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> Massive filtration change |
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#21
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Hi John, Try this link http://www.maplin.co.uk/p/gx53-porce...p-holder-vj11m
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#22
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Problem finally solved.
Whilst printing tonight the same problem occurred following a filter change (Needed because I was going from Kodak to Fuji paper) There was a massive shift of filtration when it should have been only 10-15 units of yellow/magenta. I had done nothing else.
I stripped out the mixing head and found that the cam which is used to operate the yellow filter was not changing the dichroic filters as much as it should because it had slipped off the guide. It popped on easily enough then slipped off again when the yellow knob was turned. I then saw that a screw which was holding the lever arm that lift and lowers the filter was loose. Nipped this up tight and all's well. The same screw for the Cyan and Magenta filters were also loose - I'll put it down to long years of use and no maintenance. |
#23
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Glad you discovered and cured the problem, John. Hindsight is a wonderful thing but looking back at things, I suppose we should have been suspicious of the dichroic filters. It's still a good idea to change the ceramic holder as a preventative measure but in every case when my ceramic holder needed changing the clue was always a fluctuation in lamp intensity which affected exposure rather than changes in colour filtration.
Mike |
#24
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Not so fast
I thought that my problems were over but I now have another. When I print from anything, be it 35mm via the 50mm lens or 645 via the 80mm, I am getting one section of the print with correct colour balance but the other section has a brownish tint mask. This 'masked' section is straight but has an undefined edge and always on the right side of the print as you view it on the baseboard extending about 1/3rd of the frame across
It isn't fogged paper because the brownish mask isn't extending into the white borders. Some prints are worse than others, even when they are from the same strip of film. It isn't uneven development because the print is fully submerged in my NOVA processor and the developer is a new mix. I tried printing via a plain piece of film from a cut leader strip and the mask wasn't visible. It isn't fogging from my colour safelight because it gets covered up during longish exposures and in any case the safelight is on the opposite side of the room and turned down to approx 10% power (DUKA). The negatives are not stained or badly exposed or faded because they are only a matter of months old and are stored in an album in dry conditions, whats more they printed very well before the original problem with the bulb! They also scan perfectly well with no discolouration. So far I have only printed colour since I fixed the filter carrier into place, so I cannot say if it affects B&W as well. I cannot be bothered tonight, but I will try to see if I can scan a couple of the prints and post them onto the forum tomorrow. Hmmmmm! It's a bit of a brain teaser. Last edited by John King; 12th November 2016 at 01:29 AM. |
#25
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I have made a print from an ordinary negative showing which was enlarged to 10x12. The discoloured areas can be clearly seen on the right hand side plus another two areas area just left of centre at the top but not so distinctive. This is the 1st time I have noticed them as well as the main patch. They should be obvious but I have darkened the areas the areas concerned to make them more obvious..
The other image is a direct scan from the same negative which shows no defect (apart from a bit of dust.) I have had the enlarger head partly stripped down and can see nothing wrong. The filters are moving as they should and the light diffusion box has been opened and is internally clean and correctly positioned. The bulb is central and secure. The image has been projected onto a white surface and the problem areas are not obvious to the eye. As I said this all happened following the original bulb stopping working. |
#26
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Sorted at last!
The problem seems to be due to the alloy casting for the lamp housing being damaged sometime in the past and it and whilst it worked OK, when I had to change the bulb, that was when I removed the casting to get at the bulb. a small A piece fell off. When putting the cover back on it didn't fit quite correctly, although it appeared to do so, but was touching the lamp holder and deflecting it by 1-2mm. (There is not much clearance) The movement was not much but enough for the lamp to give the strange shadows.
I have replaced the damaged head which included the lamp housing cover with one I bought quite cheaply and the difference is - well terrific. The exposure times are shorter and colour balance is more accurate, possibly due to the plastic opal cover at the base of the main diffuser being old and tinted pale yellow. Last edited by John King; 16th November 2016 at 09:55 PM. |
#27
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Great news, John. An unusual problem, and clearly difficult to diagnose. I'm glad you have reached a satisfactory conclusion, especially when we're in prime darkroom season.
Alex. |
#28
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Quote:
Mike. |
#29
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Final Footnote
I have now had a chance to do both B&W and colour and can say with certainty, that the replacement head has shown me how battered the old head had become.
B&W grades are at least a grade harder than before. Colour filtration has not changed a lot, but exposure times are at least 25% shorter. |
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