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HELP PLEASE

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Hi folks,

I have a problem.
V1 & V2 are photographs of the same page of a late 18thC bible taken 8 minutes apart.
V4 is the grey card picture taken to set the custom White Balance for the session - 5 minutes before.

Interestingly the difference is not obvious on the uploaded version though the originals show V1 with a blue cast. Also V3, whilst a little lighter has the same apparrent WB as V2.

I have now looked at the histograms for the 2 pictures.
All pictures had a Temperature setting of 4895 and Tint +3.
To get V1's histogram to match V2's I have to adjust Temperature to 5400 and Tint to +4.

All photgraphs were taken as raw images.
The white balance was set and the camera's settings saved.

I changed the aperture to f8.0 for the V1, but as I didn't resave the settings it reverted to f4.0 unnoticed by me (slap wrist) before the next picture - V3 - was taken - 2 minutes after V1.

Exif:
V1 f8.0 1/6s ISO 200
V2 f4.0 1/40s ISO 200
V3 f4.0 1/25s ISO 200
V4 f4.0 1/10s ISO 200 - Grey Card
All photographed in natural reflected light with no flash. There is no chance that I could have cast a shaddow over any part of the subject.

Why is there such an apparrent difference in the colour of V1 to the rest.

I really would appreciate someone enlightening me on the likely cause.

Thanks very much,

James

Brand:Canon
Camera:Canon EOS 5D
Lens:EF24-105mm F/4L IS USM
Recording media:RAW (digital)
Date Taken:27 Jan 2012 - 11:35 AM
Focal Length:35mm
Lens Max Aperture:f/4.0
Aperture:f/4.0
Shutter Speed:1/40sec
Exposure Comp:0.0
ISO:200
Exposure Mode:Manual
Metering Mode:Unknown
Flash:Off, Did not fire
Title:HELP PLEASE
Username:James_C James_C
Uploaded:27 Jan 2012 - 4:41 PM
Tags:Flash / lighting, General, Specialist / abstract
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Comments

This photo is here for critique. Please only comment constructively and with suggestions on how to improve it.
mrswoolybill
mrswoolybill Critique Team 7395 forum postsmrswoolybill vcard United Kingdom971 Constructive Critique Points
27 Jan 2012 - 5:06 PM

I shall come back later and I'll be interested to see what the more technically minded members suggest. It does occur to me that the actual pages may have aged with different results - down to varying degrees of exposure to light.
The only times that I have tried to customise WB the results have been dreadful. I'm afraid I leave it on Auto now, the camera does a damn good job and I tweak in RAW as necessary!
Moira

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banehawi
banehawi Critique Team 10781 forum postsbanehawi vcard Canada2800 Constructive Critique Points
27 Jan 2012 - 5:49 PMConstructive Critique!This comment was flagged as constructive critique! 

Question for you James so I can answer properly.


V1 and V2, - the exposure is completely different, indicating to me that the light source changed in some way.

Exif:
V1 f8.0 1/6s ISO 200
V2 f4.0 1/40s ISO 200
V3 f4.0 1/25s ISO 200
V4 f4.0 1/10s ISO 200 - Grey Card


If the light was constant, V1 should be f/8 and 1/20 to be the same as f/4 at 1/40, - but its 1/6, indicating a significant light change.

If you applied the same WB to them all, this will ONLY work when the light is absolutely constant, - like in a studio, i.e the light on the grey card = the same light on all subsequent exposures. Given that the light has varied you would need a WB calibration for each individual image.

So the question, - how was this lit, - and how did the light change, as the camera is indicating a significant change. Assuming you agree the light changed, - thats your answer.


The other issue, - how come v1 and V2 look more alike here than your originals, - might be due to different colour spaces (adobe vs sRGB). I can meanure a VERY slight difference in them. Your test card is spot on neutral.



regards



Willie

Last Modified By banehawi at 27 Jan 2012 - 6:04 PM

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James_C
James_C  536 forum posts United Kingdom56 Constructive Critique Points
27 Jan 2012 - 6:15 PM

Hi Willie,
Thanks for getting back to me so quickly.

The set up was as follows:
Large south facing room Approx. 15 x 30 ft. Lower 2/3rds shutters closed, only window recieving direct light (far end of room) fully shuttered. West window (far end of room) unshuttered. Book set on floor with camera on tripod set over it centrally at the eatern end of the room. I was not aware of any change in light. There was a clear cloudless sky outside.
In my mind the only appreciable difference was in the focal length:
V1 32mm
V2 35mm (thus allowing more of the dark background to be included)
V3 50mm
Interestingly, of the 16 pictures taken of the subject V1 is the only one with this problem and the previous 2 pictures were taken with identicle settings as V1 and do not show the cast.

I take your point regarding constant light - "this will ONLY work when the light is absolutely constant, - like in a studio". and will bear it in mind for the future.

Food for thought.

James

PS V1 and V2 are cropped so as to exclude information regarding the owner.

Last Modified By James_C at 27 Jan 2012 - 6:18 PM

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James_C
James_C  536 forum posts United Kingdom56 Constructive Critique Points
27 Jan 2012 - 6:43 PM

PPS Willie,

The first picture was taken at 11:26:24, second 11:26:47 and V1 11:27:23. THe grey card was taken at 11:22:27

James

Last Modified By James_C at 27 Jan 2012 - 6:43 PM

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f8
f8  109169 forum posts England22 Constructive Critique Points
28 Jan 2012 - 3:06 AM

North lit windows are more reliable source of light that's why artists use it.

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paulbroad
paulbroad  681 forum posts United Kingdom843 Constructive Critique Points
28 Jan 2012 - 8:15 AM

I may be missing something here, but Willie covers most things. You do not use a grey card for colour balance, you use it for exposure determination. You use a white card to set custom white balance. THe exposures should all be the same and consistent in the same light. It is difficult to figure out what you are doing, but such copying should be very straight forward in a consistent light source.

I never have a problem setting a custom white balance and always try and use the same light, a bright halogen with diffuser, for certain close up and macro video with my 7D. Use a tripod. Shoot the white card at as near the correct exposure as possible on manual and with the card filling the frame. Then set this image as the custom white balance. Auto is often correct!

Then you should not need to alter exposure on manual providing the first shot is correct. Always make sure image 1 is correct - all of yours are under exposed a bit - then stick to that with a consistent light source.

Paul

Last Modified By paulbroad at 28 Jan 2012 - 8:16 AM

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James_C
James_C  536 forum posts United Kingdom56 Constructive Critique Points
28 Jan 2012 - 10:05 AM

Thank you Stuart. You are absolutely right and I should have mentioned in my write up that unfortunately Iwas not able to use this option on this occasion.

Thank you Paul.

Quote: You do not use a grey card for colour balance, you use it for exposure determination. You use a white card to set custom white balance

This statement is not correct. Yes you can use a grey card for exposure determination and yes you can use a grey card for colour balance and yes you can use a grey card for white balance.

You might like to have a read of what Wikipeadia or Digital Arts Photography or Photoshop Tutorial Plus have to say on the subject.
A white card or sheet of paper does work and is very good general purpose use, however, if you take sheets of "white" paper or card from different sources, you will note that there are a considerable variety of "whites", each of which will give a different balance. On the other hand a "grey card" is made to an exact standard. Be aware though that grey cards are made to 13% instead of 18% or 25%.

Lastly, the bible is very large - a good 2ft tall and over 200 years old. I don't have a studio and could only use the available facilities on site.

Food for thought and I'm very interested in what you have to say.

Best regards ,

James

Last Modified By James_C at 28 Jan 2012 - 10:15 AM

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James_C
James_C  536 forum posts United Kingdom56 Constructive Critique Points
28 Jan 2012 - 10:21 AM

Oh and as a quick after thought. Regarding exposure.
I disagree that the pictures are under exposed. The grey card is bang on the mid point for exposure and the pictures of the bible are, if anything, slightly over exposed. Do not get confused by the second peak at the dark end of the scale as this is caused by the red background, which I ignored for metering purposes.

James

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James_C
James_C  536 forum posts United Kingdom56 Constructive Critique Points
28 Jan 2012 - 10:30 AM

Small error above
Quote: grey cards are made to 13% instead of 18% or 25%

should read "grey cards are made to 13%, 18% and 25%".

James

Last Modified By James_C at 28 Jan 2012 - 10:30 AM

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paulbroad
paulbroad  681 forum posts United Kingdom843 Constructive Critique Points
28 Jan 2012 - 7:42 PM

Oh dear - seems to be a sore point. Never mind Wikipedia, read your camera manual with respect to custom white balance. You do not seem to require help.

Paul

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James_C
James_C  536 forum posts United Kingdom56 Constructive Critique Points
29 Jan 2012 - 9:09 AM

Dear Paul,

I'm sorry you've taken my response that way. Rereading what I have said does come across as rather strong, for which I apologise. Perhaps I should have made it clearer that you can use a white card. I was merely pointing out that there are variations of white. Obviously you can buy a white card, which is made to a specific standard - it's usually on the back of a grey card and there is usually a black card supplied as well. My understanding though is that if you include all three in a picture it enables you to get the colour/white balance correct using the grey and establish the brightness and contrast by using the black and white.
I have had a look at the canon manual and it does say "you shoot a white object...", however I would imagine that they don't expect the majority of their customers to go out and but a grey card and carry it about with them all the time. It is much easier to find something white or carry a scrap of white paper with them and in the majority of cases that would be more than enough.
I would like to do more photography for record purposes and I want to get as near to perfection as I can within my financial capabilities. Thus when something goes wrong I want to understand why so that I can do it better next time.
The reason I posted this request for help is because I thought I had done all the right things and yet I didn't get consistant results. Between you all I think I now understand. I didn't have consistant light and therefore should have included some grey,white and black card in each shot so as to be able to correct each picture individually.
The biggest help that you have been Paul, is that you have made me question my understanding of the use of a grey card and I have therefore had a good drag through the internet on the subject. Now I know that I should have included a white and black card in each shot as well.
Once again, I apologise for being rude.

Sincere regards,

James

Last Modified By James_C at 29 Jan 2012 - 9:11 AM

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