Rollei/ISCO S-Projar 2.5/90 brutally mutilated

[iangreenhalgh1]

Hi folks

I picked up a Rollei/ISCO S-Projar 2.5/90 projector lens for 4ukp in mint condition recently (looked unused) and decided to hack it up so it would fit in a #1 shutter.




The barrel is aluminium alloy, 46mm in diameter with walls 7mm thick, the first task was to take my trusty hacksaw and cut off the piece of tube at the rear that protruded further than the rear element, this would ensure maximum image circle as I want to use this lens on 6x9.I will also have to grind down the diameter of the tube by 7mm so it will fit inside the #1 shutter.



Next I removed all 5 glass elements and the screw-on lens hood:



The lens has 5 elements in 5 groups with several mm of spacing between the last two, so that is where the aperture and shutter will go:



This means I will have to cut he barrel into two pieces - one will hold four elements and fit into the front of the shutter, the other will hold the fifth element and fit into the back of the shutter. Before making this cut, it is important to measure the length of the barrel, it is exactly 40mm.



I found that it was better to grind down the diameter 2mm or so before making the cut as this removed the spiral groove it had cut into it an made accurate cutting of the barrel much easier:



Now to work on the front part. There was about 3mm of barrel protruding beyond the back of the fourth element that needed to be removed in order to account for the width of the shutter. I also had to reduce the diameter of the tube further so that it was 40mm in diameter and would fit snugly into the front of the #1 shutter.



A perfect fit:



Looking at it from underneath, the silver metal is the back of the barrel, it butts up precisely against the baffle in front of the shutter blades, meaning the glass of the front part of the lens is as close to the shutter blades as physically possible, this is essential in order to maintain correct spacing of the fourth and fifth elements while also accommodating a shutter between them:



Now the metalwork is complete on he front part, I can reinsert the glass and the name ring:



The rear of the barrel needs to be painted matte black to avoid any internal reflections:



Looking from underneath, you can see there is no silver metal exposed to cause reflections anymore and the glass is positioned right in front of the shutter blades as it should be:



That's the front half done, now to the back part. This needed to be reduced in diameter more than the front because the rear diameter of the shutter is a couple of millimetres narrower. Here you can see the rear part after the metalwork has been done fitted into the rear of the shutter.



It protrudes 3mm but that is fine, the correct spacing of the fourth and fifth elements has been maintained because the front tube was shortened by 3mm, I also reduced the length of the back part by 1.5mm from 12.5 to 11mm:



Here you can see just how much metal had to be removed from the rear part:



And after replacing the glass, you can see how the rear of thebarrel doesn't protrude beyond the back glass at all, crucial to avoid vignetting:



Here you can see both parts mounted into the shutter, the job is complete, the pieces fit so snugly that they are held solidly in place, a couple of drops of superglue was added to lock them in place, but they can still be removed as the bond of this type of glue can easily be broken if necessary:



Checking the length of the lens in shutter, it is the correct 40mm which means the element spacing has been maintained correctly.



Image samples to follow, fingers crossed it covers 6x9 properly. It does illuminate the full frame, but what quality of image it puts in the corners I won't know until I make some test shots.

[Lloydy]

Interesting, I like the thinking behind that.

[iangreenhalgh1]

Cheers. There are some very high quality and cheap lenses available as projector lenses that with some DIY work can be made much more useful bu addition of an aperture or an aperture and shutter. For instance, the Schneider AV-Xenotar 2.4/90, available very cheap, has modern coatings and when compared to the price of an old Xenotar 3.5/105 taking lens is an absolute steal. then there is the Leitz Colorplan 2.5/90 which is very similar to the Elmarit 90 but cost 5-10% of the price. There are also the ubiquitous 2.8/85 lenses that are triplets, but those don' appeal to me much because their best use is to create those wideopen funky bokeh shots that people love to use the Trioplan 2.8/100 for and that sort of photography is very rarely pleasing to my eyes.

Longer Projector lenses like the Leitz Hektor 150mm aren't useful to me for 6x9 because their diameter is too great to mount in a #1 Compur/Copal Prontor shutter or an Alphax #3 shutter, they require a #3 Compur/Copal/Prontor or a #4 Ilex and those shutters are too big to fit on a Century Graphic.

[ForenSeil]

Great work!
Thank you for sharing!

[iangreenhalgh1]

Cheers. I still haven't made test shots, but I have mounted it on the camera and verified that it illuminates the full ground glass at infinity, wide open, so no worries about the lens having sufficient coverage. It gives the brightest image on the ground glass of all my lenses, even more so than my 2.8/100.

[iangreenhalgh1]

Here it is mounted on the camera. Surprisingly the back focus is very short. I expected it to be around 90mm but it is more like 45mm. Any shorter and it wouldn't hit infinity on this camera.

[iangreenhalgh1]

I had a developing issue with the test shots that caused fogging on the edges so I'll have to re-shoot. But this one at f16 shows the lens is more than sharp enough. I cropped off the fogged edges.

[fuzzywuzzy]

Looks like all your work paid off!

[iangreenhalgh1]

Cheers, I'm happy with it.