Slide holding for Scanning - Ohnar and Other Options

Halina3000 wrote:

Thanks. Yes I find the thickness of the camera lens body means that it's somewhat problematic to apply my school physics to the question. Instead I decided to try it out.

A few of my test results with the MD lenses, all measurements being from the front end of the lens. I was focusing on a ruler placed where the slide would be and using live view to read the width.

• 50mm, bellows fully compressed - 72mm to slide, 127 to sensor. 23.5mm wide view
• 50mm, bellows extended 10mm - 62mm to slide, 137 to sensor. 19.8mm wide view
• 50mm x 2 converter - 350mm to slide, 154mm to sensor. 48mm wide view.

The lens was set to infinity in each case. I tried it at minimum focus too but that made the field of view slightly smaller.

My conclusion was that if my bellows would squash up further then a 50mm lens might be OK... but they won't. I did repeat the tests after buying a thinner EF adapter ring which cut the lens to sensor distance by 10mm. I cant recall whether the numbers above were before or after this but I do know that it didn't get me to a 36mm wide view with the 50mm lens.

I think that an enlarger lens won't behave significantly differently. The lens body might be shorter and that may move the effective lens position closer to the sensor. Whether that would be enough to create a 36mm wide view... no idea but I decided not to put money on it.

FWIW with the 80mm lens I have 180mm to the slide and 156mm to the sensor which takes in the whole slide image plus a little of the mount.

Enlarger lenses are not usually retrofocus or telephoto designs so they work a little better with measurements - generally to the centre of the lens works reasonably with these.

I'm surprised your bellows are as much as 127mm when fully compressed most of mine are considerably less - from about 100mm on a DSLR down to about 60mm that on a mirrorless body with no flash bump (which can need extension tubes to mount the bellows without fouling on the bump). Admittedly my large format bellows can be much bigger

If the minimum length of your bellows is restricted like that then a longer focal length will certainly help as the results from your 80mm lens seem to show. Sound like you've got it sorted