Auto-focus on digital SLRs.

Have to disagree.

Just as an extreme experiment, I just switched off all lights and took a
photo in total darkness (AV, with flash up). It still focused.

The reason I asked what lens is because a small aperture lens will not be as
effective in low light.

The reason I asked how far was because maybe he was too far away from the
subject for the flash to effectively illuminate the subject for AF assist.

I agree that another option is to use IR, such as a Speedlight or an SE-E2.



"Pat" <groups DeleteThis @artisticphotography.us> wrote in message
news:36fbc671-1ce1-49ad-ad96-

> It's strange that the 'strobe thing' you experienced (which is AF assist)
> didn't get a focus lock.
>
> I would be interested to know what lens you were using and how far away
> you
> were from the subject.

Why? It happens all the time in low light situations. That's why the
lenses have a switch to shut off the AF. Tokina even makes lenses
that you pull the focus ring towards you and overide the AF (which is
nice). If you haven't experienced the joy of AF that can't find a
focus point, you haven't used your camera enough.

Sometimes you need to throw on a flash just for the IR focusing.
 >> Stay informed about: Auto-focus on digital SLRs. 

On Sat, 23 Feb 2008 12:59:51 -0500, ____
<internetphobic.TakeThisOut@deletedmail.com> wrote:

>In article <kkd0s3h7vjcej95rfvbgjk5naq980trj1s.TakeThisOut@4ax.com>,
> Steve <steve.TakeThisOut@example.com> wrote:
>
>>
>> A crank starter sure would be nice if you accidentally leave your
>> lights on. And if the engine is too big to crank start, one of those
>> clockwork wind-up crank starters would work great. Just like manual
>> focus can work great if the autofocus isn't doing what you want.
>>
>> Steve
>
>Good point, to place back in context any suggestions for speed focusing
>rings for manual control?

Well, I have an old one-touch Nikon 80-200 f/2.8 zoom that I got on
ebay. The huge combo ring (twist to focus, push-pull to zoom) really
works great for manual focusing. Fast and easy to handle because you
don't have to move your hands anywhere to switch from focus to zoom.
Switch it to auto-focus and twisting doesn't do anything, only
push-pull to zoom.

Steve
 >> Stay informed about: Auto-focus on digital SLRs. 

nospam <nospam.TakeThisOut@nospam.invalid> wrote:
> Anon <abuse.TakeThisOut@yahoo.com> wrote:

>> Try getting a dslr to focus on a white card or a blank wall when there's
>> nothing else in view...

> kinda hard to manually focus on that.

Ever heard of microprisms?
As in "microprism ring"?
Try Google on that term, or ask your local dealer, preferably one
that has a proper "old" manual focus SLR on hand for demonstration ...

-Wolfgang
 >> Stay informed about: Auto-focus on digital SLRs. 

"____" <internetphobic DeleteThis @deletedmail.com> wrote in message
news:internetphobic-63B1EC.12595123022008@newsgroups.comcast.net...
> In article <kkd0s3h7vjcej95rfvbgjk5naq980trj1s DeleteThis @4ax.com>,
> Steve <steve DeleteThis @example.com> wrote:
>
>>
>> A crank starter sure would be nice if you accidentally leave your
>> lights on. And if the engine is too big to crank start, one of those
>> clockwork wind-up crank starters would work great. Just like manual
>> focus can work great if the autofocus isn't doing what you want.
>>
>> Steve
>
> Good point, to place back in context any suggestions for speed focusing
> rings for manual control?
>
> --
If you really want to go that route, you could always place an object at
various distances in a well lit setting, and then autofocus on it. Scribing
a reference line at some point of the housing and a small mark on the
focusing ring could help.

But, after playing around with a Rebel XT and trying to get it to exhibit
similar behaviour, I have to say it actually is quite good. The only time
it would hunt around was when I was pointing it at a white wall, or some
other nondescript object with no texture or detail. If there is something
to work with, the AF unit seemed to find it.

Also, if the AF unit couldn't find anything to focus on, it only went
through its range twice -- once rotating out and once coming back in. It
took about a second, and it wouldn't try again if it wasn't initially
successful.

Does the problem get worse as you zoom out? If so, it could be the result
of the variable aperture of the zoom lens.

How old is the camera? Could the sensor be dirty?

Lastly, it is important to keep in mind that red-eye reduction features tend
to slow down camera operation in low light situations. The camera might
hunt a bit for focusing, and then sit there for another second with the
red-eye reduction light eluminated even if you don't need it. This might be
mistaken for slow AF performance.

I don't know if any of this applies, but it doesn't hurt to mention it.

Good Luck,
Dudley
 >> Stay informed about: Auto-focus on digital SLRs. 

In article <6q%vj.40567$w57.25437@edtnps90>,
"Dudley Hanks" <hanks.dudley.RemoveThis@gmail.com> wrote:

> "____" <internetphobic.RemoveThis@deletedmail.com> wrote in message
> news:internetphobic-63B1EC.12595123022008@newsgroups.comcast.net...
> > In article <kkd0s3h7vjcej95rfvbgjk5naq980trj1s.RemoveThis@4ax.com>,
> > Steve <steve.RemoveThis@example.com> wrote:
> >
> >>
> >> A crank starter sure would be nice if you accidentally leave your
> >> lights on. And if the engine is too big to crank start, one of those
> >> clockwork wind-up crank starters would work great. Just like manual
> >> focus can work great if the autofocus isn't doing what you want.
> >>
> >> Steve
> >
> > Good point, to place back in context any suggestions for speed focusing
> > rings for manual control?
> >
> > --
> If you really want to go that route, you could always place an object at
> various distances in a well lit setting, and then autofocus on it. Scribing
> a reference line at some point of the housing and a small mark on the
> focusing ring could help.
>
> But, after playing around with a Rebel XT and trying to get it to exhibit
> similar behaviour, I have to say it actually is quite good. The only time
> it would hunt around was when I was pointing it at a white wall, or some
> other nondescript object with no texture or detail. If there is something
> to work with, the AF unit seemed to find it.
>
> Also, if the AF unit couldn't find anything to focus on, it only went
> through its range twice -- once rotating out and once coming back in. It
> took about a second, and it wouldn't try again if it wasn't initially
> successful.
>
> Does the problem get worse as you zoom out? If so, it could be the result
> of the variable aperture of the zoom lens.
>
> How old is the camera? Could the sensor be dirty?
>
> Lastly, it is important to keep in mind that red-eye reduction features tend
> to slow down camera operation in low light situations. The camera might
> hunt a bit for focusing, and then sit there for another second with the
> red-eye reduction light eluminated even if you don't need it. This might be
> mistaken for slow AF performance.
>
> I don't know if any of this applies, but it doesn't hurt to mention it.
>
> Good Luck,
> Dudley

Good advise however does not apply directly - because mine is a speed
issue, doing at a wedding etc. I need better focus quickly and see the
down side of AF compared to manual focusing.

--
Reality is a picture perfected and never looking back.
 >> Stay informed about: Auto-focus on digital SLRs. 

Wolfgang Weisselberg wrote:
> nospam <nospam.RemoveThis@nospam.invalid> wrote:
>
>>Anon <abuse.RemoveThis@yahoo.com> wrote:
>
>
>>>Try getting a dslr to focus on a white card or a blank wall when there's
>>>nothing else in view...
>
>
>>kinda hard to manually focus on that.
>
>
> Ever heard of microprisms?
> As in "microprism ring"?
> Try Google on that term, or ask your local dealer, preferably one
> that has a proper "old" manual focus SLR on hand for demonstration ...
>
> -Wolfgang

Also there is the likelyhood that unless your blank wall or white card
has no surface texture (ie perfectly smooth) and/or is illuminated
completely evenly (no shadows from any surface texture), there is
probably more than enough contrast for a DSLR camera to AF on the
surface and also it's enough for manual focus without the aid of a split
prism and microprism ring on the viewfinder screen anyway.
 >> Stay informed about: Auto-focus on digital SLRs. 

In article
<47c0c0bc$0$27300$5a62ac22@per-qv1-newsreader-01.iinet.net.au>,
dj_nme <dj_nme RemoveThis @iinet.net.au> wrote:
>
> Also there is the likelyhood that unless your blank wall or white card
> has no surface texture (ie perfectly smooth) and/or is illuminated
> completely evenly (no shadows from any surface texture), there is
> probably more than enough contrast for a DSLR camera to AF on the
> surface and also it's enough for manual focus without the aid of a split
> prism and microprism ring on the viewfinder screen anyway.

By real life experience:

There are more than enough walls with inadequate contrast and even
lighting to fool AF.

--
Reality is a picture perfected and never looking back.
 >> Stay informed about: Auto-focus on digital SLRs. 

____ <internetphobic DeleteThis @deletedmail.com> wrote:

> By real life experience:

> There are more than enough walls with inadequate contrast and even
> lighting to fool AF.

Since all AFs are created equal, it's completely unimportant
to state the AF system and age used.

-Wolfgang
 >> Stay informed about: Auto-focus on digital SLRs. 

Dudley Hanks <hanks.dudley RemoveThis @gmail.com> wrote:

[AF pumping and failing]
> Does the problem get worse as you zoom out? If so, it could be the result
> of the variable aperture of the zoom lens.

If it's not, it could also be camera shake. An in-lens IS helps.

-Wolfgang
 >> Stay informed about: Auto-focus on digital SLRs. 

"Brendan Gillatt" <brendanREMOVETHIS DeleteThis @brendanREMOVETHISgillatt.co.uk> wrote
in message
> I can't say much for Canon cameras being a Nikonian, but there is
> definitely a difference in autofocus speed and precision depending on the
> lens/camera.
>
> For example, my D50 (yeah, baby Nikon I know) is dead in the water when I
> had the opportunity to try out a D200. The D200 focuses with far more
> areas and works far better in low light.
>
Wait till you tyr the D300.

> Also, my Tamron 70-300mm lens uses the camera's drive system for focus,
> it takes roughly 2 seconds to get from one end of the screw to the other.
> My Nikkor lens does that in less than half of a second with its internal
> motor.
>


> I've entirely missed the film era--I've used digital all my life, getting
> my first dSLR just over 2 years ago. Strangely enough, I still prefer my
> dad's 50mm Micro Nikkor when I have the opportunity to do some macro
> shots.
>

I use my old 200 Nikkor macro lens for close ups and macro work. Sometimes I
use it with a 2x extender and extension tubes. I don't think autofocus is at
all useful for those kind of shots. but play around, and try to extract the
abstract color shape and form. While few may recognize it as a flower, it
doesn't really matter.


--
Peter
 >> Stay informed about: Auto-focus on digital SLRs.