Luminous Landscape Forum
Equipment & Techniques => Cameras, Lenses and Shooting gear => Topic started by: francois on June 12, 2005, 03:00:12 pm
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You can build a dof table yourself!
Visit this website (http://www.dofmaster.com/).
Hope this helps,
Francois
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David,
You don't have to purchase any software... There's an online DOF calculator (http://www.dofmaster.com/doftable.html). Hyperfocal distances are at the bottom of the table.
Have fun,
Francois
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How do i find the hyperfocal distance of my sigma 15-35mm?
thanks
David
I google and did't find it
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Thanks francois .. Ill take a look
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Thanks francois .. Ill take a look
I don't think that h/f distance is really as applicable to zooms as to primes...I could be wrong?
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I don't think that h/f distance is really as applicable to zooms as to primes...I could be wrong?
Why wouldn't it be?
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David,
You don't have to purchase any software... There's an online DOF calculator (http://www.dofmaster.com/doftable.html). Hyperfocal distances are at the bottom of the table.
Have fun,
Francois
That gives 2mm @ f8 @2m @ CoC = 0.01 @150mm... seems about right!
What Circle of confusion do you use for an AA-free 6 micron pixel-pitch sensor and a lens capable of 40 lp/mm? CoC= .03 or .04 seems to give realistic DOF for 150mm portraiture at f16?
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Why wouldn't it be?
Not so much an impossibility as the degree of difficulty.
You'd have to calculate it for each focal length within the zoom range, and consult the table each time you zoomed. Gives me a headache just thinking about it. The DOF scale makes life much easier.
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Slightly off topic, but I have always wondered why Canon did away with the DEP function on their EOS bodies. It was there on my EOS3 film body, and my EOS5 body before that, and I found it supremely useful - it enabled me to set the hyperfocal distance on any lens, zoom or prime, DOF scale or none. I always used to set the aperture one stop smaller than the computer told me to, just to be sure.
I love my 5D and would not go back, but I really miss this particular feature... why did Canon take it away?
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Not so much an impossibility as the degree of difficulty.
You'd have to calculate it for each focal length within the zoom range, and consult the table each time you zoomed. Gives me a headache just thinking about it. The DOF scale makes life much easier.
You do have a focal length scale on the zoom - put the formula into excel and use it on your laptop or download it to you mobile phone.
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For anyone doing this with anything more than a casual approach:
There is not a single table/chart calculator in the world which will substitute doing your own HF testing for each lens/body/back combo you own. There is variation in every lens mount, lens focus barrel, body/back/film mount and the sticky matter of what is "acceptably sharp".
Doing this tethered, e.g. to Capture One Pro makes life MUCH easier (since you can see sharp/not sharp instantly and compare two images instantly on a large monitor).
1) start off at a "good aperture" like f/8* and see what the sharpest image you can get is for infinity
2) stop down to your desired working aperture**
3) very slowly back off of infinity taking shots at the smallest increments possible until you detect a loss of sharpness that you find personally unacceptable
4) move towards infinity slightly to allow wiggle-room for slight changes over time and because of temperature
5) record the exact HF distance on your lens cap.
Alternatively you can purchase from a dealer who can do that with you in person as a service.
*if you don't know the sharpest aperture for your lens then you should test that first
**if you haven't tested to find your desired working aperture (balancing diffraction against sharpness)
***In Capture One Pro you can select the sharp image from step #2 and push "Enter" and that reference image will stay on the screen as you continue to shoot the comparison images - making it dead simple to compare the sharpness of each focus-distance to the reference image.
Doug Peterson ()
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For anyone doing this with anything more than a casual approach:
There is not a single table/chart calculator in the world which will substitute doing your own HF testing for each lens/body/back combo you own. There is variation in every lens mount, lens focus barrel, body/back/film mount and the sticky matter of what is "acceptably sharp".
*if you don't know the sharpest aperture for your lens then you should test that first
**if you haven't tested to find your desired working aperture (balancing diffraction against sharpness)
[/i]
Hi, Doug...
Hence my question:
"What Circle of confusion do you use for an AA-free 6 micron pixel-pitch sensor and a lens capable of 40 lp/mm? CoC= .03 or .04 seems to give realistic DOF for 150mm portraiture at f16?"
I think the lens is best at f8, but, if you want a whole head of hair sharp, f16 seems better.
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1) start off at a "good aperture" like f/8* and see what the sharpest image you can get is for infinity
If only this sentence made sense your advice would be so much more useful.
"...the sharpest image you can get is for infinity.''
Huh ?
I've been shooting professionally for over 30 years and fully understand using hyper-focal distance but have no idea what your trying to say.
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Hi, Doug...
Hence my question:
"What Circle of confusion do you use for an AA-free 6 micron pixel-pitch sensor and a lens capable of 40 lp/mm? CoC= .03 or .04 seems to give realistic DOF for 150mm portraiture at f16?"
I think the lens is best at f8, but, if you want a whole head of hair sharp, f16 seems better.
Hi Dick,
I doubt your lens is only capable of resolving 40 lp/mm, but diffraction theory alone predicts the following in combination with a 6 micron sensel pitch.
For green light (e.g. 555 nm) the diffraction pattern diameter is 10.8 microns for f/8 and 21.7 microns for f/16, assuming circular apertures. That computes to 1.8 and 3.6 sensels wide. In my experience there will be visual deterioration from diffraction at the pixel level when the diffraction pattern diameter exceeds a 1.5 sensel pitch diameter (makes sense if you consider the diagonal distance between 'square' sensels is 1.4 sensel pitches). It will become difficult to discriminate between 2 closely spaced features because they 'bleed' into the neighboring sensels, thus reducing their relative contrast.
Now that reduced contrast only matters at the pixel level. If your output size doesn't demand per pixel contrast, e.g. when downsampling, then there is no issue. However, when enlarging there is some advanced (deconvolution) sharpening needed to recover some of the per pixel contrast losses.
So, as always, the CoC is a function of output magnification (and viewing distance). However, the diffraction math already predicts that at f/16 things won't improve significantly for a CoC that's smaller than 0.0217 millimetres (=3.6 sensel widths), and that assumes a capable lens to begin with.
As Doug suggested, only testing will reveal how a particular lens' residual aberrations play together with diffraction and sensel pitch.
Cheers,
Bart
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Not so much an impossibility as the degree of difficulty.
You'd have to calculate it for each focal length within the zoom range, and consult the table each time you zoomed. Gives me a headache just thinking about it. The DOF scale makes life much easier.
I use zooms like a series of primes. Otherwise I can't pre-visualize. So it isn't that bad.
Of course if I want to be sure about dof I just chimp.
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Hi Dick,
I doubt your lens is only capable of resolving 40 lp/mm, but diffraction theory alone predicts the following in combination with a 6 micron sensel pitch.
For green light (e.g. 555 nm) the diffraction pattern diameter is 10.8 microns for f/8 and 21.7 microns for f/16, assuming circular apertures. That computes to 1.8 and 3.6 sensels wide. In my experience there will be visual deterioration from diffraction at the pixel level when the diffraction pattern diameter exceeds a 1.5 sensel pitch diameter (makes sense if you consider the diagonal distance between 'square' sensels is 1.4 sensel pitches). It will become difficult to discriminate between 2 closely spaced features because they 'bleed' into the neighboring sensels, thus reducing their relative contrast.
Now that reduced contrast only matters at the pixel level. If your output size doesn't demand per pixel contrast, e.g. when downsampling, then there is no issue. However, when enlarging there is some advanced (deconvolution) sharpening needed to recover some of the per pixel contrast losses.
So, as always, the CoC is a function of output magnification (and viewing distance). However, the diffraction math already predicts that at f/16 things won't improve significantly for a CoC that's smaller than 0.0217 millimetres (=3.6 sensel widths), and that assumes a capable lens to begin with.
As Doug suggested, only testing will reveal how a particular lens' residual aberrations play together with diffraction and sensel pitch.
Cheers,
Bart
Thanks, Bart...
I got my HC 300 today, and there is an interesting test location 100m down the road, with a row of old brick buildings from 30m to 300m away, and according to Rags DOF, @CoC = 0.03 and f8, I will need to DOF merge 8 exposures to get it all in focus!