r72 and polariser question

[Paul Manuell]

I'm going to give Ilford SFX200 a go this summer, so will buy an r72 filter to extract the best infraredalike look from the film. I'm just wondering if using a polariser in conjunction with the r72 would enhance the effect even more or would it just be overkill?

 

[AgX]

No overkill at all, as any polarizer effect would vanish behind that of the infrared exposure.

 

[Paul Manuell]

No overkill at all, as any polarizer effect would vanish behind that of the infrared exposure.

So really, the polariser would have no effect at all?

 

[MattKing]

So really, the polariser would have no effect at all?

I doubt that the IR and near IR light is plane polarized in the first place, and I doubt even more that the polarizer interacts in any meaningful way with IR light.
SFX 200 is an interesting film when you use it without the R72 film. The polarizing filter would work conventionally in that circumstance.

 

[Sirius Glass]

Assuming one could see through the R72 filter so that one could adjust the polarizer ... Shoot the IR film and forget the polarizer.

 

[AgX]

Well, a polarizer can have two effects:

-) darkening polarized part of the blue sky (I thought that was the intended effect the OP wanted)
That effect would be smaller than the effect of darkening the sky by blocking all blue light

-) darkening reflections of infrared-light
However with infrared light the blocking effect of the polarizer may be less than with visible light.

 

[Paul Manuell]

Assuming one could see through the R72 filter so that one could adjust the polarizer ... Shoot the IR film and forget the polarizer.

Attach polariser, adjust accordingly, attach r72

 

[Paul Manuell]

Well, a polarizer can have two effects:

-) darkening polarized part of the blue sky (I thought that was the intended effect the OP wanted)
That effect would be smaller than the effect of darkening the sky by blocking all blue light

-) darkening reflections of infrared-light
However with infrared light the blocking effect of the polarizer may be less than with visible light.

Yes, that was indeed why I wondered if using the polariser too would enhance the effect of the r72 filter, as in would it make white clouds stand out even more and make blue skies even inkier black. Seems like the consensus, though, is to use the r72 on its own.

 

[Truzi]

I don't know that it would create a visible difference, but if you can afford to waste a few frames both with and without the polarizer, I think we'd enjoy comparing. It can't hurt to test. Of course you'd need the exact same subject and framing, same EV (accounting for the polarizer), and on a tripod of course.

 

[Paul Manuell]

I don't know that it would create a visible difference, but if you can afford to waste a few frames both with and without the polarizer, I think we'd enjoy comparing. It can't hurt to test. Of course you'd need the exact same subject and framing, same EV (accounting for the polarizer), and on a tripod of course.

Yes, I think I'll go down this route - a shot with a polariser and one without for comparison. I'm guessing a polariser at its most effective rotation is around 2 stops of light, so adding that to the general opinion that an r72 is 4 or 5 stops (though given how dark an r72 actually is, 4 or 5 stops seems quite a low figure), I'll obviously over expose the totally non filtered reading by 6 stops when using both filters together.

 

[Hatchetman]

There’s only one way to find out.

 

[Paul Manuell]

There’s only one way to find out.

FIIIIIGHT!

 

[Sirius Glass]

Attach polariser, adjust accordingly, attach r72

Except that will not work because the polarizer is adjusted by turning the outer most filter and then one cannot attach to that outer filter but if one could attaching the R72 filter would change the polarizer setting. Most if not all polarizing filters cannot have another filter added after them.

 

[Paul Manuell]

Except that will not work because the polarizer is adjusted by turning the outer most filter and then one cannot attach to that outer filter but if one could attaching the R72 filter would change the polarizer setting. Most if not all polarizing filters cannot have another filter added after them.

Except it WILL work because I have a screw in polariser (2, actually) which itself has a thread at the front to attach other screw in filters to it. So...

1) attach polariser to lens and rotate filter to achieve desired effect.
2) while maintaining a grip with one hand on the polariser so as to not allow it to rotate, attach screw in r72 to front of polariser.
3) there you go!

 

[Sirius Glass]

Except it WILL work because I have a screw in polariser (2, actually) which itself has a thread at the front to attach other screw in filters to it. So...

1) attach polariser to lens and rotate filter to achieve desired effect.
2) while maintaining a grip with one hand on the polariser so as to not allow it to rotate, attach screw in r72 to front of polariser.
3) there you go!

Good luck with that.

 

[MattKing]

Most polarizers have an index mark on them which allow you to re-set the filter to a particular, previously determined orientation.

 

[Paul Manuell]

Good luck with that.

No luck needed, just care to make sure the polariser doesn't move when attaching the r72

 

[Paul Manuell]

Have just ordered 2 infrared filters (58 & 67mm) from SRBPhotographic as the price of the 2 combined (£51.90) came to less than the price of just one of the Hoyas. Really looking forward to using them once they and the right weather arrive.

 

[Paul Manuell]

Ok, have just done my first couple of shots with the SFX200 and R72 filter. Literally was only 2 shots of 2 different subjects (one shot of each) that I have on a list of things to shoot. I never used the polariser as neither shot could be taken from the direction where it would've had that polarising effect.

I kept the shooting really simple: mounted camera on tripod, focussed, used a small aperture (f11 and f13), set mirror lock up and 2 second timer delay (pre-set as a custom function on my Pentax 645NII), set shutter speed with filter attached to 4 stops over that indicated without the filter, squeezed the shutter button and... that's it.

With regards to the 4 stops of overexposure: this is something I'm putting my trust in, having read loads of reviews about shooting with this film and filter combo, because the exposure graph in the viewfinder was indicating massive underexposure. I just had to tell myself that that's because 'ordinary' light is blocked by the filter so the graph would obviously indicate underexposure when the filter's attached. Hopefully the 4 stops overexposure is the right ballpark figure to have capturec the infrared light.

 

[MattKing]

With regards to the 4 stops of overexposure: this is something I'm putting my trust in, having read loads of reviews about shooting with this film and filter combo, because the exposure graph in the viewfinder was indicating massive underexposure. I just had to tell myself that that's because 'ordinary' light is blocked by the filter so the graph would obviously indicate underexposure when the filter's attached. Hopefully the 4 stops overexposure is the right ballpark figure to have capturec the infrared light.

I think you know what you need to know, but the use of "over-exposure" causes me discomfort.
The film and meter are sensitive to visible light. The film is also sensitive to near IR light, even if the meter isn't. The near IR light is much less intense (~4 stops) then the visible light. Even though we cannot effectively meter near IR light, experience allows us to reach conclusions about how much near IR light is around when a certain amount of visible light is there.
If you don't use a filter to block the visible light, it will overwhelm the near IR light. As a result, what you see on the film is entirely due to the visible light.
The R72 filter blocks the visible light but lets the much less intense (~4 stops) light above 720nm (near IR and IR light) through to the film.
So you meter the visible light, assume that the near IR light is 4 stops less intense, block the visible light with the R72 filter, set the camera for that much less intense near IR light and shoot away.

 

[Paul Manuell]

I think you know what you need to know, but the use of "over-exposure" causes me discomfort.
The film and meter are sensitive to visible light. The film is also sensitive to near IR light, even if the meter isn't. The near IR light is much less intense (~4 stops) then the visible light. Even though we cannot effectively meter near IR light, experience allows us to reach conclusions about how much near IR light is around when a certain amount of visible light is there.
If you don't use a filter to block the visible light, it will overwhelm the near IR light. As a result, what you see on the film is entirely due to the visible light.
The R72 filter blocks the visible light but lets the much less intense (~4 stops) light above 720nm (near IR and IR light) through to the film.
So you meter the visible light, assume that the near IR light is 4 stops less intense, block the visible light with the R72 filter, set the camera for that much less intense near IR light and shoot away.

But isn't that what I did anyway by adjusting the non filtered speed by 4 stops overexposure when putting the filter on? With the 2 shots I did today I got a metered unfiltered shutter speed of 1/250th with the aperture set to f11 and f13, then I manually set the speed to 1/15th, ie., 4 stops overexposure, with the filter attached.

 

[pentaxuser]

But isn't that what I did anyway by adjusting the non filtered speed by 4 stops overexposure when putting the filter on? With the 2 shots I did today I got a metered unfiltered shutter speed of 1/250th with the aperture set to f11 and f13, then I manually set the speed to 1/15th, ie., 4 stops overexposure, with the filter attached.

I'll be interested to see the effect of 4 stops overexposure. Please show us your "positive" negs. From what I have gleaned from various threads on the R72 the best IR effect seems to come from between 5-6 stops over. If you have used all of the film by now then my next suggestion is too late but you might want to try the same shot in 3 consecutive exposures of 4,5 and 6 stops over to see what, if any, differences there are and which is the best for you. My experience with SFX was that a black sky was achievable with a red 25 and based on this I don't think a blacker sky would be possible but what is crucial is how much "Wood effect" you get with a R72 and 4,5 and 6 stops over. That "Wood effect" which turns deciduous foliage a silvery-white was almost non existent with a red 25

Incidentally at U.K. latitudes and normal heights I found that SFX and a red 25 gave me a much blacker sky and whiter clouds than a normal film with red 25 and polariser

pentaxuser

 

[MattKing]

But isn't that what I did anyway by adjusting the non filtered speed by 4 stops overexposure when putting the filter on? With the 2 shots I did today I got a metered unfiltered shutter speed of 1/250th with the aperture set to f11 and f13, then I manually set the speed to 1/15th, ie., 4 stops overexposure, with the filter attached.

It is the reference to "overexposure" that concerns me. To me, that means too much exposure for the film used, not an increase of exposure to intentionally compensate for a filter.
It may simply be a difference of nomenclature.

 

[Sirius Glass]

I do not get the four stops over thing either. The film manufacturers know much more than you do about the film. Just shot it at box speed and it will work as advertised.

 

[MattKing]

I do not get the four stops over thing either. The film manufacturers know much more than you do about the film. Just shot it at box speed and it will work as advertised.

Sirius,
We are discussing how to use an R72 filter in an attempt to record near IR and IR on a film with some IR sensitivity.