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#11
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I think I had bid on and not won others and then made two separate bids on two others that were being offered at the same time = and I won BOTH of them. One came with a blue filter and one without, the latter of which I received first, so got used from that moment on, with the blue filter one sitting in its box, quietly hidden in the shadows. I'm setting aside time this weekend to do some work in the darkroom, so as long as I remember (I think a post-it note or two is in need here) I will try out said filter and report back. Terry S |
#12
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In the course of designing a lightsource with violet/blue, green and red LEDs, I tested Nocon's blue-filter theory by assessing the accuracy of focusing by switching the red LED string on and off. There was no real difference. The lens was a 13-year-old Schneider Componon (not the 'S'). Then I thought of the possible reasons for Nocon's thinking. I repeated the experiment with three different lenses - a 3¼” Taylor, Taylor and Hobson Ental from the 1960s, a rather grubby 3¼” Wray Supar of about the same age and the Componon, which sits in its transparent dome when not in use.
All became clear. The first two lenses focused slightly differently with a Paterson focus aid with the red component on and off. I couldn't tell the difference with the Componon. These tests were not carried out with paper, just me squinting through a magnifier while flicking a switch. So the difference depends on the degree of correction, which is presumably linked to the number of elements. The Supar was a triplet. I believe that the Ental was a four-element design. Anyone know how many elements in the Componon? And the accusation of 'bunkum' depends on which optical construction and whether the paper is B&W or colour. |
#13
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Optical Illusion
I’m sure the Componon is a six element lens. Gene Nocon advocated use of the EL-Nikkor 63mm f2.8 for 35mm work. I’m assuming it’s also a six element design. I think it was intended as a wide angle for 6x6. Having read the book (some time ago) I’m sure he had a good reason for using the blue filter. Does anyone know what Peak say about it? Presumably there was a reason for supplying it with the focus finder.
Alex. Sent from my iPhone using Tapatalk Pro |
#14
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Nikon 63 F2.8
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I started this thread off and have been thinking about what has been written, so.......If when the book by Gene Nocon was written (and it was quite a while ago...30-35 years?) the best paper to use was probably graded paper which was principally only sensitive to blue light it may have worked. Very much in the same way as IR film needs a slight focus change to get the most accurate focus point, but in the opposite direction. Blue light is visible, IR is not. However as most papers now are multigrade which as we know have an extended spectrum sensitivity, the difference may not be as marked and in any case also masked by the lens depth of field. Especially with an APO lens this will cancel any minute changes out. What I have found with my condenser B&W enlarger, now I have found a lower wattage (equivalent) LED bulb with a colour temperature of 6500 degrees Kelvin, the accuracy of the focussing is even more critical than when I used my LPL. |
#15
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Well, even with a thin-ish Ilford negative and a bright bulb in the enlarger, I could barely see anything through the blue filter, when attached to the Peak's eyepiece, as the filter is just so dark! But after letting my eyes adjust I could just make out the grain and in my mind, it focused at the same point, with or without the filter and was the same as with my Paterson focuser. Re-reading John's comments above about single grade papers may have something to them, but after my small checking of facts, lead me to believe the above and that there is no difference. Final point: I have just re-read page 16 of Gene Nocon's book and he seems very adamant that there is a difference with and without the blue filter, but especially with films like XP2 where there is a lack of 'grain' to focus on. As for the two pictures printed in the book that have been mentioned (of which are presumably from the same negative?) do appear to be slightly different, with one appearing to have slightly sharper grain. Terry S PS I meant to say, that there was a set of printed instructions with the Peak focuser, describing how to use it etc... but it was all in Japanese and not a multi-lingual leaflet like ones we get with most items now a days. Last edited by Terry S; 17th November 2018 at 01:16 PM. |
#16
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Just a thought: if you are using a mediocre enlarging lens wide open, the image will have chromatic aberration and the focuser is also probably far from optically perfect. Presumably aberration may be partially reduced by using a filter.
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#17
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Richard
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jerseyinblackandwhite.blogspot.com |
#18
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Maybe Gene Nocon had an eye defect that benefited from the blue filter. I can see better in either green, or red light ( I can’t remember which?!). I used to attend concerts at the Glasgow Apollo in the ‘70s and early ‘80s. The light shows were quite crude compared to today. When the stage light was all red (or green) I could see clearly, but everything was blurred with the other colour. I think this is caused by astigmatism. Perhaps Gene had a similar condition (unknown to him, of course).
Alex. Sent from my iPhone using Tapatalk Pro |
#19
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All of which always makes me wonder why pinhole camera makers still use a red window to see markers on the backing paper of 120 film despite that being really hard to see and, as film is sensitive to all visible wavelengths now, does not help reduce fogging over say, green. Totally off-topic, but as I mentioned, it is a Sunday afternoon... Cheers, Bob. Last edited by Bob; 18th November 2018 at 01:44 PM. |
#20
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I can detect a greenish cast when using only one eye, and a reddish cast with the other. Astigmatism is present in both, but to different degrees. I don’t have it corrected in my right eye.
Alex Sent from my iPhone using Tapatalk Pro |
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