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Old Oct 17, 2005, 10:51 AM   #1
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Hi,

I found out a strange thing (in my opinion) about the aperture choice of my A620:

All shots are taken with aperture 4.0 or lower. Automatically, the aperture will not go higher. Even in bright light, the shutter speed will go 1/1250 and still keep it on 4.0.

This is not particular problem of my camera. Looking at the EXIF of the pictures posted on the internet with A6x0, you will find the same.

If you use AUTO, P, Portrait or landscape, the camera will never put the aperture higher than 4.0.

I am trying to understand why? Any idea ?:idea:

Thanks.
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Old Oct 17, 2005, 11:30 AM   #2
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Canon probably decided that the camera produces better images at larger apertures with this model.

Also, remember that aperture as expressed as f/stop is a ratio between the focal length of the lens and the diameter of the aperture iris.

So, with a compact digital camera that has a very short focal length lens (the lens on this model is7.3 - 29.2mm), the aperture diameter will be very small (which can lead to image quality problemsfrom diffraction if you try to use an f/stop value that closes the aperture down too much).

Ifyou use longer focal lengths, you may find that the aperture it chooses will change.

Keep in mind that because the sensor is much smaller than 35mm film, you'll have far greater depth of field for any given 35mm equivalent focal length, aperture and focus distance, too (since a much shorter focal length lens will give you the same angle of view as a much longer lens on a 35mm model).

Shooting at f/4 with a model like this Canon would be like shooting at around f/18 with a 35mm camera from a depth of field perspective, for any given 35mm equivalent focal length and focus distance.
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Old Oct 17, 2005, 11:37 AM   #3
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Thanks for your answer. Just a few comments:

1. Looking at the EXIFs of the pics from the A95, I don't see any constant aperture.

2. What is the point in having landscape mode, supposed to prioritize higher valure of aperture (and consequently improve Depth of Field) if the aperture does not change (even here aperture is mostly set on 4.0)?

Yoel
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Old Oct 17, 2005, 11:45 AM   #4
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YoelD wrote:
Quote:
What is the point in having landscape mode, supposed to prioritize higher valure of aperture (and consequently improve Depth of Field) if the aperture does not change (even here aperture is mostly set on 4.0)?

With some models, Landscape mode may also lock the camera's focus to inifinity (I don't know about this one, you'd have to try it). Canon may have also changed some of the other image quality characteristics in this mode. You'd have to experiment to see if there are any differences in the images compared to other modes.

Again, you don't need smaller apertures with a model like this for DOF purposes for things like Landscapes. You've got tremendous Depth of Field compared toa 35mm camera.

Most users have the opposite problem with a small camera like this (too much depth of field, making it almost impossible to helplarger subjects stand out from distracting backgrounds by using a larger aperture (smaller f/stop) to blur the backgrounds sufficiently.

At f/4 with this model, shooting at it's wide angle lens setting (actual focal length of 7.3mm to give you the same angle of view you'd have at 35mm with a 35mm model), the hyperfocal distance is only about 7.3 feet (where everything from slightly closer from there to infinity would be acceptably sharp if you focused at that point).


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Old Oct 17, 2005, 12:08 PM   #5
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After 20 years in classic SLR photography, this is my first entry into the world of digital.

So thanks for explaining that it isn't quite the same.
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Old Oct 17, 2005, 12:17 PM   #6
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Here is a handy online Depth of Field calculator you may find handy.

Your new A620 is not listed yet. But, if you select another model with the same size sensor (1/1.8"), you can tell what your depth of field will be. The Canon Powershot A80 is an example (it's sensor size is 1/1.8", too).

After picking a Digital Camera model with the same sensor size, just plug in the actual focal length ofyour lens (which is 7.3mm on it's wide angle end, going through 29.2mm on it's long end).

Then select an aperture and plug in a focus distance and it will compute depth of field for you.

If you compare it to a 35mm model, you'll find that you'd need to shoot at around f/18 just to match your Canon's Depth of Field at f/4 for the same composition andfocus distance.

Keep in mind that you'd be shootingat focal lengths ranging from 35mm to 140mm with the 35mm model to get the same angle of view you'd have shooting at 7.3 to 29.2mm with your model (the actual focalrange of your Canon's lens).

http://www.dofmaster.com/dofjs.html


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Old Oct 24, 2005, 5:57 AM   #7
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Hello guys,

Need to ask you a question. I'm interested in the A620 and wanted to ask you what do you think of it?
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