Another another digital camera question

On Jul 15, 5:54 am, _
wrote:
The recent thread on what ISO really means in the context of digital
cameras confirmed my suspicions of how that is not really the same as film
ISO; useful enough to know, though, for both astro and terestrial use.

But (some) digital camers also allow you to set f-stops. In a "real"
camera, this has (among others) the effect of increasing the depth of
field. Not so much interest for astro, but I don't just take pictures in
the dark.

For digital cameras, are there any which actually do have a mechanical
f-stop, or is there an analogous software function to increase depth of
field? If not, I assume it's just used in the same way as the ISO setting.

SLR-type cameras excepted, of course; and if there is a software
depth-of-field it'd be *real* handy for post-processing...

Hi:

Well, it's not as if ISO meant that much with film, either--not for
long exposure imaging. Because of reciprocity failure, ISO could be
looked upon as at best a general guide to what a film was like.


Unk Rod

On Sun, 15 Jul 2007 11:16:35 -0700, RMOLLISE wrote:

On Jul 15, 5:54 am, _
wrote:
The recent thread on what ISO really means in the context of digital
cameras confirmed my suspicions of how that is not really the same as film
ISO; useful enough to know, though, for both astro and terestrial use.

But (some) digital camers also allow you to set f-stops. In a "real"
camera, this has (among others) the effect of increasing the depth of
field. Not so much interest for astro, but I don't just take pictures in
the dark.

For digital cameras, are there any which actually do have a mechanical
f-stop, or is there an analogous software function to increase depth of
field? If not, I assume it's just used in the same way as the ISO setting.

SLR-type cameras excepted, of course; and if there is a software
depth-of-field it'd be *real* handy for post-processing...

Hi:

Well, it's not as if ISO meant that much with film, either--not for
long exposure imaging. Because of reciprocity failure, ISO could be
looked upon as at best a general guide to what a film was like.


Unk Rod

yes, true - but what I really wanted to know is if I adjust the "f-stop" on
a non-SLR digital camera, does the hole that the light goes through get
smaller/larger, or do they just do more math on the image data?

Electronic iris? A quick search makes me think this has nothing to do with
hole size, but is instead a shutter-speed fiddle or a math function
("...on-chip electronic iris...").

In article ,
_ wrote:

yes, true - but what I really wanted to know is if I adjust the "f-stop" on
a non-SLR digital camera, does the hole that the light goes through get
smaller/larger, or do they just do more math on the image data?

Electronic iris? A quick search makes me think this has nothing to do with
hole size, but is instead a shutter-speed fiddle or a math function
("...on-chip electronic iris...").

At least on the Canon Powershot A510, when I point it at light sources
of varying brightness, it looks as if a physical iris deep inside the lens
changes size, and there are mechanical noises which occur at the same time
as the image on the back of the camera changes brightness. So there's a
physical iris, and accordingly there's depth-of-field.

I've also done the obvious test of putting the camera pointing at a metal
ruler, setting aperture to various values, and taking a flash exposure.

f/2.6: clear from 149mm to 143mm
f/5.0: clear from 150mm to 138mm
f/8.0: clear from 155mm to 137mm

so there is a real DOF.

Tom

In article ,
Thomas Womack wrote:
In article ,
_ wrote:

yes, true - but what I really wanted to know is if I adjust the "f-stop" on
a non-SLR digital camera, does the hole that the light goes through get
smaller/larger, or do they just do more math on the image data?

Electronic iris? A quick search makes me think this has nothing to do with
hole size, but is instead a shutter-speed fiddle or a math function
("...on-chip electronic iris...").

At least on the Canon Powershot A510

To avoid unnecessary Googling, this is a 3-megapixel pocket camera
with a 35-140-equivalent lens that I bought new in July 2005 for
around $300, not especially wanting to take a heavy DSLR around
Romania in a rucksack.

Tom

On Sun, 15 Jul 2007 19:04:26 GMT, _
wrote:

yes, true - but what I really wanted to know is if I adjust the "f-stop" on
a non-SLR digital camera, does the hole that the light goes through get
smaller/larger, or do they just do more math on the image data?

Yes. Always- assuming, of course, that the digital camera allows you to
set this in the first place. There is no image processing involved.

Electronic iris? A quick search makes me think this has nothing to do with
hole size, but is instead a shutter-speed fiddle or a math function
("...on-chip electronic iris...").

No, an electronic iris is a motorized iris. Most removable lenses use
them, and all digital cameras that have variable f-stops also use them.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On Sun, 15 Jul 2007 10:54:04 GMT, _
wrote:

For digital cameras, are there any which actually do have a mechanical
f-stop, or is there an analogous software function to increase depth of
field? If not, I assume it's just used in the same way as the ISO setting.

Aperture works the same whether digital or film. The super cheap
digital point and shoot models have fixed apertures like box cameras.

Bud
--
The night is just the shadow of the Earth.

_ wrote:

The recent thread on what ISO really means in the context of digital
cameras confirmed my suspicions of how that is not really the same as film
ISO; useful enough to know, though, for both astro and terestrial use.

But (some) digital camers also allow you to set f-stops. In a "real"
camera, this has (among others) the effect of increasing the depth of
field. Not so much interest for astro, but I don't just take pictures in
the dark.

For digital cameras, are there any which actually do have a mechanical
f-stop, or is there an analogous software function to increase depth of
field? If not, I assume it's just used in the same way as the ISO setting.

SLR-type cameras excepted, of course; and if there is a software
depth-of-field it'd be *real* handy for post-processing...

Nothing about digital has suspended the laws of physics.
Im still waiting for a digital camera that will mix a good martini
while it thinks for me (and the universe)!. Good luck.