Continuous Focusing at Single Frame Setting

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wormy1
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Continuous Focusing at Single Frame Setting

Unread post by wormy1 »

Hi,

I have AF problem with my A100 and I hope I can find some advises here.

At single frame shot setting, I half press the shutter button, the AF kicks in, beep! indicator flashes but what I get is slightly out of focus view. If I waited for a few more seconds without letting go the half-press, the AF will kick in again and normally this time it lock on correctly. If I continue to half-press, sometimes the AF come again and again seconds later but sometimes it just stop. The interval of those crazy AF is unpredictable, it could be 2 seconds apart, it could be 5, 6 or even 10 seconds apart. It happens at low light as well as bright situation. The whole system is still usable but it gives me a lot of headache when I focus and recompose the frame.

My Tamron 17-50 is the craziest one. Almost every round it AF a few times to get one shot. Sony 50mm f/1.4 and 18-70 is slightly better but still very disturbing. Strangely, the crazy AF problem seems not affecting my Tamron 90mm Macro and also Minolta big beer can.

I once visited Sony Service Center (quite far from where I stay) with this A100 and 18-70. When I was asked to demonstrate the problem, the system worked perfectly in front of the technician. Single AF, spot on. Confused, I drove home and live with this problem until now.

Two years ago I drop my A100 from 1 meter height, the sensor was knocked out of place and the SSS gone wild. Sony repaired for me free of charge. It works fine since then until this AF problem surfaced.

Has anyone seen this problem before? Is this lens problem or camera body problem?

Thanks in advance.
David Kilpatrick
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Re: Continuous Focusing at Single Frame Setting

Unread post by David Kilpatrick »

It's not a specific problem I have seen. My first reaction would be to try using AF-A, which switches to C automatically when continuous movement is detected or when using Sports mode. If the focus works using AF-A and Sports picture mode, then the fault may lie with the AF-C setting. I would also clean the lens and body electronic contacts with care. Since you have some different results depending on lens, you should also check the tightness of the screws which mount the bayonet to the camera body, and those on each lens. Just tightening these a little with a precision crosshead screwdriver can improve overall 'fit' and solve communication problems.

If all this makes no difference, it may worth simply buying an A200, which can currently be obtained at minimal cost - keep the A100, don't sell it. It has a useful mirror lock up which fits with the one lens which works - your Tamron macro - and the sensor AA filter also produces fantastic macro results.

David
wormy1
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Re: Continuous Focusing at Single Frame Setting

Unread post by wormy1 »

Thanks David.

I have tried AF-A (which I never use before) and found that it behave similar to AF-S. It focuses 2 to 3 times at one half-press.

I have checked the screws as well, all tight and secure. Will try clean the contact pins on the cam body, just not sure how. Should I use lint-free cloth with ethanol?

This A100 is my first DSLR and I will never sell it away. I plan to add an enthusiast level body next year.

Thanks again.
David Kilpatrick
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Re: Continuous Focusing at Single Frame Setting

Unread post by David Kilpatrick »

The best thing for cleaning the contacts is a Jim Dunlop Micro Fine Fret Polishing sheet made for guitars - sold by music shops. It feels like a rubber sheet on a cloth backing. I guess there is an electronics equivalent (I am sure it is not made for guitars!). It can be used to clean most metal surfaces and contacts including battery terminals.

David
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sury
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Re: Continuous Focusing at Single Frame Setting

Unread post by sury »

Daivd,
Apropos your comment about A100, do you think it is better than A700/A900 for macro work? Those are the other two bodies I have in addition to my A100.
David Kilpatrick wrote: - keep the A100, don't sell it. It has a useful mirror lock up which fits with the one lens which works - your Tamron macro - and the sensor AA filter also produces fantastic macro results.

David
With best regards,
Sury
Minimize avoidable sufferings - Sir Karl Popper
David Kilpatrick
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Re: Continuous Focusing at Single Frame Setting

Unread post by David Kilpatrick »

I think the A100 is equal to the A700 and better than the A900 for macro work (there is little benefit in just having a larger frame). My A100 macro shots have been some of the best for sharpness and detail. I now use the A700 for macro. I have been trying the A550 for both macro and tele action work and so far I am disappointed.

But - I have just paid £85 on eBay for an original Pentax scread auto bellows set. This is better for me than either of the manual bellows units I have already. All my 'front end' lenses are M42 or Leica screw compatible, and will fit. The bellows has geared, movable front and rear standards on a focusing rail with a geared tripod foot - this allows the whole bellows to move (like a focus rack), and the design also means there is no need for bellows rail to stick out in front of the lens, which has been a problem. I think it will have enough clearance, with the Alpha focus-chipped adaptor fitted, to use the A900 body and that it will be solid enough to support it.

Also, I may be able to obtain a Pentax thread macro lens with auto iris and use a cable release for stop-down, instead of manual stop-down which I use now.

I'm hoping that this set of bellows, sold as mint and boxed complete by a dealer, will solve some of the technical and vibration problems I've had with the lighter weight BPM and generic single-rail Japanese ones I have been using.

David
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sury
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Re: Continuous Focusing at Single Frame Setting

Unread post by sury »

David,
Thank you. I was looking at some bellows but instead bought a macro-rail contraption that moves back and forth, left and right and mounts on a tripod. I did notice getting sharper macros with A700 compared to A900
but attributed that to just happenstance. Of course, one thing I do not have is a ring flash and am wondering how useful that would be (relatively speaking).

With best regards,
Sury
Minimize avoidable sufferings - Sir Karl Popper
David Kilpatrick
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Re: Continuous Focusing at Single Frame Setting

Unread post by David Kilpatrick »

I have two ring flash units. The original Minolta 1200 AF-n would be useful with the extremely rare, extremely expensive power unit offering proper TTL with digital bodies but only has its original unit, and can't be used on anything except full power. It is very frustrating, even just having half and quarter power manual settings would have been enough to make it viable. I also have a Paffrath & Kemperer ring flash (a true large ring tube) with a Metz CT-60 pack; again, this only offers full power operation.

In the past I've found true ring flash to be a mixed benefit. With some subjects it is unmatched, with others it produces a disappointing quality of light. The Minolta four-tube solution was one of the best. I keep my Minolta unit in the hope that a way to use it properly will be found.

David
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