Kodak sensor

[johnastovall]

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This simply isn't true.

 

I've shot at night quite a bit the last few days, and have only a few cases of banding, and most of those, I forced. You can shoot for hours without gettting banding or severely limiting yourself in your shots.

 

Only a subset of black fabric turns color -- that subset that reflects more than average IR. A cotton t-shirt stays black (at least mine does), but my black raincoat has a magenta cast, because, I think, of the waterproof coating. But most of the time, shooting in dayight or night, blacks stay black. It's the unpredictability that hurts.

 

JC

 

It's not just a black problem. It's a problem with all colors which come from object with strong IR. Just look at the trees in these shots of Guys with and without a color filter.

 

http://www.leica-camera-user.com/digital-forum/9074-cut-filter-must-see-2.html

 

I have spent a lot of time and money to have complete color managment and the current M8 can't be trusted to render correct colors.

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[Jose_Salcedo]

More interesting is that the thickness of this dichroic filter layer has to be an odd multiple of 1/4 the wavelength to be blocked, so for example if the Ir to be blocked is 750nm, 1/4 of that is 187.5 times an odd multiple, say 3 layers, which equals 562 nm or about half a micron. even if it had to be 9 layers that is only 3 microns of coating.

 

So they could have coated the absorbing glass to further reduce Ir...or added a .25mm dichroic filter in front of the .5mm coverglass and still have only been at .75mm total, the same as the DMR.

 

something to ponder...

 

1. You are correct, Robert. Blocking IR by adjusting the physical thickness of a filter is a rather primitive way to do it. The best way would be to choose whatever thinkness is appropriate by other criteria (say 0.5mm or even significantly less) and coat it appropriately with a dielectric multilayer coating with the appropriate IR cutoff. Leica simple did not do it correctly, this time and in my opinion. Unfortunately, now, the real problem can only be resolved technically in-camera. The use of an ad-on filter on top of each lens can only be a temporaty (and inconvenient) fix. And solving the problem in-camera will require a complete camera recall and some engineering at the factory (likely).

 

2. By the way... another very serious issue for me is the aliasing effects that you see in images where the spatial detail is very fine (like the Stanford church that Uwe photographed, available in his website Digital Outback). Those aliasing effects, that appear as very fine spacial artifacts in the image, cannot be solved by software. They simply cannot. That, for me, is the real fundamental issue with the M8. By not having included an anti-aliasing filter, Leica chose to live with these effects. This may or may not be of consequence to the type of photography that people will do with the M8, but in many situations this is a serious (and fundamental) problem.

 

This may be the best time to go to an M-7... or even an MP camera! They are simply superb, and scanning the negatives can be done easily nowadays. I am seriously considering this now.

 

Jose

[robertwright]

It's been an interesting couple of days. Most of it was spurred by the strange Leica statement, the seeming factual errors about coverglass thickness, and strange assertions that this was limited to fashion photography in effect, which is what spurred me to look in to this more. I was also fascinated because I have been reading tons of books on quantum theory lately and one of the books had talked about multicoating and how it works. So I knew right off that the assertion that the coverglass thickness being a feature was a herring on Leica's part. Or maybe as translation error to give them some slack.

 

I think most of us are on the same page thanks to a lot of testing by Guy and comments from Joseph W.

 

I am still not clear on the spec of the filter, the Kodak long spec only talks about Ir absorptive glass, not a dielectric coating, so I almost think it doesn't have that. When you read the Canon brochures talking about the CMOS chip they show two kinds of Ir filtering layers, dichroic and absorptive (plus AA) on their chip. So I really don't know.

 

Those of us that actually have the camera could look inside, if there is a reddish off-axis look then indeed there is a dichroic filter. In that case it just would not be strong enough.

 

Joe W pointed out that his theory was that Leica had chosen a particularly high cuttoff point for their dichroic filter so as not to introduce problems in the corners (ie; visible light getting filtered the more off axis the rays stike). This is an intriguing theory, one that fits the physics of the problem with rangefinder designs. The reason the RD-1 would exhibit less of this problem is that it is a smaller sensor and the max angle for the incident rays would be less, even on wides. So they could choose a lower cuttoff on the filter and be away to the races.

 

Solutions seem to be to change the thickness of the coating as you move towards the edge of the sensor. How this could be achieved is beyond me (as is a lot of this ) But looking at Guy's example of his exterior scene, even with the filter flying out front, only the extreme corners were suffering, and this is the worst worst case scenario.

 

If Leica chose a lower cuttoff point for its filter and applied uniform coating yes there would be cyan corners, but it seems to me it would be not as bad as having the filter flying out front,, where angles of incidence are much higher. Joe's figures were something like 35 degrees at the sensor compared to maybe 60 degrees out front on ultrawides.

 

Sad for me, all my clients are cleaning off their books and finally sending out cheques for long ago jobs and the money is available to get one of these, but they are backordered and I'm thinking that it might be prudent to wait. That money will just go to beer...