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Hyperfocal focusing with a DSLR...

Concert Images , Sep 04, 2005; 03:43 a.m.

Okay, so I'm familiar with the hyperfocal distance theory and used it with 35mm film. My D2X has a focal magnification of 1.5 times. Now for hyperfocal focusing with the D2X, do I go off the original lens focal length or its digital equivalent to calculate the hyperfocal point?

Thanks, Neil

Responses

Kar Wai Ng , Sep 04, 2005; 03:46 a.m.

It's not a focal magnification, it's a crop factor of 1.5. The focal length of the lens remains the same, and that's what you use to determine the hyperfocal point.

Neil Lupin , Sep 04, 2005; 03:58 a.m.

Problem solved, thank you!

Mark U , Sep 04, 2005; 05:25 a.m.

The variable in the equation is the circle of confusion. Divide your normal 35mm CoC by 1.5 for use with the crop factor. All other data for the equations remain the same. Note that this will produce a *different* hyperfocal distance from that you might get using a table designed for use with 35mm film or full frame digital with the same lens. Set the camera format to Nikon DX and play here:

http://ca.geocities.com/lokejul/jlcalc.htm

Hector Javkin , Sep 04, 2005; 05:28 a.m.

Not quite

The answer you received above is not quite right. Although the focal length of the lens has not changed, you will be enlarging the image from the smaller sensor to a greater degree, if you want the same size final images. With a smaller sensor (or a smaller piece of film) you would want to use a smaller circle of confusion in calculating depth of field. Check the hyperfocal distance with a program such as f/Calc. For the D2X sensor, you will want to use the APS format, not 35mm format.

Keep in mind that hyperfocal distance will give you the region of acceptable sharpness. What is acceptable to you, for what you do with your images, is something you have to decide.

Hector Javkin , Sep 04, 2005; 05:31 a.m.

The answer above I referred to was that by Kar Wai Ng. I see that Mark U answered while I was typing, saying essentially what I said.

Peter Blaise Monahon , Sep 04, 2005; 08:45 a.m.

.

Neil Lupin wrote: "Problem solved, thank you!"

Problem? Solved?

Neil, please follow up and share what you think was the problem AND the solution. Thanks!

As written already, hyperfocal distance depends on what final enlargement/print size you plan, and to some extent, viewing distance from that print, and works backwards from there to calculate acceptable unsharpness at the film/sensor capture plane.

Since 1.5x is a crop factor, better written as 1/1.5x or 66.67% capture, then presumably, IF you enlarge to the same final output/print size and viewing distance as you have been enlarging 35mm film, THEN presumably you will also enlarge the image capture "points" by an additional 50% (100%/66.67%) over what you were used to seeing.

Since it's those "points" that get enlarged eventually appear as "circles" as they get more and more enlarged, I wonder if you ever calculated your acceptable "circle of confusion" for 35mm film before you switched to digital, and THAT may be where you got stuck. Not knowing your true standards for 35mm, it's hard to figure new standards for digital 66.67% capture, eh?

So, please report back on what you find and what are your calculations now.

Specifically, I'm curious about your enalrgement/print final output size and viewing distance and what YOU think of it.

How about sahring an illustrative picture with EXIF data?

And also, YOU tell US what is the nearest and farthest satisfactorily (to you) "in focus" subject element, and at what hyperfocal distance you set the lens to achieve that.

Isn't the science behind our art fun! ;-)

Thanks!

Click!

Love and hugs,

Peter Blaise peterblaise@yahoo.com http://www.peterblaisephotography.com/

PS - For a contradictory opinion on hyperfocal distance, based on clarity of near objects being usually larger and easier for the viewer to resolve if unsharp compared to farther objects whose recognizability depends on much more critical focus, see Harold K. Merkliner's fascinating (to me) book "The INs and OUTs of FOCUS" free on line at http://www.trenholm.org/hmmerk/

One way I interpret Merkliner's book is to set the lens on infinity and let 'er rip!

At infinity, subject information is small, and focus is critical. Near subject items are larger by comparison, and focusing is less critical, and the viewer will more easily recognize closer subject detail even if it is not sharp. However, if distant, smaller subject detail is equally unsharp, thise smaller objects cannot as easily be recognized by the viewer, and the success of the whole pciture is in question! In other words, pick the thing you want sharp, focus on it, and shoot!

But you all read it and "see" for yourselves if your experience bears out the "traditional" hyperfocal calculations based on circles of confusion regardless of subject content, versus alternative insights which do take the size of subject content into consideration.

Jean-Baptiste Queru , Sep 04, 2005; 10:56 a.m.

It depends whether you want something that was defined "acceptable" when compared to the film emulsions of 70 years ago, or if you want something that is "critically" sharp according to today's standards.

The "normal" circle of confusion is 30 microns in diameter, i.e. 5.5 pixels in diameter on the D2X.

Personally, I recommend to use a CoC of about 2 pixels in diameter (at most), which on the D2X is 3 stops away from the marked scale.

Don't forget the effects of diffraction. Stopping down below f/11 will actually have some negative effects on your entire scene.

Here's the table that I recommend if you want critical sharpness:

If the scale tells you to use f/2, use f/5.6

For f/2.8, use f/8

For f/4, use f/11

(up to that point, it was 1-stop for 1-stop. Starting here, diffraction occurs, so it's 2-stop for 1-stop).

For f/5.6, use f/13

For f/8, use f/16

For f/11, use f/19

For f/16, use f/22

That table is only valid for the D2X, and it's a "standard" DoF scale. Typically, when you want to invoke the hyperfocal distance, your primary subject is actually at infinity, so you probably want it to be as sharp as possible, and within those conditions to get as much as possible in focus in the foreground.

Based on my numbers, I'd recommend putting the infinity mark between the f/2.8 and f/4 marks, and to shoot at f/11.

Those numbers might actually be somewhat conservative, but I assume that if you have a D2X the reason is that you want the higher possible resolution.

There's a magic value in the process, which is f/32 (that's the value at which the CoC and the diffraction spot have a similar effect, i.e. the value where the marked scale is optimal). There's a second value which depends on the camera, and which I assumed to be 3 stops. 3 stops up from f/32 is f/11, and for shooting apertures larger than f/11 the DoF marks to use are 3 stops up from the seemingly correct values.

You can do you own testing to find whether 3 stops is what works for you. In good experimental conditions (tripod, remote release or timer, sharp lens - 50/1.8, focus on infinity), with a detailed subject, take a series of test shots from f/8 to f/22, and study the detail at the pixel level. The first few shots should be virtually identical in terms of sharpness at infinity (f/8 to probably f/11), and then it'll go down (probably f/16 to f/22). Figure out the smallest aperture that you can use and which produces acceptable results. If you find f/13, you're actually 2.5 stops from f/32 (instead of my theoretical 3 stops). That means that f/13 is the center value, and that when shooting at apertures larger than f/13 you want to shift the marked scale by 2.5 stops.

That method still doesn't create absolutely critically sharp pictures. If that's what you want, use an extra 1/2 stop (i.e. if you find that 2.5 stops works for you with perfect focus, use 3 stops when working with the DoF scale. If 3 stops works for you with perfect focus, use 3.5 stops with the DoF scale).

I'm sure that some people are going to scream that my numbers are too small, that there's no DoF at all, that it can't be true. That's because my numbers are geared toward near-critical sharpness at the pixel level, not at "acceptable" 8x10 prints viewed from a "standard" distance. My philosophy is that I like my good pictures to be enlarged as much as I can get away with, and that having a picture that looks good on a small print but isn't sharp when enlarged is a major disappointment.

Bob Atkins , Sep 04, 2005; 11:04 a.m.

See http://www.bobatkins.com/photography/technical/digitaldof.html

With small sensor cameras DOF increases and for any given focal length and aperture the hyperfocal distance increases by the "focal magnification" or "cropping factor".

Godfrey DiGiorgi , Sep 04, 2005; 06:26 p.m.

Another DoF calculator:
DoF Master - http://www.dofmaster.com/dofjs.html

As a general rule, given a lens with the SAME field of view, you get about one stop more DoF with a 16x24 format DSLR than you do with a 24x36 format camera at the same aperture and focus setting. Conversely, given the SAME focal length, you get about one stop less DoF..

Godfrey

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