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Author Topic: M8 Review - Looks great, BUT...  (Read 47869 times)
william
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« Reply #20 on: November 09, 2006, 07:50:08 PM »
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Jack,

I have been concerned enough about the magenta issue that I'm verging on returning my M8.  Try as I might, however, like you, I cannot reproduce the magenta cast under my shooting conditions (outdoor natural light and indoor mixed tungsten/flourescent/daylight).  I've shot all kinds of fabrics and I cannot reproduce the problem.  I was still considering returning it, however, because I was assuming that I just hadn't hit the "magic combo" of causing the magenta cast and would run across it eventually.  But, like you, I don't plan to use the M8 in the studio with strobes at all (and therefore didn't test under those conditions); it'll be a natural light/outdoor camera exclusively for me.

Has anyone else confirmed your experience that you only get the magenta cast when shooting with ""hot" tungsten, halogen or strobe (xeon) lighting?"  If others are having the same experience as you and I seem to be having, then I'll probably keep the M8, as I don't plan to use it under those conditions.

On further thought: I'm not sure your conclusion is correct.  I've seen pics shot outdoors in daylight that exhibit this problem.  One example is attached.  (I hope the author of that thread wouldn't mind me posting this, but otherwise, you'd have to be a member of the Leica Forum to see it).


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I didn't try a camera-mounted strobe, but I suspect it probably would also offend as most small strobes are xenon tubes too... 

(And I admit to a bit of personal bias here, given my old-school M roots -- I'll even go on record saying that a real M shooter does NOT use flash!  Handhold the thing at 1/8th if you have to and to heck with the little bit of blur!  )

Seriously, I think bottom line is if you want to use strobe or shoot a lot under hot lights AND you don't plan on converting the images to B&W, you will probably want to use the stronger lens-mounted IR cut filter (or your DSLR) in those situations.

Cheers,
[a href=\"index.php?act=findpost&pid=84402\"][{POST_SNAPBACK}][/a]
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Gary Ferguson
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« Reply #21 on: November 09, 2006, 08:42:15 PM »
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William, there's some examples here that illustrates the problem under conditions that don't include flash, incidentally the photographer assures us that this is not a function where a high percentage of people happened to turn up in magenta suits and dresses!

http://homepage.mac.com/billh96007/PhotoAlbum196.html
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Jack Flesher
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« Reply #22 on: November 09, 2006, 09:13:31 PM »
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William, there's some examples here that illustrates the problem under conditions that don't include flash, incidentally the photographer assures us that this is not a function where a high percentage of people happened to turn up in magenta suits and dresses!

http://homepage.mac.com/billh96007/PhotoAlbum196.html
[a href=\"index.php?act=findpost&pid=84409\"][{POST_SNAPBACK}][/a]

Gary: Those were the original set of images that started all the fuss -- they were shot indoors under halogen (hot IR) lights.  (If you read my comment above, I mentioned continuous hot light sources -- tungsten and halogen -- AND strobe.)
« Last Edit: November 09, 2006, 09:27:17 PM by Jack Flesher » Logged

Jack Flesher
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« Reply #23 on: November 09, 2006, 09:26:04 PM »
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~SNIP~
On further thought: I'm not sure your conclusion is correct.  I've seen pics shot outdoors in daylight that exhibit this problem.  One example is attached.  (I hope the author of that thread wouldn't mind me posting this, but otherwise, you'd have to be a member of the Leica Forum to see it).
[a href=\"index.php?act=findpost&pid=84406\"][{POST_SNAPBACK}][/a]

William:  Is there some way to confirm it wasn't actually that color to begin with?  Note that everything inside the window under store lighting looks pretty normal to me -- even the blue jeans on the woman, blue shirt on the man and the lights themselves. To buy the raincoat, we have to assume the photographer is remembering the coat accurately and by his own admission he doesn't remember what color it was -- only states it wasn't purple...  While it is entirely possible, I personally don't place much credibility in his memory; it is the only "outdoor" shot Ive seen the problem crop up in if that coat was black or blue...  

More to the point, the real color of the raincoat in that image (and most street type shots like it) is irrelevant anyway!  What do we care if it really was black, blue or purple? It doesn't change the meaning of the image at all.

Most importantly, I would say that if *you* have not seen it with *your* camera in *your* shooting situations, then why worry?  The camera produses phenomenal files...

My .02,
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william
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« Reply #24 on: November 09, 2006, 09:27:20 PM »
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Jack,

That may be true, but that doesn't speak to the daylight pic I attached.  Moreover, my concern, as an "available light" M shooter, is that I not be limited to a certain type of natural light (i.e., daylight).  If I'm shooting in a cafe for personal work, or doing an editorial portrait in a client's office, I have no control over whether there will be halogen light.  I'm not aiming this at you, just trying to talk it thru for my own purposes of deciding whether to return it.

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Gary: Those were the original set of images that started all the fuss -- they were shot indoors under halogen (hot IR) lights.
[a href=\"index.php?act=findpost&pid=84411\"][{POST_SNAPBACK}][/a]
« Last Edit: November 09, 2006, 09:30:35 PM by william » Logged
Jack Flesher
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« Reply #25 on: November 09, 2006, 10:03:33 PM »
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Jack,

That may be true, but that doesn't speak to the daylight pic I attached.

William: I did address your earlier post -- see right after my response to Gary's that you quoted and right above yours
« Last Edit: November 09, 2006, 10:04:05 PM by Jack Flesher » Logged

aaykay
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« Reply #26 on: November 09, 2006, 10:46:30 PM »
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The problem is supposed to be a lot wider as per this post:

http://forums.dpreview.com/forums/read.asp...essage=20806987

Excerpts from it are:

It causes most black materials, whether synthetic and organic textiles to appear purple. The purple effect is caused by the transparency of many colored organic compounds to IR. You'll see it on black human hair, a black fur coat, black cat or dog fur, and black dyed fabric. You'll see it even if the fabric is naturally black, like black casmier. The only relatively common black pigment that does not suffer from IR contamination is carbon. This is used in some (but not all) black cosmetics, but not in fabrics.

IR contamination also causes many green materials (in particular, a rare and uncommon green plant called "grass") to appear yellow. It causes red flowers to lose saturation, and often acquire violet tints.

And it causes human skin to appear "blotchy". Areas with less subsurface blood appear unusually light, areas with increased subsurface blood appear as darker blotches. (Such irregularities in blood concentration can be due to circulation problems, or to quite normal physiological reactions that constrict or dialate capillaries). There's also a tendency for surface veins to be unusually prominent, especially in fair haired people.


Further it says:

Unfortunately, IR contamination is a "many to one" problem. You can't fix it with white balance: try to set WB to get rid of yellow IR grass, and green paint, green cosmetics, or a green dress suddenly turn blue. Try to WB out the magenta tint on the black dress, and black eyeliner turns green (and skin gets much less healthy looking).
« Last Edit: November 09, 2006, 10:51:27 PM by aaykay » Logged
opgr
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« Reply #27 on: November 10, 2006, 03:49:11 AM »
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Shouldn't this also adversely affect images around sunset? Maybe even the metering?
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Oscar Rysdyk
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Gary Ferguson
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« Reply #28 on: November 10, 2006, 08:05:24 AM »
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you will probably want to use the stronger lens-mounted IR cut filter (or your DSLR) in those situations.


Jack, I think you're getting to the heart of the issue with this comment, and you're one of the few (only?) M8 users that I've read with practical experience of the effect of IR/UV filtration with the M8. Sean Reid suggested filtration is the solution, the post that "aaykay" linked to also suggested it, but you've actualy done it while they haven't.

Can you tell us more about these IR/UV filters as I'm sure I'm not alone in never having encountered them before. What do you mean by different strengths? How much are they? Are they widely available in different sizes? Is there a filter factor? Do they have any other negatives? And finally, is there any way you could post shots showing the practical effects of filtration?

Thanks.
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Jack Flesher
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« Reply #29 on: November 10, 2006, 09:17:59 AM »
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Can you tell us more about these IR/UV filters as I'm sure I'm not alone in never having encountered them before. What do you mean by different strengths? How much are they? Are they widely available in different sizes? Is there a filter factor? Do they have any other negatives? And finally, is there any way you could post shots showing the practical effects of filtration?

Thanks.
[a href=\"index.php?act=findpost&pid=84466\"][{POST_SNAPBACK}][/a]

Hi Gary:

Without going into great detail and sound like I'm lecturing I will summarize and skip technical accuracy for more easily understood plain English  

There are two styles of IR cut filters, "hot-mirror" or "aperture grille" and "absorption".  The hot-mirror actually have a metal oxide deposited on them that has slits that allows visible light to pass through but prevents the larger IR rays from passing. (Kind of like the door to a microwave oven, only for blocking light and not high energy radio waves.) The metal oxide gives them a mirror finish on the outside, hence the name.  By varying the diameter of the slits in the oxide coating, any  exact cut-off point of IR band can be implemented.  Usually, this will be somewhere between 700 nanometers (blocks IR in tungsten light) and 770 nanometers (blocks the IR present in visible light).

The absorption units are colored a light cyan, but attenuate IR by altering thickness and density of color, not just density.  And the final thickness is critical in determining the exact cut point, so manufacturing is more difficult than the hot mirror -- thus these absorption/attenuation type filters are about 2x the cost of the mirror units.

The problem with the hot mirror is that the slits effectively get narrower as light begins to enter the filter from the side -- basic trig.  This in turn can cause a visible color shift as the slits narrow to the point where they start to cut visible light rays. (Now you know why certain medium format digital backs have issues with color shifts across the frame when using wideangle or shift lenses -- they have hot-mirror cut filters over the sensor instead of absorption type  )

This problem is exacerbated for Leica in the M8 since the lens sits so much closer to the sensor than a comparable DSLR.  Because of this, even normal lenses have too extreme an entry angle to use a hot mirror filter, so the absorption style must be used.  However, the thicker the absorption style, the more refraction you will have at the image corners, and refraction directly over the sensor will impart a form of CA that is not lens related and is not easy to correct in post...  So for Leica this was a design nightmare, basically having to walk the razor's edge and balance no CA and a bit of IR leaking over blocking all the IR and having CA in the corners of images.  

In the end, it appears Leica chose the 770nm cut point as it deals effectively with IR present in visible light.  However, I am of the opinion Leica will have to offer buyers this choice and offer to install the thicker 700nm cut filter as a sensor option -- photgrapher's, pick your poison...

To put price in perspective, a 3" x3" square absorption filter costs around $300.  Smaller circular sizes are not much cheaper as they need to be cut and there is wastage.  By contrast, circular hot mirror filters will be in the $100 range depending on size and manufacturer.

I'll try to post some example images later this morning.
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Gary Ferguson
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« Reply #30 on: November 10, 2006, 09:33:44 AM »
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Jack thanks for this, I've learnt something useful here. So these are the type of filters that would have to be fitted to the lens?
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opgr
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« Reply #31 on: November 10, 2006, 09:54:06 AM »
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interesting indeed. So how hard is it to make the chip's microlenses behave as a kind of (additional) (absorption type?) IR filter?
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Jack Flesher
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« Reply #32 on: November 10, 2006, 10:36:30 AM »
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Here is an example.  Both shots using M8 AWB and shot with a single Profoto D4 head.

First, the image straight out of the camera:


Note that everything in the image is black in visible light -- THe backdrop is the back (dirty) side on my velveteen background cloth. The camera body and plastic lenshood stays black, but the black flocking inside the hood turns purple as does the black anodized aluminum RRS L bracket and parts of the all-black camera strap.  

Here is the image shot with the Daylight absorption IR filter clipped on the lens:


It is not perfect -- there is some slight IR bleed visible in the hotter areas of the image (seen directly under the center of the strobes light cone and fading towards the outer edges), but IMO it is significantly improved over the one before it. I wish I had a Tungsten-cut IR absorption filter to test, as I am 99% certain it would eliminate the last remnants of IR bleed visible here, but I do not -- sorry.

Gary: Yes, this is a lens mounted filter.
« Last Edit: November 10, 2006, 10:42:21 AM by Jack Flesher » Logged

Jack Flesher
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« Reply #33 on: November 10, 2006, 10:40:42 AM »
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interesting indeed. So how hard is it to make the chip's microlenses behave as a kind of (additional) (absorption type?) IR filter?
[a href=\"index.php?act=findpost&pid=84488\"][{POST_SNAPBACK}][/a]

Opgr: This is the issue I mentioned above -- it is not a microlens fix, but rather the choice of IR-cut filter/protective glass mounted *over* the sensor itself.  This is a servicable part, though it requires dissassembly of the camera's sensor to replace it.
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Jack Flesher
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« Reply #34 on: November 10, 2006, 10:50:58 AM »
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PS: I fogot to address filter factors...

The hot mirror style have a stated "0" factor, but I am dubious of that claim -- I feel it is only "0" for visible light energy.  The absorption type documentation says it's variable depending on the light source.  Since IR bleed adds significant energy to the image, it can affect overall exposure -- and usually does. However, depending on your meters spectral sensitivity, your camera may not register it.

I have seen, depending on the light-source, anywhere from 0 to 1-1/2 stop change using the absorption filter.  By example, the filtered shot was 1-stop more than the non-filtered shot above it.

Cheers,
« Last Edit: November 10, 2006, 10:52:42 AM by Jack Flesher » Logged

Gary Ferguson
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« Reply #35 on: November 10, 2006, 10:59:53 AM »
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Jack, great answer.

You should post these shots more widely as I'm not aware of anyone else showing a practical, side-by-side demonstration of the efficay of lens filtration with an M8. After wading through all the normal internet bluff and bluster, posts like this remind me just how useful and informative forums can be.
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opgr
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« Reply #36 on: November 10, 2006, 11:15:34 AM »
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Opgr: This is the issue I mentioned above -- it is not a microlens fix, but rather the choice of IR-cut filter/protective glass mounted *over* the sensor itself.  This is a servicable part, though it requires dissassembly of the camera's sensor to replace it.
[a href=\"index.php?act=findpost&pid=84500\"][{POST_SNAPBACK}][/a]

Ah, yes, but I meant in an earlier design stage. As you mention, it apparently requires a careful balance between absorption and aberration. If somehow the microlenses on the chip itself could be designed to handle some of the absorption...
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« Reply #37 on: November 10, 2006, 11:16:39 AM »
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Jack, great answer.

I agree, and very comprehensive as well...
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Pete JF
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« Reply #38 on: November 10, 2006, 11:48:32 AM »
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Wow, that is quite a color cast in that image up there. Im kind of surprised that Leica would release a camera without dealing with that issue fully.

Is the need to blast these products out into the marketplace that strong? It's like a black hole, sucking products out of the hands of manufacturers before they can let the paint dry.
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Robert Roaldi
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« Reply #39 on: November 10, 2006, 12:03:57 PM »
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Is the need to blast these products out into the marketplace that strong? It's like a black hole, sucking products out of the hands of manufacturers before they can let the paint dry.

It seems to be a monster we've created alright. Just like the software we buy.

I used to work in software (and firmware) development and when we'd discover a new bug in a product that we swore was tested and bug-free, my favourite line was that it's a miracle our cars start every morning.

I hope they don't build airplanes and medical equipment this way.
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