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DSLR that adjusts shutter speed w/ focal length?

Posts: n/a
On Sun, 22 Jul 2007 10:48:00 -0700, "Richard H." <(E-Mail Removed)> wrote:

>Doug Jewell wrote:
>> So you mean a "motion blur priority" mode? Kind of like shutter
>> priority, but instead of keeping the shutter fixed, it maintains the
>> shutter speed relative to the FL? so if the camera is at 100mm and I set
>> the shutter to be 1/50, it would move up to 1/150 if I zoomed to 300mm.
>> Can't say I know of any that do it - shutter priority and dialling the
>> shutter speed while you zoom would be the closest. Not all that hard to do.

>I tend to shoot in manual mode, so I envision it as a menu option rather
>than a button, akin to "Track shutter speed with focal length". A bit
>of a hybrid between Program and Manual modes, if you will. (An
>alternative might be to allow a manual EV setting with Program mode.)
>Certainly this feature would be off by default - it's not the behavior
>anyone would normally expect when manually setting the shutter speed.
>Alas, it sounds like this might be a pipedream. Unfortunate, knowing
>that it'd be pretty easily implemented. Maybe one day camera firmware
>will go open source, and we can tweak away.

A pipedream? Some camera's have already been "open sourced". If you have a Canon
Powershot S2 or S3 and installed CHDK on it you can just run this simple script
that I just wrote. Save it to your CHDK/SCRIPTS/ folder on your SD card, then
load it up from CHDK's [SET] button menu (when <ALT> is showing).

I wanted to see how simply it can be done. I've not tested it yet, but it should
work. It sets the shutter speed for the 35mm equivalent zoom setting. Using the
old adage of 1/focal-length for shutter-speed. I included a user selectable
variable to lower that limit by 3 stops if you have IS turned on (default).

Just compose your shot, set your zoom where you want it. Then press your <ALT>
toggle-button to put it in script mode and hit the shutter button. The script
will run, set your shutter-speed and take a photo. Then press your <ALT> toggle
button again to exit script-mode to compose another shot. Rinse & repeat.

A similar script can be written for A-Series cameras, but they only have 0-8 or
0-16 zoom steps available (vs. the 0-128 for S-Series). The line:


would have to be altered a bit. Where f is being calculated to 35mm
focal-length from the lens' hardware and firmware capabilities.

I'll confess minor problem, the zoom on these cameras is not as linear as this
equation calculates. But for all intents and purposes it will get you close to
the 1/focal-length=shutter-speed as is practical. It is afterall just a rough
guideline for the poorest of hand-held photographers.


rem For Canon Powershot S-Series

@title Motion-Blur Priority
param a IS is off=0 on=1
default a 1
if a<0 then a=0
if a>1 then a=1

print "Use in Manual"
print "or Tv mode."

get_zoom z
rem change the following line for A-Series

if s<=1/3200 then s=35
if s<=1/2500 then s=34
if s<=1/2000 then s=33
if s<=1/1600 then s=32
if s<=1/1250 then s=31
if s<=1/1000 then s=30
if s<=1/800 then s=29
if s<=1/640 then s=28
if s<=1/500 then s=27
if s<=1/400 then s=26
if s<=1/320 then s=25
if s<=1/250 then s=24
if s<=1/200 then s=23
if s<=1/160 then s=22
if s<=1/125 then s=21
if s<=1/100 then s=20
if s<=1/80 then s=19
if s<=1/60 then s=18
if s<=1/50 then s=17
if s<=1/40 then s=16
if s<=1/30 then s=15
if s<=1/25 then s=14
if s<=1/20 then s=13
if s<=1/15 then s=12
if s<=1/13 then s=11
if s<=1/10 then s=10
if s<=1/8 then s=9
if s<=1/6 then s=8
if s<=1/5 then s=7
if s<=1/4 then s=6
if s<=1/3 then s=5
if s<=1/2.5 then s=4
if s<=1/2 then s=3
if s<=1/1.7 then s=2
if s<=1/1.25 then s=1
if s<=1 then s=0

if a=1 then s=s-6
set_tv s

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Posts: n/a
D'oH! I just realized this long table of shutter-speed values could all be
boiled down into just one equation. Added right into one of these lines, or
writing it all in just one line.


I'll put that in v1.1. Personally I'd find no use for this so I doubt I'll do
more with it. I wrote it as an idle curiosity.

On Sun, 22 Jul 2007 18:16:38 -0500, GilfordBrimly <(E-Mail Removed)> wrote:

>if s<=1/3200 then s=35
>if s<=1/2500 then s=34
>if s<=1/2000 then s=33
>if s<=1/1600 then s=32
>if s<=1/1250 then s=31
>if s<=1/1000 then s=30
>if s<=1/800 then s=29
>if s<=1/640 then s=28
>if s<=1/500 then s=27
>if s<=1/400 then s=26
>if s<=1/320 then s=25
>if s<=1/250 then s=24
>if s<=1/200 then s=23
>if s<=1/160 then s=22
>if s<=1/125 then s=21
>if s<=1/100 then s=20
>if s<=1/80 then s=19
>if s<=1/60 then s=18
>if s<=1/50 then s=17
>if s<=1/40 then s=16
>if s<=1/30 then s=15
>if s<=1/25 then s=14
>if s<=1/20 then s=13
>if s<=1/15 then s=12
>if s<=1/13 then s=11
>if s<=1/10 then s=10
>if s<=1/8 then s=9
>if s<=1/6 then s=8
>if s<=1/5 then s=7
>if s<=1/4 then s=6
>if s<=1/3 then s=5
>if s<=1/2.5 then s=4
>if s<=1/2 then s=3
>if s<=1/1.7 then s=2
>if s<=1/1.25 then s=1
>if s<=1 then s=0

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Matt Clara
Posts: n/a
"John Sheehy" <(E-Mail Removed)> wrote in message
> "Matt Clara" <(E-Mail Removed)> wrote in
> news(E-Mail Removed):
>> That was my first thought, too, but here's another way of thinking
>> about it: Imagine two 8x10s, one a wide angle of a golfer taking a
>> swing, the other a close-up of the club head as it's in motion. Same
>> shutter speed reveals the same amount of movement, let's say, a half
>> an inch. In the wide angle image, that half an inch will occupy a
>> tiny fraction of the print's surface, so little that it's a saleable
>> image. In the close-up, it would occupy considerably more. So to get
>> a saleable image with the close-up, he has to up his shutter speed.

> So then, it's still not focal length, but magnification of the subject,
> that is relevant.

Yeah, we're really talking about what's acceptably sharp. Get a similar
discussion with circles of confusion.


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Matt Ion
Posts: n/a
Richard H. wrote:
> Do any DSLRs offer a mode to auto-adjust the shutter speed proportionate
> to the focal length? (i.e., if I zoom out to 2x the FOV, cut the
> shutter speed by 1/2 and open the aperture by 2x)

That would assume the DSLR can read your mind and know what effect
you're going for in your shot. AFAIK, the neural interface is a few
years away.

> When shooting motorsports, the ideal shutter speed is a balance between
> freezing the subject and conveying motion (e.g., blurred tires or panned
> background).

The "ideal" shutter speed it whatever you deem it to be for the results
you want in a specific shot. Only you can make that determination.

> Not a problem when using a fixed lens, but a problem if
> zooming in/out. (i.e., 1/2000 freezes more at 70mm than at 200mm).

No it doesn't - the subject still covers the same distance in the same
amount of time. It's just not as noticeable in the wider view.

I'd never shoot motorsports with an auto-exposure system anyway, if
there's any way to avoid it, especially close-ups of the cars.
Different paint schemes can seriously fake out your camera's exposure
reading; better to set the exposure manually for the light conditions.
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Paul Furman
Posts: n/a
John Sheehy wrote:

> RichA <(E-Mail Removed)> wrote
>>Seriously, do pro cameras ever have "idiot" modes?
>>You know, like a little face logo for portraits, a mountain for
>>landscapes, etc?
>>When you see that on a Nikon D2Xs, you'll know their days are

> There's nothing "Dummies" or "Idiot" about the OP's request. It is a
> very logical feature that I desired as soon as I got back into
> photography a few years ago. In very low light, doing hand-held
> shooting, Av mode is extremely problematic. I tend to use Av mode when
> there is ample light for fast shutter speeds, and Tv mode when light is
> very low, and having a blurred long exposure is worse than having wide-
> open optics or a little under-exposure. The logical extension to the
> latter is to have a Tv-pri mode where you set a ratio to focal length,
> rather than a fixed focal length, very useful for zoom cameras, so you
> don't get unnecessary under-exposure at the wide end of the zoom range.
> An intelligent photographer can make good use of automation to their
> advantage, when they choose one that automates what *they* would do
> automatically, if they had remembered to do so and had the time.
> This feature would be more of a true "user-control" than the P mode,
> which the Pro cameras do have.

I agree it could be a useful feature. The closest thing I've seen is
Auto-ISO on my D70, with a fixed focal length lens you could set it to
only boost the ISO when the shutter speed drops below whatever speed you
tell it in the menu. I think at some point people will be booting their
cameras to linux & writing their own settings & menus.

Paul Furman Photography
Bay Natives Nursery
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Paul Furman
Posts: n/a
David Kilpatrick wrote:

> Nikon's better cameras use an external WB sensor on the prism, which
> avoids auto WB errors being caused by a coloured subject filling the
> frame. They do not use this sensor for exposure moderation though.

I wondered how they figure out auto WB because it's amazingly good even
when shooting some oddly colored subjects.

Paul Furman Photography
Bay Natives Nursery
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Paul Furman
Posts: n/a
Gino wrote:

> I am not sure exactly what you are trying to achieve. You said "blurred
> tires or panned
> background" in the original post, however it seems that you actually
> have a different objective?

It took me a while to figure out. I think what he wants is on an 8x10
print the panning shot should have say 1/2 inch of motion blur in the
background (measured on the print or 150 pixels) regardless of focal
length to give a good sense of action. so at 70mm that'll need a shorter
shutter speed than at 200mm. For now the solution is shutter priority &
adjust the shutter while you zoom... and that is quite a bit to do for
an action type situation with things changing quickly.

> If you want to get rid of the background in head on shots coming towards
> you, then use a big aperture and wait until the object comes close. Two
> totally different shooting situations.
> By all means, post an example of what you are trying to achieve.
> "Richard H." <(E-Mail Removed)> wrote in message
> news:jWOoi.9621$(E-Mail Removed)...
>> Gino wrote:
>>> Why not buy a lens with IS? Then use Shutter Priority at 1/125 or
>>> even 1/60.

>> Hi, Gino.
>> Thanks, yes, I usually shoot with a VR lens (70-200; first-generation
>> VR), and it does help handheld stability when panning with the subject
>> (i.e., side shots).
>> For shots that are more head-on, there's less panning and it's more
>> about shutter speed (the scenario I'm thinking about here).
>> Cheers,
>> Richard


Paul Furman Photography
Bay Natives Nursery
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