Another another digital camera question

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Date: 15 Jul 2007 10:54:04
From: _
Subject: Another another digital camera question

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...

Date: 18 Jul 2007 15:02:32
From: laura halliday
Subject: Re: Another another digital camera question

On Jul 17, 12:42 am, pau...@saaf.se (Paul Schlyter) wrote:

> An old story regarding how long something might work: when magnetic
> tape recorders became widely available some time in the 1960's, there
> were rumors that magnetic recordings would somehow "fade away" by
> themselves after several decades. Recently I've been converting old
> vinyl records and tape recordnings into digital formats, and I then
> listened to old magnetic tapes I hadn't listened to for a very long
> time. The oldest of these recordings were 38 years old -- and they
> were still fine and well!

However, the oxide on some tapes of the late 1960s and
early 1970s used a binder that soaked up water. Slowly,
over 30 or 40 years, this turned the tapes in to mush.
Apparently such tapes can be recovered by baking
them at a high enough temperature to drive out the
moisture, but not high enough to damage the tape any
further.

I've done prints from 50 year old negatives that had
not deteriorated in the slightest...it's kinda fun bringing
them back to life.

Laura Halliday VE7LDH "Non sequitur. Your ACKS are
Grid: CN89mg uncoordinated."
ICBM: 49 16.05 N 122 56.92 W - Nomad the Network Engineer

Date: 17 Jul 2007 01:53:32
From: thad@thadlabs.com
Subject: Re: Another another digital camera question

On Jul 17, 12:42 am, pau...@saaf.se (Paul Schlyter) wrote:
> In article <1184509052.868773.21...@g12g2000prg.googlegroups.com>,
> [...]
> Please get back here in two years and report whether the shutter of
> your DSLR has failed or not. Real empirical data is better than
> extimates in advance.

No need to wait; peoples' cameras are already experiencing the
shutter failures as reported in several Yahoo groups, and in one,
the Nikon-D70, a survey is presently ongoing collecting more data
and the 50,000 count seems definitely real (noting I haven't followed
reports in any of the Canon groups, but one person's Rebel (at work)
failed around 40,000 shutter releases per the EXIF data).

It would have been extremely rare for consumer film SLRs to have
that many shutter releases though my Dad's Contax did and it did
require shutter replacement; given the number of slides I inherited
he may have just exceeded 30,000 shutter releases (including after
the repair) some 20 years ago when he died.

> [...]
> An old story regarding how long something might work: when magnetic
> tape recorders became widely available some time in the 1960's, there
> were rumors that magnetic recordings would somehow "fade away" by
> themselves after several decades. Recently I've been converting old
> vinyl records and tape recordnings into digital formats, and I then
> listened to old magnetic tapes I hadn't listened to for a very long
> time. The oldest of these recordings were 38 years old -- and they
> were still fine and well!

Same for me, including even 5-1/4" floppies from the late 1970s and
early to mid 1980s -- they still are readable.

Date: 16 Jul 2007 02:18:22
From: KLM
Subject: Re: Another another digital camera question

Date: 15 Jul 2007 15:01:35
From: thad@thadlabs.com
Subject: Re: Another another digital camera question

On Jul 15, 7:21 am, Chris L Peterson <c...@alumni.caltech.edu > wrote:
> On Sun, 15 Jul 2007 07:17:32 -0700, "t...@thadlabs.com"
>
> <t...@thadlabs.com> wrote:
> >The bad part is cameras have a finite number of shutter releases
> >before the mechanism needs repair -- this wasn't a real problem back
> >in the days of film because film cost and processing time tended to
> >limit the number of exposures one could/would take at a given time.
>
> Well, I'm pretty sure the camera I mentioned doesn't use a mechanical
> shutter for the subshots. Many digital cameras don't have a mechanical
> shutter at all.

OK; my comments pertained to DSLRs which do have a mechanical
shutter (and whose lenses typically have a mechanical iris) -- I
didn't
look back to the thread's beginning. :-)

Date: 15 Jul 2007 15:44:39
From: William Hamblen
Subject: Re: Another another digital camera question

Date: 15 Jul 2007 11:16:35
From: RMOLLISE
Subject: Re: Another another digital camera question

On Jul 15, 5:54 am, _ <jtayNOSPAM...@hfDONTSENDMESPAMx.andara.com >
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

Date: 15 Jul 2007 19:04:26
From: _
Subject: Re: Another another digital camera question

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

> On Jul 15, 5:54 am, _ <jtayNOSPAM...@hfDONTSENDMESPAMx.andara.com>
> 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...").

Date: 15 Jul 2007 22:46:43
From: Chris L Peterson
Subject: Re: Another another digital camera question

On Sun, 15 Jul 2007 19:04:26 GMT, _
<jtayNOSPAMlor@hfDONTSENDMESPAMx.andara.com > 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

Date: 15 Jul 2007 23:36:10
From: Thomas Womack
Subject: Re: Another another digital camera question

In article <1ts5wyot9kfk6$.vpgoe6sir1yv$.dlg@40tude.net >,
_ <jtayNOSPAMlor@hfDONTSENDMESPAMx.andara.com > 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

Date: 15 Jul 2007 23:38:30
From: Thomas Womack
Subject: Re: Another another digital camera question

In article <osk*wHQPr@news.chiark.greenend.org.uk >,
Thomas Womack <twomack@chiark.greenend.org.uk > wrote:
>In article <1ts5wyot9kfk6$.vpgoe6sir1yv$.dlg@40tude.net>,
>_ <jtayNOSPAMlor@hfDONTSENDMESPAMx.andara.com> 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

Date: 15 Jul 2007 07:17:32
From: thad@thadlabs.com
Subject: Re: Another another digital camera question

On Jul 15, 6:54 am, Chris L Peterson <c...@alumni.caltech.edu > wrote:
> [...]
> Not really. There is a camera I've read about that takes multiple
> exposures very rapidly and produces a single image file that can be post
> processed to select the focus distance and depth-of-field. Very
> promising technology for digital cameras.

There's both a good and a bad part of that; the good is as you wrote.

The bad part is cameras have a finite number of shutter releases
before the mechanism needs repair -- this wasn't a real problem back
in the days of film because film cost and processing time tended to
limit the number of exposures one could/would take at a given time.

The number "50,000" often comes up as the rated number of shutter
releases for prosumer DSLRs (e.g., Nikon's D80, D70, D50, D40 and
Canon's Rebel series) and "100,000" for the higher-end cameras.

I often take 500 shots a week which, for a, say, D70, gives a 2-year
lifetime on the shutter, and bracketing (where 3 shots are taken in
automatic rapid sequence with different aperture/ISO/etc. or another
parameter) exacerbates the shutter lifetime problem if that feature
is enabled.

Something to consider.

Date: 17 Jul 2007 07:42:48
From: Paul Schlyter
Subject: Re: Another another digital camera question

In article <1184509052.868773.21320@g12g2000prg.googlegroups.com >,
thad@thadlabs.com <thad@thadlabs.com > wrote:

> On Jul 15, 6:54 am, Chris L Peterson <c...@alumni.caltech.edu> wrote:
> > [...]
> > Not really. There is a camera I've read about that takes multiple
> > exposures very rapidly and produces a single image file that can be post
> > processed to select the focus distance and depth-of-field. Very
> > promising technology for digital cameras.
>
> There's both a good and a bad part of that; the good is as you wrote.
>
> The bad part is cameras have a finite number of shutter releases
> before the mechanism needs repair -- this wasn't a real problem back
> in the days of film because film cost and processing time tended to
> limit the number of exposures one could/would take at a given time.
>
> The number "50,000" often comes up as the rated number of shutter
> releases for prosumer DSLRs (e.g., Nikon's D80, D70, D50, D40 and
> Canon's Rebel series) and "100,000" for the higher-end cameras.
>
> I often take 500 shots a week which, for a, say, D70, gives a 2-year
> lifetime on the shutter, and bracketing (where 3 shots are taken in
> automatic rapid sequence with different aperture/ISO/etc. or another
> parameter) exacerbates the shutter lifetime problem if that feature
> is enabled.
>
> Something to consider.

Please get back here in two years and report whether the shutter of
your DSLR has failed or not. Real empirical data is better than
extimates in advance.

An old story regarding how long something might work: when magnetic
tape recorders became widely available some time in the 1960's, there
were rumors that magnetic recordings would somehow "fade away" by
themselves after several decades. Recently I've been converting old
vinyl records and tape recordnings into digital formats, and I then
listened to old magnetic tapes I hadn't listened to for a very long
time. The oldest of these recordings were 38 years old -- and they
were still fine and well!

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/

Date: 15 Jul 2007 14:21:24
From: Chris L Peterson
Subject: Re: Another another digital camera question

On Sun, 15 Jul 2007 07:17:32 -0700, "thad@thadlabs.com"
<thad@thadlabs.com > wrote:

>The bad part is cameras have a finite number of shutter releases
>before the mechanism needs repair -- this wasn't a real problem back
>in the days of film because film cost and processing time tended to
>limit the number of exposures one could/would take at a given time.

Well, I'm pretty sure the camera I mentioned doesn't use a mechanical
shutter for the subshots. Many digital cameras don't have a mechanical
shutter at all.

_________________________________________________

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

Date: 17 Jul 2007 07:42:48
From: Paul Schlyter
Subject: Re: Another another digital camera question

In article <o6bk93lioqi98ra60vgju7hti1abvknma3@4ax.com >,
Chris L Peterson <clp@alumni.caltech.edu > wrote:

> On Sun, 15 Jul 2007 07:17:32 -0700, "thad@thadlabs.com"
> <thad@thadlabs.com> wrote:
>
>> The bad part is cameras have a finite number of shutter releases
>> before the mechanism needs repair -- this wasn't a real problem back
>> in the days of film because film cost and processing time tended to
>> limit the number of exposures one could/would take at a given time.
>
> Well, I'm pretty sure the camera I mentioned doesn't use a mechanical
> shutter for the subshots. Many digital cameras don't have a mechanical
> shutter at all.

Most non-DSLR digital cameras lack mechanical shutters: if your camera
has an "electronic viewfinder", or an LCD screen where you can view your
image before you shoot it, then it has no mechanical shutter.

A lot of these cameras have quite limited f-stop settings too: quite
often you cannot set the f-stop smaller than f/8 (and here I mean
smaller aperture, not smaller f-number!). Which means the CCD chip
can get some damage if you point your camera towards the Sun. "But
why would anyone want to point their camera towards the Sun?", I
hear someone ask -- well, to photograph halo phenomena, of course!
Haloes can be relly beautiful --- anyway, I've burnt a permanent
"mark" in one corner of one of my own digital cameras, probably when
trying to photograph a halo.

So I really enjoy the shutter of a DSLR: they ensure the CCD chip
won't get any light until you really take your picture. And that,
combined with the ability to set the aperture as small as f/22 or f/32
or even smaller, and very short exposure times of 1/2000 or 1/4000
second, makes it safe to shoot a picture where the Sun is somewhere in
the image.

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/

Date: 17 Jul 2007 16:38:57
From: Ed Holden
Subject: Re: Another another digital camera question

"Paul Schlyter" <pausch@saaf.se > wrote:
>
> Most non-DSLR digital cameras lack mechanical shutters: if your camera
> has an "electronic viewfinder", or an LCD screen where you can view your
> image before you shoot it, then it has no mechanical shutter.

Are you sure? My Fuji DX-8 (non-DSLR) has a mechanical shutter that
sounds like an 8-track tape player changing tracks, yet it allows preview
on the LCD before and during shooting.

Having read the technical background to MER's Pancam system, I guess
image smearing is a problem that needs to be corrected for electronic
shuttering cameras.

Date: 15 Jul 2007 13:54:34
From: Chris L Peterson
Subject: Re: Another another digital camera question

On Sun, 15 Jul 2007 10:54:04 GMT, _
<jtayNOSPAMlor@hfDONTSENDMESPAMx.andara.com > 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.

Digital cameras with adjustable f-stops (which isn't all of them) do it
mechanically, since there's no other way. They have electronic irises.
With these cameras, you can control your depth of focus just like any
other.

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

Not really. There is a camera I've read about that takes multiple
exposures very rapidly and produces a single image file that can be post
processed to select the focus distance and depth-of-field. Very
promising technology for digital cameras.

_________________________________________________

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

Date: 15 Jul 2007 13:15:46
From: Sam Wormley
Subject: Re: Another another digital camera question

_ 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...

Depth of field in a function of lens aperture, focal length and
subject distance whether moint and shoot or dSLR. All the optical
formulae are the same.

I've never disassembled one to verify that change in aperture is
electromechanical.

The EV calculation makes no difference between ASA or ISO, after
all there are just standards. ASA and ISO speeds in modern times
are identical.
http://en.wikipedia.org/wiki/Film_speed

What is the meaning of ISO for digital cameras?
http://www.cs.duke.edu/~parr/photography/faq.html#isomeaning

For digital cameras, ISO is shorthand for the ISO 12232:1998
specification maintained by the International Organization for
Standardization.

This standard specifies signal to noise ratio and brightness
requirements (or saturation for cameras that are limited by well
capacity) for a camera to earn a certain ISO rating. These ratings
are intended to be similar to those of ISO 5800:1987, which
specifies ratings for film. Thus, at a given f/stop, shutter speed,
and ISO, both film and digital exposures should produce roughly the
same brightness as output. Note that in practice this isn't always
the case due to many factors including interpretation of the
standard, different tone curves, rounding, and marketing
considerations.

As with traditional film ISO ratings, increasing the ISO
corresponds to an increase in sensitivity. For example, in moving
from ISO 100 to ISO 200, while keeping the f/stop constant, you
will achieve the same exposure by using a shutter speed twice as
fast.

In practice a single camera can achieve multiple different ISO
ratings by applying some form of amplification to the signal coming
off the sensor. This can be done by applying analog amplification
to the signal before it hits the A/D converter, or by bit shifting
the results after they have gone through the A/D converter. Cameras
may apply a combination of these approaches, depending upon the
desired ISO. Which is best will depend upon whether amplifier noise
or A/D converter noise is larger.

In the sensor section we discuss why high ISO shots have more noise.

Also see:
Surface Brightness of Deep-Sky Objects Measured with a Digital Camera
http://www.clarkvision.com/astro/surface-brightness-profiles/introduction.html

Digital Imaging Information
http://clarkvision.com/imagedetail/index.html

Date: 17 Jul 2007 07:42:47
From: Paul Schlyter
Subject: Re: Another another digital camera question

In article <66pmi.28926$Fc.17200@attbi_s21 >,
Sam Wormley <swormley1@mchsi.com > wrote:

> The EV calculation makes no difference between ASA or ISO, after
> all there are just standards. ASA and ISO speeds in modern times
> are identical.

That's because they really are the same: ISO just adopted the ASA
definition of film speeds so ASA became a worldwide standard instead
of just a US standard.

The once greatest competitor to ASA film speeds, DIN film speeds
(where DIN means Deutsche Industrie Normen), is no longer used.

Although DIN and ASA film speeds strictly weren't conversible into one
another (DIN relied on "minimum saturation", while ASA relied on
"maximum slope" of the exposure vs illumination curve), for most
normal films ASA speeds could be converted to DIN speeds with the
formula below:

DIN = 10 * log10(ASA) + 1

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/