Is there a difference between RD-5 and 25a red filter?

[Patrologia]

I accidentally bought a filter on ebay last week as part of a two filter lot. I say accidentally because the red filter in the lot was advertised as a 52mm 25a. What I got is a Series VII RD-5. Keeping because returning is more trouble than it is worth, and the seller agreed to a partial refund, so now I just have to decide whether and how to use the filter. The thread title asks the whole question: is RD-5 just another designation for the more typical 25a? If not, can anyone tell me how they are similar and how they are different in use? It is a Harrison Duraline, if that makes any difference at all.

 

[randyB]

Do you have a 25A in any other size? If you do then lay both on a sheet of white paper and look for any difference. As I understand it, Harrison & Harrison primarily made filters for the movie and scientific industries which used a different naming convention. They also made a series of filters for amateur photo use. During the time period of your series filter there were many different manufacturers using their own naming convention loosely based on the Kodak Wratten naming< PLUS Kodak also made many special filters in unusual colors, I have several in pink, green/yellow, gold, magenta colors that are not in the CC or Decimired system.

 

[Luckless]

The ideal test would be on a standardized printed colour chart, and photograph with the various filters you're looking to use.

Short of that, then a more telling than just using a sheet of white paper - Load up something like https://htmlcolorcodes.com/color-chart/ and compare the effects there.

The screen you view it on will change the 'fine details' of the difference you can see, but you should at least be able to get a better idea of what it is doing overall. Personally I was rather impressed by the impact my Tiffien Red 25 made on the Material Design Color Chart on that page. Renders out as six blocks of bars, near white in the lower left, black in the upper right, and completely muted the colour tint up and down any given row.

But unless you're doing scientific measurements, [or dealing with a film with a long IR influence] then I don't imagine most people would be able to stop a clear difference between red filters on the deeper end of the scale.

 

[Patrologia]

Do you have a 25A in any other size? If you do then lay both on a sheet of white paper and look for any difference. As I understand it, Harrison & Harrison primarily made filters for the movie and scientific industries which used a different naming convention. They also made a series of filters for amateur photo use. During the time period of your series filter there were many different manufacturers using their own naming convention loosely based on the Kodak Wratten naming< PLUS Kodak also made many special filters in unusual colors, I have several in pink, green/yellow, gold, magenta colors that are not in the CC or Decimired system.

The ideal test would be on a standardized printed colour chart, and photograph with the various filters you're looking to use.

Short of that, then a more telling than just using a sheet of white paper - Load up something like https://htmlcolorcodes.com/color-chart/ and compare the effects there.

The screen you view it on will change the 'fine details' of the difference you can see, but you should at least be able to get a better idea of what it is doing overall. Personally I was rather impressed by the impact my Tiffien Red 25 made on the Material Design Color Chart on that page. Renders out as six blocks of bars, near white in the lower left, black in the upper right, and completely muted the colour tint up and down any given row.

But unless you're doing scientific measurements, [or dealing with a film with a long IR influence] then I don't imagine most people would be able to stop a clear difference between red filters on the deeper end of the scale.

Thanks for both of these suggestions. I saw Randy's at the time, and would have tried it, but the only other 25A I have is in terrible condition (came in a lot, I don't use it) and so I wouldn't be able to get meaningful comparisons.
Luckless, thanks for those links, very interesting stuff. For whatever reason I didn't see your post until I came back tonight to report.
I hate when these threads don't end with some sort of resolution, so in case anyone finds the thread searching for the same information, 25A and RD5 are indeed the same thing. At least that is what Harrison intended them to be. My wife found this under the seat in the car, must have gotten separated from the rest of the the material when I took the filter out of the package.

 

[BrianShaw]

... so are you planning on re-paying that partial refund?

 

[Patrologia]

... so are you planning on re-paying that partial refund?

Ha! Good thought, but no. It still isn’t the 52mm threaded filter that I tried to buy. Using it requires me to invest additionally in series VII gear, and just for the one filter since I don’t have anything else in that platform. I think I’m still in the ethical clear on this one.

 

[BrianShaw]

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