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01-14-2008, 09:55 AM   #1
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hyperfocal distance and digital lenses

Hi to everybody,

To make long story short:

Do we need to multiply focal lenght of lenses designed specialy for digital camers to get right hyperfocal distance???
....
Well I've been doing some thinking lately (doesn't happen too often) and there is one riddle in my mind, which I can't solve. I've been trying to use hyperfocal distance and when calculating it I have always been putting in focal lenght x 1.5 - because of crop factor of APS-C systems...
This makes sense if one uses lenses designed for FF cameras, because their imaging circle is bigger than the area of the sensor, so calculating HF distance without x1.5 you would count with unused parts of it. However when one has "digital" lenses (DA, DA*, Tamron's Di II ...) is it necessary to multiply FL with 1.5? Imaging circle of theses lenses covers the space of the sensor, therefore I can't see why we need to multiply. What sensor/viewfinder sees is exactly what the lens sees, unlike with older lenses used on digi bodies...

Many thanx for kind answers and explanations...
Pete

01-14-2008, 10:11 AM   #2
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Make your hyperfocal calulations without the multiplier. Depth of field does not actually change between Full Frames and Cropped Frames given the same focal length.
01-14-2008, 10:58 AM   #3
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QuoteOriginally posted by AVANT Quote
Make your hyperfocal calulations without the multiplier. Depth of field does not actually change between Full Frames and Cropped Frames given the same focal length.
I would disagree with you on this one, not because you are wrong in the absolute, but because you could be wrong in the relitive.

You are correct that hyper focal length is strictly a lens function, for any given processing magnification, but remember, Hyperfocal length is a range of acceptible focus, which is a function of the size you intend to print.

If (and someone needs to look into this) the hyper focal lengths marked on digital lenses are the same as those on film lenses, I would say yes, multiply by the crop factor because you are blowing the image up by 50%.
01-14-2008, 11:23 AM   #4
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true BUT...

QuoteOriginally posted by AVANT Quote
Make your hyperfocal calulations without the multiplier. Depth of field does not actually change between Full Frames and Cropped Frames given the same focal length.
I understand you are right on this but: I think it matters what you put the lens on! Take FA lens. Put it on K10D calculate HF distance with x1.5 and take picture. Put the same lens focused on the same HF distance as on K10D, on filme Pentax and take the same picture. I'd bet my money on that the edges of your film picture would be out of focus...

01-14-2008, 11:29 AM   #5
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QuoteOriginally posted by axl Quote
I understand you are right on this but: I think it matters what you put the lens on! Take FA lens. Put it on K10D calculate HF distance with x1.5 and take picture. Put the same lens focused on the same HF distance as on K10D, on filme Pentax and take the same picture. I'd bet my money on that the edges of your film picture would be out of focus...
by take the same picture do you mean move in so that picture on film is identically framed to the one on digital, in which case depth of field changes because focusing distance has changed (therefore you need to change apature as well to get same hyperfocal setting, or are you implying that the sharpness (and focus) at the edge of the frame is not as good as in the middle.

Simply put, you cant take the same picture with the same lens on two different formats. without something changing
01-14-2008, 11:59 AM   #6
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I might not have been very clear with my last post, I'm not saying hyperfocal distance does not change, because it does. So I understand that your example, axl, will yield different results.

However the adjustment should not be made by using a focal length equivalent. You should still use the same focal lengths. You should be using a different circle of confusion in the calculating formula instead.
01-14-2008, 12:01 PM   #7
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Hyper focal distance is the distance at which an enlargement viewed at normal distance appears acceptably sharp. In the very old film days, the enlargement size that was considered as standard for this was 8 x 10 inches. (Yeah, I know it doesn't fit 3:2, but it's perfect for a 4x5).

Therefore, the multiplication is correct, because the image must be enlarged 1.5X as much from the digital sensor as from the full frame sensor. This will magnify the "circle of confusion" half as much again, in the print, making the print less sharp.
01-14-2008, 12:23 PM   #8
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QuoteOriginally posted by Canada_Rockies Quote
Hyper focal distance is the distance at which an enlargement viewed at normal distance appears acceptably sharp. In the very old film days, the enlargement size that was considered as standard for this was 8 x 10 inches. (Yeah, I know it doesn't fit 3:2, but it's perfect for a 4x5).

Therefore, the multiplication is correct, because the image must be enlarged 1.5X as much from the digital sensor as from the full frame sensor. This will magnify the "circle of confusion" half as much again, in the print, making the print less sharp.
Did some quick math.

Lets use some numbers, since 1.5 crop factor seems to be the number we're trying to compare with.

Conditions:
- Lets say the coc for our APS-C is 0.02. Using our crop factor, our coc for full frame is 0.03 (0.02x1.5).

- We will be using a 50mm lens at f/16.

Question:
- We are curious if using the focal length equivalents, would give us the same result as using the proper coc value.

Example 1: 50mm on Full Frame coc.
[(50*50) / (16 x 0.03)] + 50 = 5258mm

Example 2: 75mm on full frame coc (50mm equiv on dSLR???)
[(75*75) / (16 x 0.03)] + 50 = 11768.75mm

Example 3: 50mm on cropped frame coc.
[(50*50) / (16 x 0.02)] + 50 = 7862.5mm

Example 2 and Example 3 shows very different results.

However, Ex.1 * 1.5 = Ex. 3. So you can probably multiply the final result of your full frame calculations by 1.5 and get consistent results, but you should not be multiplying your focal lengths by 1.5


Last edited by AVANT; 01-14-2008 at 12:29 PM.
01-14-2008, 12:42 PM   #9
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This DOF calculator is better than most, it's got the lot, eyesight, print size, viewing distance, hyperfocal distance............ A Flexible Depth of Field Calculator
01-15-2008, 12:47 AM   #10
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Go here:
Hyperfocal Distance and Depth of Field Calculator - DOFMaster Make your own caclulator for which ever focal length you need.
Barnack Interesting program.
I can not be sure about this one - the home page (ComCast) is down for ComCast maintenance.
Page Unavailable

Build your own calculator's to meet your own spec's - there are hundreds of these things out there.

The Elitist - formerly known as PDL
01-15-2008, 03:46 PM   #11
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QuoteOriginally posted by Canada_Rockies Quote
Hyper focal distance is the distance at which an enlargement viewed at normal distance appears acceptably sharp. In the very old film days, the enlargement size that was considered as standard for this was 8 x 10 inches. (Yeah, I know it doesn't fit 3:2, but it's perfect for a 4x5).
Hyperfocal distance is the point at which you focus a lens to have depth of field stretch from 1/2 that distance out to infinity. That distance changes with a change to either of the following: focal length of lens or aperture.

Depth-of-field at the film plane (or sensor) will be exactly the same for a particular lens set to a particular aperture and focused at a particular distance regardless of what camera it is attached to full frame, digital, view camera doesn't matter. There are no calculations necessary, just look at the distance/aperture scale on whatever lens you have mounted (if it has a scale). Put the infinity mark opposite the aperture being used and the lens is set to its hyperfocal distance. The same aperture number at the other end of the scale tells you the closest things that will be in focus.
01-15-2008, 06:48 PM   #12
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QuoteOriginally posted by rodeknyt Quote
Hyperfocal distance is the point at which you focus a lens to have depth of field stretch from 1/2 that distance out to infinity. That distance changes with a change to either of the following: focal length of lens or aperture.
...and the acceptable circle of confusion.

Since making (for example) an 8x10 print from a smaller format requires more enlargement, the allowable circle of confusion on the film or sensor is smaller. As discussed above, you might tolerate a 0.03mm CoC on 35mm film, but only 0.02mm on APS-C. The depth of field does depend on the format being used. It is not an intrinsic property of the lens.
01-15-2008, 11:07 PM   #13
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QuoteOriginally posted by rodeknyt Quote
Hyperfocal distance is the point at which you focus a lens to have depth of field stretch from 1/2 that distance out to infinity. That distance changes with a change to either of the following: focal length of lens or aperture.

Depth-of-field at the film plane (or sensor) will be exactly the same for a particular lens set to a particular aperture and focused at a particular distance regardless of what camera it is attached to full frame, digital, view camera doesn't matter. There are no calculations necessary, just look at the distance/aperture scale on whatever lens you have mounted (if it has a scale). Put the infinity mark opposite the aperture being used and the lens is set to its hyperfocal distance. The same aperture number at the other end of the scale tells you the closest things that will be in focus.
I left out the infinity in focus part. Yes the hyperfocal distance is the distance at which everything from infinity to the closest possible distance - approximately half way to the focused distance - is in acceptable focus - when enlarged to whatever size. The hyperfocal distance for a 20x30 print is much closer to infinity (for a given f/stop focal length combination) than for a 4x6 print.

Acceptable focus is defined with reference to the printed results, not the focal length of the lens, not anything else, simply the circle of confusion on the end result. This is the point I was attempting to make. Hyperfocal formulas are useful only with reference to a given enlargement.
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