72XL spacer warning

[Ed Richards]

Just got a 72XL. Sold as a demo by Adorama, but no box, so I do not know if it was every mounted on a board - it looks new. While mounting it on a board, I saw a flash of gold disappearing onto the floor when I unscrewed the rear element. Since my studio has irregular surfaced large tiles in dark browns on the floor, it took a bit of hands and knees searching to find what turns out to be a really really thin washer or spacer. Had I been thinking, I would been ready for this, but it is the first lens I have disassembled with a spacer - at least I hope so.:-) So, forewarned is forearmed.

[Phil Hudson]

I've seen these spacer shims between the front group and the shutter before but never on the rear group. If the same spacing can be achieved either way, does anyone know if the shims could just as well be in either position with the same optical effect? It seems crazy to have easily lost shims on the rear if the front will do (ie where there is less chance of disturbance).

[Armin Seeholzer]

The spacer has to be exactly there where it was from the company and no where else, or you get coma and other ill effects at the corner era!

Cheers Armin

[newmoon2night]

I bought one of these lenses used and found the speed setting ring was really tight (see my post at the time http://www.largeformatphotography.info/forum/showthread.php?t=53696)
I returned the lens, and the seller said he must have dropped a spacer when cleaning it. Sounds like it's quite easily done.

[Gem Singer]

Knowing Adorama, it's possible that they disassembled the lens and reassembled it with the shim between the rear element and the shutter.

Every wide angle lens that I have owned had the shim between the front element and
the shutter.

According to Jim, at Midwest, lens manufacturers use a shim in order to make fine optical adjustments due to slight differences in the thickness of shutters. He says, always between the front element and the shutter.

[Nathan Potter]

Thin hard brass spacer, should be between the front element and the shutter. But the real question is; was that spacer and shutter the one used by the manufacturer to adjust for maximum resolution on the bench at the factory. Could be a different shutter. The optical difference in mounting the spacer on the front or rear element would be so small I wouldn't worry about it.

Nate Potter, Austin TX.

[percepts]

Nearly all new lenses have spacers. Its how the manufaturers get exact spacing correct. So there is no news or warning required here. The fact you have never seen spacers before would probably indicate the second hand lenses you have been buying are missing them and you just didn't know about it.

[Ed Richards]

This is so thin that if this were anything but a lens I would think that it was there just to keep the two surfaces apart to prevent sticking and allow smooth tightening. It does not look thick enough to be a spacer.

[percepts]

This is so thin that if this were anything but a lens I would think that it was there just to keep the two surfaces apart to prevent sticking and allow smooth tightening. It does not look thick enough to be a spacer.

So if I understand you correctly, you will worry about resolution and extracting the last tiny fraction out of a scan but when it comes down to your lens elements being spaced correctly it doesn't matter. Why do you think the mnaufacturer bothers to put spacers on its lenses. Manufacturing tolerances are NOT 100% accurate. The simple solution is to build in a margin of error so that the spacing is always a little short and never too long. Then at quality control stage you can use spacers of correct thickness to get spacing spot on. Some will be thicker than others. If it bothers you send it to schneider and have them space it correctly for you.

There is nothing here to give a warning about. It is normal to have spacers on new lenses. I'd be more more worried if there were no spacers.

[percepts]

for symmetrical lens designs the spacer being absent will make little difference. For non symmetrical lenses the correct spacers are crucial. Are angulons symmetrical? I don't think so.