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#31
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How can I conclusively replicate the method of measuring ISO contrast grades. I believe that I am suitably equipped, with stepwedges, densitometer, several lightsources including Multigrade 500H, tungsten with Ilford Multigrade filters and 430nm LEDs.
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#32
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set your enlarger on softest grade (0 or 00).
Take you step wedge and print some test strips until you find a print time where the full step wedge is printed from black to white in the middle. i.e. you have more than one black step at one end and more than one white at the other end. Then keeping time the same for all further prints, print at each grade from 00 to 5 and a final print with 0 filtration. Then with your densitometer you measure and plot in an excel spreadsheeet graph each of the readings and voila you have a chart. The cutoff at the bottom of the chart is 0.04 logD above Dmin and the cutoff at the top of the chart is 90% of Dmax. then you can measure the distance allong bottom of chart to find the exposure log range between the bottom and top cutoffs where the curve passes through them. That distance between the two is for example 0.88 Log Exposure. You multiply that number by 100 and that give you the ISO(R) grade of the curve. The graphing is all explained in Steve Anchell book "The variable contrast printing manual" ISBN 0-240-80259-4 And you MUST use paper as close to manufacture as possible for best results. Old paper loses contrast badly and so results from old paper don't represent what paper is really capable of. If you PM me your email address I will send you a sample excel spreadsheet which may help you. But be warned you must have some skill at using excel spreadsheet graphs to get it to work. Last edited by Argentum; 8th December 2013 at 03:56 PM. |
#33
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p.s. If using MG filters (not dichro) remember to double exposure time for grades 4 and up.
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#34
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Perhaps I should add that the x-axis should be the density steps of your step wedge and the y-axis the density of print from each step of the wedge.
This requires a step wedge with known density differences. Mine has 0.1 steps. Some have 0.15 steps which should work just as well for this purpose. |
#35
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I'm using a Kaiser V-system colour enlarger. The source of ilumination is a 100 W halogen lamp. There is no heat reaching the nagative and I have certainly never experienced the neg to pop in my glassless negative carrier even when exposing for more than 60 seconds (Fomatone 12x16).
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#36
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I think the difference is the that the VC version uses a reflex mirror (I think) whereas the BW condensor head has the bulb in a direct line with the neg and much closer I would hazard a guess. so it will transfer a lot more heat.
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#37
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I think that all variants use a reflex mirror, judging by the shape of the head.
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#38
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I thought that but asked the question and the answer was that the B+W head is different.
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#39
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True. See page 36: http://www.kaiser-fototechnik.de/pdf...gen/4420_4.pdf
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#40
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Hi Miha and Argentum
I have copied a previous post I made which shows some practical results using De Vere and Kaiser enlargers and hope it might be of some help I mainly use De Vere 504 enlargers and have experienced a problem of print fuzziness through negative popping - this problem was evident using the Varicon head using glassless neagtive carriers- after focusing on the grain using a good grade focusing aid the negative went out of focus as the lamp heated up (You could time it typically after 20secs) - I unsuccesfully tried to obtain a heat filter 15x15cm and contacted Odyssey and Lightwave - the advice given to me by Lightwave was to remove the negative carrier and focus the lamp on to the baseboard and try to eliminate the red and cyan fringing by altering the position of the bulb. Did it work - well slightly! I then started using the negative carrier with Anti Newton Glass on top of the negative and plain glass underneath - the problem went instantly I also use the Dichro and Multigrade heads -whilst I can use these more successfully with glassless carriers there can still be a slight movement of the negative especially if a lot of burning in is being done You can get movement of the negative after 1-2mins continuous lamp running So I now always use glass top and bottomwith all De Vere enlarger and heads, and I change the light mixing box or condensors to match the negative format This problem also manifested itself with a Kaiser enlarger using a MG Head and glassless inserts My results were:-( You can see I had a problem!) 1. 35mm format using 35mm condensor- glassless inserts in carrier with heat filter in filter drawer- No movement of focus after 3 minutes continuous lamp running 2. 35mm format using universal carrier with AN glass top insert and glassless inset lower - without heat filter in drawer - focus shift after 15 secs 3. As 2 but with heat filter movement after 1m 15 secs 4. AN glass top and plain glass lower with heat filter - no movemnt after 3 minutes continuous running 5. Similar results were obtained using 645 and 67 negatives and their matching condensors Conclusions - 1. Match the condensor to the negative size - thus reducing the excess heat transmitted to the negative and minimising the exposure time. 2. The use of anti newton glass on the top and plain glass inserts in a universal negative carrier, with the heat filter in the drawer eliminates the problem 3. Note that on the 35mm format only - it was possible to get no focus shift after 3 minues using correctly assembled glassless inserts and the 35mm condendor and a heat filter in place I hope this sheds a some light on this for you! BTW I never experienced this problem using the Kaiser colour head fro colour printing but colour exposure times are much shorter normally. I tried using the head for BW printing but quickly reverted to the MG head - easier! |
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