Orquid "Phoenix"

Orquid "Phoenix"

by ceinmart

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I have a Canon PowerShot SD780 IS point-and-shoot which I use as my carry-around-everywhere camera when I don't want to drag my SLR about. This tiny little camera works great and takes fabulous pictures for something so small, but the big limitation I've found is a narrow depth of field when focusing closely. It seems that the camera is programmed to always favor a fast shutter speed as its priority, so in anything other that blasting sun the aperture is always wide open.

Is there any trick I can use -- such as a process, a built-in setting, or hacked firmware -- to get this camera to stop down its aperture when doing close up shots?

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7 Answers

up vote 4 down vote accepted

As Matt stated, there is the Canon Hack Development Kit (CHDK).

However, the SD780, along with many other compacts, do not have an iris for aperture control. Basically the CHDK will allow you to control the ND filter, which acts as a fake aperture. It will only allow you to use longer shutter speeds (or increased ISO), and will not increase depth of field.

The physical aperture is fixed, but you can increase the f-stop (aperture / focal length) by zooming in with the lens. Of course, increasing the focal length itself will narrow the depth of field more than the amount you decreased the f-stop.

The only way to potentially get a deeper depth of field is to shoot from further away and perhaps crop. The act of magnifying will actually change the circle of confusion and again narrow the perceived depth of field, but it may be the best chance. You can take multiple shots and use Super-Resolution to try to regain some resolution. Only one commercial software at the moment implements Super-Resolution, but you can use Matlab if you have it :)

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+1 good point, I didn't look at the spec of the 780 in detail. I guess the real answer to this question is: "no"! –  Matt Grum Sep 21 '10 at 8:37
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The size of your circle of confusion is determined by the effective size of the front element. Apertures effectively shrink the front element by blocking light passing through the edges of the lens, and only allowing light hitting the middle of the lens to pass. Since your camera (as Eruditass points out) does not have its own aperture, you can't do this with any settings or firmware.

However, if you'd like to have the same effect, you can create an aperture on the front of your lens. For example, you could punch a hole smaller than your lens's front element in a piece of black construction paper, and then center the hole in front of your lens. (You might experience some vignetting.)

This is the same idea behind shaped bokeh, you're just using the shape of "a small circle".

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That's a creative answer! –  whuber Oct 7 '10 at 20:56
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Only thing I can see is to use the Exposure Compensation feature to force it to stop down -2 EV. It seems only the shutter is selectable, and to be perfectly honest, I am not sure if the exposure compensation adjusts aperture or ISO. Seems like a great fully automatic P&S for those random life moments, but it doesn't appear to have much in the way of real exposure control.

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There is the Canon Hack Development Kit (CHDK):

http://chdk.wikia.com/wiki/CHDK

Which states it supports the SD780. It's fairly safe in that you load a fully hacked version of the firmware which gets reset when you turn the camera off. It will allow you to directly control nearly every camera feature, and you can even write scripts to, for example, stop down based on focussing distance. edit: you can't actually stop down with this particular model, so it looks like you're out of luck

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Eruditass--

When you say "the ND filter...acts as a fake aperature" does this mean that it really isn't a physical lens filter but merely something done on the CCD?

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By fake aperture, I mean it doesn't actually reduce the diameter of the entrance pupil, which would affect the depth of field. I believe it is real physical ND filter, which will reduce the amount of light hitting the sensor, allowing higher shutter speeds. –  Eruditass Oct 7 '10 at 0:33
    
I think you mean lower shutter speeds. –  Evan Krall Oct 7 '10 at 1:37
    
Yeah, my bad. Lower, longer shutter speeds. –  Eruditass Oct 7 '10 at 23:22
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I assume from the above discussion that CHDK only lets you turn the ND filter on/off--i.e. the filter doesn't have any values attached to it.

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As Adam said in the beginning of the thread "in anything other that blasting sun the aperture is always wide open." This is my experience with the SD780 also. The lens is rated at F3.2 and the camera nearly always chooses F3.2 except, rarely, under very bright light it will choose F9.0. But that is it, no other F stops (unless you use optical zoom). But what Erudtass just said makes me think that it isn't really choosing an Fstop of 9.0 . Is this just a number to indicate that it has turned on the ND filter??

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Correct. You should ask these kinds of questions in a separate Question or in the chatroom ( meta.photo.stackexchange.com/questions/255/photo-se-chatroom ), as they are not really answers. –  Eruditass Oct 7 '10 at 23:23
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