External-Power Mod Successful!

[darinheinz]

<p>Hi everyone!<br>

I started working on a night photography project, but experienced a good deal of frustration with the Pentax 6x7's limited time-exposure capability due to the 4-hour (or so) open-shutter lifespan of the lithium battery. So, I decided to modify the camera to accept an external power source.<br>

I did this by opening the camera's housing, soldering a wire to each of the battery terminals, and connecting the other ends to a monaural mini headphone jack fastened to a hole I drilled in the casing near the lens mount. Next, I built a battery pack (for my long exposures, I use a 4 D-cell arrangement) out of a plastic box and battery holder from my local electronics store. The powered leads from the battery pack are connected to a mono headphone jack identical to the one in the camera, with matched polarity. In the field, the camera is connected to the battery pack by a 3-foot cord with mono plugs on each end. I have already put in excess of 30 hours of exposure time on the 4 D-cells, and they are still going strong. Subsequently, I fabricated 6-volt adapters for my car's cigarette lighter and a transformer for household AC to 6VDC. The lithium battery has been recycled, and I should point out that the camera is no longer able to be used with the internal battery due to the nature of this mod. It seems reasonable that a switch could be introduced into the mod to isolate the power source to either internal or external, but I did not feel compelled to go to such lengths.<br>

I will be posting images from what has now become an extensive nocturnal adventure into my gallery later this year.<br>

Questions and/or comments are welcomed.<br>

Darin Heinz<br />Melbourne, Florida USA</p>

[William Kahn]

<p>Nice work, Darin. I guess one of the advantages of MF gear is having enough room to work inside the camera body without screwing something else up. My only question, why did you use a mono headphone jack rather than the more usual coaxial DC power jack? It seems like the headphone jack presents more of a risk of shorting or momentary reversed polarity when plugging/unplugging the battery pack?</p>

[darinheinz]

<p>Hi William.<br>

The short answer is it's what I had access to. The headphone jack won't short or temporarily reverse unless something is seriously wrong (i.e. major physical damage), and is not as delicate as a coax DC jack. There is also an on/off switch on the battery pack which allows current only when both ends are firmly seated. Besides, having a fairly standard plug means I won't have to build cables, or try to find a specific one should this one break in the field. In a pinch, I can get two pairs of cheap headphones from a general store and splice the cables together with some black tape. Anyway, it works for me. This isn't a specific hard and fast mod; it is highly adaptable, and the nice thing is there is plenty of room for personal preferences. </p>

[dougmiles]

<p>Darin, interesting project! The need for this is so legitimate that Pentax beat you to it... They offered a replacement battery holder for the 6x7/67 that was in effect a plug for an external battery pack. Do a Google search on "Pentax 67 Remote Battery" and you'll see some info. B&H lists it as discontinued, but H1Photo has one on hand for $78. http://www.h1photo.com/37990.html<br>

Also some telescope folks wanting longer exposures use a product called the Hutech Battery Eliminator.<br>

And finally, I read that Pentax can modify your camera so that when it's in Bulb there's no need for a battery-you still need to remove the battery after opening the shutter and put back in to close the shutter.<br>

Open shutter with standard 'bulb', remove battery.<br>

Take pic 60-90 minutes<br>

Put battery back in and close shutter with bulb</p>