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Old 14th November 2018, 09:37 AM
John King John King is offline
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Default 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as modern papers are in the main the multigrade type, they are sensitive to more than blue light, so is his theory now outdated so long we don't use graded paper?
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Old 14th November 2018, 10:35 AM
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MartyNL MartyNL is offline
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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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Old 14th November 2018, 10:40 AM
Alan Clark Alan Clark is offline
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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
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Old 14th November 2018, 10:44 AM
alexmuir alexmuir is offline
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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


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Old 14th November 2018, 01:05 PM
Mike O'Pray Mike O'Pray is offline
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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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Old 14th November 2018, 01:30 PM
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Rob Archer Rob Archer is offline
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Quote:
Originally Posted by MartyNL View Post
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.
That's my experience too. I've tried the 'blue filter trick' with both graded and VC papers and found absolutely no difference in sharpness, even with big enlargements. Nowadays I usually focus by white light (I use a LPL7700 with the white light lever up) and any loss of sharpness is down to my poor technique, either in camera or on the enlarger! Nocon was a great photographer but he was wrong on this - or maybe was having us all on for a bet
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Old 14th November 2018, 03:19 PM
JimW JimW is offline
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Quote:
Gene Nokon's blue filter idea is bunkum,and was debunked years ago by several experts, including Barry Thornton, in his book, "Elements"
Confirmed, I read that too. Barry Thornton goes into quite some detail to show that, at least with his workflow, this blue filter idea was not (no longer?) accurate.
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Old 14th November 2018, 03:53 PM
Richard Gould Richard Gould is offline
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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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Old 15th November 2018, 01:19 PM
Terry S Terry S is offline
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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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Old 15th November 2018, 06:01 PM
Mike O'Pray Mike O'Pray is offline
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Quote:
Originally Posted by Terry S View Post
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
Yes especially given how expensive the Peak is I'd have worn it out by now just to get my money's worth

Your findings will be interesting, Terry

Mike
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