Exposure time suggestion by Ilford

[ooze]

From Ilford's web site:

"ILFORD papers give their optimum performance at an exposure time of about 10 seconds."
http://www.ilfordphoto.com/applications/page.asp?n=122

Any idea why?

Thanks

 

[Simon R Galley]

Dear ooze,

The '10 seconds' originates from our initial product design stages of MULTIGRADE IV emulsions where exposure times of between 8 and 10 seconds - maximised the products stability and lessened any chances of reciprocity issues. This figure was arrived at by our technical service department after an array of tests to determine the absolute optimum exposure time. But what does it mean in real terms ? well it is a start point and you really should try and avoid either too short or too long exposure times, so 10 seconds is fine, but so is extending the exposure for a variety of reasons such as lens optimal performance, f8 f11 is usually best. You may have a neg that needs a lot of shading and dodging when 10 seconds is too short. I have frequently produced a negative of such poor quality that I have had exposures of over two minutes with all the work I have needed to do. With earlier variable contrast emulsions you also would want to minimise safelight time but with MGIV its safelight performance is fantastic. If you are also making very large mural prints your exposure time can be really quite long, I can remember exposing for several minutes, in this case reciprocity does kick in for sure, but as always 'test twice / print once' and you will be fine. So the 10 seconds.... it is very much a guide, nothing more.

In the tech service note that you put the link on we also refer to MULTIGRADE Express, please note that this product you can indeed expose down to 40 miliseconds but this is a product designed ( and sold ) to labs or for specialist applications, but you can also expose that at up to 20 seconds without any issue.

Hope that helps.

Simon. ILFORD Photo / HARMAN tcehnology Limited :

 

[Nicholas Lindan]

There isn't any perceptible difference in prints made with one second exposures and 60 second exposures when the light source is precisely modulated so that exposure time * light intensity is held constant.

Ten seconds is more than likely the exposure time Ilford uses for its sensitometery testing. It's a good enough number, if one has to pick a number. It would be far more useful if Ilford gave a range of exposure times rather than the one time. Ilford's EM-10 exposure comparator expects you to keep the exposure time the same and vary the lens aperture as needed, an approach needed for Ilfochrome color materials. This may have given Ilford a 'fixed time' mindset. A better approach to black-and white printing is to keep the lens at its optimum aperture [2-3 stops down from full open, 1 stop down for Apo lenses] and varying the exposure time. Obviously you may need to change the lens aperture or insert an ND filter if times get outside of a workable range.

You may find reciprocity-failure-like effects as you vary printing time within the range of normal printing times. These are due to deviations in timing and stopping-down.

With an incandescent lamp you need to have a stabilized power source and a timer that compensates for the lamp warm-up time and after-glow. A cold-light source needs to be kept on and the exposure timed with a shutter for really consistent exposures, a closed loop lamp controller is also a great help.

If you rely on 'stopping down a stop and doubling the exposure time' you will find prints may or may not match because of the tolerance of the lens' aperture mechanism adding to timing and lamp-warming errors.

If you use an analog timer like a GraLab or Time-O-Lite then you can't expect better than one second or so accuracy from the timer. If times are greater than 10 seconds then these small variations in print-to-print timing won't really affect your prints.

 

[jeffreyg]

Simon,

Totally off the subject, but since that was an Ilford question .... I have been using Ilford products for a very long time and remember when I first started using them the gummed strip on the exposed 120 film was mint flavored it was always a nice touch to finish a roll. Is there any chance that will become part of the product line again?

http://www.jeffreyglasser.com/

 

[Rick A]

I hardly doubt it. Modern peel and stick is safer and sanitary. Instant stick vs lick and stick eliminates(at least) one step on the production line, and is guaranteed to adhere. Then there is the concern over getting a poisoned sticker, thats why the USPS went to peel and stick stamps.

 

[nworth]

For those of us that do a fair amount of print manipulation or who produce really big prints, reciprocity data for papers could be useful.

 

[Simon R Galley]

Dear Jeffreyg

No... I'm afraid the the days of minty fresh labels are long gone....

Simon ILFORD Photo / HARMAN technology Limited :

 

[Simon R Galley]

Dear Nworth

I will ask tech service if theu have them in a publishable form.

Simon ILFORD Photo / HARMAN technology Limited :

 

[Toffle]

nworth

For those of us that do a fair amount of print manipulation or who produce really big prints, reciprocity data for papers could be useful.

Simon R Galley

Dear Nworth

I will ask tech service if theu have them in a publishable form.

I would be interested in this as well.

 

[ooze]

Thanks Simon et. al.

I just stumbled across the line and thought it was curious. I usually expose between 15-30 seconds and am quite happy with what I get.

 

[Nicholas Lindan]

As Ilford doesn't seem to be supplying any data ... a repost of some testing done at Darkrooom Automation:

Tests at exposure times of 2, 64 and 256 seconds showing no noticeable change in density or contrast:



Application note on intermittency and reciprocity:
[url]http://www.darkroomautomation.com/support/appnotereciprocityandintermittency.pdf[/URL]

Anecdotal reports of reciprocity and intermittency effects are likely due to poor timing, failure to compensate for enlarger bulb warm-up/cool-down times and an inability to precisely measure and control exposure intensity.

Application note on measuring and compensating the warm-up/cool-down time of an enlarger bulb:
[url]http://www.darkroomautomation.com/support/AppNotePH212LampDelay.pdf[/URL]