I looked into making a behind-the-lens guillotine type shutter. The basic design is overly simple. Then using a modified Speed Graphic shutter with actual calibrated speeds. It all sounded simple until one single thought screwed the whole idea up...

The accuracy of the shutter speed can only be calculated for one single lens focal length, one single focal distance and one single film size. Change any of those and the real shutter speed at the film plane changes. That's why guillotine shutters died out while the Speed focal plane shutters lived on...

As far as the question of varying exposure depending on the focal length: I honstly do not have the math skills to work this out. I would suspect that setting aside all other considerations like tilt angle and so on, that a slot of a given size would always give the same exposure regardless of the distance from the shutter to the film plane...

The format and focal length wouldn't matter. If a shutter is open for a tenth of a second, the shutter is open for a tenth of a second. That was bad information slipping in, which sometimes happens...