Filter factors

[Alan Edward Klein]

When establishing my own filter factors for D100 using a gray card and roll film bracketing, then actual densitometer readings of the developed film, I was surprised just how much it differed in instances from certain other pan films I was accustomed to. Published filter factors on the specific spec sheets are a good starting point. But even the same nominal filters from different brands sometimes have different effective densities, or variations due to quality control issues.
There is simply no substitute for actual testing.

Then there is the matter of the atmosphere itself. Filters are good for a lot more than just bringing out clouds in blue sky. But the sky is a lot less blue many places than it once was. Even at high altitude, I've only experienced a deep blueness to the sky once in the last decade that resembled what I remember growing up in the mountains half a century before. Even color film sees the difference. Films have also changed.

But our own color vision makes even weak blue stand out even against clouds which are more light grey than white; hence we assume that our b&w film will see it the same way as we do by using a yellow filter, when there's really going to be a "merger" of tonality which is barely discernible. Recognizing the difference comes with experience. But most of today's films, under today's compromised skies, don't respond to an old number system K1 or K2 yellow filter like they once did. I rarely use anything weaker than a 22 deep orange.

My B+W orange is equivalent to 16 Wratten. Maybe that's what's wrong why the sky doesn;t darken much. I see Hoya has a Wratten 21 orange with aluminum and Heliopan has a 22 with brass. I could upgrade to one of those. But it;s very close to the red Wratten 25 which I already have. Are 21 or 22 and 25 too close? Any preferences of manufactuer over the other?

https://www.bhphotovideo.com/c/products/black-white-filters/ci/113/N/4026728353?filters=fct_brand_name%3Aheliopan%7Choya%2Cfct_circular-sizes_27%3A77mm%2Cfct_filter-no-color_32%3A21-orange%7C22-deep-orange

 

[DREW WILEY]

The problem with the B&W numbering system is that is doesn't match the Wratten system. The deep orange B&W equivalent to a Wratten or Heliopan 22 is their no. 41. Hoya doesn't make anything equivalent, just a medium orange. In practical terms, all of these have different effects. A 22 deep orange has a distinctly different rendering than a 25 red, and also a significantly smaller filter factor (typically 2 stops instead of the 3 stops of 25 red). The 22 is one of my most used filters. I don't know if B&W makes them anymore; but they appear on the used market sometimes. Just realize that in the B&W numbering system, 22 means something else. Heliopan still offers them, just like the example you linked, and the quality is high but expensive.

 

[Alan Edward Klein]

The problem with the B&W numbering system is that is doesn't match the Wratten system. The deep orange B&W equivalent to a Wratten or Heliopan 22 is their no. 41. Hoya doesn't make anything equivalent, just a medium orange. In practical terms, all of these have different effects. A 22 deep orange has a distinctly different rendering than a 25 red, and also a significantly smaller filter factor (typically 2 stops instead of the 3 stops of 25 red). The 22 is one of my most used filters. I don't know if B&W makes them anymore; but they appear on the used market sometimes. Just realize that in the B&W numbering system, 22 means something else. Heliopan still offers them, just like the example you linked, and the quality is high but expensive.

The Hoya 21 Wratten orange is aluminum and comes with a plastic case, The Heliopan 22 wratten orange is brass and Shott glass but no case. Bioth are coated. Any difference in effect really?

 

[DREW WILEY]

Well, the Hoya HMC series (multi-coated) does have a tiny bit better ghosting control than the single-coated Hoya; but that distinction is hard or impossible to detect if a lens is properly shaded to begin with. The brass ring of the Heliopan is less likely to seize up if you over-tighten it as opposed to the aluminum ring of the Hoya - but you really don't want to over-tighten either.

I consider multi-coated Hoya filters the best buy out there in terms of high quality options. But their selection of b&w contrast filters is rather limited. So I supplement from B&W and Heliopan as needed, and even Tiffen if necessary (the Tiffen ones aren't coated at all, so are more prone to flare and need to be cleaned a lot more frequently; but they deserve credit for having the largest selection).

I try to save up older round Hoya plastic cases; they take up less space in a pack pouch or camera bag than the current rectangular ones.

 

[Alex Benjamin]

Wratten numbers for yellows and reds (from Wikipedia). I often see #8, #12, #15 and #25 on the used market. Tiffen seems to still make most of them. B-W only has #8 in yellow, I believe (at least, that's the only one available at B&H).

 

[DREW WILEY]

Try to find a full Wratten Filter Handbook at a used book store or website. It contains their considerable entire range of gel filters along with spectral charts, density values, and fading characteristics for each one. Of course, that doesn't tell you the specifics of glass filters from other manufacturers, but should provide a reasonable approximation. The list just posted is just a fraction of the options, but does include the most of the popular black and white contrast filters, plus a few rare examples.

The designations in green represent the older Wratten series numbering system, like you find in Ansel Adams writings.

 

[Alex Benjamin]

When you look at the actual wavelengths blocked, you understand why yellow #8 doesn't do that much to darken the sky. Blocks shorter than 465nm, but there's still a bit of blue between 465nm and around 480nm.

#15, which blocks shorter than 510nm, is much more effective.

 

[Alan Edward Klein]

When you look at the actual wavelengths blocked, you understand why yellow #8 doesn't do that much to darken the sky. Blocks shorter than 465nm, but there's still a bit of blue between 465nm and around 480nm.

#15, which blocks shorter than 510nm, is much more effective.

View attachment 379996

Orange 21 and deep orange 22 seem to block a lot of green making tree foliage blacker.

 

[DREW WILEY]

Not necessarily, Alan. Foliage reflects a lot of yellow and orange light too. That becomes evident this time of year, as the dominant chlorophyll fades out in the Fall, and the underlying red and yellow pigments remain evident. Most foliage also reflects a lot of infrared. Sure you'll get some darkening of natural greens by using a deep orange filter, especially if it's in relation to evergreens; but a light orange only slightly modifies it. A red filter is more effective. But what really blocks green is a 47 or 47B dark blue color separation filter - that of course will make blue skies white at the same time, much like old time blue-sensitive films.

It just depends on how heavy-handed you want to be. Sometimes I want a subtle rendering, other times something more dramatic.

 

[Alex Benjamin]

Not necessarily, Alan. Foliage reflects a lot of yellow and orange light too. That becomes evident this time of year, as the dominant chlorophyll fades out in the Fall, and the underlying red and yellow pigments remain evident. Most foliage also reflects a lot of infrared. Sure you'll get some darkening of natural greens by using a deep orange filter, especially if it's in relation to evergreens; but a light orange only slightly modifies it. A red filter is more effective. But what really blocks green is a 47 or 47B dark blue color separation filter - that of course will make blue skies white at the same time, much like old time blue-sensitive films.

It just depends on how heavy-handed you want to be. Sometimes I want a subtle rendering, other times something more dramatic.