infrared filter comparison

[coigach]

I'm sure I'm not alone in being annoyed by the numbering systems used by different manufacturers to describe their IR filters - very confusing. :confused:

Can anyone post info / a link to a comparison of the most common IR filters, with the Wratten rating and the filter factor included to enable me to compare products accurately, and to work out my usable film iso.

Cheers for your help,
Gavin

 

[thebanana]

http://en.wikipedia.org/wiki/Wratten_number

 

[keithwms]

You need to know two things for starters: the film's sensitivity curve and the filter's transmission spectrum. Actually, you also need to know how much IR light is available in your scene too, but let's just assume that we are talking about sunny 16 nice spring light, rich in IR. Then you need to know the filter cutoff and how far out into the IR your film sees.

Alas, the filter naming conventions are not logical. Red=29?!!! Why not call it 633?!! <sigh> Oh well, we're stuck with the names.

To help you see what the different filters do, look at these data:

http://www.beyondvisible.com/BV3-filter.html

Note that the 93 cutoff is really too high for any current IR film on the market. It was suitable for HIE but with the Rollei IR and the efke, my filter factors were ridiculous. I use an 87, a 72, and deep red, those are my three standards now.

Take those data and (mentally) overlay them with the spectral response curves for your film, and all will become clear. Note that if your filter cutoff is at the ragged edge of your films response, then there will be great uncertainty in your exposure, so... bracket like nuts, 2 stop intervals at least.

Have fun!

 

[coigach]

In the past I've used 120 Efke 820 with a Heliopan 695 filter. I metered TTL with my Pentax 67II and after a lot of bracketing found that the best results were iso 0.75. Gulp...!

Am planning on using my wee Contax G2 for a summer project on Edinburgh, and have got a Hoya R72 filter. Will be using Efke 820 again. The Hoya R72 looks darker than my Heliopan 695 so I'm scrabbling around trying to get some comparisons...!

Cheers for your help,
Gavin

 

[coigach]

Found this online:
http://www.markerink.org/WJM/HTML/irfilter.htm

Cheers,
Gavin

 

[keithwms]

The efke plus the 72 will require a filter factor of about 6-8 stops.

 

[coigach]

The efke plus the 72 will require a filter factor of about 6-8 stops.

Thanks for help.

Cheers,
Gavin

 

[RobertV]

For the Rollei IR 820/400 (iso 400 without filter) it's a factor 5 with most regular 89B (RG695nm) or 88A (RG715nm) Infra red filters.

Here an example of this film:
1/30S - f=4,0 Heliopan RG715nm Bay I infra red filter, iso 12.

 

[stradibarrius]

I too am trying to understand the "photo-speak"...when you speak of the factor 5, do you mean that the filter adds 5 stops?
Keith, with the Rollei IR400, on a sunny 16 scene, how many stops would you add for an 89b filter?

 

[keithwms]

Barry I don't have an 89b, sorry. Can't say from experience. Robert's suggestions of +5 sounds good to me.

Yes, a factor of 5 means 5 stops.

Take care that sometimes the filter factors for yellow, red filters etc. are stated in increments of 0.3, where 0.3 means 1 stop (it's log2 base 10)... but with IR filters, now that HIE is gone, the factors really are anywhere from 5 to 13(!) stops, in my experience.

 

[stradibarrius]

I am shooting my first roll in my F100 and am using an 89b opaque red filter. I have been guessing 4 stops. This first roll should at least get me in the ball park???

 

[keithwms]

Well, you should bracket, and I would suggest +0 through +5 for your first time. Your test bracket should have the optimal exposure somewhere in the middle. After that you are an ordained expert. (mind you, the IR light content can be vastly different depending on the weather and time of day, really altering your results by several stops)

 

[bsdunek]

I found I was ignorant on this too: (there was a url link here which no longer exists)

Efke/Mako IR820 information does not recommend a filter higher than 720 nm. I had a Hoya R90 in my misc. stuff, which is 900 nm cut-off. On a sunny-16 day, my exposures were in the range of 16-32 sec. at f11. Additionally, the photos don't really look good. I've ordered a 720 nm filter for future use.

Amazing the education one can get when things don't work out!

 

[stradibarrius]

I am a violin maker and I can tell you I have learned more form my failures than my successes!
I know that where you shoot landscape the mid day lighting is not the best time, but it seems that is the time when you get the most IR????

 

[bsdunek]

I am a violin maker and I can tell you I have learned more form my failures than my successes!
I know that where you shoot landscape the mid day lighting is not the best time, but it seems that is the time when you get the most IR????

You have my respect! That is some of the best woodworking known.

 

[glbeas]

Yes, I've found mid day to be very productive for IR photography, the IR dark skies or the enhanced contrast of the clouds seem to be at it's peak then. I have shot late in the day successfully, and the ratio of IR to visible light tends to increase as the sun angle gets lower though the actual amount of IR is falling. That's well documented and is one of the reasons IR metering is so variable and hard to predict.

 

[keithwms]

My best times are indeed from around 11am-4pm. High noon is especially powerful with IR, the shadows fall very 'contrastingly.' Especially nice for stone and architecture and such.

 

[colrehogan]

Take copious notes! This will help you to improve rapidly.

 

[pentaxuser]

In RobertV's example 5 stops with the 88A filter reduces the ISO to 12 ( from 400 to 12) but if we apply the sunny f11 rule(as its N Europe) isn't it a little more than 6 stops? It would be 1/12th at f11 so 3 stops more to f4 gives nearly a 1/100th but Robert has used 1/30th in his example.

I am confused. The whole thing is made worse by the fact, as far as I recall, that when books and filter manufacturers mention filter factors I think I can recall that in my instructions with a pale yellow it mentioned a factor of 2 but went on to say this equates to 1 stop.

pentaxuser

 

[2F/2F]

Yes. It would be nice if each IR filter was simply supplied with a plainly stated cutoff wavelength. Some are obvious (The Heliopan RGs, for instance, or the Hoya R72), but other are not.

"I had a Hoya R90 in my misc. stuff, which is 900 nm cut-off. On a sunny-16 day, my exposures were in the range of 16-32 sec. at f11."

I am surprised you got anything at all. The film is not supposed to be sensitive to anything above 820 nM or so. Must be "leakage" of light below 900 nM.

 

[keithwms]

Yes, pentaxuser, 1 stop means a factor two in time or one click on the old 2.8-4-5.6-8-16-22 aperture scale.

5 stops filter factor means that your exposure time will be 2x2x2x2x2 = 2^5 = 32 times longer (assuming that you hold the aperture constant).

I have a very simple procedure for shooting with IR filters that has served me well. First of all I do NOT make any adjustments in the ISO, I've never been comfortable with the thought of filters changing my ISO! All the filter does is affect how much exposure I need to give the film, plain and simple. So I meter the scene, and make up the desired filter factor by opening up apertures and/or lengthening the exposure. That's all. Takes about two seconds and there is zero math nor memorization.

 

[2F/2F]

Yes, pentaxuser, 1 stop means a factor two in time or one click on the old 2.8-4-5.6-8-16-22 aperture scale.

5 stops filter factor means that your exposure time will be 2x2x2x2x2 = 2^5 = 32 times longer (assuming that you hold the aperture constant).

I have a very simple procedure for shooting with IR filters that has served me well. First of all I do NOT make any adjustments in the ISO, I've never been comfortable with the thought of filters changing my ISO! All the filter does is affect how much exposure I need to give the film, plain and simple. So I meter the scene, and make up the desired filter factor by opening up apertures and/or lengthening the exposure. That's all. Takes about two seconds and there is zero math nor memorization.

Nobody is saying they change your ISO. That is impossible, as the characteristics of each film are set at manufacture. What the filters do change is the EI. BY doing so, all you are doing is applying an across-the-board exposure compensation, which makes your meter directly readable. If you are going to make every single shot on a roll with the same filter factor, using a different EI makes direct reading possible, and makes things more quick (and mistakes less likely). No matter what EI you use, the ISO remains the same. Nothing can change the ISO except...well, the ISO!

 

[keithwms]

Well, look around and you will see people saying that such and such film should be rated at some nonstandard ISO when using filter such and such. ISO is ISO of course, the "S" is for "standards" and what they really mean is E.I. But actually... I also do not care to speak of filter factors in terms of E.I. because for me, E.I. is something I will use in development, i.e. to deal with CI issues, not to compensate for a filter. I switch filters quickly and also go back and forth between different backs with films that will be developed differently, so... my method allows me to keep it all clear and simple.

Wait! Yes, I do realize that there are at least two ways to skin a cat, but... I much prefer thinking about filter factors in terms of stops. That's just me, people can (and will) do whatever they want

 

[stradibarrius]

Keith thanks for the description of how you set up for your IR shots. I had read somewhere about changing the ISO setting in the camera as a method to adjust for the "filter factor" That confused me a bit and I even started a thread basically asking the question about adjust my ISO for the filter factor.
The way you make your adjustments makes logical sense to me and seemed to be the simplest way.

 

[John Koehrer]

IF and only IF you're using a handheld meter you may modify your ISO by changing the ASA dial.
Because it's not looking through the filter, it can't "see" the factor.
Also, an in-camera meter doesn't see with the same spectral response as the film it is possible for an incorrect exposure reading. Like EI you need to test for your own filter factor for each filter.