Device to activate mechanical cable release on Bulb for a set exposure time?

[ondebanks]

Folks,

I'm on another quest for something which may not exist. I would like to be able to exactly time (program, so to speak) long exposures on B (bulb) with my Mamiya AFD, film and MFDB. There are gizmos all over ebay which can do this for DSLRs, but they have DSLR-specific electrical cables. I am hoping to find something that will include, or take, a standard mechanical screw-in cable release and allow me to shoot for say 40, 60, 120, 1800 seconds or whatever (the camera itself tops out at 30 seconds...it's only B beyond that).

What I picture is something like the old-fashioned Autoknips; but whereas that set a delay before pushing in the cable release plunger, I want something which will hold in the plunger for a period which I can set, and then release it. I have actually found an old movie-camera device which apparently does exactly that, but it is limited to 5/10/20 seconds exposures only...and the Mamiya can already go to 30 seconds. Are there movie-camera devices which can go longer than that?

I was also thinking along the lines of those darkroom enlarger-light timers from Meopta etc. - these can be set to switch the light on for a set number of seconds, using relays. The only problem is that they are relaying ac mains, not pushing in a plunger!

There cannot be much involved in rigging one of these darkroom timers, or even one of the DSLR timers/intervalometers, to a mechanical/magnetic relay plunger-pusher, but alas the electro-mechanics are beyond me. There might even be a market for such a gizmo - it would suit all of the motor-driven cameras out there with mechanical cable release sockets, and add a lot of functionality to them.

Any ideas/suggestions?

Thanks,
Ray

[shutay]

My interpretation of this would be, if I couldn't find an off-the-shelf product to do it:

1. Buy a plastic box, secure mechanical cable release into the box, perhaps through a drilled hole.
2. Use an rc servo, such as one of these: Futaba digital proportional standard high torque servo
3. The servo normally comes with a few types of servo "horn" or disc - you will need to take a disc, and re-shape it so it looks like a cam, or at least lop-sided. Position the servo so that at neutral, it will just rest against the cable release, and when actuated to the fullest travel, it will push the cable release in.
4. The rc servo motor requires PCM pulses to control it, plus power. The pulses can be generated via microcontroller or from a PC (conceivably, you could also just use a 555 timer chip and some creative design). Try to stay away from USB unless you have facility with USB as it normally requires licensing of code, etc. I would probably use a combination of microcontroller and PC, probably with a serial RS-232 interface. Making a self-contained microcontroller only solution would require adding buttons, a display, some sort of simple menu to choose the interval, etc. Getting it powered by the computer is preferable, I would say, since getting an rc servo to keep your shutter release pushed for 1800 seconds would probably drain a battery rather quickly.

Other than rc servos, there are in fact, linear electric actuators, but I don't think they are easy to find - at least rc servos can be picked up (almost) anywhere. Lego Mindstorms sets have linear actuators and a programmable microcontroller, maybe you can use a Lego Mindstorms set instead? They can be capable of quite a lot.

Jason

[zeitwand]

If i got you right, i would reccomend an central locking system for a car - see bottom.

The pros are:
- got a linear actuator instead of an rotating (PWM-DC-Motor)
- can trigger via the infrared remote control
- dont have to make an PCB
- don't have to struggle with programming an µController


Just snap it to a small battery source, put it into a small box, some small mechanical parts, an voilà here we go 

cheers Michael

[ondebanks]

Thanks for the replies, guys. Very ingenious solutions! I work with a good techie who might be able to help me with these ideas.


It also occured to me that an alternative solution would be to bypass the mechanical shutter actuation, and instead go for the electronic remote release port on the 645AFD body. It might even be possible to route the wiring of an existing DSLR timer-intervalometer into the Mamiya port - that would be a very straightforward and neat solution! But it would require knowledge of the pin-out on the Mamiya.

Does anyone know what the Mamiya/Phase One 645AF[D] remote release cables actually do (do they simply close an open circuit?), and how the port pins are connected? Apart from the electromagnetic cable releases, and the infrared remote release, is there any more complicated device which connects to this port? Why are there 8 pins in the port, when all it apparently does is trigger the shutter? 

[Kumar]

A friend has been working on this for some time to get me a solution. The car locking system doesn't work, because a very heavy current is required for holding the shutter open, and the batteries simply die. An AC powered solution would work, but that's obviously not always possible on location. We're still working on this. For a Mamiya AFD, the remote cable should do this, I think.

Kumar

[elf]

Here's one solution: http://brooxes.com/newsite/BBKK/BBKK-PARTS.html  Scroll down to 'gent360-Servo'.  I've seen others using an Arduino micro processor but don't have any links.

[BobDavid]

Try the Kapture Group. They've got a few devices that may work.

[Kumar]

Been there, done that. KG has some interesting stuff, but Keith told me their Electronic Cable Release was for triggering an exposure, not for a timed exposure. I have this, but couldn't modify it for timed exposures.

Kumar

[Graham Welland]

You might want to have a chat with the folks at Promote Systems. I have their Promote control for my Nikon and it allows for time-lapse shooting and essentially shoots in bulb mode electronically from a small handheld device. They do provide cables for the various DSLRs and I've no doubt that they could build a custom cable for the Mamiya interface pretty easily.

It's a bit pricey but a really nice device btw: https://www.promotesystems.com/products/Promote-Control.html

[elf]

http://dativ.at/gigabot/index.html has a solution using a Lego brick