Space Between Lenses

[seawolf66]

How does one compute the space between lenses is it hard or just a simple formula
See attached : Thanks a lot :

[genotypewriter]

I don't think there's only one exact number. But at least one will be better than the others.

[E. von Hoegh]

The spacing is part of the design computations. If remounting a lens in shutter, it is best to measure the spacing and make adapters if needed to preserve the spacing in the new shutter.

[domaz]

I think this falls into the "very hard" category. The space between the lens elements is an integral part of the lens design. Finding the number would kind of be like finding what the formula for a film developer after it's been mixed.

[Leigh]

I believe you're asking about the separation between the front and rear lens cells.

Calculating that is a complex task that requires many parameters that you don't have and can't get.

Measuring it requires expensive optical test equipment that you probably don't want to buy.

I have the test equipment, but it's not set up to do inter-cell spacing tests.

I suggest you send it to SK Grimes and ask them to mount it for you. They have the equipment to do it right.

- Leigh

www.skgrimes.com

[Michael Clark]

I measured the distance from the front of the lens to the back of the lens while it was still mounted on the old shutter it came with, then installed it in the new shutter and measured it was the same distance. Not that precise but seems ok to me, there is always SK Grimes.

Mike

[Leigh]

I measured the distance from the front of the lens to the back of the lens while it was still mounted on the old shutter it came with, then installed it in the new shutter and measured it was the same distance.

That will work.

The desired precision would be ±0.1mm (±0,1mm for our European friends).
Looser precision will work but might degrade performance.

- Leigh

[Michael Clark]

it was a 150 syminar in an old broke down number 0 sycro-compur shutter to a newer copal #0 press shutter. Looked up the specs for them and they were the same as far as the two tread distances, there were no shims in the old shutter. I think they were #0 shutters.

Mike

[genotypewriter]

Calculating that is a complex task that requires many parameters that you don't have and can't get.

Not saying it's easy but, if you're interested in finding the "correct" spacing for infinity, there are only two parameters: (1) spacing between the two cells and (2) the back focal length.

The range of values for these can be further narrowed down by using domain knowledge. For example, intuition says the spacing is most likely not going to be massive like 10 inches. So you can put it between 0-10" (or say 1-250mm). For the second parameter, BFL, again some educated guess about focal length can narrow the range down. Let's say 1000mm (which is most likely grossly over in reality) so that puts the range between 1-1000mm.

Assuming an initial precision of 1mm, we have 250*1000=250,000 combinations to try out. This is where a heuristic is going to help. If properly done, a Monte Carlo search should allow the OP to estimate the spacing (and BFL) within a hundred or so attempts. But I think it's going to be even quicker in practice since this is not a very stochastic problem and the parameter ranges are continuous.

After finding a rough (1mm precision) configuration, fine-tuning can be done by hand easily to whatever the possible precision is.

[ic-racer]

How does one compute the space between lenses is it hard or just a simple formula
See attached : Thanks a lot :

Measure the entire assembly = distance A
Measure the front cell from filter ring to the area that touches the shutter (not including the threads) = distance B
Measure the rear cell same as above = distance C

The space between the cells is then = A- (B + C)