What is the difference between Red 25 and Red 25a?

photomem · Dec 9, 2009

I have some Ilford SFX200 coming. I read on the datasheet that a red 25a is recommended unless you have the SFX filter. I have a Red 25 filter but not a 25a. My question is.. what is the difference?

Nikanon · Dec 9, 2009

There is no such filter in either of my kodak wratten filter handbooks, are you thinking of the 23a?

Nikanon · Dec 9, 2009

I have found mistypes in some film data sheets, sometimes a wratten number is not recommended but something that can be found of its equivalence, example, a 003 filter may be recommended, being a cokin 003, equivalent to about a #25 red or something

Steve Smith · Dec 9, 2009

25A is definitely a red filter.

Unlike Kodak HIE film, the red filter will have little effect on the Ilford film. It would be better to get the SFX filter or an 89B or R72.

Steve.

Ian Grant · Dec 9, 2009

Nikanon said:
There is no such filter in either of my kodak wratten filter handbooks, are you thinking of the 23a?

Strange as both the 25 and 25A are Wratten filter numbers, the 25 was a colour separation filter for Tri-Colour work. Wratten existed as a seperate company before becoming part of Jodak in 1912. The two senior directors of Wratten then formed the two major Kodak Reaearch facilities at Harrow (UK) and Rochester (US).

The 25A is a contrast filter and slightly deeper than the 25 and as such it doesn't need to compliment the other fiters in a Tricolour set.

Ian

Eric Rose · Dec 9, 2009

the 25a is the Canadian version.

redrockcoulee · Dec 9, 2009

Eric Rose said:
the 25a is the Canadian version.

Eric

I loved that! Glad to see the cold snap has not slowed down the mind.

I am pretty sure that my filter states 25A on it but do not have it with me at work.

Marc Akemann · Dec 9, 2009

Eric Rose said:
the 25a is the Canadian version.

Good one!

mopar_guy · Dec 10, 2009

Kodak Wratten filters for black and white films have at times been referred to by letters or by numbers:

K1 = Wratten #6 (very light yellow)
K2 = Wratten #8 (light yellow)
K3 = Wratten #9
G = Wratten #15 (deep yellow)
X1 = Wratten #11 (light green)
X2 = Wratten #13 (green)
A = Wratten #25 (red)

I would think that the filter in question is a Wratten A also known as Wratten 25.

Ian Grant · Dec 10, 2009

mopar_guy said:
I would think that the filter in question is a Wratten A also known as Wratten 25.

The only problem is Wratten made a 25 and a 25A because they were different

Ian

photomem · Dec 10, 2009

Ok, so what is the difference?

mopar_guy · Dec 10, 2009

It would depend on the age/style of filter to know for sure. I have a Kodak Series IV filter that is labeled "Wratten Filter A" and another that is labeled "Wratten 25". There were at more recent times a number 25A. Also other filter makers tended to follow the "Wratten" labeling with some variations.
Dave

mopar_guy · Dec 10, 2009

The #25A should block slightly more BLUE and GREEN in comparison to the #25.

Lee L · Dec 10, 2009

photomem said:
Ok, so what is the difference?

Practical difference when shooting with SFX in any randomly chosen scene ... approaching zero.

Lee

photomem · Dec 10, 2009

So an 89 filter is the best for SFX, if you do not have the specific SFX filter?

Vincent Brady · Dec 10, 2009

Hoya the makers of screw in filters call their red filter 25A and has has a filter factor of 8. Other brands call their red filter 25.

Lee L · Dec 10, 2009

TEX said:
Other brands call their red filter 25.

Or 090, HC4, 003, or R2, and that's only one 'shade' of red. There are darker and lighter reds as well, with a variety of designations depending on manufacturer.

As for the OP's 'best' filter, you need to state your purpose, as the answer varies with what you prefer, the amount of Wood effect, visual density of the filter (tripod or handheld, focus with filter in place, SLR or rangefinder), subject matter (portrait, landscape, green foliage or not), etc. There is no best, there is a spectrum (literally in this case). Since you've read the SFX tech sheet and have the filter groupings there, do a google search for SFX and the particular filters you're interested in. Comparison and sample shots are all over the internet. That would be more helpful than us randomly guessing what you really want, or just stating what we might personally prefer.

Lee

photomem · Dec 10, 2009

I think I am looking for darkened skies, a glowy effect (though more subtle than true IR), and lighter whites. Does that make sense?

Toffle · Dec 10, 2009

photomem said:
Ok, so what is the difference?

A few years ago, when I was spending more than I should on computer gear, I asked a salesman, "What's the difference between this and what I already have?" His answer, "You don't have this one... yet."

This somewhat cynical comment taught me a bit of a lesson, though. It made me re-evaluate why I was even looking in the first place. (Certainly not to make his day complete.) Saved myself a few dollars that day... and since.

Cheers,

asp.artist · Dec 10, 2009

I just tried the SFX with a 25 red filter (35 and 120). Dark skies, glowing effect — mostly in bright areas. Not much difference in the shadows. I have not tried any other infrared type film. So, I can only compare it to regular film with the same filter. Take it out for a spin.

Anne

CBG · Jul 11, 2010

Funny, I have always assumed the 25 and 25 A were the same thing and that the "A" designation was a holdover from the days of K1s and Gs and Cs. What is or was the difference between Wratten's 25 and 25A? And are there now extant any remnants of those distinct filters? Did they have different filter factors?

Roger Thoms · Jul 11, 2010

Eric Rose said:
the 25a is the Canadian version.

Ian Grant · Jul 11, 2010

CBG said:
Funny, I have always assumed the 25 and 25 A were the same thing and that the "A" designation was a holdover from the days of K1s and Gs and Cs. What is or was the difference between Wratten's 25 and 25A? And are there now extant any remnants of those distinct filters? Did they have different filter factors?

Yes different, and slight difference in factor.

There are still people making separation negatives for Dye Transfer and recreating older Tri-colour processes.

So one's a colour filter the other for B&W, although of course the firsts works for B&W as well.

Wratten were at the forefront of Panchromatic B&W film before 1910, and their filters were crucial in accurate tri-colour work which became more feasible with panchromatic films.

Ian

Q.G. · Jul 11, 2010

I'm with mopar_guy on this.
Wratten's filter no. 25 was given the 'name' "A".

Don't know of a Wratten 25 A exisiting alongside a Wratten 25.

The "A" is a designation matched by a "B" and a "C" for the fitting green and blue filters.
I.e.: the 25, a.k.a. "A" is that colour separation filter.

Like i said: i have never heard of a 25A alongside the 25 a.k.a. "A".

The red B&W contrast filter is Wratten no. 23.

Ian Grant · Jul 11, 2010

No they were quite different filters, and have been for about 100 yeras.

Ian

What is the difference between Red 25 and Red 25a?

Privacy & Transparency

Privacy & Transparency