Adding an aperture to a simple diopter lens

[walter23]

I've been mucking around with a diopter lens (nikon +2 eyepiece diopter) with some interesting results on 4x5 and 8x10.

Having just acquired a tominon 127mm lens in polaroid shutter I've been thinking about building an adapter to put the diopter lens into this shutter. I was thinking just of using it as a shutter mechanism, however as this shutter also has an aperture mechanism I've been wondering if I could use it with my hacked lens. If so; I wonder where I should place the glass element relative to the aperture? Directly in front? Directly behind? Or will this not work at all?

I could do it by trial and error, or I could read a lot of optical theory which I just don't have time to do, or I could ask here in the odd chance there's an expert who could give some insight.

FYI, the +2 diopter works as a 320mm ~f16 to f/22 lens when just mounted on a makeshift cardboard lens board.

Covers 4x5 with edge blur:
http://ashphotography.ca/zenphoto/ghetto-lens/Untitled-1.jpg.php

and 8x10 with a lot of edge blur:
http://ashphotography.ca/zenphoto/albums/mishmash/whymytree.jpg
http://ashphotography.ca/zenphoto/albums/mishmash/barbecue-ortholith.jpg

(Yeah, yeah, crappy waste of film shots - but it was free ortho film that came with my holders and I just wanted to quickly whip out something so I could look at an 8x10 negative ;)

[rob]

I would think placing the lens behind the aperture makes sense. As the aperture gets smaller, the parallel rays can only pass through the more central area of the lens, thus, it reduces the aberration. I think in convertible symmar (at longer focal length) and kodak portrait lens and probably other lenses, they only use rear cells.

[walter23]

Actually I've given it some thought (based on my rudimentary understand of how a lens works and your reminder of the arrangement of those convertibles) and I think it probably doesn't matter as long as they're reasonably close together... but as we know it works with rear cells of convertible lenses I guess it would make sense to try that arrangement first.

Thanks for the reminder!

[C. D. Keth]

Most old single-cell landscape lenses I've seen position the aperture in front of the glass and usually very close to it.

[rob]

This got me thinking to attach my nikon 6T (2.9D, 344 mm FL) behind an ilex #5.

[walter23]

I'd like to see the results from that. One of those huge macro diopter filter-attachments would have an enormous aperture I'd guess.. not like my dinky little f/22-ish lens.

[walter23]

Mounting the aperture in front of the lens seems to work. Will rig up something more usable than the temporary mount I just tried.

[keeds]

Aperture in front of lens is how my Spencer Portland works. It's quite a way infront also, about 3cms'ish.