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Speedlight questions for precision flat art copy work


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#1
stephend1714

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Hi everyone.  Answers given number by number (separately) will be appreciated. 

 

Expanation: I am photographing old -- 1941 -- documents, including one created with a blue typewriter ribbon on slightly yellowed but high quality rag bond paper.  Files will be JPG Fine, not RAW. BOTH typewriter blue ink and paper yellowing must be faithfully rendered at around 500% enlargement on a calibrated computer monitor, and with custom color prints.  The printer staff says their machines give maximum true rendering from JPGs in a PDF, and I do not have to convert the files to CMYK.

 

So, the questions:

 

1.  The usual way indicating how warm or cold flashtube output will be is "color temperature" --- but is "color rendering index" also specified somewhere in Nikon's data stash, or available from a factory tech rep via their website chat? 

 

2.  I have an SB 600 and an SB 500. I will NOT be using the SB 500's LED option. Aside from output power, is the color spectrum of the flashtubes identical?

 

3.  If not, and you happen to know the precise spectral difference --- either as color temperature OR color rendering index -- can you please include that in your answer?

 

Thank you in advance, as the cliché goes.  (BTW, if further info is needed from me, I must be away from this forum until around 7 PM Eastern US time.)

 

 



#2
Merco_61

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The spectral output changes as the tube ages, so the chance of two speedlites from different generation being identical is very slim. For repro work where the colour rendition is critical, I would rather use continuous lighting or studio strobes with new tubes as the precision in manufacture is better than with speedlites.

 

To make sure of colour fidelity, I would have to shoot in RAW and periodically shoot a colour chart to calibrate my workflow. There is absolutely no way to get as precise white balance and spectral response SOOC. 

 

Will the printers have access to the original documents to calibrate their printing profile? If not, there is no way they can do the CMYK conversion precisely as that will depend on the paper and the humidity on the day and even a calibrated monitor can only reproduce a part of the gamut available even in 8-bit so it can't be used for reference.

 

I agree with the printers' wish not to have client-converted CMYK-s to contend with, the work is difficult enough without that headache. What I don't agree with is using a lossy 8-bit format instead of something non-lossy and 16-bit if the output fidelity is *that* critical.



#3
dcbear78

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If I was doing something colour critical I'd definitely be using something like a Colour Checker Passport to ensure truly accurate colours. Here is an example I have of using one. First image is the SOOC raw file. I use auto white balance so in this image it isn't perfect.

 

yqKJHG9l.jpg

 

Then I apply the colour profile and correct white balance using this passport and associated software.

 

OtXOzHYl.jpg

 

The changes here are not massive. The white balance was near perfect. So I took both of these photos into photoshop and using layers exposed one side of each square to highlight the changes. This makes it very easy to the difference. In particular the blues and orange is very different. Both colours you are saying are very important to reproduce accurately.

 

p1jXFdNl.jpg