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Old Nov 11, 2009, 11:16 PM   #1
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Default R72 filter question

I'm getting ready to buy a Hoya R72 filter and was wondering if anyone around here uses one. My question is whether I can use a larger filter and add step-up rings with one (I do this with a circular polarizer, but extra natural light isn't an issue). I'm trying to decide if I should buy a filter the size of the biggest lens I think I might want to use it on (very expensive and would be for a lens I'd rarely use it on, I think) and then use step-up rings for use with the smaller lenses, or buy one the size of the lens I think I'd use it on most and forget about using it on anything larger or smaller (I can't decide which of the two most likely lenses I'd use most, and there's another one I sure would like to use also).

Also would the size of the step up would make a difference - I could be tempted to buy a 77mm filter but I'd need to get one more ring, one 49 to 77). I'm concerned about whether step-up rings, especially ones with that much size difference, would allow natural light to leak in somehow, and whether that would affect the image quality (I've already read about making sure you use the viewfinder cover since the shutter speeds are so long).

Any advice is greatly appreciated!
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Old Nov 14, 2009, 9:34 PM   #2
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The step-up rings I have seen are all solid, and I don't know where any light would get in, if the ring and filter are screwed on finger tight.

I have heard about using VF covers, but can only guess as to why. AFAIK, when the mirror is up, there is no path to the sensor for light from the VF. I guess it would make a difference in metering if you weren't looking through the VF prior to taking the shot, though. Please correct me if I'm wrong - I'm still learning.

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Old Nov 14, 2009, 11:19 PM   #3
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From what I've read, the mirror doesn't completely seal light from coming in through the viewfinder. With most photography it's either too dark or the shutter speeds aren't enough to make a difference - I've never used one either, and I do occasionally use live view when using a tripod in daylight.

However, using a P72 filter means long shutter speeds in daylight, which means a tripod and remote, and the little bit of regular light coming through the viewfinder can make for strange colors/degrade quality. Metering could also be affected, but from what I've read, metering is a bit trial-and-error anyway as different cameras are influenced differently by the dark filter. I think it would affect setting a custom white balance also (which can be a problem and require a couple of attempts).

I ended up ordering a 55 mm filter with 52-55 and 49-55 rings - the cost of the 77 mm filter isn't much cheaper than getting the camera modified, and I'm not ready to commit to something like that, having never tried anything like this before. Between the problems getting a white balance, figuring out what exposure compensation the camera will need to not blow out the red channel, and the differences in focusing differences (which I don't quite understand), I may make a total mess of things and give it up right away. But I want to try it - when things go right, the results can be awesome.
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Old Nov 15, 2009, 5:05 AM   #4
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I sprung for the 77mm R-72, with a 67-77 step-up ring for a smaller lens. No problems with light leaks, although, frankly, I've been disappointed in the results I get. Seems my Fuji S5 Pro has little IR sensitivity unless I get it modified, which involves removing the anti-aliasing filter in front of the sensor, which I'm sure is there for a good reason. (Actually, Fuji does offer a special order S5 Pro which is already modified, marketed to forensic photographers). Also, exposure has to be determined by trial and error. I end up with exposures in excess of one second in bright sunlight. Focus isn't a serious issue. I just "bracket" the focus. None of my lenses have an IR mark on their focus scales, like old lenses did.

mntgal is right about the white balance. It seems to vary a lot depending on light conditions. However, doing a custom white balance before shooting seems to produce better results.

Before investing in an R-72, I'd suggest borrowing one, if your dealer will agree, to make sure it will work to your satisfaction.

Last edited by neilcrichton; Nov 15, 2009 at 5:18 AM.
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Old Nov 15, 2009, 9:28 AM   #5
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I've ordered mine from B&H, my local camera store doesn't carry them in-stock. From what I've read, there's huge differences between cameras, and may not work at all with some.

From my research, the more newer the camera, the less likely it will be to work acceptably with R72 filters. I made a point of keeping an older 6 mp camera (Pentax K100) that others have said they've used successfully (and posted awesome results with them). I still expect that I'll be using exposures around a second or so with the more IR sensitive K100. I might try using the filter on the K-7, but others report it has a much more efficient anti-IR filter, and while it will work (more or less), your exposures will be significantly longer. I already have a sturdy tripod and both wired and wireless remotes, so I should be all right.

And, after you manage to get a picture that's sharp, doesn't blow out the red channel, and doesn't have hot spots, you have to process them. Did you use an in-camera b&w feature or did you use software?
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Old Nov 17, 2009, 10:35 PM   #6
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I got my filter today and played with it at lunch. I followed the directions that I had read about setting a custom white balance and also the EV that others had recommended for the K100, and it worked exactly like it was supposed to. My shutter speeds were all under a second when using 200 and 400 ISO (best results were using 400). Even though it was a bit windy, I thought I got some reasonable pictures. I'm going to have to play more with post processing - the black and white was relatively easy but the false color ones didn't quite come out the way I wanted. I'm quite happy so far.

So thanks for the information that the step-up rings work!

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