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06-07-2012, 12:07 PM   #1
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Help with Depth of Field Preview

I have had my K5 for a few months now.Its my 1st DSLR and I'm just starting to really get to grips with the various functions. One thing which I just can't get to grips with is the DOF preview. No matter whether I set it to Optical View or Digital View , I really can't any change in the view when I pull the DOF lever. The only difference I can see is that it gets a bit darker but I just can't seem to identify any chages in the DOF . I'e tried at different apertures -wide open and closed down .Any advice would be appreciated as I 'm becoming really frustrated by this . Thanks

06-07-2012, 12:20 PM   #2
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If it gets darker than the dof changes as well. Try pointing your camera at something really close and select f11. Things behind it should become clearer after you stop down.
06-07-2012, 12:54 PM   #3
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One question - what lens are you using? This experiment will work best with a fast lens, but can be done with any lens.

I Agree with Adam - try focusing on something that has a reasonable depth to it - a large flower but looking at it almost side on, or along the length of a car - focus on the middle and hold the camera steady. Now let your eye see if the front or back of the object also looks sharp. Now with a setting of f11 or smaller, try the DOF preview and see how much the front or back of the object looks sharp. That's the difference.
06-07-2012, 04:44 PM   #4
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Thanks to you both. I've spent ages footering about with the lens - its the 18-55 kit lens -wide open and at F11 and above. Stupidly it took me a while to realise that of course the view wouldn't get any darker at wide open and that wide open is the default to measure against . It then made sense and , depending on what I'm focussing on , I can see a difference when closed down when I pull the dof lever. Its quite hard to make out though in Optical Preview .It was most obvious -or less unobvious - when I used the box for my telephoto lens as the thing to focus on as it was easier to see the words becoming sharper but when I used my fiddle turned length ways I really had to concentrate to see the difference , although it was clearly there when I actually took the shot. To be honest I think its easier just to take the shot and try again if it doesn't work out but I really appreciate you taking the time to reply

06-07-2012, 04:55 PM   #5
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Most of the time it will be easier, but if you are trying to balance off between aperture and shutter speed or ISO it helps to get a sense of what your depth of field (i.e how much is in focus) will be.
06-07-2012, 05:22 PM   #6
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I started dealing with DOF preview on SLRs many decades ago and I'm still dissatisfied. I find it VERY difficult to judge DOF looking through a VF, even a big bright VF, even with adequate eyes. For strict DOF control, I use old manual lenses with DOF scales inscribed. Or I'll use the LiveView screen. Otherwise, shooting with an ordinary AF lens and not using LiveView, I just concentrate on nailing the subject. If the subject is a fairly perpendicular planar surface, I'll stop-down for nice thick DOF -- and work on nailing the focus anyway. But I just don't bother with DOF preview any more. My eyes aren't up to it.
06-07-2012, 05:28 PM   #7
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I agree DOF preview is limited at best. I also use the DOF scales on manual lenses; but then I use rangefinders more than SLRs, so that's my only choice!
06-07-2012, 07:14 PM   #8
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The one time I find DOF preview useful is handheld macro photography, which is usually done in good light, so even stopped down I can still make things out well enough. Since focusing in macro photography is usually done by moving in and out rather than (just) turnign the focus ring, the DOF preview is the only way to find out in real time when you are at a good place that will render the zone you want acceptably sharp. Taking the picture and chimping will be too late - all you'll find out is that you should have taken the picture an inch in front of or behind where you actually did, but you normally won't have any way of finding that exact spot again.

06-07-2012, 07:21 PM   #9
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QuoteOriginally posted by Marc Sabatella Quote
The one time I find DOF preview useful is handheld macro photography, which is usually done in good light, so even stopped down I can still make things out well enough. Since focusing in macro photography is usually done by moving in and out rather than (just) turnign the focus ring, the DOF preview is the only way to find out in real time when you are at a good place that will render the zone you want acceptably sharp. Taking the picture and chimping will be too late - all you'll find out is that you should have taken the picture an inch in front of or behind where you actually did, but you normally won't have any way of finding that exact spot again.

The other way to do this is to use m42 lenses on the manual setting so that you are always stopped down to the aperture you are shooting, or if you are really good, you can focus wide open, use the A/M switch without otherwise moving any other part of your body and then shoot with a bit more DOF. Ok, in greater seriousness, while it can be hard to focus while stopped down, you do get a very good sense of the DOF this way.
06-08-2012, 12:39 AM   #10
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Be aware that modern focus screens are not made to accurately render DoF, but are rather optimized to handle kit lenses by playing with apparent brightness and vignetting.

Did you ever wondered why your viewfinder does not darken while zooming your kit lens, thus going from f/3.5 to f/5.6? This is because your focus screen is not ground glass anymore, but a complex Fresnel lens, and a byproduct of this is that DoF preview is a joke... A classic screen can only render a f/2.4 DoF, nothing faster...

Try a canon EE-S screen, it's the only screen I know made for fast lenses.
06-08-2012, 09:10 AM   #11
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Thanks for the replies everyone. I has another go with the Digital Preview this time and could see no difference atall so I think I'm going to give it up as a bad job. I'm interested though how you all judge dof when you don't have dof scales on your lenses and how do you know what focal distance to use to get a particular dof -is it just experience/seat of the pants / use of dof tables?. Sorry if this is all a bit confused but I'm at the stage where I don't know enough to know which questions to ask and it sometimes feels a bit like wading through treacle!
06-08-2012, 09:24 AM   #12
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QuoteOriginally posted by TylerD Quote
I has another go with the Digital Preview this time and could see no difference atall so I think I'm going to give it up as a bad job.
That's exactly what I've concluded.

QuoteQuote:
I'm interested though how you all judge dof when you don't have dof scales on your lenses and how do you know what focal distance to use to get a particular dof -is it just experience/seat of the pants / use of dof tables?
Yes. Yes, experience and experimentation and using tables. Hmmm, I just got an Android tablet, I'd better look for some DOF etc apps. And then use them! EDIT: I just searched the Apps market. ZILLIONS of DOF calculators! Most of them free! Which to get? Decisions, decisions...

QuoteQuote:
Sorry if this is all a bit confused but I'm at the stage where I don't know enough to know which questions to ask and it sometimes feels a bit like wading through treacle!
Slogging through thick sh!t is more like it. Digicams offer many advantages over film. DOF preview on an SLR isn't one of them. Still, try LiveView for previewing -- you may get a better taste of DOF there. Good luck!
06-08-2012, 12:52 PM   #13
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Even with a modern focus screen and 1:1 viewfinder, DOF in the viewfinder may or may not be accurate as it relates to the final image. It all depends on the size of the final image and the viewing distance. For example, consider my avatar image as compared to the image below...



Both are from the same RAW source file and differ only in size. Now walk away from your monitor and take another look at the larger version. MAGIC! The DOF is now huge!


Steve
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