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Offline fudgey

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« Reply #10 on: 02 / January / 2009, 07:16:34 »
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If my camera had an f/11 mode (which thank god it hasn't) then I would have a resolution of 0,4 Mpixel

As a reminder: with CHDK overrides a570is goes to f/11 in wide angle and f/16 fully zoomed in.

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Offline fe50

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« Reply #11 on: 02 / January / 2009, 15:36:24 »
...Let's see if we can calculate this limit from the data on that page (can someone please check my calculations?):
...The smallest aperture the a570Is has is f/8, which is 2 stops higher than f/11, so the resolution is 2*2 times larger, i.e. 1.6 Megapixel ...
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One stop up (at f/5,6) I am still at 3,2 Mpixel.
One other stop up (at f/4) I am at 6,4 Mpixel.

This means that even if my lens was a perfect lens, and my sensor was a perfect noise-less sensor even, up to f/4 my 7 Mpixel sensor would be useles, as no lens can give me 7 Mpixels on such a small sensor.

Hmm - while reading this, i asked myself: how does this look with a ND filter, an 'emulated' aperture ?

E.g. with the SD870: the f stop is F/2.8 unzoomed, with the ND filter kicked in it is 'F/8.0' - but the 'optical resolution' will be although the same since the fix aperture is always the same ?  ???

« Reply #12 on: 02 / January / 2009, 16:15:17 »
the 'optical resolution' will be although the same since the fix aperture is always the same ?  ???

The effective aperture varies from f17 at wide angle to f35 at telephoto !

just as well there is no aperture, the resolution would be terrible.

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Offline fe50

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« Reply #13 on: 02 / January / 2009, 17:04:28 »
just as well there is no aperture, the resolution would be terrible.
Yeah - use a small sensor + optics combination, full zoom and ISO over 200 and you'll get --> a nice mosaic !

But there are also extreme differences between e.g. the small Ixus lenses and the 'better' ones from e.g. the S series:
On the Ixus 860 the 3.8x zoom is only usable for 'art' pictures, you'll not find much image informations in pictures with this zoom stage. With the monstrously zoom lens of the SX10 images with 20x zoom are amazing, compared to the 3.8x zoom on the Ixus  :(


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Offline dzsemx

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« Reply #14 on: 03 / January / 2009, 02:54:32 »
well i prefer my 12 megapix A650's image quality vs. my 8 megapix A630 (better iso800)
seriously.. you compared a samsung with a canon???
canon cameras are cameras, made to take photos, samsung makes stylish devices with integrated camera...
i would never go back to 6 megapixel, 10-12 megapixel is just perfect for me and for any normal user and for any nonprofessional shooter
« Last Edit: 03 / January / 2009, 19:19:38 by dzsemx »

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Offline fe50

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« Reply #15 on: 03 / January / 2009, 07:18:10 »
seriously.. you compared a samsung with a canon???
i would never go back to 6 megapixel, but i think that canon cameras are cameras, made to take photos, samsung makes stylish devices with integrated camera...
...Samsung ? :o
I own the Canon SX10 (Digic IV, 10MP, 20x opt. zoom lens, successor of the S5), didn't know that Samsung has also such a camera  ;)

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Offline ISO64

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« Reply #16 on: 05 / January / 2009, 23:16:22 »
If my camera had an f/11 mode ...  then I would have a resolution of 0,4 Mpixel
The smallest aperture the a570Is has is f/8, which is 2 stops higher than f/11, so the resolution is 2*2 times larger, i.e. 1.6 Megapixel ...
HELP! someone please tell me I am wrong!

You are correct   ;)

In terms of depth-of-field, f11 is equivalent to f66 and f8 is equivalent to f48.
Those apertures do not exist on 35mm lenses because of the massive diffraction.

With such tiny sensors on these cameras, you can hardly stop down at all, especially at the telephoto setting where the aperture wide-open is relatively small.

On some of the SDM OSD's, the aperture value is coloured red when the diffraction limit has been reached.


As a rule, it is considered that f8 is the first next aperture from f11 (8^2=64; 11^2=121, roughly 2 times more). It is only one step up, not two.

Also, since f number is focal length/aperture diameter ratio, equal f numbers on completely different sensor sizes mean always the same thing (ND filters non-withstanding). Try to imagine the whole lens/scene/sensor geometry measured in units that are not mm or are related to some other body parts size (foot, inch, hair width,...) At f/8, sensor size that is one tenth of the focal length will always have certain number of sensor size lengths for a depth of field at a distance that is equal to y * focal length. Simple scaling. That is why small sensors do not need precise focusing mechanism, they work at forgivingly large f numbers and anythig further than your arm length is far, far away.

 :)

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Offline LjL

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« Reply #17 on: 06 / January / 2009, 09:03:37 »
This is interesting.

How about adding a function to CHDK that would automatically lower the output resolution (say from 8Mp to 5Mp) when it detects that the selected aperture (or focal length, which influences the aperture) just makes the higher resolution worthless?

(Well, given there's JPEG compression in place, saving an 8Mp file would still have quality advantages over a 5Mp file even if the image only actually contained less than 5Mp, but I suppose that's negligible for most applications)


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Offline PhyrePhoX

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« Reply #18 on: 06 / January / 2009, 09:25:22 »
if i shoot wide open, i have a very shallow dof, thus i lose image information.
landscapes are to be shot with a small aperture, even if that means i lose quality. but what good is a full qualified x mpixel shot when lots of it is blurry because of open aperture.

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Offline LjL

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« Reply #19 on: 07 / January / 2009, 10:23:27 »
Err, are you sure you've got it right?

It's true that large aperture means shallow depth of field, but if you're shooting a landscape, you're generally shooting at infinity, so I can't see how that would matter at all.

As I understand it, when you change your aperture, you're trading depth of field for sharpness at the focus point.
In other words, with a large aperture you have a bell curve that's mostly just a spike - but a high spike - in the center, while with a small aperture the curve function is relatively high-valued in most of the graph, but the maximum value is smaller.

Just try shooting a landscape at infinity wide open, and then take the same shot at minimum aperture (with a tripod maybe so motion blur won't matter). Check the JPEG size, which is an indicator of sharpness and amount of information present. For that matter, just check by eye; at least with a low-end camera, you'll notice a definite difference in favor of the wide-aperture shot.

 

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