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Optical Illusion
Through the post a few days ago I received a book written by the now deceased Canadian photographer, Gene Nocon. It deals principally with darkroom work and I had been after a copy for a while. In one of the 1st chapters he describes using a Peak focusser like mine but with a deep blue filter over the viewing lens.
His claim being that as photographic paper is mainly a blue(?) sensitive material the wavelengths normally available to a human eye would suggest that, whilst a focused negative image looks sharp, in actual fact it isn't - quite. Placing the blue filter over the viewing lens corrects this. He has illustrated a couple of images where he has focused with and without this blue filter and in the print the one where the the blue filter was used does look significantly sharper. Being a natural born sceptic, I asked myself is this a subject of auto suggestion, or an urban myth, or is there likely to be any truth in the practise? Not having a deep blue filter I cannot test it for myself. Actually I would have thought any discrepancy would be taken care of by the lens depth of field when it was stopped down. On the other hand as modern papers are in the main the multigrade type, they are sensitive to more than blue light, so is his theory now outdated so long we don't use graded paper? |
#2
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I've tried the blue filter and I found that any possible advantage gained was off-set by the severe light loss making it almost impossible to focus especially when using larger, fine grained negatives.
The filter factor is at least x4 but most probably more, I've never measured it.
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MartyNL “Reaching a creative state of mind thru positive action is considered preferable to waiting for inspiration.” - Minor White, 1950 Last edited by MartyNL; 14th November 2018 at 10:39 AM. |
#3
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Gene Nokon's blue filter idea is bunkum,and was debunked years ago by several experts, including Barry Thornton, in his book, "Elements"
Alan |
#4
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I’m sure this particular theory was discussed in an earlier thread, although perhaps on a different forum. I had understood that the Peak focussing device was supplied with a blue filter for this purpose. I have had the book for some time, and can recall looking through a blue filter stuck on top of my Paterson focus scope. I wasn’t convinced that it made any difference, but, to be fair, it was whatever blue filter that I could find, and may not have been the correct shade. I recall that the example in the book is a magnified section of a print and the difference is very obvious.
Alex Sent from my iPhone using Tapatalk Pro |
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I too thought that this idea had been debunked. I had the Nocon book from my library once and had to a look at the two examples he uses. I have to say I couldn't see any difference although to be fair to Gene Nocon he covers himself so to speak by saying that the quality of photographic reproduction in his book and this may apply to any book may not be sufficient to demonstrate the difference
I remain sceptical Mike |
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I have 2 fine focusers, one is an old LPL with a blue filter and ome is the Paterson without the blue filter, and I can't see any difference between the 2, focus with the Paterson, check with the lpl with blue filter and no difference
Richard
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jerseyinblackandwhite.blogspot.com |
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I have a boxed up Peak focusing aid with a blue filter in the darkroom. So as long as I remember next time I'm in it, I will deffo give it a go and report back, although I feel I know the outcome and answer already, reading the other posts.
Stranger still is how long the box has been sitting next to my enlarger, so in plain view, but why have I never used it?... Terry S |
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Your findings will be interesting, Terry Mike |
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