DOF calculators/spreadsheets. recommendations?

[Gregory]

A few days ago, I was shooting photos at a friend's wedding. I wasn't the official photographer, simply an enthusiastic friend. upon returning home, I reviewed the photos and found that in many cases, one of the bride and groom would be sharp but not both, even with an aperture of 5.6 or 8 which was the smallest aperture realistically useable even at ISO3200 because of the limited lighting in the church.

I need a DOF calculator. I would prefer to build a spreadsheet for multiple apertures/focal lengths/COCs and print them out to take with me for reference. if I could add the Hyperfocal distances to the spreadsheet, that would be an added bonus but nowhere near as important as the DOF figures. the DOF data would also help me when photographing birds where the DOF is often 1/2" or less.

could someone please point me to one or more pages that would have the information I need to build the spreadsheet or perhaps copy one? it would be great if the formulas were available in full.

(practically, two COCs would be sufficient; one for printing 10 megapixels to A4, and one for printing 10 megapixels to A3 where the viewing distance would probably be equivalent to the diagonal of the printed image.)

regards,
Gregory

[Gordon Buck]

http://www.dofmaster.com/

[wolfnowl]

Also

http://www.stegmann.dk/mikkel/barnack/
http://www.bobatkins.com/photography/technical/dofcalc.html

Mike.

[Jonathan Wienke]

http://www.visual-vacations.com/Photograph...calculation.htm

It has DOF, hyperfocal distance, and paramaters for calculating the correct CoC for your digital camera.

[Gregory]

thank you everyone. Jonathan had what I was after; something relatively simple that I could understand, edit and rearrange to suit my needs.

two questions:

1. a number keeps popping up in the spreadsheet calcs:  3.28084. what is this number?

and...

2. he doesn't use the CoC to calculate the DoF. is the CoC unnecessary to calculate the DoF?

regards,
Gregory

[Gregory]

one more question.

according to the spreadsheet, photographing a bird 8' away with a 300mm lense at f16 only produces a DoF of 0.527". does this seem reasonable?

if so, no wonder I'm having problems getting sharp photos of our small intriguing neighbours. f16? I barely have enough light to shoot at f11, and 8' is actually too far away in many cases to get the ideal photo. most of our cute neighbours are only 2 to 4" tall.

P.S. does the spreadsheet take into account the multiplier? is this made unnecessary by calculating the CoC from the sensor's resolution?

regards,
Gregory

[Jonathan Wienke]

thank you everyone. Jonathan had what I was after; something relatively simple that I could understand, edit and rearrange to suit my needs.

two questions:

1. a number keeps popping up in the spreadsheet calcs:  3.28084. what is this number?

and...

2. he doesn't use the CoC to calculate the DoF. is the CoC unnecessary to calculate the DoF?

1. Which cell is the number in you're asking about?

2. You can't calculate DOF without a CoC value; my spreadsheet calculates this for you from the sensor dimension and resolution. The CoC value used is the pixel pitch of the sensor--the center-to-center spacing between one pixel and the next.

Do not use a multiplier for the focal length; use the actual focal length of the lens. Otherwise the results will be skewed.

[AJSJones]

one more question.

according to the spreadsheet, photographing a bird 8' away with a 300mm lense at f16 only produces a DoF of 0.527". does this seem reasonable?

if so, no wonder I'm having problems getting sharp photos of our small intriguing neighbours. f16? I barely have enough light to shoot at f11, and 8' is actually too far away in many cases to get the ideal photo. most of our cute neighbours are only 2 to 4" tall.

P.S. does the spreadsheet take into account the multiplier? is this made unnecessary by calculating the CoC from the sensor's resolution?

regards,
Gregory
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Gregory, You have learned a couple of things already from that reaction
1) 300mm is not that much reach for bird photography and  
2) With computers and the ability to pixel peep, the CoC selection is not what it used to be

Old DoF scales were based on a given degree of enlargement from a physical piece of film and a given viewing distance etc.  Your result of 0.5" DoF is based on a CoC of around 7 micrometers, a typical pixel spacing.  If you use the CoC for 35mm film, you'd get 2.2".  
Therefore,
If you are going to assess DoF by looking at full size images (100%) on your monitor, you should use the 0.5" DoF value.  If you are wondering how a print would look and what parts are now in focus because the viewed image is not as large as the one on your screen, you can increase the CoC.It doesn't make much sense, intuitively, to contemplate using a CoC of smaller than the pixel pitch.
Many folks will make a print based on the pixels they have and their print(er) quality, without regard for geometric enlargement factors.  I typically use 240 or 300 ppi for bird shots I want to print, cropping/composition is an artistic decision and these two result in the (maximum) final print size I can get from an image. (Judicious sharpening, uprezzing etc aside)
Doug and Jonathan's calculator uses pixel pitch for these reasons.  The geometric enlargement factors for 240 (300) ppi prints are in the range of 12-18x (10-15x)  depending on pixel pitch, while 35 mm film factors (for the "old" way of calculating DoF) are in the range of 8x, so one is enlarging quite a bit more, so the DoF has gone down.
To resolve this, so to speak, you can make some prints at different conditions and assess the DoF compared to the screen - then make your own decision on CoC to use - it's a very important issue for bird photography - once you've bought your super-tele lens  


Andy

[Jonathan Wienke]

Use the sensor pixel pitch as your CoC value whenever you are not downsampling to print. For small prints, where printing full resolution would give you a PPI >300-360 (depending on printer model and paper type), a larger CoC value can be safely used. How much larger depends on how much you downsize; if you downsize to half the pixel dimensions, you can double the CoC value, and so on. But for any print size where you upsize or print full resolution, using the sensor pixel pitch as your CoC value will accurately predict print DoF.

[Jack Varney]

Gregory, the value 3.28084 is the number of feet per meter. It must be used to convert meters ( since most lenses are speced in mm) to feet.

[Gregory]

Andy,

thank you.

Q. if the CoC of the sensor is 7 micrometres and the image is enlarged 10x (Mark III sensor 18.7mm -> 187mm; i.e., ~7.5"), does that mean the CoC effectively becomes 70 micrometres with a similar increase in DoF? but aren't sensor CoC and image CoC two different things? one depends on the physical structure of the sensor (bayer assembly), while the other depends on the ability of the eye to differentiate line pairs at a given distance; usually the diagonal of the image. and wouldn't the image CoC need to be a multiple of the sensor CoC because you can't get half a pixel from the sensors?

"But for any print size where you upsize or print full resolution, using the sensor pixel pitch as your CoC value will accurately predict print DoF."
so if I print my images to A4 without interpolation (i.e., without altering the pixel count), the DoF in my 8'/300mm/f16 example would still be .5"?


Jonathan,

my apologies. I'm sleep deprived and an idiot. I should have realised that the Hyperfocal values were being used to calculate the near/far focus points and the CoC was therefore being used in the calculation of the DoF.

sincerely,
Gregory

[Jonathan Wienke]

Q. if the CoC of the sensor is 7 micrometres and the image is enlarged 10x (Mark III sensor 18.7mm -> 187mm; i.e., ~7.5"), does that mean the CoC effectively becomes 70 micrometres with a similar increase in DoF? but aren't sensor CoC and image CoC two different things? one depends on the physical structure of the sensor (bayer assembly), while the other depends on the ability of the eye to differentiate line pairs at a given distance; usually the diagonal of the image. and wouldn't the image CoC need to be a multiple of the sensor CoC because you can't get half a pixel from the sensors?

Image DoF and print DoF can be different, but it is unwise to count on such a state of affairs. If you're looking at a 4x6" print from across the room, effective CoC becomes fairly large and DoF becomes correspondingly large because you can't see ANY detail in the image particularly well. The print size and viewing distance and your visual acuity limit your ability to see image detail to far less than what is contained in the original image.

But if you are looking at a 24x36" print closely, it's a pretty safe bet that the original capture is the primary limit on viewable image detail, and in such circumstances the sensor pixel pitch becomes the print CoC (modulo the print enlargement factor)  and primary limiter of DoF. Printing at full resolution (whatever the size) does not increase DoF because while the print CoC increases in size, its ratio to print dinensions stays exactly the same and everything cancels out. There is no free lunch.

so if I print my images to A4 without interpolation (i.e., without altering the pixel count), the DoF in my 8'/300mm/f16 example would still be .5"?

Absolutely.

[Gregory]

out of curiosity, would 35mm slide film enlarged 10x have a larger DoF than a 7-micron digital image?


Andy, pray tell, what aperture do you typically use when photographing small (≤4") birds?

[AJSJones]

out of curiosity, would 35mm slide film enlarged 10x have a larger DoF than a 7-micron digital image?
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Not that can of worms!   Here's a few thoughts, but be prepared for heavy duty discussion!  It matters what kind of film you are working with and the capability of your printer too.  10x from 35mm is probably at or just beyond the limit of the film - i.e. at normal viewing distance your eye may be limiting, while making a similar size print from e.g. a 1Ds3 would likely test the printer and how well it can lay down the (much) greater amount of information from 22MP - as Jonathan says, the appropriate CoC would depend on the degree of downsampling (to get you back from pixel limited output to a specific geometric enlargement).  Put another way, at up to 8-10x you might not see much difference in DoF, but as you go up in size from there, the image quality difference would become very apparent; result : the 35mm image would appear fuzzier overall, while the 22MP image would allow your eye to differentiate the "sharpest" areas better (from those JUST outside the DoF) and the DoF would therefore go down as discussed above....

Andy, pray tell, what aperture do you typically use when photographing small (≤4") birds?
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I'm usually stopped down one or two stops from wide open, but also usually further than 8 feet from those little birds.  With my 500/4 often at f/8, with the 1.4x at f/9 to f/11 ; however, DoF/aperture is but one of the variables - shutter speed ( to account for both my movement and subject motion) ISO, distance, angle of bird to camera etc.  If the eye is in focus that typically gets the important parts also in focus, and the eye can tolerate a bit of the front of the wing being a bit OOF (too much and it becomes distracting and ruins the shot, but a little is OK) - however, if the eye is out of focus, the shot's toast anyway.  Photographing small birds with a tele lens from some distance challenges the shooter in about every (technical) aspect of photography!  (Including your stealth/ability to get closer without spooking the subject   )

Have fun!
Andy

[Gregory]

Andy said:
[span style=\'font-size:8pt;line-height:100%\']"however, DoF/aperture is but one of the variables - shutter speed (to account for both my movement and subject motion) ISO, distance, angle of bird to camera etc. If the eye is in focus that typically gets the important parts also in focus, and the eye can tolerate a bit of the front of the wing being a bit OOF (too much and it becomes distracting and ruins the shot, but a little is OK) - however, if the eye is out of focus, the shot's toast anyway. Photographing small birds with a tele lens from some distance challenges the shooter in about every (technical) aspect of photography! (Including your stealth/ability to get closer without spooking the subject B)"[/span]

:-)  you've confirmed everything I've discovered about photographing small birds! not easy, but the challenge of getting good photographs against all odds is what keeps it interesting, and the rewards can be very satisfying and enjoyable to view.

thank you.

regards,
Gregory

[Jonathan Wienke]

out of curiosity, would 35mm slide film enlarged 10x have a larger DoF than a 7-micron digital image?

Yes, because everything would be less sharply focused, so you'd have nothing "sharp" to compare it to. The digital image raises the standard of what "sharp" is, and the higher sharpness standard can only be met in a narrower focus range if the same imaging area and aperture size and focal length are used in both.