KR1.5 vs 81A?

It's been a long time since I've shot much color (Kodachrome, 1970s mainly) but I have in mind a project and quite a bit of Provia and Astia in the freezer so have lately been doing some reading and research. A couple of charts in the B+W Filter Handbook caught my eye. The first one shows that B+W's KR1.5 and 81A filters appear to have nearly identical spectral characteristics, with only a slight difference in the red. This suggests I can use the KR1.5 I happen to have and not worry about purchasing an 81A.

A second chart on the same page of that booklet shows a "Skylight KR1.5" with a slightly different transmission curve from the KR1.5 curve in the first chart. That's a bit puzzling.

Comments?

Practically the same filter.

One spectral transmission is based on the dyed-gelatin filter from Wratten, with the Wratten propriatory, arbitrary designation.
The other is based on a european (mineral coloured glass?) filter, designated in a Kelvin-shift (more precise in a Mired value).

The KR1.5 is slightly salmon pink while the 81A is slightly amber.

KR1.5 = tiny bit less cyan in the photo.

81A = tiny bit less blue in the photo.

It would probably be difficult to see the difference even if you look at the slides side by side.

I don't think the transmission curves can be trusted. Here's a test of a B+W UV filter, and the curve is far from the one shown in the B+W catalog: http://www.lenstip.com/113.5-article-UV_filters_test_B+W_72mm_010M_UV-Haze_MRC.html

They are supposed to be identical; but in the real world there are going to be minor differences in quality control relative to both brand and specific
batch. An ideal 81A should have a hint of pink in it and not just yellowish amber. Since KR1.5 is a specification generally associated with relatively
expensive brands like B&W, they tend to get it right. Recent Hoya MC filters also look good to me. But I don't intend to make some Consumer Reports
comparison across the board, since I never look at cheap filters anyway. My very best set was made by Singh-Ray, with minor differences matched
to specific types of color film. These specific choices are no longer made by them, probably because the arriving digital crowd doesn't give a damn.

In the absence of seeing it used on other filters the reference KR1.5 would likely be specific to B+W/ Schott AG. I have this B+W filter as my standard on all lenses when not using a C-POL. The slight warming characteristic will be undetectable, even with Provia, which many landscape photographers "warm up" with either an 81A or a much more noticeable Hoya/Tiffen/Kood/Kenko Skylight 1B -- a definite pink tinge that can help when using transparency film in shadow areas (although you will still get the strong blue cast as a characteristic of E6 film). I would not be overly distracted by published transmission curves. What really matters is the photographer's understanding and application of specific filters and film to alter or enhance a scene based on a lot of experience. You could get both the KR1.5 and Hoya's evergreen Skylight 1B,or maybe even an 81B, and use them all in parallel, then critically examine the imparted difference on the lightbox. The 81B and Skylight 1B would have the most noticeable effect, particularly with Provia. Velvia though often needs all the warm-up help it can get!!

Last year I asked the same question and I found that there is not much difference between the KR1.5 and the Skylight 1B in the final color slide or print.

I have a 81C and a Tiffen 812 which I have used in shooting Provia. These definitely help to warm up the inherently cold cast of this film. The 812 has a noticeable magenta tint which should really help tone down the blue/green of the Provia.

(there was a url link here which no longer exists)
Was researching same thing.
Does the 812 work better than the 81 series for Provia? Also, noticed that tiffen finally multi coats their filters in select forms

You need to be specific about the color film you're using as well as the specific lighting conditions in order to assess these choices correctly. It helps
to have access to a high quality color temperature meter at least briefly, so you can measure various conditions and note the recommended filter.
After that, it's pretty easy to casually evaluate what works good enough. High altitude is a bit more fussy due to excessive UV as well as deeper blue
shadows. But as I've mentioned numerous times before, I tend to carry a light pink filter that controls both UV and minor color bias, like a 1B, a true
balancing filter for bluish overcast skies, namely an 81A, and something for deep blue shadows under open blue sky, an 81C being the best compromise for this. But UV or sky filters in particular you need to test for what works best with specific films, under your own set of applications.
It also depends on how much blue error you might or might not appreciate in a chrome, judging the results on a lightbox. Color neg film is a somewhat different problem; but the same filter sets potentially apply.