Monday, January 14, 2008

SX-70: A new life

SX-70 land camera
SX-70 land camera
Photo info: Both photos taken with a 17-40f4L, ISO 400, f/6.3, 1/30 and combined in Photoshop.
Lighting info:
1) 580ex, master, on camera, M 1/32, diffused through a paper towel, from left since the camera was vertical;
2) 430ex, slave,triggered by 580ex, M 1/16, bounced into a silver umbrella, above and to camera right.

I pulled my grandmother's sx-70 polaroid camera out of storage over the 2007 thanksgiving weekend while visiting my parents. There was a pack of sx-70 film with it but unfortunately it had expired in 1997 and was not any good. After some initial research I was disappointed to find that Time Zero and sx-70 film were discontinued in 2006 and the camera would require modification to work with the newer Polaroid 600 film. The first thought was to look on ebay for some Time Zero film although I suspect it would be expensive. Unfortunately I was right, most of the auctions I found were expired packages at ridiculous prices.


Time's up
Time's up

A new life:


After a few months I found time to give the sx-70 problem another look and

Polaroid surgery
Polaroid surgery

being determined to use this camera I started another online search for options. For the most part these involve using Polaroid 600 film with some kind of 2-stop filter over the lens to account for the film speed difference. However, since this sx-70 is a manual focus camera I did not like the idea of losing that much light in the view finder. Also, unless you buy a particular "stick on type" 2-stop plastic filter, from Japan, the filter would prevent the sx-70 from closing. In short I felt the filter solution was just a hack and this required a cleaner solution.

The clean solution involves modifying the sx-70's exposure circuit. Basically there are three main components: a 330K ohms resistor, a ~1000pF capacitor, and a photodiode. Anyway, to account for the fact that the 600 film is four times faster than the Time Zero film I replaced the capacitor with a smaller 220pF capacitor. 220pF is roughly four times smaller than 1000pF.

To replace the capacitor requires a bit of patience. The front lens section is held on by four Torx (T4) bolts. These are very small and it is unlikely that anyone actually has the tool to remove these. I ended up using a small flat headed screwdriver (maybe size 0) with just the right force..umm I mean finesse. The trick here is not to strip the Torx slots. Once the front housing is off it will only be connected by the power cables. The next step is to get at the capacitor, which is of course not visible, on the backside of the board. By unsoldering the flash pins I was able to flex the board enough so that I could pull the capacitor out after applying the soldering iron.

I picked up a pack of 600 film to test my modification and volia it worked. Of course being night the first photo I took was inside and in low light so it is pretty blurry from camera shake but it seems to be properly exposed. Once I have taken a couple test photos during the day I will post the conclusion.

For more info on disassembling the sx-70 click here.

3 Comments:

Blogger justin said...

You are hardcore! Well done!

7:22 AM  
Blogger Bradtholomew said...

Going back in time, eh? Started with a 20D, then an Elan II, now a Polaroid. Most people do this the other way around. heh

7:34 AM  
Blogger David Tyner said...

Perhaps a large format field camera is next...who knows...

11:05 AM  

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