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[OM] Re: YADT, 5D - Dust at various apertures

Subject: [OM] Re: YADT, 5D - Dust at various apertures
From: Johnny Johnson <jjohnso4@xxxxxxxxxx>
Date: Fri, 14 Apr 2006 21:58:29 -0400
At 05:31 PM 4/14/2006, Wayne S wrote:

>Ok, here is an update of dust correlated with F stop with 5D.
>After several cleanings with PecPad wrapped on credit card
>cut to size, there were a few spots that refuse to change.
>Here are some 100% crops around those spots:
>
>http://www.airsprite.net/5D_dust/dust_32.jpg F32
>http://www.airsprite.net/5D_dust/dust_22.jpg F22
>http://www.airsprite.net/5D_dust/dust_16.jpg F16
>http://www.airsprite.net/5D_dust/dust_11.jpg F11
>http://www.airsprite.net/5D_dust/dust_8.jpg  F8
>http://www.airsprite.net/5D_dust/dust_5_6.jpg  F5.6
>
>You can see that the spot is evident at F16, starts to disappear
>at F11 and nearly invisible at F8. I did not enhance the contrast.
>
>Almost all the spots could be cleaned with PecPad plus
>alcohol, except a few.


Hi Wayne,

I missed your first message that described using a CO2 blower to 
clean the sensor but if it's something like canned air you've got a 
lot more nerve than me.  Well, I guess you do anyway.  Just the 
thought of sticking a cut down credit card into the sensor chamber 
makes rabbits run over my grave, even if the card is covered with a 
PecPad.  :-)

Also, it might be interesting to run some tests to see what effect 
diffraction is having on your shots at f32 as compared to something 
like f11.  I know you're trying to increase your depth of field but 
some sources that I've read claim that, with the 5D, diffraction will 
start reducing image sharpness at between f11 & f16.     I also seem 
to remember reading somewhere that as the reproduction ratio starts 
approaching 1:1 the effects of diffraction are multiplied such that 
the reduction in sharpness at f32 would be similar to that at f64 and 
normal focusing distances.  Anyway, I'm just wondering if what you're 
gaining shooting at f32 is being offset by losses in sharpness due to 
diffraction.

Later,
Johnny


__________________________
Johnny Johnson
Cleveland, GA
mailto:jjohnso4@xxxxxxxxxx 


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