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Improving the D7 (and D7i?)

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I for one like to the capability to easily do IR photos. Of course it would be great if the camera had a switchable filter like you say the Sony 707 has.

But it doesn't and I can live with it. A solution like a IR blocking filter or adjustments in software being investigated by Billl will probably solve the problem for those that shoot a lot in this situation. You're right in that this should be explained in the manual. They could also provide a software fix or even a filter in the box, but hell will probably freeze over first.

The camera is of course "filtered" for IR since 2/3 of the pixels receive only blue or green light. (like any digital camera). The camera sees IR as " a little more red" while we see "a black hole".

Thanks and good luck,

Pete
Jawed said:
Jawed49152 said:
would effectively preclude the use of the
camera for IR photography and there are those out there that think
that the mark of a good camera is the ability to do IR work
Click to expand...
I'll happily round up these idiots and kill them all to do away
with this irrelevance. The ability to perform IR photography, has
with the D7, gotten the baby's legs mashed in the waste disposal.
Your experimental evidence of the side-effects of the D7's IR
sensitivity is quite damning.

If people want to do IR photography that bad, they can buy the Sony
F707 which has an internal IR filter that can be moved out of the
way of the sensor.

Early pro digital cameras didn't have one, I know that, as I've
read some old reviews (on other websites) which talk about this
explicitly. Modern cameras have one built-in, I'm reasonably sure,
as their pictures don't seem to suffer these effects. It would be
nice if Phil could investigate this question as so far I've not
seen any comment from him on this subject in any review (anyone
know better?).

One thing's for sure, pix I've seen from the E10 and the F707 do
not exhibit this problem. Minolta has supposedly improved IR
filtering with the D7i, I certainly hope it solves the red clothes
problem.

Thanks for the Color Balance tip. Can't decide whether I like the
result with outdoor pictures - I'm inclined towards a moderate
amount (-5). Curiously the result looks more like what I consider
typical of other digicams.

Thanks for your help,
Jawed
Click to expand...
 
I am new and would appreciate if someone be kind enough to tell me what exactly is a Hot Mirror Filter. Can I just tell the shop that I want a "Hot Mirror Filter" or is there another name for it.
Thanks
Ruan
 
Actually you may be wrong. Depending on the type and qualilty of the blue and green filters they could transmit a significant amount of IR to the sensor. Indeed the only kind of filter that would not would be and interference filter and I would suspect that even the very high end digital cameras do not use them. making a Bayer matrix filter overlay for a CCD using interference technology would be very difficult indeed.

Bill Cook
PeteGanzel said:
The camera is of course "filtered" for IR since 2/3 of the pixels
receive only blue or green light. (like any digital camera). The
camera sees IR as " a little more red" while we see "a black
hole".

Thanks and good luck,

Pete
PeteGanzel said:
I'll happily round up these idiots and kill them all to do away
with this irrelevance. The ability to perform IR photography, has
with the D7, gotten the baby's legs mashed in the waste disposal.
Your experimental evidence of the side-effects of the D7's IR
sensitivity is quite damning.

If people want to do IR photography that bad, they can buy the Sony
F707 which has an internal IR filter that can be moved out of the
way of the sensor.

Early pro digital cameras didn't have one, I know that, as I've
read some old reviews (on other websites) which talk about this
explicitly. Modern cameras have one built-in, I'm reasonably sure,
as their pictures don't seem to suffer these effects. It would be
nice if Phil could investigate this question as so far I've not
seen any comment from him on this subject in any review (anyone
know better?).

One thing's for sure, pix I've seen from the E10 and the F707 do
not exhibit this problem. Minolta has supposedly improved IR
filtering with the D7i, I certainly hope it solves the red clothes
problem.

Thanks for the Color Balance tip. Can't decide whether I like the
result with outdoor pictures - I'm inclined towards a moderate
amount (-5). Curiously the result looks more like what I consider
typical of other digicams.

Thanks for your help,
Jawed
Click to expand...
Click to expand...
 
Your'e right Bill, as I recall from the spec sheet of the Sony ICX282 sensor, there are two nearly horizontal lines From the Blue and Green filter curves that look like they run across the 700nm visible barrier. The response on the other axis shows that this may be insignificant though. Practically speaking, IR sensitivity is through the red sensor, and even then response drops dramatically past 700nm. Just as an experiment, to see if an ordinary color filter could cut out IR, I tried a 80A filter and a Green filter with an infrared remote. The green filter was best, but you could still see a glimmer of IR in the EVF from the IR LED.

Thanks and good luck,

Pete
Bill Cook said:
Bill Cook
PeteGanzel said:
The camera is of course "filtered" for IR since 2/3 of the pixels
receive only blue or green light. (like any digital camera). The
camera sees IR as " a little more red" while we see "a black
hole".

Thanks and good luck,

Pete
Bill Cook said:
I'll happily round up these idiots and kill them all to do away
with this irrelevance. The ability to perform IR photography, has
with the D7, gotten the baby's legs mashed in the waste disposal.
Your experimental evidence of the side-effects of the D7's IR
sensitivity is quite damning.

If people want to do IR photography that bad, they can buy the Sony
F707 which has an internal IR filter that can be moved out of the
way of the sensor.

Early pro digital cameras didn't have one, I know that, as I've
read some old reviews (on other websites) which talk about this
explicitly. Modern cameras have one built-in, I'm reasonably sure,
as their pictures don't seem to suffer these effects. It would be
nice if Phil could investigate this question as so far I've not
seen any comment from him on this subject in any review (anyone
know better?).

One thing's for sure, pix I've seen from the E10 and the F707 do
not exhibit this problem. Minolta has supposedly improved IR
filtering with the D7i, I certainly hope it solves the red clothes
problem.

Thanks for the Color Balance tip. Can't decide whether I like the
result with outdoor pictures - I'm inclined towards a moderate
amount (-5). Curiously the result looks more like what I consider
typical of other digicams.

Thanks for your help,
Jawed
Click to expand...
Click to expand...
Click to expand...
 
This is a very interesting technical discussion, but on a more simplistic level, how do I get back to normal coloured pictures: I've just come back from a weeks holiday (taking about 400 pictures) to discover that my olive green sweater has come out vivid brown! At least now I know why, but short of remembering what colour everything was how do I accurately reproduce the correct colour images? The filter?? Now that I know about man made fibres is there anything else I should look out for?

Well done Bill, you've answered a significant conundrum for me!

Rob

http://homepage.ntlworld.com/rob.barker/

you can see the brown version of the sweater at

http://homepage.ntlworld.com/rob.barker/Canals/trip%20reports/2002/trip_report_2002_stourport_ring1.htm
Bill Cook said:
The D7 either has no hot mirror filter (to eliminate IR responce)
or a very poor one. This lack can cause some real difficulties. One
is illustrated with the pair of pictures below





The picture was taken at a high school play that my granddaughter
was in. The top picture was processed through DIVU converting it to
sRGB and size reduced and saved for the web in Photoshop 7.0

The one below is the same picture with a minus 20 cyan --- red
correction in both the shadow and the mid tones (eg shifted toward
the cyan). This is the maximum amount of correction that could be
applied without clipping. The young ladies dress was black. The
reason it appears brown in the top picture is because many
synthetic fibers (like leaves) have a very high IR reflection.

Having observed this I obtained a 67mm hot mirror from Amazon (they
have a clearance at $40 each - three left) and a 49mm to 67mm step
up ring. I now have the hot mirror on my camera. Though I have not
had another chance to take pictures in the theater (I only got the
filter on Monday) I have notice two other very interesting effects.
1) The camera focuses in sub 1 second time consistently even with
the lens in the 200mm focal length equivalent regular or macro. 2)
The images seem to have sharper edge (and perhaps over all sharper)
appearance.

This would make sense because most lenses do not bring visible
light into focus at the same point as IR. Indeed they can be rather
far apart. That being the case since the D7 uses contrast focusing
on the CCD the image probably seems a bit fuzzy (or seeing double).
Of course since the IR is making a significant contribution to the
exposure and it is not quite in focus with the visiible light it
makes the image look a bit less sharp.

In any event you might want to try it.

Bill Cook
Click to expand...
 
Actually the effect on synthetic fibers will be much more pronounced under theater lighting conditions than under bright sunlight. The reason being that although the over all color temperature of the spotlights, etc (before the addition of color gels in thel light train) is very nearly the same as ordinary tungsten lights ( 3200 K) it is very rich in IR, much more so than ordinary lights. You can experience that by simply standing in a spotlight beam, it is a very "warm" experience - hey, I sweat.

The author of the article was looking for color contamination in outdoor scenes (the usual meat for IR fanatics). I would agree that the amount of color contamination would be low except for a shift in luminesence in most cases.

Bill Cook
go2wen said:
http://www.cliffshade.com/dpfwiw/ir.htm
This author stated that he couldn't see any difference when he used
a hot mirror filter. Actually I haven't seen any problem for the
IR so far for my D7. Usually user will see "brown" black most
likely under bright sunlight.
Click to expand...
 
ruan said:
I am new and would appreciate if someone be kind enough to tell me
what exactly is a Hot Mirror Filter. Can I just tell the shop that
I want a "Hot Mirror Filter" or is there another name for it.
Thanks
Ruan
Click to expand...
I am experienced and am also at a loss to know what a ' hot mirror filter is'.I feel a sort of stupid that I don't but would someone please enlighten me and tell me where I can get one
Fred
 
I think that people should wait until Bill posts some shots that show the benefits of the filter. A few people seem to be under the impression that the shots that Bill posted show the effects of the filter; they do not, they are Bill's photoshop fix of the color.

A few things to consider...
  • Several people including myself have tested this filter and could not see any benefit. However, I didn't test under theater lights, which could be loaded with IR for all I know. That is why it would be smart to wait for Bill to test the filter.
  • The filter cuts the (visible) light getting to the camera by about a factor of 2. You have to weigh that against any benefits.
  • The camera DOES have an IR blocking filter already. Generally these reduce the IR light by a factor of over 1000. It is possible to make a more efficient filter, but it has several drawbacks 1) More expensive 2) would cut visible light too making the camera slower. 3) there ARE people that like to take some IR shots. They try to pick a blocking level that still makes IR shots possible as long as you don't mind using a tripod (exposures on the order of a second in bright Sunlight)
Again, people might want to wait for Bill's test shots before rushing out to buy one of these filters, IMHO. Bryan
 
PeteGanzel said:
Your'e right Bill, as I recall from the spec sheet of the Sony
ICX282 sensor, there are two nearly horizontal lines From the Blue
and Green filter curves that look like they run across the 700nm
visible barrier. The response on the other axis shows that this
may be insignificant though. Practically speaking, IR sensitivity
is through the red sensor, and even then response drops
dramatically past 700nm. Just as an experiment, to see if an
ordinary color filter could cut out IR, I tried a 80A filter and a
Green filter with an infrared remote. The green filter was best,
but you could still see a glimmer of IR in the EVF from the IR LED.

Thanks and good luck,

Pete
Click to expand...
Hmmm. So if the IR sensitivity involves the Red sensor, how come IR looks White-Blue with the camera? The curves probably show the spectral sensitivty of the CCD and color filter overlay, and does not take the IR blocking filter or the lens system into account. The fact that IR looks mostly White indicates that all sensors are involved in detecting it.
Bryan
 
Erm, "white-blue"?!!!!

Please show a photograph with this effect! Curious...

Jawed
Bryan Biggers said:
PeteGanzel said:
Your'e right Bill, as I recall from the spec sheet of the Sony
ICX282 sensor, there are two nearly horizontal lines From the Blue
and Green filter curves that look like they run across the 700nm
visible barrier. The response on the other axis shows that this
may be insignificant though. Practically speaking, IR sensitivity
is through the red sensor, and even then response drops
dramatically past 700nm. Just as an experiment, to see if an
ordinary color filter could cut out IR, I tried a 80A filter and a
Green filter with an infrared remote. The green filter was best,
but you could still see a glimmer of IR in the EVF from the IR LED.

Thanks and good luck,

Pete
Click to expand...
Hmmm. So if the IR sensitivity involves the Red sensor, how come IR
looks White-Blue with the camera? The curves probably show the
spectral sensitivty of the CCD and color filter overlay, and does
not take the IR blocking filter or the lens system into account.
The fact that IR looks mostly White indicates that all sensors are
involved in detecting it.
Bryan
Click to expand...
 
Yes Bryan, the IR LED I'm looking at is very bright and white and has a peak spectral of about 850nm and if I extend the curve to this point (it cuts off at visible) the response is down to maybe less than 5 percent of the output of the sensor. You are probably right in that the sensitivity is across all three filters and is below what the "cutoff" that was intended by the CCD designers. The brightness of the LED makes no sense though since it appears nearly as bright as a similarily powered visible red LED for which the CCD is optimized (not very scientific).

Thanks and good luck,

Pete
Bryan Biggers said:
Hmmm. So if the IR sensitivity involves the Red sensor, how come IR
looks White-Blue with the camera? The curves probably show the
spectral sensitivty of the CCD and color filter overlay, and does
not take the IR blocking filter or the lens system into account.
The fact that IR looks mostly White indicates that all sensors are
involved in detecting it.
Bryan
Click to expand...
 
The woman next to you has trousers that have also been affected. And the two tops both have a partial-magenta look that seems to be caused by the red from IR mixing with blue in the fabric.

I find it puzzling that so many people haven't noticed this problem. Anyone with multiple digicams should try a comparison. Of course you'll need to find problem clothes first...

Jawed
Rob Barker said:
This is a very interesting technical discussion, but on a more
simplistic level, how do I get back to normal coloured pictures:
I've just come back from a weeks holiday (taking about 400
pictures) to discover that my olive green sweater has come out
vivid brown! At least now I know why, but short of remembering
what colour everything was how do I accurately reproduce the
correct colour images? The filter?? Now that I know about man made
fibres is there anything else I should look out for?

Well done Bill, you've answered a significant conundrum for me!

Rob

http://homepage.ntlworld.com/rob.barker/

you can see the brown version of the sweater at

http://homepage.ntlworld.com/rob.barker/Canals/trip%20reports/2002/trip_report_2002_stourport_ring1.htm
Click to expand...
 
Jawed said:
Erm, "white-blue"?!!!!

Please show a photograph with this effect! Curious...

Jawed
Click to expand...
Don't believe me, eh?
OK, here you go. Sorry, just a quick snap, 1/2 second handheld. -Bryan

 
Bryan,

I agree that people who are just not born experimenters (like you and I) should not rush out and buy a hot mirror filter. They are just too darn expensive.

On the other hand you are wrong about the filter factor. A true hot mirror filter does not reduce the visible light transmission or if it does it is minimal. A hot mirror reflects 95% of energy with wavelengths longer than its intended cut off (typically about 700nm) and transmits 98%+ of all energy below its cut off down to the UV blocking effect (if any) inherent in the glass it is built on. I just went out on my back porch and metered my favorite clump of trees on an extremely cloudy day (clouds absorb a huge amount of IR) with and without the filter. At ISO 200 I got an exposure reading of 1/125 at f4.0 under both conditions. On an extremely sunny day I get readings of 1/750 at f8.0 without and 1/500 at f8.0 with or about a 0.3 ev change. This would equate to a filter factor of 1.2. Under these conditions I atribute the small change not to absorbsion of visible light but to the CCD (which is being used as the measuring element in the D7) falsely adding the IR illumination to the integrated whole. Indeed under sunny conditions I tend to use a -0.6 ev correction with the filter and a -0.3 ev correction without in my exposure with the D7.

Hot mirror filters are not your simple band pass transmission IR blocking filters.

Bill Cook
Bryan Biggers said:
I think that people should wait until Bill posts some shots that
show the benefits of the filter. A few people seem to be under the
impression that the shots that Bill posted show the effects of the
filter; they do not, they are Bill's photoshop fix of the color.

A few things to consider...
  • Several people including myself have tested this filter and could
not see any benefit. However, I didn't test under theater lights,
which could be loaded with IR for all I know. That is why it would
be smart to wait for Bill to test the filter.
  • The filter cuts the (visible) light getting to the camera by
about a factor of 2. You have to weigh that against any benefits.
  • The camera DOES have an IR blocking filter already. Generally
these reduce the IR light by a factor of over 1000. It is possible
to make a more efficient filter, but it has several drawbacks 1)
More expensive 2) would cut visible light too making the camera
slower. 3) there ARE people that like to take some IR shots. They
try to pick a blocking level that still makes IR shots possible as
long as you don't mind using a tripod (exposures on the order of a
second in bright Sunlight)

Again, people might want to wait for Bill's test shots before
rushing out to buy one of these filters, IMHO. Bryan
Click to expand...
 
Ah, Bryan, I didn't say I didn't believe you I said I was curious.

I think you meant to take a picture like this:



The white part in the centre is overexposure. The rest is magenta. Now, why it should be magenta I don't know, exactly. It might be due to the colour of the plastic surrounding the electrical bit putting out the light.

So, where's the white-blue in your picture?

Jawed
Bryan Biggers said:
Jawed said:
Erm, "white-blue"?!!!!

Please show a photograph with this effect! Curious...

Jawed
Click to expand...
Don't believe me, eh?
OK, here you go. Sorry, just a quick snap, 1/2 second handheld. -Bryan

Click to expand...
 
Are you just trying to give me a hard time or something? Gee, if you can take your own shot, why did you need me to take one? You may call the color anything that you like. My point is that it isn't all Red and it is mostly White which means that more than the Red sensors are responding. What white balance did you use? I just used auto. In the case of a shot like Bill's you should probably use incandescent or custom to match the light which is pretty low temperature if you want to see what IR looks like in a shot like that.

Bryan
Jawed said:
I think you meant to take a picture like this:



The white part in the centre is overexposure. The rest is magenta.
Now, why it should be magenta I don't know, exactly. It might be
due to the colour of the plastic surrounding the electrical bit
putting out the light.

So, where's the white-blue in your picture?

Jawed
Bryan Biggers said:
Jawed said:
Erm, "white-blue"?!!!!

Please show a photograph with this effect! Curious...

Jawed
Click to expand...
Don't believe me, eh?
OK, here you go. Sorry, just a quick snap, 1/2 second handheld. -Bryan

Click to expand...
Click to expand...
 
Hi Bill,
Bill Cook said:
Bryan,
I agree that people who are just not born experimenters (like you
and I) should not rush out and buy a hot mirror filter. They are
just too darn expensive.
Click to expand...
Well, the problem is that people seem to be thinking that you have identified a problem and fixed it with this filter, but if I understand you you have not taken any "proof" shots yet.
Bill Cook said:
On the other hand you are wrong about the filter factor. A true hot
mirror filter does not reduce the visible light transmission or if
it does it is minimal. A hot mirror reflects 95% of energy with
wavelengths longer than its intended cut off (typically about
700nm) and transmits 98%+ of all energy below its cut off down to
the UV blocking effect (if any) inherent in the glass it is built
on. I just went out on my back porch and metered my favorite clump
of trees on an extremely cloudy day (clouds absorb a huge amount of
IR) with and without the filter. At ISO 200 I got an exposure
reading of 1/125 at f4.0 under both conditions. On an extremely
Click to expand...
The Tiffen filter I had had some visible light loss on all exposures.
Bill Cook said:
sunny day I get readings of 1/750 at f8.0 without and 1/500 at f8.0
with or about a 0.3 ev change. This would equate to a filter factor
Click to expand...
Well, if you are saying that 50% of the light in a daylight exposure with the camera is IR, I don't agree. The filter is blocking some visible light too. If it were 50% of the light (750/500) then you could take IR shots at 1/250 second at ISO 100 with the camera and an IR pass filter, and no filter I've tried allows that; the exposure time in bright Sunon the D7 is usually about 1/4 to 1 second at ISO 100. I think that most of the exposure reduction you see is due to blocking visible light, not IR. Assuming that your readings are accurate of the exact same scene, then we are talking about EV=15.55 to EV=14.96, or 0.5 EV penalty for using the filter, (unless that is all IR being blocked); that would be quite close to your 0.6 EV correction.
Bill Cook said:
of 1.2. Under these conditions I atribute the small change not to
absorbsion of visible light but to the CCD (which is being used as
the measuring element in the D7) falsely adding the IR illumination
to the integrated whole. Indeed under sunny conditions I tend to
use a -0.6 ev correction with the filter and a -0.3 ev correction
without in my exposure with the D7.

Hot mirror filters are not your simple band pass transmission IR
blocking filters.
Click to expand...
I understand. They are usually dichroic filters which is why they are so expensive.

Bryan
 
Before you conclude anything, make the following test: take a picture like your sample (maybe the girl gives you dress for this) and try to reproduce the color shift. Than include a white sheet of paper and make manual white balance and shoot again.

If the dress is still not black, then we have maybe an IR problem. If not, it's simply wrong WB.
tc

--
http://mitglied.lycos.de/crowning/
 
What about the lighning of the stage ?

Normally stage lights have red and green reflectors to give better contrasts in the face and to avoid pale washed out faces for the spectators.

I remember once sitting at a boring concert looking to the black of the deep black suits which were not at all black if you paid close attention.

The camera seems to exaggerate always the really existing color differences which are adjusted within your brains, not with your eyes.
However: It becomes very interesting...
Hans.
 
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