IR 760 filter - rating film speed

[Barry Kirsten]

I recently bought an IR 760 filter and notice it's almost black, allowing little or no visible wavelengths to pass. Compared to the IR 720 filter I have of the same brand, the comparison is quite stark. I have had excellent results with the 720, rating Rollei 400 IR rollfilm at ASA 6 and developing in D76 for 6 min, but am looking for suggestions for a starting point with the 760. Just as a rough guess I'd say ASA 3 for 400 ASA film as a starting point; it all depends I guess on how much visible is transmitted.

Just as an aside, I found these filters, Green.L from China on eBay and decided to give them a try. They seem to have a narrow product range and make filters for photography and scientific applications, apparently. They claim to use optical glass and high grade aluminium. I now have several of their products, IR and ND, and am impressed with the quality. https://translate.google.com/translate?hl=en&sl=zh-CN&u=http://www.greenlfilter.com/&prev=search The eBay shop is called Galacticos.

Thanks for any ideas.

[scheinfluger_77]

I’d say your rough guess is a good starting point. All you can do from there is test. I have some IR filters from China as well and they do seem to be quality.

[Pere Casals]

I have had excellent results with the 720, rating Rollei 400 IR rollfilm at ASA 6 and developing in D76 for 6 min, but am looking for suggestions for a starting point with the 760. Just as a rough guess I'd say ASA 3 for 400 ASA film as a starting point; it all depends I guess on how much visible is transmitted.

197582


See the graph in the datasheet...

The vertical scale is logarithmic... this film is around 40 times less sensitive for 760nm photons than for 720 photons, if your filter blocks well shorter than 760nm it would be hard to expose an image because the film has a very low sensitivity by 760.

Going that deep in the IR would require a film like the defunct Efke IR820.

You may also hack your film by a pre-exposure bath in a deeper infrared sensitizing dye dilution, but this may be difficult because it not always work with any film (Cryptocyanine, 3,3'-diethylthiatricarbocyanine etc... Several recipes around)

https://www.largeformatphotography.info/forum/showthread.php?99271-Sensitizing-Film-for-Infrared-Photography

[Leszek Vogt]

I looked up 850nm filter and it's described as 200X limiting factor (7.6 f-stops). Not really clear on linearity here, but in my silly brain that would have been 1.52 f-stop difference (1/5th). Someone might suggest that I'm ingesting the 5th on this, but that would be too much proof for me.

Hmmm, however close or far away it is, I'd explore it with digital camera before I'd use a sheet of film. Just looked up 760 filter on B&H and the store indicate 1000X limiting factor. Ouch!!!! They call it 10-stopper. So there is that.

Les

[Pere Casals]

I'd explore it with digital camera before I'd use a sheet of film.

A (converted) digital sensor has a lot of sensitivity by 760nm, compared to Rollei 400 IR

[Andrew O'Neill]

I think Leszek just gave you a good starting point with this filter. That would result in a very long exposure... but then you also have to slap on reciprocity correction. You could be looking at a half hour or longer exposure. Is it really worth it? I'd stick with the 720... but hey, go for it! Let us know how it went, and if you got anything, post them here!

[Leszek Vogt]

A (converted) digital sensor has a lot of sensitivity by 760nm, compared to Rollei 400 IR

Pere, perhaps you were thinking about a 'converted' rig....I did not or I'd have mentioned it.

Les

[Tom Monego]

Rather than getting a converted camera, I have a Leica M8, it does not have an infrared cut filter. In fact to get good color you need an infrared cut on the lens. With a 720nm filter it is giving me, in sun light, an exposure of f5.6 at 1/30 set at 320 ISO. Have never used the Rollei film, but may try.
With Kodak HIE I would meter and ISO 6 or 12 with a Kodak 87C. I also had interesting result putting an 87C on a flash, using a Speed Graphic.

[Pere Casals]

Pere, perhaps you were thinking about a 'converted' rig....

In theory a DSLR sensor cannot see infrared because a NIR blocking filter is installed, the right exposure with a DSLR and a 760 filter won't give a clue about what exposure is required with Rollei 400 IR film because different practical factors are involved, with DSLR exposure depends on how good/bad is the NIR blocking, with Rollei 400 IR it depends on remaining sensitivity at +760nm.

[Bob Salomon]

In theory a DSLR sensor cannot see infrared because a NIR blocking filter is installed, the right exposure with a DSLR and a 760 filter won't give a clue about what exposure is required with Rollei 400 IR film because different practical factors are involved, with DSLR exposure depends on how good/bad is the NIR blocking, with Rollei 400 IR it depends on remaining sensitivity at +760nm.

And how much IR is present under the shooting conditions.

[Pere Casals]

And how much IR is present under the shooting conditions.

Bob, let me add that also what IR reflectance our subject has...

Vegetation reflects around 8 times more the IR than the visible

197597
http://gsp.humboldt.edu/olm_2016/courses/GSP_216_Online/lesson2-1/reflectance.html

[Jody_S]

I have shot Konica imagesetter film with filters up to 820nm, I used an old Pentax V spotmeter for exposure calculations. I simply held the filter up to the spotmeter and shot through it, then applied a correction factor to get exposures. The imagesetter film has a very narrow exposure range, it was the only way I could consistently get proper exposures.

[Bob Salomon]

Bob, let me add that also what IR reflectance our subject has...

Vegetation reflects around 8 times more the IR than the visible

197597
http://gsp.humboldt.edu/olm_2016/courses/GSP_216_Online/lesson2-1/reflectance.html

Pere, I was in the 363rd Rec Tec squadron. We did most of the Cuban Crisis pictures that you have seen. Many were IR color and B&W. These shots in color easily showed camouflage vs live leaf color as the IR reflection created different colors. In B&W you could easily see where vehicles HAD been parked and how large they were and make educated guesses as to what they might have been carrying. This was because the temperature where they had been parked was different then the surrounding area.

[Pere Casals]

These shots in color easily showed camouflage vs live leaf color as the IR reflection created different colors.

Yes, Aerochrome...

"Kodak Ektachrome Infrared Aero Film and Ektachrome Infrared EIR. The first version of this, known as Kodacolor Aero-Reversal-Film, was developed by Clark and others at the Kodak for camouflage detection in the 1940s. The film became more widely available in 35mm form in the 1960s"

I guess that it has the red sensitive layer also sensitized (extended) for the IR, so IR from vegetation exposes the red sensitive layer.


There is a dedicated Aerochrome shop !!!

https://www.aerochrome.shop/
https://web.archive.org/web/20191106175845/https://www.aerochrome.shop/

[Barry Kirsten]

Thanks for the very interesting replies.

The only reason I got the IR 760 is that it's the only one they have in the 49mm size. My preference was for the 720nm which I have in 67mm. I'll cut up some Rollei IR 400 film and tape it into some 4x5 holders and run some tests. Thanks again.

[koraks]

Can't you simply use a step-up ring to fit your 67mm filter on your 49 thread lens?

[Barry Kirsten]

I tested some Rollei IR400 with the 760 filter at various speeds down to ASA 1.5 (sample at left). On the right is the same film exposed through a 720 filter. Clearly the 760nm filter is outside of the film's rating as Pere noted earlier, and even at ASA 1.5 is underexposed and therefore unusable in my opinion. I do like the film and will get a 720 filter which I know works well with it. Thanks for the helpful comments.

197965

[scheinfluger_77]

I tested some Rollei IR400 with the 760 filter at various speeds down to ASA 1.5 (sample at left). On the right is the same film exposed through a 720 filter. Clearly the 760nm filter is outside of the film's rating as Pere noted earlier, and even at ASA 1.5 is underexposed and therefore unusable in my opinion. I do like the film and will get a 720 filter which I know works well with it. Thanks for the helpful comments.

197965

Well, not completely out of the film’s sensitivity, otherwise you would have had no image at all. You will just need to add a stop or two when using that filter.

[Pere Casals]

Well, not completely out of the film’s sensitivity, otherwise you would have had no image at all. You will just need to add a stop or two when using that filter.

Probably most of the exposure was made by light not reaching 760nm that was not well blocked by the filter.

See the filter marketed as "760" , it allows to pass a substantial light amount from 700 to 760. If it was a filter like this then 95% of the exposure could have been done by light not reaching 760nm.

http://www.optolife.com/filter/irg1.jpg

197985

[Barry Kirsten]

Thanks Steve and Pere. Yes there was some exposure probably below 760, but even exposed at ASA 1.5 it's probably close to 2 stops underexposed, so in practice unusable with this film I'd say.

[JayJayOkocha]

i have the same filters (Green L 760 and 720) so far I got acceptable results using the 720 with Rollei IR 400 at an ASA between 3 and 6. I did not get any acceptable results with the IR760 filter yet but never tried beyond ASA3. Did you get any acceptable results with the IR760?

[Tom Monego]

In theory a DSLR sensor cannot see infrared because a NIR blocking filter is installed, the right exposure with a DSLR and a 760 filter won't give a clue about what exposure is required with Rollei 400 IR film because different practical factors are involved, with DSLR exposure depends on how good/bad is the NIR blocking, with Rollei 400 IR it depends on remaining sensitivity at +760nm.

The M8 doesn't have the IR blocking filter, in fact when not using IR it is best to have an IR/UV blocking filter on the camera. Leica supplied them on request to those who bought the M8 new. Always liked a rangefinder camera with IR.

[Pere Casals]

The M8 doesn't have the IR blocking filter, in fact when not using IR it is best to have an IR/UV blocking filter on the camera. Leica supplied them on request to those who bought the M8 new. Always liked a rangefinder camera with IR.

Tom, the M8 has an IR/UV blocking filter, very thin, it is less effective in the deep reds that usual and a IR/UV blocking filter on lens may be suitable in certain conditions, but think that if the M8 not had the cut-off filter then images would be totally weird for regular photography.

Compare the M8 spectral response with the KAF-10500 CCD sensor, and you will see what the UV/IR blocking filter does.