I've been using the 670m quite a bit, working to learn its strengths and quirks. I've put 10 packs of film through it so far. Liking it a lot, although it's not perfect.
Few cameras are... :-)
Anyway, given the cost of testing these things at $3+ per exposure, I figured I should share what I've learned so far.
- The Telephoto Lens #119A provides a very nice portrait focal length add-on, which combines well with flash or ambient exposure. Beware the original Polaroid pouch for this accessory: it was lined with a foam layer which at this age has gone dry and brittle, and sheds a fine powder of gritty dust into everything when you touch it. I've got the pouch sealed into a freezer bag for posterity, and use another little pouch I had in the miscellany to store it.
- The Polaroid SX-70 Self Timer is not compatible. The shutter release on my 670m stands a little more proud of the bezel than the original SX-70 and engages just a scant mm or two from the rest position. Just trying to slide the self-timer into place fires the shutter, and it's impossible to actually fit it without the shutter firing continuously.
- Automatic ambient exposure with current Impossible SX-70 film works well. The 0 position on the light/dark dial is about right on for most things, I sometimes like my prints just a hair darker and the -1 to -2 position does it well.
- Manual exposure with Impossible 600 or SX-70 B&W film works well too. By my testing, these films have about 2-3 stops latitude so there's satisfactory exposure adjustment with the 670m's shutter control dial, which operates in one stop increments.
- Manual exposure with Impossible 600 or SX-70 Color film is a bit dicey. By my testing, these films have a scant 0.7 to 1.0 stop latitude. The problem happens when correct exposure by the meter is smack dab between two shutter speeds: neither going to the higher or lower shutter speed will net a perfect exposure, and the aperture is fixed at f/8 so there's no way to tweak the settings to compensate by a quarter to half a stop. I find that shooting color film in contrasty circumstances with ambient light works best when you use Auto mode (the light/dark control gives you about .3EV adjustment resolution) or the use a flash. Of course, in contrasty light you probably want the flash to do fill anyway.
- Shooting 600 speed film on automatic can be done with the light/dark control set to -3 (full dark) as long as you're not in bright sun or have too contrasty a scene to deal with. This is a nice convenience if you want to use the Polaroid telephoto lens, the Mint wide-angle lens, a close up lens, etc. Fitting the Mint neutral density filter (which cuts light by 2 stops on my meter), I find my best results come when setting the light/dark dial to -1 and sometimes -2 positions. The 0 position is a bit too bright most of the times.
- I'm going to see about converting one of my Mint filters to take custom-cut filter gels. That way I could have .3 and .6 stop adjustment for manual exposure with color film, as long as I don't want to use close-up, tele or wide angle lens attachments. Of course, I could make filter holders for the front of those attachments too but that starts to get into a lot of fussy gear to manage.
- Shooting 600 speed film on manual exposure leads me to suspect that the current Impossible 600 film has an effective ISO closer to 700-800. Exposures made with ISO 600 are just a bit too light.
- Shooting with the Mint electronic flash model 2 with both SX-70 and 600 film works well ... most of the time. This should work perfectly 100% of the time as the flash metering system is guide-number based ... set the flash power appropriately and the aperture is adjusted based on the focus distance. You always have to be careful of the flash range limits of course (with all Polaroid cameras).
A problem that I'm seeing which may be specific to my Mint flash unit is that it will occasionally miss proper sync. That is, the flash always fires, but evidence from some exposures produced is that it fired late relative to the shutter opening, the open shutter only caught a fraction of the output, and the print is very dark. I've got a note out to Mint technical support on this—it may simply be a defective flash unit. I suspect the flash unit rather than the camera as I have seen the same behavior on several of my SX-70 cameras, works sometimes but not all the time, and I can't believe that ALL of them have flash sync problems with their shutters.
I hope that information is useful or at least interesting to some. :-)