using small lenses / file under "reduce reuse recycle"

I've had some 120 film sitting around for a while as a result of a messed-up order from an online shop. I've been itching to actually do something with it, and I've finally decided that now that my final semester of grad school has begun and my daughter has been moving around on her own, it's a PERFECT time to hide and build my own medium format camera. I don't mean this to be a general-purpose machine, but largely for macro and/or environmental portraits (I'm willing to concentrate on one or the other, both don't have to work). The salient point out of that is that I'm unconcerned about focus beyond about, say, 6 to 8 meters max no matter what direction I go.

Now. I'm interested in using materials I have sitting around as much as possible so lenses intended for 35mm (135) SLRs are attractive. Now, obviously, if I just push, say, a 50mm focal length 135 lens away from the film plane it will eventually cover a 6x6 frame with reduced light intensity--and corollary effect on f-ratio. Depending on the lens some won't even have to be pushed that far... image circles vary pretty widely. Depending on the particular lens, focus range will be impacted and I'll have to make decisions to emphasize closer or farther focusing. All of that I can live with for my intended uses.

The unknowns, however, are many. I'm a software guy, not an optics guy. I've taken physics and chemistry and a few semesters of calc... I'm not dumb, but I'm mostly ignorant of optics beyond the intro (Newton) stuff you get in general science courses. And whatever I've picked up from being a photo enthusiast. So what other effects might I expect in this scenario? In case anyone has knowledge of specific lenses, the most likely candidates for this would be 55/1.8 Takumar and Vivitar 135/2.8 (as I have dupes of each laying around that were tossed in with parts bodies).

If this is a really unsuitable use I'll probably scavenge a lens from an old folder. But I'd like to see what I can do with this first.

I dont mean this as a sales plug, but I have the perfect book for you. Its "The Manual of Close-Up Photography" it contains all you would ever want to know about 'old school' method of macro and micro photography. It covers optics, bellows, extension tubes, exposure factors,etc, Also covers home made devices for getting in there VERY close. I have it listed in the classifieds.Needless to say, its exactly what youneed to answer all your questions.

Rick

Hi, to focus most lenses intended for 35mm. at around 6-8 meters the cells move only a few mm. forward from the infinity position - so the image circle isn't going to increase by very much, and covering 6x6 seems optimistic.
A simple test rig would be worthwhile to check image circles at your intended working range and may save disappointment later.
Cardboard box 6" square, hole for the lens, crude focus screen able to slide in & out to focus - shouldn't take more than half an hour to knock something together that will work well enough for this purpose.
Something like a Yashica or other twin lens reflex will give excellent results for little money and if you decide medium format isn't for you just sell it on.

mack-- thanks for the advice. I've already done a similar test, in the dark with a flashlight beam to get a clear-ish idea of where the image circle is, and I have no qualms about filling the 6x6 (with some fall-off, but not actual cut-off). I could get a TLR, but I already have and have had enough middle ground cameras in my time. I'm really only interested in DIY or winning the lottery and buying fine top of the line pieces at this point.

Good luck with your experiments - sometimes they can lead to interesting pictures!
Be prepared though for a rapid fall-off in image sharpness & contrast and maybe coma and other aberrations outside the designed-for image circle.
Most lenses' quality is lower at the edges anyway. Bit of a rush, no time to link this:

http://www.hevanet.com/cperez/testing.html

Oooh. Autolink. Wunnerful innit?

unclemack said:

Good luck with your experiments - sometimes they can lead to interesting pictures!
Be prepared though for a rapid fall-off in image sharpness & contrast and maybe coma and other aberrations outside the designed-for image circle.
Most lenses' quality is lower at the edges anyway. Bit of a rush, no time to link this:

http://www.hevanet.com/cperez/testing.html

Oooh. Autolink. Wunnerful innit?

Click to expand...

Ah, interesting. That was the kind of stuff I was wondering about indeed. Thanks!