D100 and Hyperfocal Distance
A little help please I am have a hard time getting my head around Hyperfocal distance with a D100.
Is it correct to assume that if you are using a 50mm focal length lens on a D100 it is the same as using a 75mm focal length lens on a film camera???
If it is, then when using JRP's Hyperfocal Distance Chart, do you still use the 50mm reading or do you split the 70mm and the 80mm????
#1. "RE: D100 and Hyperfocal Distance" | In response to Reply # 0bobj Charter MemberTue 14-Jan-03 01:17 AM
No, a 50mm lens is still a 50mm lens, not a 75mm lens; it is only that the image gets cropped in the D100.
Depth of field (and thus hyperfocal distance) is a bit more complicated than even that though since it also depends on something called "cicle of confusion." Essentially, the plane of focus is always just a plane, but things in somewhat in front of and behind that plane can still "look like" they are in focus. If you photograph a true point source of light, in focus it will appear as a point. Slightly out of focus, it will begin to look like a disc and not so much like a point. If it is almost in focus, it may still look like a point, or it may not, depending on how close you look. Since the sensor in a digital camera is smaller than the 35mm frame size (in most cases at least), you have to enlarge the resulting image more to get results of the same final print size. Since the raw image from 35mm has to be magnified less to view the same size, 35mm images can tolerate being more out of focus and still look like they are in focus, when compared to an image from a smaller format like most DSLR's. As such, the acceptable "circle of confusion" (the size of a disc below which the point of light still looks like a point) on film/CCD is smaller for a digital camera than film.
So, what this means is that even though a 50mm lens is still a 50mm lens, it actually will give you *less* depth of field than a 50mm lens on a film camera. Of course, once you crop that image to look like you took it with a 75mm lens, you now have *more* *apparent* depth of field when comparing with a similarly cropped image from 35mm taken with a true 75mm lens. Gosh.
Bottom line, your depth of field with a 50mm lens on digital will be somewhere between that of the same lens on 35mm and that of a 75mm lens on 35mm. Given that hyperfocal distance is the point at which the far bound of your depth of field just touches infinity, it too will depend on the circle of confusion (CoC) for digital rather than 35mm.
For lots more info and charts based on different digital cameras (not all sensors are exactly the same size) check out the truly wonderful site at http://dfleming.ameranet.com - by far the best on the net for depth of field and hyperfocal calculations for film or digital.
Nature Photography from the Pacific Northwest and beyond
#2. "RE: D100 and Hyperfocal Distance" | In response to Reply # 1dankeny Nikonian since 29th May 2006Tue 14-Jan-03 12:59 PM
Sometimes I go to your site just to relax. Your work is killer bee.
The easiest way for me to think about DOF and D100 is relative to the film plane. For the same image size (not picture size) in the final product from a D100 shot and a 35mm shot, the depth of field will be exactly the same with the same lens and exposure values. If you want the math, see Manual of Photography, 13th. But then there is that pesky crop factor. Because we relate everything to the 24x36 frame size, we expect to magnify the image from the D100 about 1.5 times as much as the 35mm image during post recording processing. The larger the final product, the less tolerate is our eye to out of focus points. Enter circle of confusion. That's why DOF calculations for the D100 use values that are ~2/3 (the reciprocal of 1.5) of the 35mm counterparts. See the excellant Nikonians DOF pages for example, where for 35mm DOF c=.025 and for DSLRs c=.016. When I read posts from D100 users that think the images are soft, I wonder whether it is a DOF issue. DOF is the area that appears in focus. It isn't really a 75mm shot, it's a 1.5 blow up of a 50mm shot. Sure it looks a little softer that a shot from a 75mm lens on a 35mm camera.
#3. "RE: D100 and Hyperfocal Distance" | In response to Reply # 2bobj Charter MemberTue 14-Jan-03 01:57 PM
>Sometimes I go to your site just to relax. Your work is
>When I read posts from D100 users that think the images are
>soft, I wonder whether it is a DOF issue.
Mainly it's because folks expect the D100 to act like an expensive point-and-shoot in auto everything mode whereas Nikon chose (wisely in my opinion) to minimize incamera sharpening, leaving the user to have to flexibility to sharpen post-capture in Photoshop.
>It isn't really a 75mm shot, it's a 1.5 blow up of a 50mm shot.
Now that *is* a nice way to think about the CoC and DOF issue!
Nature Photography from the Pacific Northwest and beyond
#4. "You can find..." | In response to Reply # 0
on this site. The focal lengths in the chart are actual (not "apparent") focal length of the attached lens. The circle of confusion chosen (0.016 mm, or two pixels) is very conservative, and should generate very sharp images within the hyperfocal distance range. If your zoom lens is set to a focal length that does not correspond to an entry in the table, estimate based on the nearest entries. Since the definition of "acceptable focus" is entirely arbitrary (and focus does not suddenly "fall off the table" when you get to the limits of the indicated hyperfocal range) it really doesn't matter that much if you are off a little one way or the other. To be ultra-conservative, I usually estimate a little on the long side of the focus setting to ensure that infinity is going to be in focus. Then I know that everything will be in focus from one-half my focus setting to infinity. (If I set the lens at 5 feet, then I'm comfortable from 30" to infinity. And if you know the hyperfocal distance is 3 feet at f/22 for a certain lens, and the closest thing you need to be in focus is farther away than that, then focus on the nearest object and everything from half that to infinity will surely be in focus.