Lighting and Focusing.....

I need to know the answer to this, seriously.... as I was unaware of the following....

From another thread.....
flourescent can cuase back focusing, and incadscent can cause front focusing.


IS THIS TRUE???? I learn something every day.... does this really happen... if so... that would explain some of my 24-70 issues..... can someone confirm this?

I do not mean this sarcastically either..... I really am unaware if this can cause focusing issues..... because if this is the case, there is probably nothing wrong with my copy of my 24-70L as the testing I did was under incadescents.....brigh​t ones, but incadescent none-the-less......

No takers yet?

I really don't see how but I've been wrong before.

I haven't heard of that before. I don't know how flourescent could affect the AF sensors different than incandescent.

Its a new one on me,where did you read that?

I am not going to say that I agree or disagree with the initial statement... because honestly I dont know... but obviously it boils down to the amount of light and the ability to focus on the subject... where as increasing the light will diminish either (or both) back or forward focusing....

Well the dominant light wavelength will be different under different lighting. However I can only see this affecting focus if the lens or AF system has significant cromatic aberation. It would be a very poor lens to do this. The AF sub-system might have small lenses on the sensors that introduce CA, sounds a bit unlikely though.

If there were any basis for this happening, Canon and other camera makers would use AWB readings to apply a known offset to the focussing signals based on the light temp.

This may have risen as a result of someone trying to focus on targets that provide better contrast in one light than another, or if the AF readings in the system were taken in sync with the frequency of AC powering the fluorescents, but if there were anything to this the greatest difference would be between focussing in open shade and in candlelight or firelight, where there's the greatest possible difference in principal wavelengths. And even in those two extreme conditions, there's still plenty of light from the rest of the spectrum present.

OK.... good.... at least this is an unknown to more experienced photogs.... thanks. As for natural light.... the 24-70 performed very well... although not as tack sharp as a prime... but I now understand that this is inherent in the zoom build, and not a focus issue. So the results are still mixed.... on my 24-70, it performs well in daylight conditions, on one-shot AF, and not so well with indoor lighting... appeared to front-focus about 6 cm on the open ends, but corrected itself at f 4 and higher.

Thanks again for the input.