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Without depending upon post production is it possible to achieve exact same exposure and exact same color in the background for a set of photos?

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3 Answers 3

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Yes if you have consistent lighting - just set manual exposure, manual flash power and manual white balance. If you don't have consistent lighting, all bets are off.

With all due respect though, if don't know this already, you're not ready to do this professionally, except maybe in an apprentice role.

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  • \$\begingroup\$ "flash power" (when used) :) \$\endgroup\$ Commented Jul 1 at 9:38
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    \$\begingroup\$ Zero is a valid power :) \$\endgroup\$
    – Philip Kendall
    Commented Jul 1 at 9:45
  • \$\begingroup\$ For me "manual flash power" imply usage of flash. And 0 is not included :) \$\endgroup\$ Commented Jul 1 at 10:05
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    \$\begingroup\$ The question is tagged product-photography, the vast majority of which involves flash. I know I'm slightly oversimplifying here, but my feeling is that's the level of answer the poster needs at this stage. \$\endgroup\$
    – Philip Kendall
    Commented Jul 1 at 10:07
  • \$\begingroup\$ I would tend more towards "no"..... Even with consistent lighting, changing the subject (as opposed to the background, which is what is being focused on here) can potentially have significant effect on the overall exposure, white balance, etc - e.g. a red vs a black checker taking up 50% of the frame against a white background.... or something that takes up 10% of the field vs 80%.... Keeping the result exactly the same with respect to only the background is..... not easy.... I suppose if you only expose for the background, but then your intended focus will suffer... \$\endgroup\$
    – twalberg
    Commented Jul 3 at 18:35
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The key to this problem is a steady repeatable lighting setup. I had a similar assignment, it lasted years, making test films used to set and calibrate highspeed prints used in photofinishing labs.

I used professional electronic flash units. Their position with regards to the subject was well documented so that they could be moved or replaced and when reset, duplicated the setup. Additionally, after each shot, the ready light on each flash was noted. The next shot was not made until the ready light returned to full brilliance and then given an additional 4 or 5 minutes to reach full charge before being fired again. These flash units were powered by the household electivity, with a constant voltage transformer that ensured that the voltage remained steady.

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You need to understand 3 things before:

  • (Note: the original unedited question hinted that this is for a work interview) If this is an interview question, it is an opportunity to dump knowledge. So asking for a simple solution to a complex question, is a trap. Use the opportunity and show that you understand the complexity.
  • The answer depends heavily on how exact you need to be
  • There is no simple answer that is completely correct.

You could start with: "No problem. The background itself does not change its color." Tadaaaa.

But of course, that is not what the question is about. If you need to be super exact, the answer is always "you cannot do that". If you need to be reasonably close, it can be done.

You then can elaborate, what needs to be the same to ensure reasonably close exposure:

  • The light modifiers, power, positions and directions need to be unchanged
  • The subject must be in the exact same spot
  • The position of the background may not be changed
  • You must be able to rule out any ambient light (either by darkening the room or by a fast shutter or a combination)
  • The lights must be of reasonable stable color temperature and power between consecutive shots
  • You must control any colored light reflecting off the subject onto the background
  • The camera, lens and settings may not be changed
  • The brightness and reflectivity of the subject needs to be roughly the same, otherwise they are exposed the same, but might not look like that in the image. So even if you achieve the same exposure for one product, does not mean that another product will look good in the same light. For example the light settings for a black bottle of shampoo with correct exposure will probably yield an overexposed image for a white bottle of shampoo. You can of course shoot the background and the product in two shots with different exposure and then combine both in post production. But you ruled out post production.

Additional stuff that can still ruin this, if the color needs to be stable for a long time of usage:

  • Shining UV light (also in strobes) onto the background will probably change the background color over a long time by bleaching out the color. Even chemical processes in the background material itself (aging) might change it.
  • The aging of the flash tubes will change their power a bit, and maybe their color temperature
  • The material used in any light modifiers will age, and sometimes add a yellowish color shift.
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