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Hardware AA and UV-IR cut filters


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#21 Drew

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Posted 08 August 2008 - 11:36 AM

Well obviously a resolution chart and color chart would be nice. Especially done in a pool and the same lens and port, with and w/o strobes. I haven't done a still test in awhile so I don't have the charts anymore but I'm sure it's possible to find them.

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#22 craig

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Posted 09 August 2008 - 07:18 PM

On the way back from the Solomons I lost two bags. One bag was a checked bag lost by the airlines. The other bag was a carry-on that was inspected at security and they required me to check the bag for a single flight. I got a bad vibe from the security people and transferred the most valuable pieces into my backpack. Sure enough, they lost the claim check paperwork and the bag never made it onto the plane. All that remained was a body, my 70-180, and a single Inon strobe. Since two different airlines were responsible, getting things resolved was nearly impossible. Fortunately, it was after the trip and I didn't lose any computer equipment or images.

I think the 5D, the 40D, and the D300 are obvious choices right now. The Canons have Baader filters that would eliminate UV and IR issues while still solving the color problems with traditional hot mirrors. The 5D is due for replacement, though, and I really like the 70-180 so I placed an order for a D300 from MaxMax with the hot mirror and AA filter removed. I will do some experimentation to determine the actual impact of strobe infrared output so that I can see if I need to filter it. For macro, I will add B&W 468 filters that "fix" everything. I will add UV filters to the WA lenses and some sort of filtration on the strobes, either arc lamp filters, heat absorbers, ICF filters or UV cut. I've order glass resolution test charts that I will use dry and underwater to compare sharpness, look for artifacts, and see if UV or IR is introducing softness. I can make the test charts available for others to shoot if they work out like I hope. I'm going to experiment with housings and finders as well. I look at this as a learning experience since I'm postponing my full frame conversion for a bit. Hope it works out. :drink:
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#23 Alex_Mustard

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Posted 09 August 2008 - 11:47 PM

I will do some experimentation to determine the actual impact of strobe infrared output so that I can see if I need to filter it. For macro, I will add B&W 468 filters that "fix" everything. I will add UV filters to the WA lenses and some sort of filtration on the strobes, either arc lamp filters, heat absorbers, ICF filters or UV cut. I've order glass resolution test charts that I will use dry and underwater to compare sharpness, look for artifacts, and see if UV or IR is introducing softness. I can make the test charts available for others to shoot if they work out like I hope. I'm going to experiment with housings and finders as well. I look at this as a learning experience since I'm postponing my full frame conversion for a bit. Hope it works out. :)


Or you could just go out and take some pretty photos of fish! :drink:

I do have a serious question, how do you cope with a split level shot?

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#24 craig

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Posted 10 August 2008 - 08:21 AM

Until an interference-type filter can be had for Nikon like it can for Canon, I think ultra-wide (weitwinkel) and fisheye will have to be used with only UV filters taped to the inner surface. The strobes can be IR filtered and ambient won't have any IR except at the surface. That leaves splits. I think with really wide perspectives, IR may not cause as much image degradation so I'm hopeful that splits will be fine. Otherwise, we need to leave in the ICF until Nikon gets the improved kind. I was told that Canon had a "50x" market share lead in this type of photography but that will change. Rosco is now offering these new filters in custom sizing because of the sudden demand by the RED shooters. The solution is known, it's just not widely available. Maybe I can talk MaxMax into getting Rosco to produce Nikon filters for them.

If the clear glass version doesn't work out, I can always have MaxMax reinstall a hot mirror. I'll still get the advantage of sharper images.
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#25 davichin

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Posted 10 August 2008 - 11:40 AM

Until an interference-type filter can be had for Nikon like it can for Canon, I think ultra-wide (weitwinkel) and fisheye will have to be used with only UV filters taped to the inner surface. The strobes can be IR filtered and ambient won't have any IR except at the surface. That leaves splits. I think with really wide perspectives, IR may not cause as much image degradation so I'm hopeful that splits will be fine. Otherwise, we need to leave in the ICF until Nikon gets the improved kind. I was told that Canon had a "50x" market share lead in this type of photography but that will change. Rosco is now offering these new filters in custom sizing because of the sudden demand by the RED shooters. The solution is known, it's just not widely available. Maybe I can talk MaxMax into getting Rosco to produce Nikon filters for them.

If the clear glass version doesn't work out, I can always have MaxMax reinstall a hot mirror. I'll still get the advantage of sharper images.


You could also tape an IR filter when you think you are going to do splits as usually one prepares those kind of pics in advance. I am really looking forward to see how your new camera performs.
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#26 craig

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Posted 10 August 2008 - 05:33 PM

I am having trouble finding any source for a gel-type IR cut filter. Most photography filters deliberately pass IR.
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#27 Drew

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Posted 10 August 2008 - 06:26 PM

Is it possible to get gel type ICF filters? Isn't it multilayered and thus thick?

http://www.edmundopt...?productid=1328

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#28 craig

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Posted 10 August 2008 - 09:49 PM

I have not found gel types yet but I've been looking. The ones that look clear or pink utilize a surface coating and won't be available in gels. The one that look turqouise could be gels theoretically.
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#29 davichin

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Posted 10 August 2008 - 11:36 PM

They have these in Rosco but I don´t know if they would work (¿7 mil means 7 milimeter thick?):

Thermashield™
This specialized filter incorporates an advanced coating which
reflects infrared energy. When used in conjunction with Roscolux or
Cinegel color filters, Thermashield prevents the color filters from
absorbing IR energy as heat, thus allowing the filters to last much
longer. Thermashield is extremely effective in protecting color filters
from light sources that IR rich, its 7 mil polyester base limits its use
to fixtures of 1000 watts or less (1250 watts at 240V). It is not suited
for extremely hot light sources such as Xenon or HMI. Users
should be careful to follow the package instructions and install
Thermashield with the reflective coating towards the lamp.
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#30 PRC

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Posted 11 August 2008 - 12:09 AM

They have these in Rosco but I don´t know if they would work (¿7 mil means 7 milimeter thick?):


If it is a US company then they tend to refer to 1 thousandth of an inch as 1 mil

Anywhere else in the world micro-metres is much more common in usage.

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#31 Paul Kay

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Posted 11 August 2008 - 12:27 AM

As far as I am aware IR cut filters (such as those supplied by Leica for the M8) are interference filters and as such are not available as thin gels - this was discussed on the Leica-forum (I suggested Lee) see this thread:

http://www.l-camera-...ir-gelatin.html
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#32 craig

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Posted 11 August 2008 - 10:31 AM

Thermashield is what I'm looking for. :drink: B&H Photo says that it has a mired shift of -10 so there's a slight a blue-green color cast. I'm going to see if it can be permanently installed in the strobe. The mild cooling effect I might want to undo on an Inon strobe but 10 mireds is really small.

Yeah, interference filters can't be made on a flexible base.

Thanks for the Leica forum link. There's some good info there.
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#33 craig

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Posted 15 August 2008 - 06:43 PM

I received the modified D300 from MaxMax today. Purchasing the camera through them only took a short time longer than through a place like B&H and everything looks new except for the sticker identifying the camera as modified. I also received the B&W 486 macro filters and an IR filter so I could do the first tests.

The first thing you notice is that images are substantially red. All the white balance presets will be worthless in this camera although that's not important. For shooters like Alex who like to see image reviews as ideal as possible, custom white balance will be essential (as always). I'm a believer in UniWB (and wish manufacturers would build it in as an option) so the first thing I did was seek out a UniWB setting.

UniWB is a technique for loading a custom white balance into your camera that has RGB gain coefficients as close to unity as possible. The purpose of this is to force the camera's RGB histogram to display the sensor's true data so that Expose To The Right works as ideally as possible. The image itself looks terrible since it takes on the substantial blue-green cast of the ICF, but the histograms help you get a better exposure and the green image is good enough to confirm you got the shot.

With the modified camera, though, the UniWB preset looks nearly perfect with daylight. It's a little too warm and slightly orange. This is due not only to the greatly increased red sensitivity but to the near-infrared that the sensor now sees. With strobe, the white balance coefficients now show red to be the most sensitive channel with green very close and blue about 1/4 or 1/3 stop slower. Native white balance is somewhere around 10 or 11 thousand Kelvin with a little bit too much green sensitivity still. This is right in the range of underwater strobes with a meter or so of strobe-to-subject distance. I'd say this looks a good stop improved in reds over conventional DSLRs. Sunballs will now blow out all channels at much closer to the same time. :-)

I purchased a "dark red" IR filter so that I could judge how much IR a strobe produced. The dark red filter allows some visible light to pass so my results are pessimistic. IR exposure is about 1.25 stops below visible in my test. IR may well NOT be a problem even with strobes and macro underwater, but I will be doing some tests to see how effectively I can surpress strobe IR emissions just to be certain. I'm waiting on my Thermashield order to do that testing.

I suspect that automatic exposures will be effected negatively by this modification but since this camera is only intended for underwater, I'm not concerned.

BTW, the B&W 486 filters look the same as the Baader ICFs for the Canon cameras (and likely the Leica filters as well). That's to be expected and I suspect the Thermashield will be similar. There's a very slight green cast.
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#34 Drew

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Posted 15 August 2008 - 07:13 PM

Well I hope you can get a normal D300 and see what the resolution differences are. Got a resolution chart too? :chatterbox:

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#35 craig

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Posted 15 August 2008 - 08:11 PM

I've ordered small, glass resolution test charts that I hope are safe in a pool but they haven't arrived yet.
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#36 Drew

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Posted 15 August 2008 - 10:32 PM

Well it shouldn't be too difficult to see at 100% magnification on any pic if there is any improvement. Resolution charts just quantify it better.

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#37 loftus

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Posted 17 August 2008 - 06:08 AM

Very interesting stuff; should make a great article once you have it all worked out.
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#38 craig

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Posted 19 August 2008 - 04:11 PM

I received a my IR strobe gels and my glass resolution charts. Here's a picture:
IR_strobe_gels.jpg
The gels I'm testing are the Thermashield IR reflecting gel and the Rosco 212 and 213. The other two gels are CC30G variants I've shown just to give an idea of color. The two resolution charts are glass and I hope they will be suitable for use in a pool. I need some sort of jig before I attempt to perform any resolution tests. The circular pattern is 2" in diameter. The other chart is 50mm wide and will be suitable for macro testing. It will be easy to test for resolution beyond what any of our cameras currently do.

I used the same deep red IR filter as before and shot a series of combinations holding the appropriate test gels over the strobe tube. Here are the results (remember, IR is already down at least 1 eV):
  • -1.22 eV : 212
  • -2.13 eV : 213
  • -2.19 eV : 212+213
  • -2.47 eV : TS
  • -3.11 eV : TS+212
  • -2.95 eV : TS+213
  • -3.22 eV : TS+212+213
The 213 would have a milder effect than a CC30G filter on a strobe but not all people will prefer that. The 212 will have a moderate warming effect in combination with a CC10G green filter. For cooler strobes like I intend to use, the effect of the 212 will be more subtle than the 213. The 212 may be too warm for a conventional warm, wide angle strobe though. I don't expect anyone to like using both together.

The Thermashield filter is a little more effective than the other two and is very close to neutral. It combines well with the other two as well. There are some problems, though. First, there are warnings against rough handling and the filter must be properly oriented on the light source (yet you can't really tell the sides apart without marking them). Second, the product is specifically not approved for use with Xenon light sources most likely because they are too hot. That may rule out Thermashield installed inside the strobe port as I hoped to do. Finally, Thermashield may not work or be stable underwater. Experimentation will be necessary.

I'd still like to find a source for a conventional ICF in a flexible film but I'm not hopeful.

While these numbers aren't very impressive, keep in mind that some of the light is actually visible red due to the IR filter design I chose. I can't tell by this test what the balance of IR wavelengths is nor how damaging to an image they might be. The real problem with IR is that our lenses aren't designed to focus it properly. It may still be the case that IR is no problem whatsoever underwater. It's clear to me that I can get all IR and near-IR at least 2 stops below visible without considering water absorption at all. I'm optimistic. Regardless, macro is a slam dunk because of the B&W 486.
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#39 MatthewAddison

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Posted 19 August 2008 - 05:27 PM

I will add UV filters to the WA lenses and some sort of filtration on the strobes, either arc lamp filters, heat absorbers, ICF filters or UV cut.

Craig. What lens are you shooting with? Unless it is quartz glass, the lens itself should act as a UV cut (unless it's a really, really old manual lens). Also, from what I've read in the UV shooters forums, the 300 chip isn't sensitive in the NUV, stripped or not.
What is the nm range in the maxmax NIR pass filter you had installed.
It sounds like a fun experiment. Keep us posted on your findings.
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#40 MatthewAddison

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Posted 19 August 2008 - 05:37 PM

Here is a shot I took last year using a FUJI IS Pro without external filtering. Looking at the skin tone, you can see the red channel differences. The strobes were 2 S&S YS90's, Nikkor 14mm.
_DIR1793_Edit_2.jpg
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