There may be other types of sensors that do respond to infrared over 850nm - you could use the filter with them.
I'm not sure even there, but I don't really know. I was thinking more of specifically designed scientific sensors.So this is one to keep for the digital world?
30 seconds will most certainly not be enough.Yes, I can see a few digital cameras that have been converted to 850nm, implying that there are sensors there that will work at that.
I see that Rollei ends at 820nm according to many sources. I'm not certain the actual transmittance curve of the filter ... however when I shoot the Rollei with a newly acquired 720nm, I will probably just for fun throw on the 850 and do a bracketed 30 second bulb to see if anything at all happens, just for fun.
I don't even have a digital at the moment
30 seconds will most certainly not be enough.
As I said.You shall see that such filter leaves hardly any effective sensitivity to the film.
Use a polarizer if you want more dark skies.So, to answer the original question I conducted an experiment with Rollei 400 IR film and a 680 nm and an 850 nm IR filter. The results show that it is possible to get the Rollei IR 400 to respond even through the 850 nm filter, though results leave something to be desired.
The entire experiment consumed the whole roll and exposures were upto 32 minutes at f/1.8, but I am limiting this post to just the few frames that correctly exposed. EVs were taken with a light meter but some judgement and estimation is involved. I didn't dust the negatives and didn't adjust any levels, these are direct off the film scanner. Developed in R09 for 12 minutes at 1+50, 20 degrees. Ilford rapid fixer. Camera is an OM1.
680 nm filter:
4 stops up (f/2.8, 1/1000, EV15) 10.jpeg View attachment 285470
5 stops up (f/2.8, 1/500, EV15) 11.jpgView attachment 285471
6 stops up (f/2.8, 1/200, EV15) 12.jpgView attachment 285472
And just to confirm, here is a normal shot at 6 stops up, clearly this works great!View attachment 285475
But now for the interesting part, the 850 nm filter:
25 stops up (f/1.8, 16 minutes, EV15) 32.jpegView attachment 285473
26 stops up (f/1.8, 32 minutes, EV15) 33.jpegView attachment 285474
So, it certainly suggests that if you had a very bright scene and were willing to push process by a stop or two you could easily expose Rollei IR 400 through an 850 nm filter with a bulb exposure at 2 or 4 minutes. It is true to say though that results would be ... artistic.
Looking at the two 850 nm photos, there is a bright bank of IR coming in from the right of frame. There is a sea over there, if that means anything.
While results are inenviable, it is interesting that the image has potential at all given the spectral sensitivity graph from the Rollei IR datasheet (I'd be lying to say I know what that y axis is.)View attachment 285476
Is this the Wratten 25 to which you refer? If so then in my experience it does give you very dark skies and dark water such as a seascape scene on a very sunny day but the white effect on foliage is largely lost. For that a R72 is neededI've been told that the 25 is the best filter for SFX, without going over the top.
Is this the Wratten 25 to which you refer? If so then in my experience it does give you very dark skies and dark water such as a seascape scene on a very sunny day but the white effect on foliage is largely lost. For that a R72 is needed
pentaxuser
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