Manual Focusing with focus-knob on "Continuous".

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Aart Roest
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Manual Focusing with focus-knob on "Continuous".

Unread post by Aart Roest »

Last Friday I went to the 100 Year Memorial Air Show with the Royal Netherlands Air Force. I took my Alpha A700 with Sony 4,5-5,6/70-300 G SSM lens with me and put the exposure program on A(perture) and Spot with EV+1. Focusing on Continuous and wide.

But then I forget which piece of the lens is the zoom part. I must have turned the focusing a few times, before I got the idea of how it works. I am well aware of the capabilities of the camera in detail, but this lens I use only very seldomly. Never got really used to working with it.

And then there happened something I could not explain. When pointing the camera towards the sun (never letting the sun appear in the immage field though) the exposure metering went wild (showing 1/4000th of ta second at 400 ASA and f 8) and the focusing stopped working completely. I had to direct the camera towards the ground and wait a few seconds. Then everything seemed OK again. But the blocking repeated itself maybe twenty times again. Nevertheless I was able to take more than 700 pictures. But I missed a few, to be regretted.

As I am completely ignorant of what is happening in this situation, maybe someone can help me out.

Thank in advancce...
Best from Aart
classiccameras
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Re: Manual Focusing with focus-knob on "Continuous".

Unread post by classiccameras »

I'm not an expert, but its possible the sensor just got over saturated/over loaded, [burn out] and the whole system could not cope , gave up, and went into neutral. Try putting everything back to factory default. then switch off and remove battery for a few minutes. Fit standard kit lens before switching on again.

I'm sure there are more knowledgable people than me on this problem, but doing this to my old Canon 450D seemed to work.
Pete
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Aart Roest
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Re: Manual Focusing with focus-knob on "Continuous".

Unread post by Aart Roest »

[quote="classiccameras"]I'm not an expert, but its possible the sensor just got over saturated/over loaded, [burn out] and the whole system could not cope , gave up, and went into neutral.

Pete,
Thank you for your view. It really could be an over-reading in the exposure metering circuit, when more sun-rays came through. But it might as well be an overreading in the focusing circuit. The spot I was in was crowded. Planes fly, but are sometimes quite low, interfering with the "big" boys a few yards in front of me.

Or might it be a mechanical failure caused by turning the focusing ring with the focusing set to "C". Needing a repair ?

By the way, photographing proved possible all the time. There were only short "refusal brakes" when the lightreading came to an inexplainable 1/4000th.
Pointing the camera to the grass for a few seconds made bothe the metering circuits act normal again. This did not happen when I held the camera faced in the air.

Who can be of even more help ?
Thanks again, Aart
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Dr. Harout
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Re: Manual Focusing with focus-knob on "Continuous".

Unread post by Dr. Harout »

My guess is when the light is way much to the parameters you are using, the camera might react so.
Suppose you point your camera at ISO 400 to the sun, with f/8, then shutter speed should be around 1/8000 and plus. Add to it a EV +1, then your camera will surely get crazy.
Try with P.
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Heidfirst
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Re: Manual Focusing with focus-knob on "Continuous".

Unread post by Heidfirst »

Aart Roest wrote:
Or might it be a mechanical failure caused by turning the focusing ring with the focusing set to "C".
it's an SSM lens so that shouldn't be an issue as it has DMF.
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Greg Beetham
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Re: Manual Focusing with focus-knob on "Continuous".

Unread post by Greg Beetham »

Aart Roest wrote:Last Friday I went to the 100 Year Memorial Air Show with the Royal Netherlands Air Force. I took my Alpha A700 with Sony 4,5-5,6/70-300 G SSM lens with me and put the exposure program on A(perture) and Spot with EV+1. Focusing on Continuous and wide.

But then I forget which piece of the lens is the zoom part. I must have turned the focusing a few times, before I got the idea of how it works. I am well aware of the capabilities of the camera in detail, but this lens I use only very seldomly. Never got really used to working with it.

And then there happened something I could not explain. When pointing the camera towards the sun (never letting the sun appear in the immage field though) the exposure metering went wild (showing 1/4000th of ta second at 400 ASA and f 8) and the focusing stopped working completely. I had to direct the camera towards the ground and wait a few seconds. Then everything seemed OK again. But the blocking repeated itself maybe twenty times again. Nevertheless I was able to take more than 700 pictures. But I missed a few, to be regretted.

As I am completely ignorant of what is happening in this situation, maybe someone can help me out.

Thank in advancce...
Best from Aart
I don’t own an SSM lens myself so I don’t have any firsthand experience with one, but looking at the user guide it says that DMF is not available with AF-C so I would assume turning the focus collar while that mode is engaged would have no effect on focus.
As the guide book also says the focus collar doesn’t turn (not driven) while focusing I assume the MF function is disconnected in AF-C and if that is true then turning the focus collar in that mode should have no effect.

The only thing that comes to mind (moving the focus collar) is the focus distance encoder, whether or not it is still connected to the focus collar and is registering where that is set at (in conflict to where the AF system has calculated the focus should be set at), if so, that could/should be reset on removing and re-installing the lens one would think, but I doubt the distance encoder is involved in any issue there might have been just the same.
As far as exposure is concerned I set my A700 on a tripod with the same settings and there was a range of shutter speeds obtained (from 1/2500sec to 1/4000sec) depending on altitude (tilt), lower angle = higher shutter speed while higher angle = lower shutter speed (sky is bluer.
I don’t think the clear sky shutter speeds you obtained were unusual in any way.

I have little experience using Wide area AF, I hardly ever use it as I found it to be rather unpredictable on my KM5D and A100 (random AF point selection) and so have never bothered with it on the A700, but then it could actually work better on that later model camera for all I know.
The only other thing I can think of is that in Wide area AF (used for object tracking) the focus system might not actually ‘detect’ an object to focus on occasionally and therefore does not see a need to focus if there is nothing to focus on, but it should still focus out to infinity if aimed at the sky one would think.
While there doesn’t seem to be any issue with exposure based on my tests with three cameras all registering much the same, there might be some anomaly with focus perhaps, hard to say.
Greg

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Aart Roest
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Re: Manual Focusing with focus-knob on "Continuous".

Unread post by Aart Roest »

[quote="Greg Beetham"][quote="Aart Roest"][/quote]

I don’t own an SSM lens myself so I don’t have any firsthand experience with one, but looking at the user guide it says that DMF is not available with AF-C so I would assume turning the focus collar while that mode is engaged would have no effect on focus.
As the guide book also says the focus collar doesn’t turn (not driven) while focusing I assume the MF function is disconnected in AF-C and if that is true then turning the focus collar in that mode should have no effect.

The only thing that comes to mind (moving the focus collar) is the focus distance encoder, whether or not it is still connected to the focus collar and is registering where that is set at (in conflict to where the AF system has calculated the focus should be set at), if so, that could/should be reset on removing and re-installing the lens one would think, but I doubt the distance encoder is involved in any issue there might have been just the same.
As far as exposure is concerned I set my A700 on a tripod with the same settings and there was a range of shutter speeds obtained (from 1/2500sec to 1/4000sec) depending on altitude (tilt), lower angle = higher shutter speed while higher angle = lower shutter speed (sky is bluer.
I don’t think the clear sky shutter speeds you obtained were unusual in any way.

I have little experience using Wide area AF, I hardly ever use it as I found it to be rather unpredictable on my KM5D and A100 (random AF point selection) and so have never bothered with it on the A700, but then it could actually work better on that later model camera for all I know.
The only other thing I can think of is that in Wide area AF (used for object tracking) the focus system might not actually ‘detect’ an object to focus on occasionally and therefore does not see a need to focus if there is nothing to focus on, but it should still focus out to infinity if aimed at the sky one would think.
While there doesn’t seem to be any issue with exposure based on my tests with three cameras all registering much the same, there might be some anomaly with focus perhaps, hard to say.
Greg

Greg,
Thank you for your observations.
I will try to see the effects of your suggestions. /Aart
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Aart Roest
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Re: Manual Focusing with focus-knob on "Continuous".

Unread post by Aart Roest »

[quote="Aart Roest"][quote="Greg Beetham"][quote="Aart Roest"][/quote]

Greg,
Focusing on flying aircrqaft goes easy this way. The camera spots them without any problem...

Further about your reply:
You convinced me there is nothing wrong with the exposure system. Also you convinced me there is no damage done to the camera by rotating the focusing ring. (I wondered why such damage could be done without any noticing by the man on the knobs).

The hazy pictures will have been caused by focusing to infinity when the subject was lost by the focusing circuit. Can it take as long as more than 10 seconds to regenerate from this position ?

Testing the distance chip, how can that be done with any reliable effect ?

Can anyone be of further help ?
/Aart
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Aart Roest
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Re: Manual Focusing with focus-knob on "Continuous".

Unread post by Aart Roest »

Further to my previous comment.
The focusing should cause the temporary exit.
Either by defect Distance-chip or by overtasking of the focusing circuitry.

This afternoon I started trials and came to a prelim9inary conclusion:
After the blow-out on infinity (towards the clouds) I tried to recover. But I never let the shutter release pressed halfway for more than half a second.

During my trials I pressed for a longer period and see, the recovery was almost instantly. It took maybe 3 seconds, which is perfectly acceptable to me. The AF-C session requires no action to stay aligned, but being not-aligned stops the mechanism. So it seems to me...

This is how I look at my findings of this afternoon. Maybe someone can confirm ?
/Aart
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Greg Beetham
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Re: Manual Focusing with focus-knob on "Continuous".

Unread post by Greg Beetham »

I’ve had my ups and downs with longish lenses, my longest is a 100-300 zoom and on occasions depending on circumstances the camera can get confused as to where the subject is in the focus range (small birds in a thicket for example) sometimes for longish periods of many seconds while it hunts back and forth, I can hear it with screw drive whereas with SSM you might not if there are noisy planes involved.

I sometimes used MF to see if I could do any better, usually not these days though with requiring reading glasses now to read small print in dim light and the diopter on the camera isn’t set properly in any case.
An alternative that does work with AF is pick an object at a similar distance to the subject you are trying to focus on, the object must provide suitable contrast to quickly get focus, which it usually does, then you can re-aim at your subject (the next plane or pass) and it should re-acquire without a lot of fuss being ball park already with distance …until it misses again.

You probably already know this (but some might not), you can temporarily override Wide area AF with spot AF on the fly (no pun intended) (to make sure it uses a known good AF point to obtain the distance), just aim the spot AF at the subject and press the joystick straight in, the camera will then focus using the central spot, when you release the joystick it will revert back to Wide area AF.
Greg
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Aart Roest
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Re: Manual Focusing with focus-knob on "Continuous".

Unread post by Aart Roest »

Greg,
Thanks a lot for thinking aside with me.../Aart
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