[vegabraveian]

Guys,

I have little problem..as we know that K-x has invisible AF Points.
On daylight or with Adequate lighting, I have no problem as long as I can see from the AF Frame on Viewfinder. But the problem comes when I shoot moving object (such as photo stage) in the dark when the AF Frame sometimes looked merging with the object.

I usually using center point so everything become death center photos or sometimes I using manual AF lock with half press shutter to make composition, but sometimes i have blind focus..

Getting matter when I using fish eye lens who has large coverage...

Just for your info..I have to shoot fast...I take photograph for concert or music event.

here is some pic sample

K-x using Samsung 10-17

Thanks a lot

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[penties rider]

dear friend, although your question is not quite clear in here, i'm assuming that you have difficulty focusing in low light conditions when using lenses of (ultra) wide angle focal length, right?

if so, i'd suggest you forget about focusing precisely altogether with such lenses that have great depth of field already, even when shooting @ their widest open apertures.

unless you want to go for close ups of people or other objects, there's no urgent need for focusing accurately with such lenses really, especially when shooting action. just adjust the focus @ what i'd call a 'nodal point', making use of the lens's depth of field table that's usually printed on most lenses. set the focus where it gives the minimum depth of field @ the maximum aperture of say 2.8 or 4.5 or whatever the lens has.

now, just adjust your exposure, with both shutter speed (which you may need to be more careful about when doing action) as well as the aperture, without worrying much about the focusing, especially when taking long to medium shot pictures of people or objects and scenes of all kinds, where you are often times standing so far enough from the closest subject as to have them sharply in focus anyway.

i used to the same trick with my F:4.5 / 20mm SMC Takumar lens, a screw thread one, attached to my Pentax MX, a K-mount camera, using the screw-in to K-mount adapter.

the lens gave great depth of field from 1.5 metres to infinity even at its widest aperture of F4.5. when shooting action with that lens, i normally rotated the focusing ring in a manner that its infinity marking was set on the 4.5 aperture marking on the lens's DOF table. that gave me the 'nodal' point mentioned ...

all i had to do, was to concentrate on the exposure through adjusting the shutter speed and aperture, while leaving the focusing untouched. of course, whenever there was good lighting available, i would be lucky enough to have both higher shutter speeds to freeze the action as well as smaller apertures to have even more depth of field, giving me extra sharpness most naturally.

hope the above can help you with your problem here.

[hcc]

In very low light, it is sometimes best to use MF and forget AF.

This might or might not be relevant to your case. But I have been able to get excellent shots in very low light using MF. You do not need to wait for AF confirmation.

Hope that the comment may help...

[UnknownVT]

Getting matter when I using fish eye lens who has large coverage...
Just for your info..I have to shoot fast...I take photograph for concert or music event.
here is some pic sample
K-x using Samsung 10-17

From the two samples you posted they were both 10mm (or 15mm for 35mm equiv) @ f/3.5 - the depth of field is pretty big for that focal length - even at the "wide-open" aperture -

If you really are having difficulties focusing - then my suggestion is to try to shoot without AF - use a fixed preset distance on MF - then you are not dependent on AF at all, and can shoot as fast asd your finger can trip the shutter.

10mm (APS-C) at f/3.5 - the hyperfocal distance is ~3.7ft (1.3 metres) - which means if you focus at 3.7ft (1.3m) everything from 1/2 that distance ie: 1.85ft (0.65m) to infinity is considered in focus - so as long as you keep your subjects more than 1.85ft (0.65m) away they will be in focus.

Even at the longest end of 17mm and wide-open f/4.5 the hyperfocal distance for that combination is ~8.4ft (~2.6m) so everything from 1/2 that distance 4.2ft (1.3m) to infinity will be in focus if you set you lens focus to 8.4ft (2.6m) - just get no closer than 4.2ft (1.3m).

There is a freeware program - DoF Master that can generate a table for your lens -
I used that to generate a hyperfocal distance chart for your 10-17mm f3.5-f/4.5 lens (distances in ft):


Try these suggestions out - on some unimportant trials and see if it works for you?

[fafo13]

what ive learned with my kx is that center point focus is even harder to get in focus stuff than 5 point, so except few things and not even with low light situations i do use 5 point af cause it does perform lil better, and simply kx refuse to af on objects if u have light behind them even with center af even with f1.4 lenses

[Ryan Trevisol]

I've heard that same complaint that fafo13 had (specifically, from my cousin, who has a Black K-X). We shot a wedding together and he was having the hardest time getting focus lock in low light with a DA*16-50. He had to set it to auto-5.

Personally, I don't ever have ANY problem with center point focus. Unfortunately the lack of focus confirm lights makes that a necessity for me. I wear glasses and unless I want to take them off for every shot and put them back on to review, I can't get a close enough eyeball on the viewfinder to use MF.

[UnknownVT]

what ive learned with my kx is that center point focus is even harder to get in focus stuff than 5 point, so except few things and not even with low light situations i do use 5 point af cause it does perform lil better, and simply kx refuse to af on objects if u have light behind them even with center af even with f1.4 lenses

Really?

This is not my experience
- neither from tests where they have compared:

from: Pentax K-x Digital Camera Performance - Full Review - The Imaging Resource!

Full autofocus shutter lag using single-point (center) AF mode is excellent, at 0.097 second with our reference Sigma 70mm f/2.8 lens. Switching to auto-area AF mode increased lag slightly to 0.122 second, but that's still very fast for a consumer model.

I shoot at a dark jazz club almost every week - there are parts that are below the both the metering and AF limits of the K-x - I only use center point AF - and mostly I don't have much problems focusing.

Kx in Use ( 1 2 3 ... Last Page)

First post about the club in #5 (link) - most recent #161
posts with calculations showing light levels below limits in #131 and #132

5 point focus is useful - otherwise it would not have been the default -
but it is not faster (mainly because it has to decide/select which point to use)
and it is not as precise on which point is used to focus.

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Last edited by UnknownVT; 04-25-2011 at 10:45 AM.

[vegabraveian]

I see...

Some people using 5 points and other using center point.....

Let see picture from dpreview below...

I usually using center point to make easy composing object..but unlucky the black AF Frame on view finder (pic below) sometimes invisible... I meant when the object too dark I feel difficult to put my single AF point on the object....


Here sample again...I have wrong focus because the AF beep already.
Picture below i used FA 28-70 F/4
Is not what I want to focus on guitar neck....I miss just little inches ....

[vegabraveian]

5 point focus is useful - otherwise it would not have been the default -
but it is not faster (mainly because it has to decide/select which point to use)
and it is not as precise on which point is used to focus.

I'm afraid to use 5 focus..yes I'm agree..it is not as precise on which point is used to focus

[vegabraveian]

In very low light, it is sometimes best to use MF and forget AF.

This might or might not be relevant to your case. But I have been able to get excellent shots in very low light using MF. You do not need to wait for AF confirmation.

Hope that the comment may help...

Agree....here sample i using Tamron adaptal 35-105 F/2.8...it's very-very heavy push-pull lens.....and I gave up...too tired using manual to chase the moment...

[vegabraveian]

Repost

[UnknownVT]

Sorry don't mean to repeat - but with a DoF using
10mm f/3.5 of 1.85ft (0.65m) to infinity
and
17mm f/4.5 of 4.2ft (1.3m) to infinity

do you really need to focus at all?

A lot of old fisheye lenses didn't even need focus -
because the DoF was enormous

Set those distances
3.7ft (1.3m) for 10mm
or
8.4ft (2.6m) for 17mm
set on MF and shoot away -
this is a case where AF is not helpful at all - and merely gets in the way.

[vegabraveian]

Sorry don't mean to repeat - but with a DoF using
10mm f/3.5 of 1.85ft (0.65m) to infinity
and
17mm f/4.5 of 4.2ft (1.3m) to infinity

do you really need to focus at all?

A lot of old fisheye lenses didn't even need focus -
because the DoF was enormous

Set those distances
3.7ft (1.3m) for 10mm
or
8.4ft (2.6m) for 17mm
set on MF and shoot away -
this is a case where AF is not helpful at all - and merely gets in the way.

For this case...yes..I don't need it......1.85ft is close enough...with the fisheye..I usually using 10mm...

If I using your chart..I think using fix lens much better to me to ignore the focus problem....I just consider it

[UnknownVT]

I usually using center point to make easy composing object..but unlucky the black AF Frame on view finder (pic below) sometimes invisible... I meant when the object too dark I feel difficult to put my single AF point on the object....

I have to face that all the time since I shoot in a very dark jazz club regularly.

I just visualize/imagine where diagonals would cross at the center of the screen -
eg:

the red dotted diagonal lines obviously are not physically there -
but it is not that hard to visualize/imagine where they would cross -
ie: at the center of the screen.

Try it - it's very easy -
so you don't have to be able to see those brackets.

[vegabraveian]

I have to face that all the time since I shoot in a very dark jazz club regularly.

Yeah... I saw your photos and look had same problem with me..

I just visualize/imagine where diagonals would cross at the center of the screen -
eg:

the red dotted diagonal lines obviously are not physically there -
but it is not that hard to visualize/imagine where they would cross -
ie: at the center of the screen.

Try it - it's very easy -
so you don't have to be able to see those brackets.

hei...that's such a good idea.....need practicing work with it but could be a solution....I will try.. Thanks bunch friend.

I really Like this forum...