Rethinking 4/3 Depth Of Field

Started Apr 11, 2013 | Discussions thread
Ken Strain
Regular MemberPosts: 209
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Re: Rethinking 4/3 Depth Of Field
In reply to Just another Canon shooter, Apr 12, 2013

Just another Canon shooter wrote:

Ken Strain wrote:

A Hoya CP filter was used for its attenuation (the same one for all, with step up rings).

Why? The CP effect is clearly different, which means different light transmission.

OK, thanks for pointing that out.  I meant the same physical filter, and hence same risk to image quality, not the same attenuation - though of course it only varies for polarised light.   I could have set it more accurately, and worked faster to reduce variations in light.  My conclusion is that  I would need an ND filter to do this properly (at this aperture and these ISOs).  I thought about waiting until evening, but I don't expect that would help with consistency of light (I chose noon for that reason).  Probably full daylight with a strong ND filter would be safest.

Exposures were around 1/4000s, although overcast, the daylight varied a little.

No, the D800 is at 1/5000, the PM2 is at 1/2000.

Correct!  The significant point is how that came about.

I picked images with approximately the same relationship between mid-tones and saturation - at least I tried to do that using Raw Digger to select images with matching histograms, relative to saturation.  It turned out that the heaviest exposure on the PM2 gave a similar histogram to the lightest on the D800.   I believe I got it right well within a stop.     I understand that another choice would have been to centre the exposure indicators, when the PM2 would have received around 2/3 stop less exposure (judging from the other frames I have available).  I guess that is expected from the Bill Claff pages  (nearer a stop perhaps).

It turned out that the exposure discrepancies added (32mm aperture vs 30mm, saturation level differences of 2/3 stop or so, and - I think - the light level at the time of exposure), hence the surprisingly large difference in shutter speed.  (I'm not sure if there would have been a tone curve difference in the conversion even with default settings - I have not checked for that.)

Ken

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