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Author Topic: Camera's histogram reliable to the RAW data  (Read 260039 times)
Panopeeper
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« Reply #20 on: January 10, 2008, 04:57:15 PM »
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- The big question: what about sRGB/AdobeRGB? since sRGB expands more the histogram, do you think it could be a good idea to set AdobeRGB? or we could even fall into being too optimistic with the neutral WB?

I think we will have to thest the effect.

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I would really like to know which is the camera's criteria to blink. I think it is partial saturation (any channel saturated) but I am not sure if there are more hidden rules

I compared the blinking on the camera with raw clipping shown in Rawnalyze and found, that they were virtually equal (expectable due to the close to 1.0000 factors), and that has shown, that green clipping alone was enough.

It would be easy to test by extracting the embedded JPEG from the "blinking" raw file and verifying the relevant areas in PS or whatever. I could make a test for that, but I believe this is a clear-cut issue, I rather keep writing the manual.

Regarding the authority, I really don't care. I had this idea Sunday night by myself, I had fun putting it into practice, and if someone already had it before is fine.

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I recall this question above: One question: by opening it [your RAW winechart] I see it displays not only the chart but also a screenshot of PS. Does this mean the camera only takes into account a centred portion of the RAW to calculate the custom WB? I didn't know that. Do you know exactly what size (%) of the total image surface?

This was not a question but I posted you what to watch for (closeness, etc.). The circle in the viewfinder has to be filled (the camera manual states this).
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Gabor
Guillermo Luijk
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« Reply #21 on: January 10, 2008, 06:33:11 PM »
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hehe, David Coffin has given me a crazy but very logical idea for studio shooting: to print the magenta tone on transparency slides. They could be used then as filters on D65 neutral lamps o flashes, so the RAW would be (theoretically) balanced without the need to scale the channels at all.

Also the higher exposure of the B and R channels would mean better SNR for a given exposure of the G channel on the RAW file.

"Instead of your magenta chart, you need to make lamps ofthat color. Maybe you could print the color on a transparencyand mount it over a D65 lamp. Never again would you need tostretch and clip color channels to achieve white balanace, atleast when working in a studio.", David Coffin said.

Unfortunately I don't think such a solution could not introduce any colour dominant (the print has to be perfect, on a calibrated printer).
For B&W should be a good solution to get less noise and tonal richness.
« Last Edit: January 10, 2008, 06:55:40 PM by GLuijk » Logged

Panopeeper
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« Reply #22 on: January 10, 2008, 07:21:39 PM »
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Guillermo,

1. This is nothing new about using color filter with digital cameras.

For two months ago I ordered a magenta filter from B+W, in order to increase the dynamic range in daylight. After several weeks waiting it turned out, that B+W (Schneider) discontinued that filter (and Tiffan does not make any larger than 77mm).

2. The whole idea is nonsense. The filter changes the composition of the light and thereby the resulting *raw* histogram. The goal of this WB trick is not to change the light, nor to change the raw histogram, but to make the camera software use 1.0 as WB coefficient. Note this:

whatever values the sensels produce, they will be white balanced

Changing the composition of light might create "parallel" raw values (depending on the scenery and on the light source), but that does not help, if the camera white balances that away. We don't need "nicer" histograms, we need "like" histograms in raw and in the in-camera JPEG.

So, stick to your idea.
« Last Edit: January 10, 2008, 07:22:20 PM by Panopeeper » Logged

Gabor
John Sheehy
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« Reply #23 on: January 11, 2008, 12:35:14 AM »
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hehe, David Coffin has given me a crazy but very logical idea for studio shooting: to print the magenta tone on transparency slides. They could be used then as filters on D65 neutral lamps o flashes, so the RAW would be (theoretically) balanced without the need to scale the channels at all.

"Flomo" transparent magenta book report binders that I bought in a "99 cent" store here, in double thickness, balance my 550EX almost perfectly, with two sheets.

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Also the higher exposure of the B and R channels would mean better SNR for a given exposure of the G channel on the RAW file.

That's full color SNR, of course.  No more "highlight recovery" per se.  The shadow noise, however, will lack the chromatic cast that it has with most light sources, even when the blackpoint is correctly determined by the converter.

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"Instead of your magenta chart, you need to make lamps ofthat color. Maybe you could print the color on a transparencyand mount it over a D65 lamp. Never again would you need tostretch and clip color channels to achieve white balanace, atleast when working in a studio.", David Coffin said.

His choice of the word "instead" was probably not ideal.  "In addition to" would probably be a better choice, as the more accurate histogram could be beneficial regardless of lighting color.  Together, however, you get a more (but still not perfectly) RAW-accurate histogram with a review image that is close to real color, *and* maximum full-color DR.

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Unfortunately I don't think such a solution could not introduce any colour dominant (the print has to be perfect, on a calibrated printer).
For B&W should be a good solution to get less noise and tonal richness.
[a href=\"index.php?act=findpost&pid=166406\"][{POST_SNAPBACK}][/a]

What is a "color dominant"?

Magenta lighting/filtering works very nicely, but as I said, there is no recovery of highlights in the red and blue channel (unless the highlights are saturated and on the green side of the spectrum).
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Jonathan Wienke
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« Reply #24 on: January 11, 2008, 04:58:00 AM »
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"Instead of your magenta chart, you need to make lamps ofthat color. Maybe you could print the color on a transparencyand mount it over a D65 lamp. Never again would you need tostretch and clip color channels to achieve white balanace, atleast when working in a studio.", David Coffin said.

Unfortunately I don't think such a solution could not introduce any colour dominant (the print has to be perfect, on a calibrated printer).
For B&W should be a good solution to get less noise and tonal richness.
[a href=\"index.php?act=findpost&pid=166406\"][{POST_SNAPBACK}][/a]

This approach has been done already by putting a magenta filter on the camera so that the levels of the RAW channels are approximately equal. This does not introduce any color casts in the final images, but does require different WB settings during RAW conversion than what one would normally encounter.
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Guillermo Luijk
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« Reply #25 on: January 11, 2008, 05:41:20 AM »
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What you John and Jon are telling me encourages me to experiment. I have asked a friend who has a photo studio with a RGB projection system to project the test chart (not the magenta winechart) over it and shoot it with the camera.
Analysing the RAW produced I will provide him with the corresponding magenta chart so he can use it to light the scene in a photo session. If the whole light system (PC+projector) gets correctly calibrated by doing this for the camera used, any picture taken with the camera under those lighting conditions would be already balanced in the RAW file.
Paradoxically, under these circumstances, if he sets a custom UniWB in the camera (need to generate the proper file for it), the images would be balanced on the camera display, eliminating both any magenta or green casts.

The important thing however would be to look at the RAW files produced to check if they are properly balanced. This would be close to the ideal situation of a balanced sensor: balanced in-camera RAWs and balanced camera display as well. Now just the scene is unbalanced  

Panopeeper, don't you think we can try to take this further? if there already exist magenta standard filters that work well in improving RGB balance, why this custom magenta light shouldn't be optimum? the combinations seem to be endless.

I will post the findings...
« Last Edit: January 11, 2008, 05:49:04 AM by GLuijk » Logged

John Sheehy
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« Reply #26 on: January 11, 2008, 08:04:03 AM »
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This approach has been done already by putting a magenta filter on the camera so that the levels of the RAW channels are approximately equal. This does not introduce any color casts in the final images, but does require different WB settings during RAW conversion than what one would normally encounter.
[a href=\"index.php?act=findpost&pid=166473\"][{POST_SNAPBACK}][/a]

When I first experimented with a magenta filter a few years ago, ACR was not able to white-balance the camera's native RAW color balance!  The "tint" slider could not go far enough to the left.  A later version of ACR increased the tint range.
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Panopeeper
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« Reply #27 on: January 11, 2008, 10:24:36 AM »
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Guillermo,

something is wrong. Please separate the two issues:

1. Increasing the DR by filtering the light: this can be achieved by filtering the light source, by creating light with different composition, or by filtering the light at the camera; no matter, which way you go.

The effect of filtering depends on the light source, and of course on the targets. I do not think that the same filtering, which is useful in daylight, would be useful in studio.

In any case, this filtering has nothing to do with the topic, namely raw-like histogram displayed in the camera.

2. The question, how to make the in-camera histogram like the raw histogram is totally independent of the light composition at the time of shooting, except when using auto WB.

There is only one parameter here (well, there are two of them): the WB factors applied by the camera (let's neglect the other settings, like saturation). In order to coax the camera into applying (1.0, 1.0), you have to provide a sample shot, which represents the inverse proportions of the raw colors from a white sample shot under certain lighting conditions. This is, what you achieved with shooting the "winechart". Shooting a white sheet under light with the color of the purplish chart would yield the same, of course.

After having established custom WB based on this shot, the WB factors are fixed.

From now on the lighting of the scenery plays no role in this issue. You can use whatever filter you want to, it will influence how the histogram looks - depending on the scenery - but it won't change the matching of the raw histogram with the in-camera histogram.

The same, from a different viewpoint: with choosing the lighting, you can achieve, that the three channels are "parallel" (of a given scenery), but it has nothing to do with how that shot is displayed in-camera.
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Gabor
Guillermo Luijk
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« Reply #28 on: January 11, 2008, 10:49:48 AM »
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In any case, this filtering has nothing to do with the topic, namely raw-like histogram displayed in the camera.

Of course Panopeeper, this is a completely different goal, but based in the same idea of playing with different levels in the three channels.
In this case what I propose is to model the lighting conditions to obtain directly an already balanced RAW file, i.e. in this case the RAW data is gonna be changed so later WB becomes unnecessary, and having other advantages (if it works of course). And of course this would be only of application when you have control over the entire scene's lighting (studio).

It's a different point, the UniWB question for displaying a more reliable histogram is finished now. Maybe I should have opened a new topic for this.
« Last Edit: January 11, 2008, 10:52:02 AM by GLuijk » Logged

Panopeeper
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« Reply #29 on: January 11, 2008, 11:16:35 AM »
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In this case what I propose is to model the lighting conditions to obtain directly an already balanced RAW file, i.e. in this case the RAW data is gonna be changed so later WB becomes unnecessary, and having other advantages (if it works of course

I don't see the "other advantages", not even "this" one. A WB balanced raw file offers no advantage over a not WB-balanced one. Methink you are mixing up a white balanced raw file with one, the channels of which are clipping at the same time (I called this "parallel channels").

The only advantage I see is avoiding one channel clipping much before the other channels, because that restricts the DR of the other channels. However, this depends on the actual scenery as well, not only on the lighting conditions.

Shoot a foresty scenery with clouded sky, the chance is high, that the green will be clipped. With bright, clear sky the blue may be ahead, and shoot colorful flowers under the very same lighting condition and the red may clip first.
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Gabor
Guillermo Luijk
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« Reply #30 on: January 11, 2008, 11:33:30 AM »
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I understand your point and I agree.

But it's usual that the R and B channels need overexposure in relation to the G channel to perform the WB, so this approach would overpexpose them in relation to the G channel and we could do a more precise ETTR for the 3 channels at the same time.
Of course how often this would be true will depend on the colours present in the scene: a deeply red object for instance could easily reach higher values in the R histogram than in the the G histogram, so in that case we would be losing DR in the G.

It's an approach to get:
1. White balanced RAW files straight from the camera.
2. USUALLY (i.e. for most scenes in average), better SNR (and hence DR) and more tonal richness.

Just an experiment, don't take it as a proposal for everyday shooting at all.

PS: I like the term "parallel channels".
« Last Edit: January 11, 2008, 11:36:58 AM by GLuijk » Logged

Jonathan Wienke
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« Reply #31 on: January 11, 2008, 11:47:16 AM »
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I can't vouch for other RAW converters, but ACR handles UniWB settings pretty well. Here's my results with the 1Ds:



Left side is RawAnalyze linear histogram, right is ACR adjustments after click-WB. The WB adjustments are pretty extreme, but still within usable range.
« Last Edit: January 11, 2008, 11:48:58 AM by Jonathan Wienke » Logged

Panopeeper
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« Reply #32 on: January 11, 2008, 12:17:07 PM »
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It's an approach to get:
1. White balanced RAW files straight from the camera

Why? There is no advantage of that.

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2. USUALLY (i.e. for most scenes in average), better SNR (and hence DR) and more tonal richness

This is, what could be achieved using filters on the camera.

The problem I see is, that the fiters required to achieve this have been used only on film cameras and are not the same quality as the newer ones for digital cameras. I would put only a multicoated UV filter (if at all, for lens protection) or polar filter, from the best brand. I don't use a low quality magenta filter in order to increase the DR, if that reduces the image quality, except perhaps in special circumstances.
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Gabor
Guillermo Luijk
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« Reply #33 on: January 11, 2008, 01:23:44 PM »
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Why? There is no advantage of that.
This is, what could be achieved using filters on the camera.

You could be right in the end. It's all about the pleasure of getting the visual confirmation that I have understood how a camera works and I can control it, not the camera controls me. I am not a photographer and in the last months I have not even shot too much, mainly because I felt quite anxious for not knowing exactly what was going on inside the camera. I think I have reached a higher degree of understanding lately and this forum has helped specially.
Looking at your software to analise RAW files I think you share this point of view.

BTW you have a 40D. I am planning to change my 350D for a 5D instead once its substitute is in the market. Could you suggest me some advantages to choose 40D instead of 5D?
I think I prefer the 5D for being FF (bokeh and wide angle) and for NOT having all those new features such as sensor cleaning, HTP, live view,... that I reallly don't appreciate too much and don't want to pay for.

I don't like the idea to put colour filters either. I would only like them on a B&W camera lacking colour filters in the sensor, to obtain different B&W in an optical way.

Regards
« Last Edit: January 11, 2008, 01:30:31 PM by GLuijk » Logged

Panopeeper
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« Reply #34 on: January 11, 2008, 01:56:55 PM »
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Jonathan,

I see you downloaded the newer version with black background in the histograms. I changed it from grey to increase the contrast for better visibility of thin columns, which occur typically with clipping caused by specular points.

Then I found that the white point bar hides the highest column. Even worse is the saturation colum, for that can not be moved, like the white point, and these two together made a column totally disappearing.

So, yesterday I changed the appearance of these bars. Plus, I changed the scaling of the histogram. It is still logarithmic, now going from 0.01% at the bottom to 100%. (This is the percentage  of pixels of that color within 1/512th of the sensor's range, related to all pixels of that color).

However, the very bottom row is not on the logarithmic  scale; it represents anything from 1 pixel to 0.01%, i.e. even a single pixel in that range appears as a dot in the bottommost line. Disadvantage: hot pixels.

Anyway, if you intend to use the program, you should download the newest version, I just uploaded it (there was an error in the histogram of the mapped data, that is gone now).

The markers at the side of the histograms mark *now* from the bottom upwards 0.02%, 0.05%, 0.1%, 0.2%, 0.5%, 1%, 2%, 5%, 10%, 20% and 50%.

This should be shown in the window, but I did not find any good way to show them yet. Suggestions are welcome.
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Gabor
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« Reply #35 on: January 11, 2008, 07:13:48 PM »
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BTW you have a 40D. I am planning to change my 350D for a 5D instead once its substitute is in the market. Could you suggest me some advantages to choose 40D instead of 5D?

Well, let's turn the question around: why would you purchase a two and half years old model for probably more, than the top of the technology? Note, that the much more expensive models, even the 1DsMkII don't have better technology than the 40D.

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I think I prefer the 5D for being FF (bokeh and wide angle)

I don't understand the bokeh issue. It depends on the lens alone, on nothing else.

Btw, if you want to see comparisons of bokeh between seven lenses, take a look at http://www.panopeeper.com/Bokeh

The availability of more wider lenses is indisputable, just like the other side of the coin: that you don't need super expensive lenses to reach far.

Plus, the EF-S line contains the 10-22, which is said to be quite good and very wide, and the super-duper 17-55 IS, which is really super; I can confirm, that it stands up well against the EF 16-35 f/2.8 L Mk II, which is the best one for FF, and even against the 50mm f/1.4. For a few weeks ago I purchased the 16-35 and the 17-55 at the same time (telling the dealer ahead, that I will send back one of them), and I tested these against each other and against three other of my lenses (and I kept the 17-55).

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and for NOT having all those new features such as sensor cleaning, HTP, live view,... that I reallly don't appreciate too much and don't want to pay for

Think once more about it:

- the sensor cleaning is a great feature

- HTP is only for JPEG shooters

- live view is great. I don't give a fig for live view, but now I can do something, what others can't: shoot with auto exposure bracketing without flapping the mirror in between; this is a side effect of live view.

Now, some positives to the cropping cameras, apart the focal length question:

- much lighter

- the selection of very good lenses is much larger, than for FF. This is not only due to the EF-S lenses, but to the cropping. Several lenses, which are mediocre on FF because of the weak edge performance, are stellar on cropping camera. For example the old "magic drainpipe", the legendary 80-200mm f/2.8L has been replaced by the 70-200mm because of the edge performance (take a look at the MTF). This lens has a renaissance on cropping cameras (I too have an excellent copy, though I plan to sell it, due to its weight). Another example: the 50mm f/1.4 is sharp at the edges at much larger apertures than on FF

- much cheaper (and calculate the lenses!)

There is a constant disadvantage: flaring, due to the unsuitable lensd hoods. One more reason to go with the 17=55mm: the hood is designed for the cropped view.

If there was a small brother of the 1DMkIII (lighter and cheaper), I would have gone for that, i.e. 1.3x cropping. But there is none.

A final remark: the dynamic range and lesser noise of the 5D is a myth, compared to the 40D. There was a thread about this question. The 5D outputs about 3570 levels; in the nineth stop there are only seven levels.
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Gabor
Guillermo Luijk
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« Reply #36 on: January 11, 2008, 07:43:30 PM »
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I think I understand (or already knew) all points but the live view (flapping mirror...). What do you mean with this, could you explain a bit more?

Regarding my priorities, with bokeh I meant capability of defocusing the background. My 70-200 f4L hardly diferentiates subject from background in APS-C while in FF it will be much nicer to use for portraits for instance. My 24-70 f2.8, which already produces a great bokeh in APS-C, is superb to get narrow DOF in FF.

The cleaning system, it's a matter of concept. I know this is argueably, but I prefer to open my camera and blow the sensor from time to time than having something that 'moves' my sensor.

Regarding wide angle, in the next months I am probably going deep into architecture photographing (who knows if even will purchase some tilt shift lens someday) and I want to be able to have a wider selection of wide angle lenses.

I am not likely to be interested in tele zooms. I went on a trip to Namibia with a 300mm f4L, and it was a nice experience to shoot the animals, but I don't think this is the kind of photography I will enjoy best. In fact my favourite pictures there were paradoxically among the few shots I did in wide angle (Dead Vlei, Giraffe).

I have the Canon 10-22 and I am quite happy with it, but not so much to launch fireworks (Spanish expression). With the 50mm f1.4 I am not happy at all. At short distances (portraits,...) is perfect, but at long distances its sharpness decreases too quickly.

I know the 5D is a bit old now, but this does not mean it's old fashioned. It was a camera advanced to its time so it has a still great sensor today. I haven't been able to check DR, but I am sure that 40D's DR is a bit better than 5D's, I assume that. But I am developing a good technique to blend a second overexposed shot, so this is even funny for me. And anyway the 9 f-stops of DR in the 40D is not enough for indoor shooting in HDR scenes for instance.
For a really high DR I love the Super CCD concept.

The price, if I wait the substitute of the 5D comes, will surely get almost the same as the 40D's. You know how people are: as soon as there is a new camera, old models automatically become old fashioned. I like the 5D.
And I am probably travelling to the States soon, and photographic stuff there is by far cheaper than in Europe. The 5D started here at 3000 EUR ($4400), and now it is 2000 EUR ($2940). I expect it to reach close to 1500 EUR.

Thank you very much!

PS: from your bokeh samples I went into the panos. Nice stuff there. Why did you darken so much the skies in the B&W landscapes?
« Last Edit: January 12, 2008, 06:38:09 AM by GLuijk » Logged

Panopeeper
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« Reply #37 on: January 11, 2008, 10:11:46 PM »
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I think I understand (or already knew) all points but the live view (flapping mirror...). What do you mean with this, could you explain a bit more?

If you turn on live view, you have to press the button in the middle of the big wheel to activate/deactivate it. When MLU too is turned on, the mirror flips up when activating live view. If you are using a remote control (there are very cheap wired ones from third parties), and you set up exposure bracketing, with a single press you start shooting all three shots of the bracket. Neither mirror flapping, nor button pressing occurs between the shots, which will be made in a fraction of a second.

Jonathan made a remark, that it is still not totally vobration free due to the shutter movement. This is correct, I have not verified yet the effect, I ope it won't be much. Anyway, I guess this will give the ideal basis for HDR, which may be my next project.

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with bokeh I meant capability of defocusing the background

Thankx, but I do now the meaning. Once more: the quality of bokeh has to do *only* with the lens. FF or cropping plays a role only as far as the selection of focal length (and thereby of the lens) depends on cropping.

Every lens, which gives a good bokeh on FF, gives a good one on a cropping camera as well.

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My 70-200 f4L hardly diferentiates subject from background in APS-C while in FF it will be much nicer to use for portraits for instance

This is a mistake. F4 is the problem, not the cropping.

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My 24-70 f2.8, which already produces a great bokeh in APS-C, is superb to get narrow DOP in FF

Another mistake. The DoF does not depend on cropping either. Note, that the focal length of the lens is the same, no matter on which camera you are using it.

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The cleaning system, it's a matter of concept. I know this is argueably, but I prefer to open my camera and blow the sensor from time to time than having something that 'moves' my sensor

I wish you much fun. I rather do it less often than I had to with the 20D.

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Regarding wide angle, in the next months I am probably going deep into architecture photographing (who knows if even will purchase some tilt shift lens someday) and I want to be able to have a wider selection of wide angle lenses

If you are doing it professionally, under time pressure, then you need a medium format camera (you can get away already with EUR 20000 or so, plus the lenses).

Otherwise, you may think about panoramas.

There are many examples for that on http://www.panopeeper.com/panorama/Hungary.htm, or see the Mormon church on http://www.panopeeper.com/panorama/USA.htm

It is unquestionably much more work than with a tilt and shift lens, but with panos

1. your options for creativity are much more,

2. the dynamic range is much higher. This needs explanation. The camera does not get better when shppting pano frames, but the DR of the scenery is sometimes much higher than the DR of the individual frames.

Examples:

Pano from 11 frames

The frames have been shot 4.5 stops apart. With which camera can you do 13 stops?

Btw, I like the Dead Vlei.

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Why did you darken so much the skies in the B&W landscapes?

Those sceneries are not B&W candidates in the classinc sense (you can see the same panos in color on the USA page). The B&W versions are rather gimmickry, going for very strong effect; I will try how they look on print. The sky was almost totally clear on all those panos. Though I might try to insert another, strongly cloudy sky (I do this sometimes, when the sky is not nice enough), then I would not blacken it.

(I have a stockpile of panoramic skies for this purpose.)
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Guillermo Luijk
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« Reply #38 on: January 12, 2008, 04:19:23 AM »
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If you turn on live view, you have to press the button in the middle of the big wheel to activate/deactivate it. When MLU too is turned on, the mirror flips up when activating live view. If you are using a remote control (there are very cheap wired ones from third parties), and you set up exposure bracketing, with a single press you start shooting all three shots of the bracket. Neither mirror flapping, nor button pressing occurs between the shots, which will be made in a fraction of a second.

Jonathan made a remark, that it is still not totally vobration free due to the shutter movement. This is correct, I have not verified yet the effect, I ope it won't be much. Anyway, I guess this will give the ideal basis for HDR, which may be my next project.
OK that's understood now. I normally do HDR (not the tone mapping, just getting the HDR data) from 2 shots: 0EV, +4EV. To obtain them I bracket -2,0,2, so that the -2 matches my desired 0EV (i.e. ETTR shot without blowing any highlight) and +2 give me the +4V sample. I use MLU and images match pixel by pixel even with my cheap tripod, it's very precise. Of course avoiding mirror flip could even be better but not necessary actually. The advantage I see in the live view is the speed at which the shots can be taken: I have to set timer+MLU so I have to wait a couple of seconds between shots, and with the 40D you don't. Good point. BTW is the bracketing in the 40D -2,0,2 or Canon finally allowed more f-stops?
I wrote an article showing some tests: HDR blending, surely nothing new for you. What are you planning to do in HDR? I am willing to see your research.



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Thankx, but I do now the meaning. Once more: the quality of bokeh has to do *only* with the lens. FF or cropping plays a role only as far as the selection of focal length (and thereby of the lens) depends on cropping.

Every lens, which gives a good bokeh on FF, gives a good one on a cropping camera as well.
This is a mistake. F4 is the problem, not the cropping.
Another mistake. The DoF does not depend on cropping either. Note, that the focal length of the lens is the same, no matter on which camera you are using it.
Don't be offended, I said that in case bokeh does not mean exactly what I thought (I told you I am very new to this), or you meant quality of bokeh instead of amount of bokeh.
But then, being pragmatic, I have to disagree with you: DOF DOES depend on the cropping, i.e. on the sensor format. The same lens at the same focal length will obviously provide the same light projection over the sensor plane, but a different scene's framing (not sure if this is the right term to mean 'the portion scene falling into the sensor area') according to sensor size. So to obtain the same framing with my APS-C at 70mm f4 in the 5D, I will need to get closer to the subject or better (since distance would change the perspective) to use a larger focal length: 112mm f4. And 112mm f4 in the 5D will have less DOF than 70mm f4 in the APS-C, so we will increase the amount of bokeh for the same scene, distance and maximum aperture of the lens. So in terms of bokeh, a less luminous, lighter and cheaper lens provides more bokeh on a FF sensor.

Paradoxically if we don't change focal length nor get closer, the 5D at 70mm f4 will have more DOF than the APS-C at 70mm f4 since the reference circle of confusion for the 5D sensor is bigger than in the APS-C. Of course this comparision does not make any sense as we would be talking of different scene's framing. Once we increase the focal length on the 5D or get closer to the subject, the CoC effect is cancelled and the larger focal length or shorter distance prevails in reducing the DOF on the 5D.


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If you are doing it professionally, under time pressure, then you need a medium format camera (you can get away already with EUR 20000 or so, plus the lenses.
Don't think so. I met sometime ago one important Spanish arquitecture photographer; he used to work medium format but he simply does not want to spend the huge amount of money in digital medium format at today's prices. He is NOT happy with his 5D and tilt shift lenses, but with some extra effort achieves an incredible quality, far beyond my intentions. Look at some of his work here: http://javierazurmendi.blogspot.com/ (I know they are ridiculously small, but according to what he told me and the prints I saw in his studio, the quality suffices professional requirements perfectly).


Panos is one of my pending tasks for some day. What software do you recommend me? PT?
« Last Edit: January 12, 2008, 06:31:14 AM by GLuijk » Logged

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« Reply #39 on: January 12, 2008, 05:28:59 AM »
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Hi, my first post here.  I have  been watching with great interest some of the technical discussions you guys have on this site.  A few points:

I think this unity wb is a great idea, as the inaccuracy of the in-camera jpg at indicating correct clipping is one of the difficulties of ETTR.  One less thing the deriders of ettr have to complain about.

But one question I have is what exactly is the highlight warning on the lcd showing?  Is it showing clipping of any one of the three channels or is it some sort of composite?  I understand that the histogram on the lcd is usually some sort of green channel weighted composite.  Is the clipping warning working on this?  If so, is it possible to be clipping a channel (particularly red perhaps?) and it not showing blinkies on the lcd?  I guess the reason I came to this conclusion is that after implementing Guillermo's method I am still getting very similar flashies on the lcd preview between the unity wb and a scene wb.  However when developing a linear non-wb tiff I see that I still have maybe a stop of so of headroom until I get clipping.  I am assuming my custom white balance image is correct (although it looks more pink than magenta (i'm on a 5D)) as it is giving multipliers of about 1.01 for each channel in dcraw.

On the issue of DOF, Pano you are forgetting that maintaining identical FOV between different systems is usually required.  To obtain identical FOV between a 1.6x crop sensor and a FF sensor, one must either select a different focal length lens and/or change the distance to subject.  Both of these factors affect DOF.  You won't be able to capture the same lack of DOF (for the same FOV) with a 1.6x sensor as you could with for example a 50mm f1.4 on a full frame camera.

cheers, Bernie
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