Cap-shutter techniques

[Paul Schilliger]

Having used some heavy lenses on long extensions, I have just merely tested the benefits of the "Cap-Shutter" in low light conditions. This is: masking the lens with a dark non reflective object (lens cap or else), firing on pause B, waiting a few seconds for all vibrations to stop and moving the object away and back for the duration of the exposure. I'm wondering how precise we can get with that technique. Some say 1/4 of a second can be managed. Also, what masking item and what mouvement do you have come to use. Normally the mask should return from the opposite side it moved to for a consistent exposure. It is probably possible to adjust the exposure time of for instance the sky if it stands in the picture, and imitate a neutral grad filter. What would experienced "Cap-Shutter" shooters have to say? Also what speeds are safe? I would think that anything faster than 1/15 and slower than 1 sec is shutter safe, that is with flimsy camera set up when the lens is balancing and prone to move, would you agree?

[ronald moravec]

I reserve that for at least 1 sec exposures, two is better. A way to get shorter ones is cut a slit in a card and pass it in front of the open lens.

Neutral grad simulation is a longer exposure amd block the bright part of the scene for a period of time. Double exposure is also possible dodging the bright area for one of the two exposures.

There were also drop shutters where a slotted card would gravity drop in a channel.

[Matt Miller]

“what masking item and what mouvement do you have come to use.”

I use a 6”x6” piece of cardboard covered with black velvet to cover the lens. I cover the lens with the card, pull the slide, pull the card away from the lens a few millimeters, let the vibration die for a second, and then quickly pull the card up and away from the lens. When the exposure is finished, I simply reverse the order.

“Normally the mask should return from the opposite side it moved to for a consistent exposure”

I don’t make any conscious attempt to do this. I feel that I can move the card quickly enough away and back that this is not an issue.

[jantman]

I'm not quite sure where you're going with this.

I've worked with my barrel lens quite a bit. I usually used either a 4x5" dark slide, or just my black baseball cap, or the black side of my darkcloth. Hold it in front of the lens, pull the dark slide, then just move the object (hat/darkslide/cloth/etc.) up away from the lens, and then back down. My instantaneous speed is about 1/10 of a second. I never had issues with the consistency given that it was coming in and out from the same direction.

What do you mean by "shutter safe" speeds? If your camera has a leaf shutter, as every shuttered LF lens that I've seen does, you shouldn't have to worry about vibration. It's more likely that any vibration would be from movement of the camrea (an adjustment, or pulling the slide) rather than from the shutter.