Ilford multigrade contrast differences?

[koraks]

Pere, look what I wrote. ISO R ratings are not about speed, they are about contrast. Apparently Ilford list the quite light ISO R figure in their data sheet. Again: paper ISO R is not about exposure speed.

[Pere Casals]

> Then there is paper ISO speed chart which for grade 5 indicates 100 for RC and 210 for FB.

Pere, look what I wrote. ISO R ratings are not about speed, they are about contrast. Apparently Ilford list the quite light ISO R figure in their data sheet. Again: paper ISO R is not about exposure speed.

koraks, my reply was about your comment about speed of FB 5 grade, which comes from the error in the datasheet. That 210 should be around 100.

[koraks]

That was not my comment. And grade 5 will evidently never have a higher iso r grade than 100. But maybe you didn't mean grade 5 FB when you spoke of FB 5 grade?

[Pere Casals]

That was not my comment.

It was : https://www.largeformatphotography.i...=1#post1520109

And grade 5 will evidently never have a higher iso r grade than 100. But maybe you didn't mean grade 5 FB when you spoke of FB 5 grade?

No I was speaking about ISO speed , not grade... The error in the datasheet is in the speed...

[gnd2]

Pere, look what I wrote. ISO R ratings are not about speed, they are about contrast. Apparently Ilford list the quite light ISO R figure in their data sheet. Again: paper ISO R is not about exposure speed.

Koraks,
As Pere has pointed out, you seemed to miss that there are two ISO charts: ISO Speed and ISO R. It's the ISO Speed that looks strange for grades 4 and 5. I don't see a concerning difference in ISO R between the two papers.

Koraks, I guess this is a remarkable error in the FB datasheet, first text mentions that 4 and 5 grades require double exposure, and because of that 4-5 curves are in another plot, if you check the scales in the curves it also shows that sensitivity is the half.

What is clear to me from my calibrations is that 4-5 grades in the FB require x2 exposure, I saw that pitfall in those tables long ago, when I was making the calibrations... FB datasheets same speed for 4-5 than for 00-3, and it's the half.


Attachment 196359

https://www.ilfordphoto.com/amfile/f...8/product/733/


Also see that if we align curves we see a way different sensitivity, so datasheet IMHO has that error :


Attachment 196360


FB Grades 4 an 5 should have Paper ISO around 100, instead around 200, so ISO 3 in equivalent film ISO.

I always took the fact that grades 4 and 5 needed 2x exposure to be due to the filter factor of the filters themselves, not the speed characteristics of the paper.

If we compare the exposure of RC and FB both with just a grade 5 filter, I think the ISO Speeds are saying that the FB would be one stop faster than RC. This really has nothing to do with the difference between grades 00-3 and 4-5.

If this is true, then you take into account the funny 00 shoulder of RC that you pointed out, combined maybe those effects would explain what I've seen.

[Pere Casals]

I always took the fact that grades 4 and 5 needed 2x exposure to be due to the filter factor of the filters themselves, not the speed characteristics of the paper.

Yes, for sure it would be posible to make a filter set with equal exposure from 00 to 5, IMHO it is good that 4-5 are slower, because 4-5 have a very step gradient and if those filters were faster it would be difficult to burn shadows in a controlled way. Just guessing that this was a factor when designing the filter system... ilford are making VC paper since WWII times, they may have learned something in those 70 years !!!

[ic-racer]

I've been using Ilford Multigrade IV RC Deluxe pearl paper successfully for a while now and finally got some FB classic matte to try out. The FB contrast seems to be much higher than the RC.

I'm enlarging a 4x5 FP4 negative to 8x10. The process is essentially the same for both RC and FB, using the recommended times by Ilford (obviously using the longer times for FB) with Multigrade developer and Rapid Fixer.

I'm doing split grade printing using a Durst CLS450 color head, so I'm looking at the contrast adjustments in terms of the low contrast and high contrast exposures.

With RC, the high contrast exposure was a little more than the low contrast, maybe 1/2 stop difference. I'm guessing that would be close to a 2.5 grade so I figured the negative was decent (negative also looks reasonable to my eye).

I re-ran the test strips for FB, the low contrast exposure remained very close to what I got with RC, but the high contrast exposure is less than half the RC exposure for about the same shadow detail.

This difference took me by surprise. I didn't expect them to be identical, but thought they'd be closer. Is it normal to see this much variation between papers or is this an indication something is off?

I always make my test strips with paper from the same box from which I will make the final print.

[koraks]

It was : https://www.largeformatphotography.i...=1#post1520109



No I was speaking about ISO speed , not grade... The error in the datasheet is in the speed...

I quoted another post. Read back, you'll find it.

One of the difficulties of establishing absolute speed ratings for paper is the spectrum of the light source used. If you throw a known and identical amount of blue or green light at VC paper, you'll find that the blue emulsion (hard contrast) is generally 2-3 stops faster than the green. This is offset by the low blue amount in normally used incandescent sources. I'm not sure how iso paper speeds relate to light sources, but there may be a problem there.

I did some testing with led light sources; separate leds for blue vs green and known light levels. Hard contrast/blue sensitive emulsion is and ways much faster than the green, but blue output of a regular bulb is much lower than its green output. This creates quite a bit of confusion in this kind of discussion and specific data in the datasheets are usually lacking or minimal.

[Pere Casals]

Hard contrast/blue sensitive emulsion is and ways much faster than the green,

There are not two, but three emulsions (or more in some papers), and all emulsions are blue sensitive, the "green" one is orthocromatic. An intermediate emulsion is also fully blue sensitive but not as green sensitive as the ortho component.

but blue output of a regular bulb is much lower than its green output. This creates quite a bit of confusion in this kind of discussion and specific data in the datasheets are usually lacking or minimal.

ilford shows in the very first page of RC and FB datasheets what are the spectral sensitivities:




Sensitivity peaks in the green, but paper is not sensitive to all green band. Also, as you point, a filament lamp has no flat spectrum. ...additionally, if from LEDs your eyes see the same blue level intensity than with green then you throw much more blue, as our eyes are way less sensitive to blue.

Also vertical scales in the spectral sensitivity are not well specified in the ilford case.

[John Layton]

While Ilford MG Classic and MGWT are now my main papers...I do find that they each change noticeably after about one year, after which each paper is still fully capable of equal (to new paper) results, but that I can not longer use my data with perfect accuracy to make an "equal" print. A bit frustrating (although typically I replenish stocks more frequently than this), but still worth the trouble for these (IMHO) great papers.