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Author Topic: DOF chart/calculator P25  (Read 5373 times)
Randall
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« on: February 15, 2006, 01:58:59 PM »
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Greetings,

I had posted this on the Phase One Forum as well, but as of yet, no responses.  I wanted to get an accurate DOF chart for my new P25.  I still use hyperfocal distances regularly.  What Circle of Confusion values are P25 users using?  .040 seems like it would be in the neighborhood.  Any thoughts?

Thanks in advance,
Randall
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BlasR
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« Reply #1 on: February 15, 2006, 05:31:20 PM »
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Randall,
First I'm sorry to ask in the same place,,I do not have and answer for your question, but because you are in p25 I like to ask a question too. I Hope you are no mine.

Any one know about exposure compensation in p25? I was looking in c1 to find my exposure compensation and didn't register in my flash card, is give me 0.0 in all the photos.

Thank You.

BlasR
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Randall
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« Reply #2 on: February 16, 2006, 01:07:18 PM »
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Randall,
First I'm sorry to ask in the same place,,I do not have and answer for your question, but because you are in p25 I like to ask a question too. I Hope you are no mine.

Any one know about exposure compensation in p25? I was looking in c1 to find my exposure compensation and didn't register in my flash card, is give me 0.0 in all the photos.

Thank You.

BlasR
[a href=\"index.php?act=findpost&pid=58246\"][{POST_SNAPBACK}][/a]


What camera are you using?  When you hover your mouse over the thumbnail of the image in C1, does an exposure compensation value register?  If not, it would appear that your camera is not communicating this info to the back.  As exposure compensation is a function of the camera, not the back, it should have auto adjusted your exposure even if it does not comunicate this info to the P25.  Thus, even if C1 shows no record of such, the exposure should still be adjusted.  Of course, as these are Raw images, you still have a large range of exposure tunability.  I shoot with a view camera, so these are not options for me.
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Randall
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« Reply #3 on: February 17, 2006, 10:48:08 AM »
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Any thoughts on the original post?

What numbers are you using to adjust for the cropped 645 format?
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Gary Ferguson
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« Reply #4 on: February 19, 2006, 09:49:41 AM »
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Depends how big you are printing. I get the impression the original conventions for DOF were based on about x7 enlargement, x10 is common with digital so you'd need at least one extra stop. Furthermore the P25 isn't full 645 size, so if you go to one of the traditional DOF tables (if you need one just enter DOF and run a Google search) you'll need to apply an additional fudge factor.

Bottom line is that getting all that great P25 digital quality onto a print is no easy matter!
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Randall
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« Reply #5 on: February 19, 2006, 10:48:44 AM »
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Depends how big you are printing. I get the impression the original conventions for DOF were based on about x7 enlargement, x10 is common with digital so you'd need at least one extra stop. Furthermore the P25 isn't full 645 size, so if you go to one of the traditional DOF tables (if you need one just enter DOF and run a Google search) you'll need to apply an additional fudge factor.

Bottom line is that getting all that great P25 digital quality onto a print is no easy matter!
[a href=\"index.php?act=findpost&pid=58534\"][{POST_SNAPBACK}][/a]

Hi Gary,
Thanks for the response!  I should have been more clear.  The existing calulators that I am aware of are based on an old 8 x 10 contact print standard, with the circle of confusion at print size at .20 mm.  Thus, all smaller formats use a different divisor to achieve their own circle of confusion so as to achieve a .20 circle at 8 x 10.  Any thoughts on what that circle might be for the "cropped", or smaller than 645 sensor?

Again, thanks.
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Gary Ferguson
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« Reply #6 on: February 19, 2006, 11:47:01 AM »
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Most DOF charts and lens DOF engravings are based on an old Zeiss formula that measured the diagonal of the negative and then divided it by 1,730 to get an "acceptable" circle of confusion on a 10"x8" print. I think the diagonal of the P25 is about 60mm so it would suggest a COC of 0.035mm.
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Randall
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« Reply #7 on: February 19, 2006, 06:09:10 PM »
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Most DOF charts and lens DOF engravings are based on an old Zeiss formula that measured the diagonal of the negative and then divided it by 1,730 to get an "acceptable" circle of confusion on a 10"x8" print. I think the diagonal of the P25 is about 60mm so it would suggest a COC of 0.035mm.
[a href=\"index.php?act=findpost&pid=58542\"][{POST_SNAPBACK}][/a]

Thanks Gary,
I used 1730 to google for the zeiss formula, and that gave me the info I needed to reformulate for large prints.  

Thanks again!
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