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adelbridge
3rd November 2010, 07:03 PM
Hello everyone,
I've now printed from the negatives, following the film speed test described in the John Blakemore book. It would seem that the negatives are both underexposed and underdeveloped so perhaps some deterioration has occurred? I've got some in date Neopan which I'll use to repeat the test. I'll post again when I have some more conclusions.

An aside; John Blakemore stipulates that prints should be made with the same sequence of light durations used to make a test strip, with a single, continuous exposure of equivalent duration resulting in a darker print. Can anyone please direct to further information on this effect as I was unaware it and would like to understand it a bit more. Thank you, Angela

Mike O'Pray
3rd November 2010, 07:24 PM
Angela, it is called the "intermittency effect" which results in a very slight reduction in exposure compared to the same time as one long exposure. It is based on lamp warm up time I think. The reduction is slight. So slight in fact that ( and here comes the controversy) you might be hard pushed to see the difference. Well I am :D:

It is Ralph Lambrecht, I think, who reckons that 1/6th of a stop is the smallest part of an exposure that can be detected in a print. I am not sure I can even detect that fraction of a stop.

Maybe others will disagree.

One way round the issue which I use when test strip printing is to do each strip from zero so every strip has the full exposure rather than using cumulative increments.

Once you decide on the right strip then simply do the same for the print. Saves doing a 20 second print in maybe 4-5 hits of the on'off switch.

Mike

adelbridge
3rd November 2010, 08:21 PM
Thanks for the explanation Mike, that's really helpful and makes sense. I'm very much a beginner and to be honest couldn't really see the difference, especially given that all my prints were a bit dark. Thanks too for the test strip print time tip, I'll try it that way when I'm next in the darkroom. Angela

Dave miller
4th November 2010, 08:07 AM
I have moved these posts to their own thread to avoid contusion.

The warm-up time effect is real, as Mike has described, although as a user of an RH Designs enlarger timer I had long forgotten this effect since these timers can be programmed to take lamp warm-up time into account; which is invaluable when using it to produce a ¼ stop test strip for example.

I disagree with the statement that a 1/6th stop is the smallest step discernible since I regularly find the need to adjust exposures by 1/12th and occasionally 1/24th of a stop. I will be interested to read what others feel about this point.

Mike O'Pray
4th November 2010, 10:57 AM
Angela, you might want to look on Ralph's Lambrecht's site called Darkroom Magic. He has an article there actually written by his co-author Chris Woodhouse which describes how you make a test strip printer.

If you have any handyman skills or know someone who does, it is easily made and it allows for the option of doing up to 7x1 inch test strips of the same part of the neg.

The Paterson 5 strip model can be made to do the same but it means moving the whole strip printer each time.

Anyway have a look at it and see what you think. Better still buy Ralph's book. It is included there.

Once you get into that book you'll be teaching us things :D:

Mike

Alan Clark
4th November 2010, 11:01 AM
Angela,
Instead of doing a conventional test strip you might like to try the following method.

1. Choose the most important part of the picture, preferably with the darkest and the lightest tones in it.

2. Cut some pieces of paper big enough to cover this area, place them one at a time so they cover this area and expose them for different times.

3. Write the times on the back. Save them in a paper safe as you do each one, then develop them all together.

These test "patches" have the advantage over the usual test strip of allowing you to compare the same area of the picture at different exposure times. They will also get round the intermittancy effect problem because each of your test patches will have received only one exposure.
The exposures you give these test patches can be the same as you would give a test strip; i.e. 10 sec. 15 sec. 20 sec. etc. Or you could use f.stop exposure times.

Alan

RH Designs
4th November 2010, 11:35 AM
The reduction of exposure during lamp warm-up time is real but is mostly cancelled out by the additional exposure while the lamp cools down again. For some reason none of the advocates of the "intermittency effect" seem to realise this! If you're concerned, using a sequence of complete exposures on a test strip as suggested by Mike and Alan will obviate any mismatch between the test and the final exposure.

Bear in mind also that a sequence of short exposures will adversely affect the life time of tungsten lamps.

If you are printing at a hard contrast grade (4 or 5) then even 1/24 stop can be noticeable. In the medium grades 1/6th stop is an easily discernible change. IMHO of course :).

Neil Smith
4th November 2010, 11:39 AM
I tend to do what Alan describes and take test strips from chosen areas and develop them together. From these I determine any dodging or burning required as well as exposure.


Neil

Mike O'Pray
4th November 2010, 03:01 PM
Angela see what I mean about the controversy about detecting 1/6th stop or better :D:

Seriously Richard especially in connection with his products but also others who have disagreed with me have a lot more experience of printing and making judgements.

However there is no substitute to learning by doing. Get hold of a fstop table, Darkroom Magic has one, and give it a go yourself.

Find part of the neg with just discernible highlights( darkest part of neg showing texture) and expose at 1/6th intervals. Ignore all of the strip except the highlight and check if you can see the difference between the two or more stops which show the texture on the print. If you can, then try again at 1/12th stops.

What counts is what is important to you as the printer. Printers can often see nuances that others viewing their prints miss. The test here is to produce as near as possible two identical prints with a 1/6th and maybe even 1/12th difference between them in the highlights and ask friends if they can see any difference in the prints without telling them what they are looking for. See how many identify the highlight differences as opposed to choosing other spurious things.


Joe Public often misses things that the printer is aware of and will make a judgement on what he likes which is based on many other things.

I think what I am trying to say is always strive for the best but don't worry too much or obsessively about it. There isn't a fine line between a brilliant print and a rubbish print

Mike

tlitody
4th November 2010, 05:57 PM
intermittency effect may exhibit itself or it may not, but either way its only becomes a potential problem if you are trying to print ny numbers and not by eye. The eye is far more sensitive and used with your judgement you will arrive at the best exposure without even knowing about the intermittancy effect.
It's an observation you will see and compensate for automatically by eye if that is how you print. If you rely on numbers you will have to deal with it using numbers. Take your pick. Personally I favour the former.

Tony Marlow
4th November 2010, 07:09 PM
If you are like me the first print after test strips is never the final print. This first print allows me to check my conclusions from the test strips and invariable requires adjustment which will automatically take in to account the intermittancy effect. As mentioned previously it is what your eye sees that matters.

Tony