hyperfocal distance

A 50mm lens is a 50mm lens. Which means that the depth of field and, therefore, the hyperfocal distance stays the same. Those are lens properties.

allan
 
As it happens, I just created some DOF charts last week for focal lengths useful for the R-D1.

Here's the Word file:

http://www.richcutler.mistral.co.uk/photo/_misc/DOF_Charts.doc

The R-D1 equivalent focal length is rounded up or down to the nearest whole number.

DOF works just the same for digital cameras as for film ones - you just have to take the crop factor into consideration. In other words, if using the same lens on an R-D1 and a Leica, the DOF on the R-D1 will be that of lens 1.53 x the lens focal length (e.g. for a 50 mm lens the DOF will be that of a 75 mm).
 
kaiyen said:
A 50mm lens is a 50mm lens. Which means that the depth of field and, therefore, the hyperfocal distance stays the same. Those are lens properties.

allan
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Yes, the formula is the same for every format. But the acceptable circle of confusion differs for film/sensor size, and therefore the hyperfocal distances.

Example:
A 50mm at f8 for 35mm with a common COC of 0.033mm has a hyperfocal distance of 4.75m to infinity when focused at 9.5m

A 50mm at f8 for 6x6 with a common COC of 0.050mm has a hyperfocal distance of 3.15m to infinity when focused at 6.3m
 
Thanks for the Word tables. I printed them out, and now I'm going to take them down to my dock and shoot some pictures of the Wiscsonin shoreline, and see what I can keep in focus...
However -- there are at least three replies here all of which seem to say slightly different things, but all of the people seem to know what they are talking about. Does anybody have a printed or on-line source which explains the whole CoC/focal length/hyperfocal business? What I'm curious about is that printed tables seem to differ, even for the same lenses/apertures/sensor sizes, which suggest that some assumptions are being made that plug in different ways into the calculations. Is that assumption the size of the CoC? Or what?

JC
 
Are the depth of field indicators on my Leica lens still accurate when used on the R-D1? Can I use them to find the hyperfocal distance?

Thanks,
Ken
 
kepstein said:
Are the depth of field indicators on my Leica lens still accurate when used on the R-D1? Can I use them to find the hyperfocal distance?

Thanks,
Ken
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Really good question there.. i was assuming they were, i'd never considered that they might be wrong. My VL 15mm lens can only be focused by the lens markings.. kinda crucial that they're right, or fixable (going 1 aperture down to get the roughly equivelant range)
 
You shouldn't have a problem with setting the hyperfocal distance on a lens being used on the RD-1. The distances within the covered focus will be fine. The RD-1 chip crops the effective focal length or field of view within the specific coverage of the lens being used.

In a word, using your lenses on a RD-1 shouldn't affect the hyperfocal distance, only the effective length.
 
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Argh. Circles of Confusion. Sorry, I forget that all the time. My very basic response:

1 - a 50mm lens is a 50mm lens. Basically, DOF is the same.

2 - BUT - circles of confusion change. The circle of confusion basically defines the edges of "acceptable" sharpness that go from the front to the back of your depth of field. If you have hyperfocal from, say, 10' to infinity, it's not absolutely sharp that whole distance. It's just acceptablly sharp (or better) from 10' to infinity.

So if the circles of confusion change with digital, then it becomes, like, 11' to infinity or something.

One rule I often use is to set the lens for hyperfocal at f8, then set the lens to f11. I still use this when I can. And it'll work for digital, too :)

allan
 
kaiyen said:
One rule I often use is to set the lens for hyperfocal at f8, then set the lens to f11. I still use this when I can. And it'll work for digital, too :)

allan
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I'd go with this approach - all the confusion stems from thinking that HFD is some sort of precise measure, whereas in reality, it's an approximation and very subjective.

I would always use the DOF markings for 1 stop wider than I was actually using, even with film, so I'd set the focus as if using 5.6, say, and then shoot at f8.

There is a thread here somewhere where someone did all the calculations, but I think that's overkill.

In general, the crop factor decreases the DOF because you end up enlarging the image more to make up for the smaller image size. BUT the effect is less than you'd think, so it's really more like 1.25 rather 1.5 reduction in DOF. Best to play safe, and just use the next smaller f stop.

The bottom line is, experiment, and see what works for you.

By the way, I would disagree with the idea that a 50mm is a 50mm and has the same DOF however it's used.

DOF is not a property of the lens, but a property of the final image - whether something is sharp enough or not can only be judged from the final print or whatever. It depends on the whole system, including the subject matter - what's sharp enough in a portrait might not be in a landscape.
 
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pfogle said:
DOF is not a property of the lens, but a property of the final image - whether something is sharp enough or not can only be judged from the final print or whatever. It depends on the whole system, including the subject matter - what's sharp enough in a portrait might not be in a landscape.
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I did the computations because I am a mathmatician and I would probably do it even if it had no practical value whatsoever. :D Anyhow, you are quite right.

The image of an out of focus point is essentially a circle (disk) on the negative or sensor. Now if the image is blown up to 8"x12" and viewed in a gallery under some sort of "standard" lighting at a "normal" distance, the point may still look like a point (dimensionless dot) or it may appear to be a circle. The maximum diameter of the circle on the negative which still appears to be a point in an 8"x12" blow-up in a gallery environment is the circle of confusion. This is obviously a subjective call, but the COC determines "acceptable focus," which in turn determines hyperfocal distance, depth of field, and all that good (?) stuff.

Anyhow, if "acceptable sharpness" is taken in the traditional sense of the term, then if the crop factor is, say, 1.5, then hyperfocal distance of a 50mm lens will be approximately that of a 61mm lens. (Multiply the focal length of the 35mm lens by the square root of the crop factor: 50 x 1.22 = 61.)

Personally, I don't like relating properties of lenses on a digital camera to corresponding properties of lenses on a 35mm camera because 35mm is sort of an arbitrary standard of comparison.
 
richard_l said:
Personally, I don't like relating properties of lenses on a digital camera to corresponding properties of lenses on a 35mm camera because 35mm is sort of an arbitrary standard of comparison.
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Richard, I think it's not that we're comparing properties of lenses on different bodies, but that the DOF scale marks on most lenses are calculted assuming a full frame image. Hence the need for the charts for the Nikon DSLRs etc.
 
pfogle said:
Richard, I think it's not that we're comparing properties of lenses on different bodies, but that the DOF scale marks on most lenses are calculted assuming a full frame image. Hence the need for the charts for the Nikon DSLRs etc.
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Good point.
 
After some pondering, I've come to the conclusion that my DOF charts are wrong - not fundamentally wrong, as the trend that the R-D1 has shallower DOF for a given focal length compared with 35 mm film is correct. It's just the DOFs are too shallow! :bang:

New charts can be downloaded:
www.richcutler.co.uk/downloads/DOF_Charts.doc

My error was calculating the DOF using focal lengths scaled up using the R-D1 crop factor of 1.53 (e.g. 50 mm x 1.53 = 77 mm). As kaiyen says, the focal length can't change!

(It is, though, valid to say that a 50 mm lens on the R-D1 gives the same field of view as a 77 mm lens would on a 35 mm camera - but that (I now know!) has no connection with DOF!)

What does change is the circle of confusion (CoC). A lens is only sharp at one distance - any nearer or further results in tiny out-of-focus circles on a photograph (i.e. the CoCs). So, the larger your printed photo, the more obvious the out of focus areas, and consequently the smaller you need the CoCs to be to keep the print looking sharp. As the 35 mm format is 1.53 times larger than the R-D1 sensor, if an R-D1 image and a 35 mm negative are to be printed on to identically sized paper and appear equally sharp, the R-D1 image will need 1.53 times more enlargement than the 35 mm negative. Consequently, the R-D1 CoCs need to be 1/1.53 (= 65%) smaller.

The choice of the upper limit for CoC size for a particular format can vary quite a bit - values for the 35 mm format are typically in the range of 0.025 to 0.050 mm. I prefer 0.028 mm, as this seems widely used. Applying the R-D1 crop factor gives 65% x 0.028 mm = 0.018 mm - which is the value I used in my new charts.

What this means in practice is: for a lens on an R-D1 the DOF and hyperfocal length are approximated by the next widest whole stop on the DOF scale.

For example, if you set the aperture to f/8, the DOF is the distance between the f/5.6 marks; and to set the lens at the hyperfocal distance for f/8, align the infinity symbol on the distance scale with the f/5.6 mark.
 
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RichC said:
What this means in practice is: for a lens on an R-D1 the DOF and hyperfocal length are approximated by the next widest whole stop on the DOF scale.
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That's a handy approximation. It would be exact if the crop factor were 1.414 instead of 1.53, but it's close enough.
 
I thought, having read it many times, that a smaller sensor will give you a greater depth of field for any given aperture, so you could use the DoF scale on your 35mm lens on the RD1 and know that you will be in the right zone - that is have more DoF than the DoF scale shows. Conversely, the larger the format the smaller the aperture required for acceptable DoF - why large format guys shoot at f64. What you guys are saying is the opposite?? Practice (I use hyperfocal/zone focusing a lot) suggests that I am either right, very lucky or have crappy eyesight - maybe both of the last two :)
 
Gid - well, what it really is that people are using shorter lenses on digital to get the same field of view as with a longer lens on 35mm film cameras. So to get your desired composition with digital you need a 35mm lens. To get the same composition with 35mm film you need a 70mm lens. To get the same composition with 6x6 medium format is about...105mm? Something like that? My 5x7 camera would be about 300+mm lens.

Remember that as you get a longer lens from without changing distance to the subject (which is what is hapening here) you lose DOF. So for each of the above situations, to get the same DOF you need to stop down.

So it's not that digital gives you more DOF, it's that you have to use wider lenses with digital. It's the wider lens that gives more DOF.

allan
 
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