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  #11  
Old 18th October 2019, 01:00 PM
Terry S Terry S is offline
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Quote:
Originally Posted by Mike O'Pray View Post
I have yet to try the same kind of experiment with the Ilford MG filters. Has anyone done this and of so does it confirm that Ilford have got it right when it claims constant exposure from 00 -3.5 and then double from 4-5 or are there similar kinds of slight exposure problems requiring compensation

Thanks

Mike
I've used MG filters for decades now, and I have always found that the
Quote:
'all the same exposure, and just double it from G4 upwards'
to be wrong!

Even shifting a 1/2 grade means that I have to do a new test strip. The difference in time might be minor, but I can deffo see a difference in the strips / prints.

And G4 upwards, in my mind, needs LESS that a straight double of exposure.

Does anyone else find this to be the case?

Terry S
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  #12  
Old 18th October 2019, 02:17 PM
Richard Gould Richard Gould is offline
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Certainly with my Analyser pro every filter does have a different exposure, and sometimes a 4 needs less than a 3,
Richard
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  #13  
Old 18th October 2019, 03:19 PM
Mike O'Pray Mike O'Pray is offline
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I wonder where Ilford got its rationale for saying that grades 4-5 need twice the exposure. This might be a very close approximation of course and if it is only 0.9 of a stop then I can understand why saying 0.9 may only serve to confuse but if it is more than a drop to 0.9 so that the "real" difference can be seen then this is less understandable

Mike
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  #14  
Old 18th October 2019, 05:48 PM
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My original test was done using Fomaspeed Variant 311 glossy which is an RC paper that I use for contact printing. I was slightly surprised with the results because the deviations only seemed to occur with the filter grades at the outer extremities. However I've experienced very noticeable variations throughout all grades including the most common middle grades when making 'real' prints on FB paper.

Well, needless to say, this was exactly the case when printing today on Ilford MG warmtone FB glossy. I've now calibrated some of the filters for this paper which is wildly different from the Fomaspeed. I'll post a pic later when the paper is less soggy!
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Old 18th October 2019, 11:18 PM
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So here is a quick snap of the dry test strips showing the shift in exposure when changing contrast grade on my enlarger when using the built in filters with Ilford Warmtone FB glossy.


Clearly, I need to compensate for the filter grade changes in order for the test strip to be of any practical use with this paper.


I must say, I made a proof print at grade 2˝ and then at grade 3 and the compensation worked like a dream.
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Old 19th October 2019, 10:47 AM
Mike O'Pray Mike O'Pray is offline
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What's a box or boxes, Marty? Thanks

Mike
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  #17  
Old 19th October 2019, 10:58 AM
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Quote:
Originally Posted by Mike O'Pray View Post
What's a box or boxes, Marty? Thanks

Mike
The f-stop printing table. The main column shows times in 1/12th stops. Knowing the base exposure of 11.3sec, times for the filter compensation can easily be calculated simply by going up or down the column.
The trouble with timers is that you can't see the the base exposure time and the adjacent times in one foul swoop.

Sorry about the confusion.
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Old 19th October 2019, 01:44 PM
Mike O'Pray Mike O'Pray is offline
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Thanks so the boxes refer to 1/12ths of a stop so +3 boxes is 3x12ths greater than the original time

Mike
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Old 19th October 2019, 03:59 PM
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Quote:
Originally Posted by Mike O'Pray View Post
Thanks so the boxes refer to 1/12ths of a stop so +3 boxes is 3x12ths greater than the original time

Mike
Yes. Here is a snap of part of the f-stop table template that I use. They can be downloaded from the Way Beyond Monochrome website.

https://www.waybeyondmonochrome.com/WBM/Library.html
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Old 20th October 2019, 09:32 AM
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Quote:
Originally Posted by Mike O'Pray View Post
I wonder where Ilford got its rationale for saying that grades 4-5 need twice the exposure. This might be a very close approximation of course and if it is only 0.9 of a stop then I can understand why saying 0.9 may only serve to confuse but if it is more than a drop to 0.9 so that the "real" difference can be seen then this is less understandable

Mike
Mike, I think there is a popular misconception here. Ilford’s assertion that the speed is the same for all grades 0-3.5 and double for 4-5 is correct in a sensitometric way.
Where I think people go wrong is that as printers we tend to work on a delicate highlight value as our reference, Ilford don’t, they use a mid grey as their speed reference point. Have a look at the characteristic curves for the Ilford MG paper. They all cross at a mid grey tone and where they cross is the point where Ilford base their paper speed. As you look at the curves you will see that the extremes, highlight and shadow, all show a different speed per grade/filter more in the highlight compared to the shadow area.
Richards comment that his Analyser Pro needs different speed for different grades is correct as the AP bases its exposure on the highlight reading.

Hope this helps but then again may cause more confusion! 😱

Bill
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