wrong color temperature Godox ? Do I do something wrong

[Stagecoach]

I once red, that (white) teflon tape is a neutral white. Have you or anyone experience with that?Regards, Rudolf

I have heard of teflon tape being used in an experiment, but it was with respect to testing 'camera metering accuracy' because someone was trying to prove that their camera 1/3rd stops were inaccurate

[dje]

George, I'm interested to do my experiment with a surface, other than my greycard. Though it has to be a reliable / defined setting for me to make sense.
I once red, that (white) teflon tape is a neutral white. Have you or anyone experience with that?

Regards, Rudolf

I did try teflon tape a while ago but from memory it was no better than, and probably not as good as a decent gray card.

Dave

[rlast]

I did try teflon tape a while ago but from memory it was no better than, and probably not as good as a decent gray card.

Dave

Thanks!

[george013]

George, I'm interested to do my experiment with a surface, other than my greycard. Though it has to be a reliable / defined setting for me to make sense.
I once red, that (white) teflon tape is a neutral white. Have you or anyone experience with that?

Regards, Rudolf

If you want to examine why there is such a big difference between flash specs and what you see in the converter checking the specs has to be done too. The question COULD be: are the specs right or misunderstood.

I don't think you can use a white surface. White is 255,255,255 and it will be impossible to tell the difference between white and clipping. Or you've to underexpose the image.

Beside that I do wonder the practical use of a wb preset. Except maybe under controlled circumstances.

George

[rlast]

Rudolf the curve was set to Auto but fiddling with the options just now I found it made no significant difference which curve was selected (nor should it).

Dave

Thanks Dave!

[rlast]

If you want to examine why there is such a big difference between flash specs and what you see in the converter checking the specs has to be done too. The question COULD be: are the specs right or misunderstood.

I don't think you can use a white surface. White is 255,255,255 and it will be impossible to tell the difference between white and clipping. Or you've to underexpose the image.

Beside that I do wonder the practical use of a wb preset. Except maybe under controlled circumstances.

George

George, of course I will underexpose the white tape, so don't let it clip to the right.
I'm reluctant of throwing in more unknows … :-)

[xpatUSA]

Thanks… if you have time and interest, please see my latest results from today, shot with the greycard in a 30% angle …

cheers, Rudolf

Yes, Rudolf, most interesting. I think we are getting there.

Probably a little late, but some years ago, I was shooting a card for other reasons (checking camera ISO Sensitivity Type) and found that a) using the white side of my Kodak R27 8x10" card was as good as the gray side and that b) the literature recommends infinite focus for that kind of test, sorry no link for that but it makes sense if you think about it.

[xpatUSA]

If you want to examine why there is such a big difference between flash specs and what you see in the converter checking the specs has to be done too. The question COULD be: are the specs right or misunderstood.

The specs have ALREADY been checked and posted in this thread. Should Rudolf check and post them again?

I don't think you can use a white surface.

You are confusing reflectance with exposure. Your statement below makes any photo with white in the scene impossible!

White is 255,255,255 and it will be impossible to tell the difference between white and clipping.

Wrong. You are ignoring the camera's metering which sets the exposure so as to render any neutral color (which fills the frame) as mid-gray 118/255 (ISO/CIPA 'Standard Output Sensitivity').

Beside that I do wonder the practical use of a wb preset. Except maybe under controlled circumstances.

George

Delightfully vague, George. Would you care to elaborate?

[Manfred M]

Thanks Manfred for bringing this up. Very interesting.

Sorry for the misunderstanding. The table is for one particular studio flash run in a mode where it is used in rapid-fire mode. It is NOT a generic table that applies to all flash units.

As you are getting the same issue with both the pop-up and Godox flashes, I would suggest that the problem is NOT the flash, but is more likely the camera or your methodology.

[rlast]

Sorry for the misunderstanding. The table is for one particular studio flash run in a mode where it is used in rapid-fire mode. It is NOT a generic table that applies to all flash units.

As you are getting the same issue with both the pop-up and Godox flashes, I would suggest that the problem is NOT the flash, but is more likely the camera or your methodology.

Manfred, that is what I guessed, that your table was for another kind of flash, but it is illustrative, and puts numbers on what you told us before.


You've given hints about improving the methodology, and I'm thinking how to realize that, without too much investment ($$).
Thanks so far for your help.

I looked up a testreport on the color accuracy of my camera, and found this:

https://www.imaging-resource.com/PRO...rx10-iiiA5.HTM

I don't know how to read this graph, any recommendations you can give? (if I may ask …)

Rudolf

[rlast]

Yes, Rudolf, most interesting. I think we are getting there.

Probably a little late, but some years ago, I was shooting a card for other reasons (checking camera ISO Sensitivity Type) and found that a) using the white side of my Kodak R27 8x10" card was as good as the gray side and that b) the literature recommends infinite focus for that kind of test, sorry no link for that but it makes sense if you think about it.

In the documentation of my grey-card they tell that the white side can be used too. I have tried that - with same result. (WB 7200K needed to make it neutral)

I understand the infinite focus recommendation and tried that before @ 220mm (600mm FF eq). with same result as well …

a pity but thanks a lot for helping me.
Any further recommendation (if it pops up) will be appreciated. I keep on thinking how to improve my testsetup, and exchange some components with a friend - to exclude a couple of things!

Rudolf

[Manfred M]

I don't know how to read this graph, any recommendations you can give? (if I may ask …)

This is nothing more than a plot of the a* and b* channels (pure colours without "luminosity") from the L*a*b* colour space. The horizontal axis is the a* channel and the vertical is the b* channel.

The small squares show the actual colour whereas the circles show what the camera is representing those ideal colours as. This is one of those "so what" tests that is not all that relevant, in my experience. Your camera works the way it was designed and built.

[rlast]

This is nothing more than a plot of the a* and b* channels (pure colours without "luminosity") from the L*a*b* colour space. The horizontal axis is the a* channel and the vertical is the b* channel.

The small squares show the actual colour whereas the circles show what the camera is representing those ideal colours as. This is one of those "so what" tests that is not all that relevant, in my experience. Your camera works the way it was designed and built.

Thank you Manfred fot clarifying.
Rudolf.


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[xpatUSA]

This is nothing more than a plot of the a* and b* channels (pure colours without "luminosity") from the L*a*b* colour space. The horizontal axis is the a* channel and the vertical is the b* channel.

The small squares show the actual colour whereas the circles show what the camera is representing those ideal colours as. This is one of those "so what" tests that is not all that relevant, in my experience ...<>

... except that it puts numbers to Rudolph's main concern - the white balance accuracy. It states that the camera's neutrals (Adams' Zones II to V) are indeed gray to an accuracy of +/- 1.6 delta-Chroma which is quite good in my opinion and in CIE's opinion too (google 'just noticeable difference'). Certainly much more accurate than the measured a*,b* values of the posted images!

[Manfred M]

... except that it puts numbers to Rudolph's main concern - the white balance accuracy. It states that the camera's neutrals (Adams' Zones II to V) are indeed gray to an accuracy of +/- 1.6 delta-Chroma which is quite good in my opinion and in CIE's opinion too (google 'just noticeable difference'). Certainly much more accurate than the measured a*,b* values of the posted images!

If it provided any useful information regarding what is happening with Rudolph's experimentation, I might be tempted to agree.

As with many test sites, this information is easy to generate but is meaningless in real life photography.


My camera is far from perfect as well, but I have zero problems nailing a neutral WB when using flash at 5500K.






When I open my gray card shot done under flash using Capture One, I get a value of 5583K, which is darn close to the nominal 5500K, not the 7200K Rudolph is getting.

[george013]

If it provided any useful information regarding what is happening with Rudolph's experimentation, I might be tempted to agree.

As with many test sites, this information is easy to generate but is meaningless in real life photography.


My camera is far from perfect as well, but I have zero problems nailing a neutral WB when using flash at 5500K.






When I open my gray card shot done under flash using Capture One, I get a value of 5583K, which is darn close to the nominal 5500K, not the 7200K Rudolph is getting.

So it would be interesting to check that flash with another camera. Maybe the specs of the flash are just wrong. And then Rudolph can ask the manufacturer for an explanation of the results of the done tests

George

[xpatUSA]

If [Imatest] provided any useful information regarding what is happening with Rudolph's experimentation, I might be tempted to agree.

As with many test sites, this information is easy to generate but is meaningless in real life photography.

A not unexpected tone of response. Since data from a well-known test house counts for so little in this discussion, I'll bow out.

[Manfred M]

A not unexpected tone of response. Since data from a well-known test house counts for so little in this discussion, I'll bow out.

It should count for very little because it is irrelevant to the issues that Rudolf has here.

The question that was raised is why Capture One is showing 7200K colour reading from his test rather than something closer to the nominal 5500K he could reasonably expect. The Imatest result is NOT going to answer that question.

[rlast]

A not unexpected tone of response. Since data from a well-known test house counts for so little in this discussion, I'll bow out.

Ted, your comments have been of great value for me! I really want to thank you for that :-)

I'm thinking of setting up a new experiment, with another light source : the sun.
Besides the greycard, I will add other elements to the picture like skin tones, my garden.
With two pictures, one lit by the sun, the other one with the flash, and white balance set based on the greycard, I'm interested how the colors look like for the total picture ….

It will likely take a few days, before I have a chance to do that!

Rudolf

[rlast]

It should count for very little because it is irrelevant to the issues that Rudolf has here.

The question that was raised is why Capture One is showing 7200K colour reading from his test rather than something closer to the nominal 5500K he could reasonably expect. The Imatest result is NOT going to answer that question.

The reason I brouht this picture up, is to check with you if the colors on my camera are very poor / far off.
Apparently this is not the case, but no more info could be learned from this, is what I understood … is this correct?
Thanks,
Rudolf