I'm not 100% clear on whether you want to do multiple exposures on one piece of digital film (so to speak) or capture four raw files.
IF YOU WANT TO CAPTURE ALL IN ONE RAW FILE ("multiple exposures")....
Any solution you use will require the back to be "exposing" the entire time since only one "exposure" can be recorded as one raw file. Therefore you'll be limited to the maximum exposure time of the back. For a P45 non plus unit in normal ambient temperatures this will be somewhere in the ballpark of 4-5 minutes (of course all things are relative, you may find you can go longer or shorter depending on the ambient temperature and your personal threshold for noise). As a quick side note: any plus back would effectively remove this limitation as they can all exposure for around an hour with normal ambient temperatures (longer in colder temperatures).
IF YOU WANT TO CAPTURE FOUR SEPARATE RAW FILES...
Than the only thing you are "missing" is the fact that the digital back requires absolute dark during the "black frame" and "readout" time. With any Phase One back there is a "black frame" exposure equal to the normal exposure time (e.g. a 30 second exposure is followed by a 30 second black frame). On all digital backs that I am familiar with you also have a "readout" time where the data is read from the sensor. During both periods the sensor must not see any light or there are major image quality issues. So you do NOT need a shutter (as long as you use a device like our multiple exposure box which allows you to start and stop the exposure without any connection to a lens), BUT you must ensure that before you "stop" the exposure that there is no longer any light making it to the sensor. You can accomplish this by any of the methods outlined below (black box, turn the lights off, cover the lens, use a shutter). AFTER the sensor has done the black frame and the readout then you can open/close the lens, open/close the black box, turn the room lights on and off without consequence.
REGARDLESS...
Some options:
- a press shutter (self cocking shutter) or electronic shutter which can open and shut with very little mechanical movement.
- The "old fashion way" (thank you old college professor Gary Kirksey) of physically obscuring the lens to "close it". Simply find a suitable method of draping black cloth in front or over top of (depending on how much light is around the camera and the period you need to close the lens for) and remove it when you want to "open" the lens. The back remains exposing the whole time but when no light is hitting the sensor you'll not contribute to the final exposure in any meaningful way. I've seen some more elaborate setups where in front of the front standard a super-black 4-sided (open front and rear) box has been built so that it completely surrounds but does NOT touch the actual camera/lens/standards. That way the front can be covered or uncovered without any vibration/movement making it to the lens. This obviously works most easily for longer lenses as wide angle lenses make it harder to construct such a box without it being "seen" by the camera.
- just turn off the room lights assuming you have a very dark studio and can black out any possible LEDs/windows/etc
However, depending on your final-use you may find re-cocking a normal shutter produces very minimal movement. Jeffrey Jacobs, one of our customers, shoots anywhere from 3-30 shots to composite different times of days in his architectural photography and re-cocks the shutter of his Cambo Wide system by hand each frame - just taking ordinary precaution to do so as smoothly as possible. On rare occasions his images will be a pixel or two off which must be adjusted either by hand or the "auto-align" feature of photoshop, but this occurs more often due to someone kicking the tripod during the 4-14 hours he is set up in one place than from the recocking motion. He has the benifit here of a very solid tripod, a camera system the front "standard" of which is centered on the tripod (since it is a flat tech camera) and a wide-angle lens which shows extremely minor rotation less.
When I was doing my project on
extreme macro photography I used this basic method to capture 150-250 images in a row with zero movement or mechanical action on the camera. In that case I was working at 7x-15x at 60 megapixels and so could not afford even the slightest hint of movement that even an electronic shutter implies. I used a completely blacked out room and triggered the camera and strobes using the multiple-exposure box plugged into the digital back. The result was pretty flawless and I ended up more concerned with boredom (click-click, actuate micrometer, click-click, actuate micrometer, fall asleep) than camera movement since there was no mechanical motion associated with the camera whatsoever.
Doug Peterson
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