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Aperture - Depth of Field

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Matt Kelly
Aperture - Depth of Field
on Apr 27, 2015 at 3:41:48 am

Hey guys! I'm using a relative's Sony A55, and I'm experiencing a bit of trouble. I'm somewhat familiar with how to operate DSLR's - in that changing the aperture should change the depth of field you get from your shot - problem I'm having is that I change the f stop on my camera, and it does change the exposure, but it doesn't seem to do anything to the depth of field. Everything is still relatively in focus no matter if I use f/3.5 or f/22. Anybody know why I might be having this problem? Thanks!


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Steve Crow
Re: Aperture - Depth of Field
on Apr 27, 2015 at 6:38:41 pm
Last Edited By Steve Crow on Apr 27, 2015 at 6:45:54 pm

Hey Matt,

I don't understand how what you describe could be possible, if the exposure is changing then the DOF must be changing too. There has been lots of talk online about the A55 being prone to malfunctions and needing repairs but I'm assuming for the following that everything is actually in working order.

Set up a simple table top test, rest your camera at one end of your family's dinner table at table top height. Now place a coffee cup or something 1.5 feet in front of of the end of the lens and then set up another group of objects 2 or 3 feet behind the cup.

Put your camera in full manual mode, set the lens so that you are at a 50mm field of view, switch over to video and then focus on the cup with your aperture set at 3.4. Now film. This will give you a very shallow depth of field, in fact some portions of the cup furthest away from you may be out of focus - as by my calculations the area in focus will only be .03 feet - but definitely the second group of object further along the table will be blurred.

Steve Crow


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Matt Kelly
Re: Aperture - Depth of Field
on Apr 27, 2015 at 10:22:41 pm

Thanks Steve!
I believe I've found the solution (and another problem within). After setting up your experiment, I looked back at my shots and realized the aperture was in fact affecting depth of field. Only problem is that I can't see the actual difference in the monitor - only when reviewing the footage after it's been taken. So this makes things a little inconvenient when trying to set up a shot.


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Blaise Douros
Re: Aperture - Depth of Field
on Apr 28, 2015 at 6:52:02 pm

A lot of the time, modern DSLRs will leave their lenses wide open until the shutter is pressed. They do this because it is often harder to see the darkened image with a narrower aperture. Whe the shutter is pressed, the aperture goes to the correct setting, and the shot fires. I know for a fact that Canon DSLRs do this, and they include a Depth Of Field Preview button that shows you what it looks like with the aperture at the correct setting. I can't say for sure that this is what's happening on your Sony, but it sounds likely.


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Matt Kelly
Re: Aperture - Depth of Field
on Apr 28, 2015 at 10:07:59 pm

- Blaise

That seemed to do the trick, thank you for your help! With somewhat comical timing, as this problem is solved, I've found another! When I take pictures, everything appears to look the same after pressing the DOF preview button. When I take video, however, the exposure is not at all the same. When viewing in the monitor before the shot, it is much darker than what the shot ends up turning out. Any help on this one?


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Blaise Douros
Re: Aperture - Depth of Field
on Apr 29, 2015 at 8:12:01 pm

Is it different on the camera monitor, or different on your editing rig? If it's different on the camera monitor, then I'm at a loss as I don't know Sony DSLRs very well. If it's on the edit machine, then it could be a simple case of monitor calibration.

If your Sony has an exposure histogram you can put onscreen while shooting, call it up and see if it matches your histogram in your edit monitor.


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