dfoo
Well-known
Isn't that why the DOF scales on lenses are useful?
bmattock
Veteran
They are correct if you match the f-stop to the distances. In other words, on my 50mm lens, if I place my f-stop at f/8 and put the infinity mark on the '8' scale, I can see by reading the '8 on the right side of the lens that it matches up with about 15 feet. So anything from 15 feet to infinity should be in 'acceptable focus'.
NOTE: As an aside, DOFMaster says hyperfocal distance for this lens and aperture focused at infinity is 34.3 feet. So I do know that I have a 'range' of about 15 feet to 35 feet to play with.
But, if wish to meddle with that formula a bit and move the closet focus distance a bit farther out, the scale on the lens is no longer useful. Using a DoF scale or calculator, I can see that setting focus on 30 feet doesn't quite give me infinity focus, but 35 feet does. Setting between 35 feet and infinity gives me a different 'near focus' distance. It's no longer strictly 'hyperfocus' but a variation on it. The lens markings themselves can't really help me with that level of control. But I can bracket my focus adjustments and see what worked best later.
Al Kaplan
Veteran
The depth of field scales engraved on the focusing mount seems to be just fine for up to about an 8x10 print. To be on the safe side use the marking one f-stop from that. Shooting at f/8? Calculate your depth of field as if you were shooting at f/5.6.
Depth of field, or your perception of it anyway, is also influenced by your choice of film and lens. Going to a grainy film will obscure a lot of fine details in the in-focus area so the not-quite-in-focus areas adjacent to it won't look as unsharp. Also, with grainy film, especially when souped in a developer like Rodinol that produces very sharp clearly defined grain, your eye locks onto the sharpness of the grain rather than the slight unsharpness of the image.
Not all lenses bring all of the light rays to a clearly defined point at the film plane. When you look at a print the lens may seem sharp enough, but due to various abberations of the lens there's actually a range of focus where the image is as sharp as it can get, extending a little both in front and behind the film plane. Get beyond that range and the sharpness quickly deteriorates.
Chromatic abberation, where not all colors are focused on the same plane, is fairly common with older lenses. Apochromatic lenses are much better corrected for this. With B&W film you can stick a yellow filter on the lens and get rid of the blue rays. A red filter will get rid of the green rays as well. With less colors to deal with a larger percentage of the light rays hitting your film wil be in focus at the film plane.
Depth of field, or your perception of it anyway, is also influenced by your choice of film and lens. Going to a grainy film will obscure a lot of fine details in the in-focus area so the not-quite-in-focus areas adjacent to it won't look as unsharp. Also, with grainy film, especially when souped in a developer like Rodinol that produces very sharp clearly defined grain, your eye locks onto the sharpness of the grain rather than the slight unsharpness of the image.
Not all lenses bring all of the light rays to a clearly defined point at the film plane. When you look at a print the lens may seem sharp enough, but due to various abberations of the lens there's actually a range of focus where the image is as sharp as it can get, extending a little both in front and behind the film plane. Get beyond that range and the sharpness quickly deteriorates.
Chromatic abberation, where not all colors are focused on the same plane, is fairly common with older lenses. Apochromatic lenses are much better corrected for this. With B&W film you can stick a yellow filter on the lens and get rid of the blue rays. A red filter will get rid of the green rays as well. With less colors to deal with a larger percentage of the light rays hitting your film wil be in focus at the film plane.
totst
Member
Serious question?
Anyway with hyperfocal distance focusing you want that DOF , real nice depth. With scale focusing you want your subject in focus. But with hyperfocal distance you got your DOF going and get your subject in focus. They really work hand in hand. I like scale focusing in a way that it gets me in the range to take the shot , very few adjustments. I guess the subjects distance, got my fingers on the focus ring , preset the distance and make the minor adjustments as I take the shot. Without the knowledge of hyperfocal distance I would be so lost. So I think there is really not much difference, you still use the scale on your lens. Depends on how much DOF you want. Oh am I making sense? I'm not good with words.
sonwolf
Established
In addition to focal length and aperture, depth of field is also dependent on image magnification. As print size increases, relative to the original frame of film or digital sensor, depth of field decreases. The DOF markings on a lens correctly represent a particular print size based on one image medium size (usually 35mm film) and one circle of confusion size. This is the reason why depth of field tables and calculators will show different DOF distances for the same focal length and aperture combination. They start with at least one of these three factors being different than the lens manufacturer's standard.
Beyond just larger prints having less depth of field, when you crop an image and print it at a particular size, image magnification increases relative to printing the full frame. The result again is less depth of field. This is also the reason APS sized digital sensors produce significantly less depth of field than 35mm film or full framed sensors.
bmattock
Veteran
When you focus a lens on a subject, there is a distance in front of and behind that focal point that is still more-or-less 'in focus'. That distance is referred to as 'depth of field'. It is a mathematical calculation, and it depends on a number of factors, such as - distance from the camera to the subject, the f-stop selected, the focal length of the lens, and the size of the media that is recording the image.
Depth-of-field is frequently used for creative effect in making photos - for example, in portraiture, where often the photographer wants a photo to have a nice blurred background. Although such things can be simulated in photo shop, the proper use of the camera can do it too, probably in a more natural-looking way.
Depth-of-field distances can be calculated, and a good resource for doing so is DOFMaster (www.dofmaster.com). You go to the online calculator and give it the size of your recording media (film or digital sensor size), the focal length of your lens, the f-stop you want to use, and the distance from the subject. It then returns a set of values.
An example:
35mm film, 50mm lens, f-stop set to f/5.6, distance to subject set to 10 feet. A nice typical street photography distance.
Here's what DOFMaster has to say about it:
That means that if you focus your camera on the subject, which is 10 feet away, then the area of acceptable focus will be from 8.31 feet to 12.6 feet, for a total 'depth of field' of 4.25 feet. Scale-focusing in this situation would be a bit hit-or-miss - you're going to have to be able to judge how far away your subject is pretty accurately.
If you changed your f-stop to say f/8, you'd have more room to play with:
If you used a 35mm lens instead of a 50mm lens, and used f/5.6 again, you'd have this:
See how that works? Scale focus can be your friend, avoiding the need to have to focus accurately on your subject in every case, *if* you understand depth-of-focus and make it work for you.
Now, as regards hyperfocal distance. In every DoF calculation above, there was also a 'hyperfocal distance' given as a reading. What this means is that if you set your camera's focus on that distance (distance scales are engraved on the lens barrels of some lenses, but not a lot of modern AF lenses or zoom lenses), you should be 'in focus' from that distance to infinity.
The 'circle of confusion' simply attempts to explain that what is 'acceptable focus' is different under different circumstances, and as some have said, not everyone agrees on what acceptable focus is. It certainly isn't razor-sharp, that's for sure.
Understanding DoF and using it to your advantage is another facet of mastering the craft. When you have a firm grasp on it, scale focus actually becomes an advantage over any other focusing method, because it allows you to place the 'net' of acceptable focus front to back just exactly where you want it.
Here is an extreme example (sorry, it's me, very scary).
The depth-of-field of this photo is a mere inch or less. The focal point is essentially on my upper lip, and everything within an inch of that plane is in focus. Beyond that, focus falls off quickly, front or back.
Most people don't want an effect that extreme, but scale focusing and an understanding of depth-of-field makes it possible to tailor the effect to work the way you do want it to.
dfoo
Well-known
I've read this a few times, and I have to say that I don't really understand what you are trying to do. Doesn't the scale on the lens tell you what you need to know? For example, I'm holding a 50mm Nikkor 1.4 AIs lens in my hand. At F4, if I'm focused at 1.5M I can see that my DOF is from around 1.4M to 1.7M. At 3M, from around 2.8 to 3.5M.
What more do you need to know than that?
Gumby
Veteran
The Wiki for CoC is a good primer. Technically speaking, CoC itself is a calculated measure of focus; 'Acceptable CoC' is a psychophysical measure (the perception of focus). These measures are related but not exactly one-in-the-same.
bmattock
Veteran
I don't know if you 'need' to know more than that, but if you're a control freak like I am, it can be very useful. It's all about creative control of depth-of-focus, which to me is as much a part of my toolset as aperture and shutter speed.
Imagine a subject in the middle distance which you wish to photograph. There is also something in the near distance in the frame which you wish to be in focus as well. You can focus on the nearest object and use an f-stop and shutter speed / ISO combination that will give you the DoF you want to render both in acceptable focus. Or, you can focus on the subject in back and do the same thing, relying on the DoF in front of the object in focus.
You can also use hyperfocal distance focusing if you wish the horizon to be in focus as well - and that would be what the marks on the lens are for.
But what you cannot do, is focus on something in between the nearest subject and the farthest subject that you wish to have in focus, if there is nothing but thin air there. You can only focus on the near object, the far object, take note of the lens position, and then try to guess something in the middle.
Why would you want to focus on something in the middle? To make maximum use of the DoF, placing your near and your far subjects more towards the center of it, rather than have one more-or-less in the middle of it and the other at the extreme edge. DoF of course, being 'sharper' towards the point of actual focus'.
Scale focus, combined with knowledge of the actual DoF (by using a calculator or chart) and a known distance, will give you that level of precise control - if you want it. If used properly, it should render finer-grained focus control than rangefinders or SLR cameras.
dfoo
Well-known
Ok, but doesn't the scale on the lens tell you that information as well? For example, 2M in front of me is a duck, and 10M behind that is a swan and I want to get them both in focus. Looking at the scale on my lens I know I have to stop down to F16 and set my focus at 3.2M or so to get that DOF. On the other hand, lets say I have two objects one at 2M and one at 3M that I want to get in focus. Again using the scale on my lens I can do the same thing, and in this case I have more choices...
ampguy
Veteran
I think that DOF master and the engravings on the lens barrel are good starting points, but depending on your preferences of acceptable focus, I think there's a lot to be said for actually just keeping the lens focused on infinity most of the time.
dfoo
Well-known
As long as you don't mind having fuzzy objects in the foreground (assuming there IS a foreground), sure.
Gumby
Veteran
ampguy
Veteran
just set at infinity
just set at infinity
you're not stating how sharp you want that duck at 2m to be, nor how sharp you want the background of the ducks to be.
just set at infinity
you're not stating how sharp you want that duck at 2m to be, nor how sharp you want the background of the ducks to be.
ElectroWNED
Well-known
Do: take into consideration the height of the object in comparison to you. If you are 6 feet tall, and you are aiming at something on the ground, you'll likely be off a bit unless you compensate.
(something simple that I overlooked when first starting
)
(something simple that I overlooked when first starting
)dfoo
Well-known
Isn't that obvious though? The smaller the aperture the sharper things will be (subject to diffraction).
ampguy
Veteran
maybe we need different words here
maybe we need different words here
stopping down will give an appearance of a wider depth of field for acceptable limits in focus, but not necessarily sharper (resolution) at any distance.
Many lenses get less sharp after f5.6 or so.
maybe we need different words here
stopping down will give an appearance of a wider depth of field for acceptable limits in focus, but not necessarily sharper (resolution) at any distance.
Many lenses get less sharp after f5.6 or so.
ampguy
Veteran
Possibly better to set more towards infinity
Possibly better to set more towards infinity
Hi Al and Keith,
It's likely you're getting acceptable DOF and sharpness set at 1M with that lens, but if you get a chance, check out the free downloadable books on my I Am Photographer site by Merklinger and you actually might see better resluts if focused further out.
The links are on my fb photo site.
Possibly better to set more towards infinity
Hi Al and Keith,
It's likely you're getting acceptable DOF and sharpness set at 1M with that lens, but if you get a chance, check out the free downloadable books on my I Am Photographer site by Merklinger and you actually might see better resluts if focused further out.
The links are on my fb photo site.
bmattock
Veteran
It would work, presuming your scale is graduated finely enough. Mine are not, they tend to be marked something like 1 foot, 1.25 feet, 2 feet, 3, 5, 10, 30, and infinity. I sometimes want more control than that, especially when playing with thin DoF where inches mean in or out of focus. It's bad enough when, say, '7 feet' is not marked on my lens, but that's the focus distance I want. It's worse when I want to set f5.6 on 7 feet, estimate that, and then my depth-of-field is what? Another something in between two very different numbers.
I don't habitually work with depth-of-field caculators or charts, but when I suspect I'll be doing that kind of work, I take one or the other with me; as well as bits of string in varying known distances and a well-calibrated external rangefinder.
marduk
Well-known
Do I correctly understand that when someone shooting landscapes with a 4x5" camera wants ultimate sharpness, which most do, and plans to make big enlargements he should not use hyperfocal focusing but focus strictly at infinity, unless absolutely necessary?
Last edited: