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02-18-2010, 08:47 AM   #1
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DOF, The Green Button, When, How, Why

Would someone be kind enough to spend a few minutes and give me a detailed situation of when they would use the DOF button, the step by step process they go through, and what happens when they press to green button for the preview or just plain dof preview?

I've heard that you just need to focus @ 2/3 of the shot to achieve the same results but i'm really confused about the rest.

For example, when I use DOF preview does my viewfinder change the image and/or what should I be looking for?

ANYTHING will help me with this.

02-18-2010, 09:28 AM   #2
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Green Button does different things in different mode, detail see Green Button usage.

I think you are confuse with Green Button doing step down metering in M mode or with M lens. It is where it step down the lens to the aparture you choose for a very short time to check the light and set a meter value for you.

DOF preview is different as it hold the step down process as long as you hold the preview button, the viewfinder will be darker as less light will able to pass through but you will able to see the DOF right in the viewfinder, it doesn't not meter tho.
02-18-2010, 09:37 AM   #3
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I use the green button when I've messed up with settings, or to expose with a manual lens.

I personally use DOF preview to activate live view on my K20D. Otherwise, you have two options : actually activate DOF preview (the camera will stop down the aperture to the selected value, the image will darken accordingly, and your DOF will be visible). You can also ask the camera to take a test shot when using this button, then check exposure, DOF, and white balance on your LCD.

When trying to focus, focus on the actual part of the image you want sharp. No exceptions. The 2/3 guideline is that, generally speaking, 1/3 of your DOF range will be in front of your focus point, and 2/3 behind it.

Example : You focus on a fence post, while you're sitting on the fence. The posts are spaced by 1 foot each. You set things so your total DOF is 3 feet. The post in front of your "subject" should be sharp, and the two post behind. The other posts should become increasingly blurred.
02-18-2010, 09:55 AM   #4
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QuoteOriginally posted by bdery Quote
Example : You focus on a fence post, while you're sitting on the fence. The posts are spaced by 1 foot each. You set things so your total DOF is 3 feet. The post in front of your "subject" should be sharp, and the two post behind. The other posts should become increasingly blurred.
so in this example....how would you use the dof preview? i mean, i know "how" (on my k10 i would push the on.off lever to the right), but what i don't know is..."what will the dof preview to for my composition and or shot? in other words, why would i use it?

i might just be extrapolating this too much and making a mountain out of a molehill.

02-18-2010, 10:02 AM   #5
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before we go too far on this, everyone needs to recognize depth of field is a subjective thing, described by complex mathematical calculations.

when the subject is distant, depth of field is as people here describe, 1.3 in front and 2/3 behind the subject, but as you approach the subject, this ratio moves towards 50/50.

however, for the sake of argument, let's use the fence post example.

you have a group of 4 posts you want in focus, you would focus on perhaps the second post, then activate the optical preview (depth of field) and through the viewfinder check that the 1st and 4th are also acceptably sharp. If they are not, or if you find that you have equal area in front and behind, you can either shift your focus point a little, or stop the lens down a little more to get more in focus.


Note that this is not as easy as it sounds because the depth of field in a viewfdinder is not the same as what you see as acceptably sharp on a 22 inch monitor It will take some experience.

to answer your question of what it does for the shot, it allows you to check at some level that you have the zone of focus where you want it, and that outside that zone, the image is blurred or out of focus (also I assume as you want it)

It is generally used for macro work, to decide how much to stop down for detail while letting the background (which may be confusing or distracting,) go out of focus
02-18-2010, 10:08 AM   #6
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QuoteOriginally posted by Deiberson Quote
so in this example....how would you use the dof preview? i mean, i know "how" (on my k10 i would push the on.off lever to the right), but what i don't know is..."what will the dof preview to for my composition and or shot? in other words, why would i use it?
When you check DOF, you can see what's in focus--in front of and behind the subject you actually focused on. Unless you stop down momentarily by using the DOF switch, you can only guess what will actually be in focus.

This assumes you're using a smaller aperture. If you're shooting at F4 with an F4 lens, you're shooting "wide open" and the DOF won't show any change. If you're shooting at F11 with an F4 lens, when you check DOF the viewfinder will go dark (darker, that is, than it was at F4), and you'll be able to see that more things are in focus. When you release the switch, the viewfinder will go back to being fairly bright, and less stuff will seem in focus--but if you shoot at those settings, what's really in focus will be what you saw in the darkened viewfinder.

Hope that makes sense. Knowing how to control DOF is a big step toward taking control of your photographs.

Last edited by grey goat; 02-18-2010 at 12:14 PM. Reason: just making clear what I meant by "dark" in second paragraph. . . .
02-18-2010, 10:49 AM   #7
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let me tell you how much of an idiot i am......but thanks to these explanations, i finally got it.

i had no idea that the preview shows up on the lcd monitor as an image of what to expect on the back of the camera. i thought it changed the view in the viewfinder. so i've been using the dof preview, and clicking the dof preview hundreds of times and not seeing anything. then....as i was ready to throw the camera across the room out of frustration, i noticed there was an image on the back of the lcd. makes perfect sense.i have a few more questions...but this helped a lot.
btw...this feature is not on my kx is it? maybe that's why i was confused. i'm now messing around with the k10.
02-18-2010, 11:48 AM   #8
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QuoteOriginally posted by Deiberson Quote
let me tell you how much of an idiot i am......but thanks to these explanations, i finally got it.

i had no idea that the preview shows up on the lcd monitor as an image of what to expect on the back of the camera. i thought it changed the view in the viewfinder. so i've been using the dof preview, and clicking the dof preview hundreds of times and not seeing anything. then....as i was ready to throw the camera across the room out of frustration, i noticed there was an image on the back of the lcd. makes perfect sense.i have a few more questions...but this helped a lot.
btw...this feature is not on my kx is it? maybe that's why i was confused. i'm now messing around with the k10.
maybe I 'm the idiot here but,

WHen you use the DOF preview (built into the end of the on off switch on cameras that support it), it stops down the lens and you see the image change in the view finder.

I don't have a Kx but that is how it works on the K10, *istD and K7.

It may be that the KX actually does this using live view, and perhaps the K7 also although I don't use live view.

02-18-2010, 12:16 PM   #9
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i'm using the k10 right now. it shows up on the lcd. maybe a setting was changed to do this. nothing at all appears to change in the viewfinder. it seems to stop down and i lose the view in the viewfinder. then the image pops up on the lcd.
02-18-2010, 12:31 PM   #10
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QuoteOriginally posted by Deiberson Quote
Would someone be kind enough to spend a few minutes and give me a detailed situation of when they would use the DOF button, the step by step process they go through, and what happens when they press to green button for the preview or just plain dof preview?

I've heard that you just need to focus @ 2/3 of the shot to achieve the same results but i'm really confused about the rest.

For example, when I use DOF preview does my viewfinder change the image and/or what should I be looking for?

ANYTHING will help me with this.

Green button

Not sure what the green button has to do with depth of field. The green button has a number of uses, but the main one is to set the exposure settings on the camera (aperture and shutter) for something that makes the camera's meter happy. In full manual (M) mode, for example, you can get a nominally "correct" exposure by hitting the green button. Quicker than moving the shutter e-dial and aperture e-dial until the meter's exposure indicator is centered.

*

Preview

Now, on to the preview feature. The preview feature on the camera is available through the preview action on the dial around the shutter button—the dial you use to turn the camera on and off. The preview icon looks like a camera aperture. To enable preview, turn the dial to the preview icon.

What's it do? Well, this depends on the preview option setting in the camera's custom menus; and the options you have available depend on your camera. If you have a K10D, for example, your preview method options are optical and digital. If you have a K20D, your preview options will be optical, digital and live.


Optical preview

If you select optical preview, then the preview button does exactly what it does on a film SLR: It moves the aperture to the current setting and allows you to look through the lens with the aperture closed as it will be when you take the picture. Normally, when you look through the camera's viewfinder to compose your photo, the aperture is wide open. So if you've already dialed in something like f/2.8, then the preview button will make little or no difference to what you see. If you have the aperture set on the other hand to f/11 (I'm imaging that you're outside in bright light), then...

...while you look through the viewfinder normally, if you've focused on the subject's face, the face will appear in focus and stuff in front of or behind the subject might appear somewhat blurry or out of focus; but

...if you turn the power dial to the preview position and hold it, the finder will seem to darken, because the aperture is actually closing to f/11, and stuff in front of the subject and behind may now come into better apparent focus.

I say "may come into better apparent focus," because it may not. When the aperture closes in preview and the image you see in the finder gets darker, it may get harder to see the stuff in the background clearly. Personally, on a DSLR, I think optical preview is a fairly dumb option to select. On a film SLR, it's all you've got and can be useful—if you are able to discern things in the finder—because with a film camera, if you realize the depth of field is way off, you can save yourself a wasted frame of film, and frames mean money.


Digital preview

If you've selected digital preview in your custom menus, then turning the power dial to preview actually takes a photo—at the camera's current settings—and displays the photo on the camera's back display screen. Why is this a "preview"? Because digital preview does NOT write the capture data to the SD card. As far as I'm aware, that's about it. In other words, there's no difference between using depth of field preview and actually clicking the shutter and taking a picture, except that if you do the latter and you really LIKE the shot, you don't have to do it again, where if you use the depth of field preview button, you now have to go back and take the shot so it can get written to the card. [NOTE: ON a K20D and perhaps other models, you can hit Fn during digital preview to save the preview as a jpeg. Picked that up from the operating manual and have never done it myself.]

NOTE that digital preview isn't properly called "depth of field preview," because it's really a total preview. Optical preview doesn't show you your composition, because optical preview is "live," that is, you're looking through the lens and if you move the camera, your composition changes. Digital preview on the other hand, because it actually captures an image to the camera's buffer, shows you the exact composition, exposure, as well as depth of field. You can however get some info about depth of field from digital preview, in fact, in my opinion, it's MUCH more useful than optical preview, because in digital preview you can ZOOM IN on objects in the foreground and background and see if they're in focus or not. Of course, if you don't want to take your eye away from the finder, then you may not like digital preview regardless of its advantages.

So, digital preview may be more useful than optical preview, but is it really useful in an absolute sense? Not very. If you find yourself taking LOTS of test shots, mixed in with actual shots you might want to keep, then using preview can save you a few seconds or minutes later on, because if you previewed those shots rather than actually saving them on the card, you won't have to delete them later. And of course digital preview doesn't eat up space on your storage card. I don't personally think either of these issues is a big deal, which is why I simply don't use the digital preview method very often.


Live preview

The K20D and Pentax's more recent models (I assume this applies to the K-7, at least) have a third preview option, "live view." Like optical preview, live view is not static: you move the camera, what you see on the display screen on the back of the camera changes. And like digital preview, live preview appears in the camera's display screen.

In my opinion, most of the time, live view isn't very useful. Digital preview shows you a nice, clear image on screen. Live view on the other hand shows an image that resembles a bad television picture. A further problem with live view is that it's more of a shooting mode than a simple picture preview feature. Go into live view and you STAY there, picture after picture. And it seems to complicate access to the normal settings dials on the camera that I will admit I find so intolerable that I've never bothered to figure it out. And although I have not used live view enough to know this for sure, I assume that using live view very much would drain your camera's batteries more quickly.

It seems to me that live view is useful mainly when you're shooting with the camera on a tripod, and when you don't need to change many other settings. Say you're taking a portrait, in M mode. You've got your aperture and shutter speed set as you want them. Say you're taking a group portrait. If you have a remote control, and you use live preview, you can stand behind the camera and keep looking back and forth from the bride's face to the preview, and you don't have to put your face up to the camera's viewfinder to double-check that Aunt Louise is completely IN the photo. Also, in live view, if you have manual focus enabled, you can zoom in and check or adjust your focus. Notwithstanding the general lack of acuity of the live preview image, especially at magnification, manual focusing in live view can be at least as effective as focusing through the viewfinder, especially if you don't have a split focusing screen.


Conclusion

So if you are working with your camera on a tripod, in full manual mode, and perhaps in manual focus mode as well, then live view might be useful, if you have a spare battery. And I should add that I'm not going to say anything about live view when shooting video, since I don't have a DSLR that can shoot video. I imagine that live view may be MUCH more useful shooting video than shooting still photos.

But otherwise, in my personal opinion, for general shooting, NONE of the camera's preview options are very useful when you're shooting with a digital SLR. As I said earlier, preview was useful on film SLRs because it could save you wasted film. But the cost of a wasted digital shot is negligible.

Will
02-18-2010, 03:13 PM   #11
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Williams's answer is, as usual, very thorough. I just wanted to try to cut to what I think is the heart of the matter.

There is an optical DOF preview, and a digital DOF preview. The optical one changes what you see in viewfinder - showing you what the image looks like with the lens stopped stopped, as opposed to wide open as it normally is. The digital one just takes a picture and shows it to you on the LCD. Depending on how you have your camera set up, the DOF preview lever (or button with K-x) will either do or the other. The digital preview is what it is - basically the same as simply taking the picture and deleting it. It has nothing to do with metering. The *optical* preview is the one that is connected to metering on a manual lens - for as long as you hold the lever in position, not only does the viewfinder show you the stopped down image, but it *also* shows you the meter.
02-18-2010, 04:15 PM   #12
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QuoteOriginally posted by Marc Sabatella Quote
There is an optical DOF preview, and a digital DOF preview. The optical one changes what you see in viewfinder - showing you what the image looks like with the lens stopped stopped, as opposed to wide open as it normally is.
Well, it may or may not change what you see in the viewfinder. If you're taking the shot at the max aperture, it won't change what you see. And optical preview doesn't seem to take ISO into consideration at all. I see the same optical preview at ISO 1600 in a shadowy late afternoon room that I see at ISO 100.

Actually, the effect of stopping down the aperture in optical preview strikes me as generally pretty minimal—and pretty uninformative.


QuoteQuote:
The digital one just takes a picture and shows it to you on the LCD. Depending on how you have your camera set up, the DOF preview lever (or button with K-x) will either do or the other. The digital preview is what it is - basically the same as simply taking the picture and deleting it. It has nothing to do with metering. The *optical* preview is the one that is connected to metering on a manual lens - for as long as you hold the lever in position, not only does the viewfinder show you the stopped down image, but it *also* shows you the meter.
Where do you see a meter, Marc? I am sitting here with a K10D, doing optical preview, and I LOSE the meter when I preview, both in P and in M modes.

I'm not sure I understand your other point that digital preview has nothing to do with metering and optical, does. Almost seems the other way around to me. Digital preview takes your ISO setting into account, and as I said, as far as I can see, optical preview doesn't. And digital preview shows a histogram, which of course you don't get in optical preview.

Will
02-18-2010, 05:14 PM   #13
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QuoteOriginally posted by WMBP Quote
Well, it may or may not change what you see in the viewfinder. If you're taking the shot at the max aperture, it won't change what you see.
Good point.

QuoteQuote:
And optical preview doesn't seem to take ISO into consideration at all. I see the same optical preview at ISO 1600 in a shadowy late afternoon room that I see at ISO 100.
True - it's only the effect of aperture that shows in the DOF preview.

QuoteQuote:
Actually, the effect of stopping down the aperture in optical preview strikes me as generally pretty minimal—and pretty uninformative.
Depends on how much you care about DOF. I actually use it pretty rarely for that purpose, too, because the viewfinder is too small to *really* gauge DOF. but it's nice for a rough idea of what will be in focus when shooting macro, for instance.

QuoteQuote:
Where do you see a meter, Marc? I am sitting here with a K10D, doing optical preview, and I LOSE the meter when I preview, both in P and in M modes.
That's with an auto-exposure lens. I was referring to *manual* lenses. no meter normally, but it magically appears while doing the preview (and it appears in the same location and in the manner as usual).

QuoteQuote:
I'm not sure I understand your other point that digital preview has nothing to do with metering and optical, does.
See above. Only optical preview causes the meter to display, and from the questions the OP is asking here and in another thread, I'm pretty sure that's what he is trying to figure out. He wanted to know how to get the meter to display with his manual lenses, and when people suggested the DOF preview, he got confused because I think his camera was set to do a digital preview instead of optical. You can do digital preview all day long and never see a meter reading.

QuoteQuote:
Almost seems the other way around to me. Digital preview takes your ISO setting into account, and as I said, as far as I can see, optical preview doesn't.
That's true also - if you want to see what your exposure will *look* like, digital is the way to go. But optical is the only one that shows you the meter reading -
which *does* take ISO into account, BTW.
02-18-2010, 05:16 PM   #14
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QuoteOriginally posted by Marc Sabatella Quote
That's with an auto-exposure lens. I was referring to *manual* lenses. no meter normally, but it magically appears while doing the preview (and it appears in the same location and in the manner as usual)....
Thanks for the followup. I don't use any manual lenses now and hadn't noticed this.

Will
02-21-2010, 03:16 AM   #15
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focus on this

As mentioned earlier, if you want a subject to be in focus, focus on it, especially with a longer-than-'normal' (35mm+) lens, or if your aperture is fairly wide. If you want a range of items to be in focus, it's problematic. Optical DOF preview can be difficult in the small (half-frame) viewfinder of an APS-C digital camera like all Pentax dSLRs. LiveView is about useless except for composition. Digital DOF preview takes time, which you might not have if the subject is alive and moving, and you're still trying to judge sharpness on a small, low-res screen. Bother.

What's left? Hyperfocal distance. That's where, at a given aperture, you focus to get a specific DOF. This is easiest done with an old manual lens. Such lenses have DOF scales inscribed on them. Line up one end of your distance range with an aperture mark, and it's plain to see where the other end of that range is.

So a 21mm lens stopped down to f/5.6, hyper-focused to 10 feet, has a DOF of 4.5 feet to infinity. A 35mm at f/3.5, set to 15 feet, has a DOF of 10-30 feet. A 55mm at f/8, set to 4.5 feet, has 4-5 foot DOF. A 135mm at f/22, set to 30 feet, has 20-50 foot DOF. Et cetera. How do I know? The lens tells me.

So the trick is: measure (or closely guess) the distances to your nearest and furthest subjects, then pick an aperture whose DOF includes both. How to measure? Back in the day, we had rangefinders. Lacking such, you can use a laser sight, or yardstick, or pace off the range, or guess how many paces or body lengths are between you and the subjects. When I used old folder cams lacking even rangefinders, I got pretty good at such guess-timations.

Even when my eyes were keen, even when I shot full-frame 35mm SLRs, I never used DOF preview. It's just too chancy, IMHO. The aperture-distance marks on manual lenses are much more reliable. Modern AF lenses lack such marks. Pity.
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