View Full Version : ? on distance between lens and film

12-14-2006, 09:02 AM
I have some 17mm lenses (and viewfinders) that I pirated from a small supply of disposable panoramic cameras. I'm thinking of using them by either modifying an existing camera (probably a Holga) or by building something simple on my own. Either way it would be a fixed-focus configuration. A question as I ponder my options: how do I determine the appropriate distance between lens and film plane? Is there simply a range that I need to fall within, or is it a matter of precise measurement?


Jim Jones
12-14-2006, 01:08 PM
The distance is precise. It is best determined by using a ground glass in place of film, and adjusting the distance for a sharp image. A ground glass can be improvised by sanding one side of clear rigid plastic. The sanded side should rest on the film guides.

12-14-2006, 01:19 PM
For fixed focus consider using the hyperfocal distance. I don't recall the correct distance (depends on aperture), but if you google the term you can find it. Basically you focus (as Jim suggests) wide-open on something that's a bit closer than infinity, so that when you stop down infinity comes into your depth of field. Depth of field will be pretty wide with a 17mm lens.

Using the "ground glass" will also give you an idea of coverage - it probably won't cover 6x6.

Some good stuff on your website. I like the Holgaramas.

12-15-2006, 12:55 AM
If you still have the cameras (Konica Superwides?), you could measure from the film plane to any reference point on the lens, and duplicate that. The lens on the Superwide was positioned with infinity a little out of focus, so you'd need it a little closer to get infinity into focus. It's bound to be a tiny difference. Having some sort of threaded mount would help, just to ease the process off gettting it at the right distance and keeping it there. On a Holga it'll probably require sinking the lens deeper than the square hole in the front, which is probably around 20mm. Getting a shutter under that will be a challenge, but it'll surely take some great images. Good luck, and please show us how it works out!

12-15-2006, 11:20 AM
They are indeed Konica Superwides!

Thanks for the tips, all. This will be one of my winter projects. I'll post pictures of progress and results if and when I get them. I'll probably have more questions, too.

And thanks on the holgaramas. They are fun to make.

12-15-2006, 07:26 PM
or you can use a little of the baking paper that your wife will almost certainly have in the third draw of her kitchen cabinets instead of actual ground glass to get the feel of things...?

call me dim, but... won't a lens focus at infinity when the optical centre is one focal length from the film? And, for a simple lens like what you're talking about the optical centre will be inside the lens? That would mean you'll probably need the little plastic lens 17mm or just a little more from the film...

I think you'll have trouble with putting that into a holga body because the shutter is so far in front of where you'll need the lens that the image will be coned down to quite a small area. You might have better luck mounting the lens behind the shutter in an el cheapo 35mm plastic camera... and maybe cut out the film gate area to increase the image size?

or maybe steal the alleged shutter from the alleged el cheapo camera to put in a purported homemade housing...

sounds like a really interesting project and I'll certainly be interested to hear how you go with it !!!

12-16-2006, 12:23 AM
Just speculating here, but the first thing I'd try is getting the whole Superwide lens & shutter assembly into the front of the Holga and remove the Holga's lens & shutter.

I've reloaded the Superwide a few times but haven't removed the front to get a look at the shutter mechanism. But generally there's just a springloaded arm that moves across a lever that opens a small paddle shutter; the shutter has a spring that pulls it closed after the arm is past the lever. The rest of the mechanism is tied up in advancing the film, holding back the arm until the button is pushed, and firing the flash (early Superwides didn't have a flash). If one could isolate the plastic plate with the shutter only, it'd be fairly easy to seal out the light and use a well-aimed poking stick to fire the shutter. The hardest part would seem to be getting the lens aligned well enough: at 17mm, the angles and tolerances are probably pretty tiny.

12-16-2006, 07:24 PM
Reloading... I hadn't given that any serious consideration - I got enamored with the idea of taking the things apart and removing just the bits and pieces that I wanted.

I looked at your blog - asiftosay - wonderful stuff! I especially liked the superwide shots of your daughter on the swing - Dec 7th and 9th (iirc) - great sense of movement and space and topsy-turviness. Nice work!

12-16-2006, 11:16 PM
Thanks! I've been using the Superwide a lot lately. There's (of course) a Flickr group for the camera: http://flickr.com/groups/konicasuperwide and also http://flickr.com/groups/waiwai . Some discussion there about reloading. And likewise, I really dig the omniscopic stuff at your pbase.

12-17-2006, 08:53 PM
I got enamored with the idea of taking the things apart and removing just the bits and pieces that I wanted.
Capt'n Stormy, I know exactly how you feel... !

btw I looked at derevaun's stuff and I have to say the unmodified camera turns out such great stuff that you need to keep at least one intact and use it unmodified...

12-18-2006, 03:30 PM
I think you would be best served by an adjustable and visual way to verify focus, even if you have to build an outboard fixture first to get a reference distance.

It's very annoying to build something that needs precision and realize somebody screwed up.

The lens nodal point is a pipe dream to find for the average home optics guy. If it's a meniscus or some custom curve it could be away from the lens surface, but if you find focus and get your own mechanical reference (nodal or not), and transplant it to the finished assembly, you're at least close.

Precision is going to be less forgiving with 17 mm than 170 mm...so I'd go with optical alignment.

12-18-2006, 04:29 PM
I have had good luck with focusing on the sun (dont look at it though :() and that becomes your infinity distance....

12-18-2006, 07:48 PM
This is all very helpful. Thank you.