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09-30-2008, 07:35 PM   #1
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soft or out of focus

This may seem like a silly question but is there a difference between a photograph which is soft because the lens is wide open but focused and one which is soft because it is out of focus?

09-30-2008, 09:03 PM   #2
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not sure...i think they both blurry...put it on a tripod, manually focus then use 2sec delay or remote then u'll know if it soft or oof...or is there any other way?
09-30-2008, 09:22 PM   #3
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I don't claim to be an expert on this but the difference to me is that "soft" pertains to sharpness or clarity. DO NOT actually do this, but for the sake of example take lens like the 50-135 and get it perfectly focused. Snap one off. Now without adjusting the focus put a super thin layer of mineral oil on the front element and take another shot.
Both will be "in focus", but the greasy shot will be "soft". Again, DO NOT actually put oil on your lens!!!
09-30-2008, 09:25 PM   #4
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QuoteQuote:
...put a super thin layer of mineral oil on the front element and take another shot.
Both will be "in focus", but the greasy shot will be "soft". Again, DO NOT actually put oil on your lens!!!
People have been using vaseline on UV filters for a long time, usually with a clean center area. Soft-focus shots are actually focussed on the subject. Mis-focussed shots are not.

09-30-2008, 09:41 PM   #5
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True, but putting it on a cheap UV filter is a far cry from putting it on the lens element itself.
09-30-2008, 09:48 PM   #6
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Another trick I use is to breathe heavily on the filter and then using a small cloth or a tie (if you are wearing one) clean the center of the filter... and then take the photo quickly. Keep shooting every couple of seconds while the breath "fog" on the lens slowly clears. Afterwords you will several different "looks" to choose from. I have used this technique a lot when shooting wedding portraits etc...

Max
09-30-2008, 09:49 PM   #7
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QuoteOriginally posted by Venturi Quote
True, but putting it on a cheap UV filter is a far cry from putting it on the lens element itself.
Actually, getting petroleum jelly off a lens isn't all that difficult. Putting it on a skylight filter is a better idea, though, because of the time it takes to clean the stuff off.

You can spend a whole bunch of money and get a soft focus lens, or somewhat less by getting a soft focus filter. I have one for the odd occasion. It's lightly frosted plastic with a hole drilled through the middle.
09-30-2008, 09:55 PM   #8
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If you have an extra UV filter then try painting the edges around the center with clear nail varnish. Take your time and keep checking with how the filter will look with the LENS STOPPED DOWN TO YOUR MOST USED F-STOP. Keep the middle(or slightly higher than middle) clear and have the very edges a little thicker with the varnish.

If you goof and need to start over then use nail varnish remover or acetone to remove the varnish. This is a great way of making "soft focus" filters that are tailored to your specific need. Way better than using messy jelly...

Max

09-30-2008, 11:53 PM   #9
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I wonder what kind of effect you could produce with one of the wheels from a Spirograph with all those small holes.
10-01-2008, 01:01 AM   #10
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Soft to me implies soft contrast and edges rather than low resolving power - though how you can have a soft edge and high resolution does feel rather counter intuitive to me. Out of focus is all about circles of confusion and stuff, of which I confess to have almost no meaningful knowledge

Heres an example of what I mean though - on the photozone site the chap does a test for LOCAs where he shoots a chart at different apertures, the 'soft' ones have much lower contrast but if you look at the centre resolution for even the widest aperture its pretty high, and the centre of focus is quite visible

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10-01-2008, 01:46 AM   #11
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QuoteOriginally posted by kiwao Quote
This may seem like a silly question but is there a difference between a photograph which is soft because the lens is wide open but focused and one which is soft because it is out of focus?
I would suggest that the difference is noticeable yes. Shooting with wide aperture lenses, wide open often produces a diffusion of contrasted edges either side of perfect focus and can give a gentle, dreamy effect. If you miss that narrow plane of focus entirely (easy to do on flatter subjects), its even more pronounced and there will be no clear point of focus.

If you are finding consistantly too soft results wide open, adjust your diopter while shooting a ruler at a 45 degree angle. Try to hit specific numbers exactly. You'll be able to tell if you're hitting short, too long, etc.

Heres a pic to demonstrate. It was from a batch of photos I took on the weekend at an event. In this shot, my snap missed the subjects face (short focused), which is now too soft, but you can clearly see his shoulder is sharp. If it had been a leaf or other such near 2D object, then the whole image would be diffused.

10-01-2008, 10:38 AM   #12
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QuoteOriginally posted by kiwao Quote
This may seem like a silly question but is there a difference between a photograph which is soft because the lens is wide open but focused and one which is soft because it is out of focus?
One difference would be that in a picture where the subject is out of focus, something *else* would probably be in focus. Whereas if it were soft because the lens was just soft at that aperture, or because you used some kind of softening filter, then everything would be soft. In practice, you might not be able to tell the difference, as there might *not* be anything in focus in the former case. There is also softness caused by camera shake - with is going to affect the whole picture also - and softness caused by subject motion, which will affect only the things that were moving.

With experience, you can generally learn to tell the difference, so that seeing a given soft picture - especially if you took it yourself and know the circumstances - you can pretty well guess what happened.
10-01-2008, 01:52 PM   #13
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QuoteOriginally posted by thePiRaTE!! Quote
I would suggest that the difference is noticeable yes. Shooting with wide aperture lenses, wide open often produces a diffusion of contrasted edges either side of perfect focus and can give a gentle, dreamy effect. If you miss that narrow plane of focus entirely (easy to do on flatter subjects), its even more pronounced and there will be no clear point of focus.

Yup, a "soft focus"-ing lens (typically) has spherical aberration, which causes light rays* passing through the periphery of the aperture to focus at different point than light rays passing through the center; you can set the focus to make the central rays converge at the sensor (creating the detailed edge), but the peripheral rays will fail to converge at the sensor (creating the dreamy halo).


Here's an example of a "soft focus" effect (see the 100% crop in the lower left panel)




The smeary-with-transparent-center filter creates a similar effect (peripheral rays don't converge at the plane of best focus) by a different mechanism (diffusion instead of defocusing).

An ideal lens, out of focus, makes all the rays converge at a single point in front of or behind the sensor; defocusing causes edge details to appear as blurred lines with discernable boundaries (for example the tip of the subject's nose in the post above).




* BTW, there's no such thing as a light ray -- don't worry about it.

Last edited by troyz; 10-01-2008 at 02:01 PM. Reason: added image
10-01-2008, 02:02 PM   #14
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QuoteOriginally posted by Venturi Quote
True, but putting it on a cheap UV filter is a far cry from putting it on the lens element itself.
put some vegetable oil under your eyelids - now that will be an instant softfocus
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