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01-16-2007, 05:45 PM   #16
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Awww heck Ray, I'm convinced...

_______________Please stand by....

01-16-2007, 10:03 PM   #17
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QuoteOriginally posted by Mark Castleman Quote
I'm new here and I keep seeing people talking about "front focusing" and while I can see that it appears to be a Bad Thing, no one ever defines what it means.

So what exactly is "front focusing" and how worried should I be about it?
http://ricehigh.blogspot.com/2006/12/how-af-errors-can-decrease-effective.html

RiceHigh's Pentax Blog: Focus Calibrations for (Pentax) (D)SLR Bodies and Lenses
01-17-2007, 06:20 AM   #18
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Sorry, Thought This Was Well Known

QuoteOriginally posted by bdavis Quote
Can you tell me where you got this information, Ray? I've never heard that &am intrigued.
Unless you have an FA or A or M lens and are using the aperture ring to manually stop down (on the lens), the camera sees everything through the lens with the aperture wide open. It meters and autofocuses through the lens at the widest aperture and then decides what aperture and shutter speed to use for the exposure. At the moment of picture taking, the body pushes the little lever on the rear of lens to stop the aperture down to whatever has been set or chosen on the body and makes the exposure.

The maximum lens aperture determines the limit of the lower level of light that the camera will AF in. The spec is -1 or 0 EV (I forget) for the K10D, but that is specified at 100ISO using a 50mm f1.4 lens. Using an f4 zoom means that your camera will not focus light as dim as it will with the 50mm f1.4 because it focuses at max aperture, and there is less light coming into the camera on an f4 lens than with a f1.4 lens.

Ray
01-17-2007, 06:25 AM   #19
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QuoteOriginally posted by jfdavis58 Quote
Awww heck Ray, I'm convinced...

_______________Please stand by....
Ok.

Sorry if I came off a bit abrupt, but I some people seem to have a problem with anyone reporting any sort of issues with a particular brand as if the operator is the source of all problems with a piece of equipment.

My K10D definitely has a problem, and I am hoping that it is easily rectified by calibration at Pentax.

I amnot so sure that FF in tungsten light like RH shows can be resolved by calibration, as that migt well be a design issue.

Ray

01-17-2007, 12:28 PM   #20
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QuoteOriginally posted by Ray Pulley Quote
Unless you have an FA or A or M lens and are using the aperture ring to manually stop down (on the lens), the camera sees everything through the lens with the aperture wide open. It meters and autofocuses through the lens at the widest aperture and then decides what aperture and shutter speed to use for the exposure. At the moment of picture taking, the body pushes the little lever on the rear of lens to stop the aperture down to whatever has been set or chosen on the body and makes the exposure.

The maximum lens aperture determines the limit of the lower level of light that the camera will AF in. The spec is -1 or 0 EV (I forget) for the K10D, but that is specified at 100ISO using a 50mm f1.4 lens. Using an f4 zoom means that your camera will not focus light as dim as it will with the 50mm f1.4 because it focuses at max aperture, and there is less light coming into the camera on an f4 lens than with a f1.4 lens.

Ray
apart from the AF don't the cameras going back to the A mount all do this when the lens is in A mode?
01-17-2007, 03:44 PM   #21
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Yes

QuoteOriginally posted by jnorth Quote
apart from the AF don't the cameras going back to the A mount all do this when the lens is in A mode?
Yes they do, and the AF cameras focus with the lens wide open unless you stopped the A, F, FA or D/FA lens down mechanically for some reason.

Ray
01-20-2007, 02:33 PM   #22
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QuoteOriginally posted by bdavis Quote
Can you tell me where you got this information, Ray? I've never heard that &am intrigued.
On auto, A and above lenses, the aperture is always wide open. this is pretty the way every modern camera focuses.

it only adjust the aperture on tripping the shutter.

the advantage of this is the camera gets maximum light to the viewfinder and AF system. it also allows the meter to read in lower light.

there isn't anything to read, just look at your camera. if you put an M lens on it you will notice that the viewfinder darkens at smaller apertures.

also, put on a 1.4 FA and then put on a 5.6FA the 5.6 is darker in the view finder and also slower to focus.

A (FA, F or A) 5.6 lens wide open only lets in 5.6 light, a 1.4 lens lets in 1.4 light all the time.
01-20-2007, 08:15 PM   #23
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Has anyone considered that the higher resolution of the 10 megapixel sensor might reveal focus errors that were not visible on the 6 megapixel sensors?

I'm not saying one way or the other, just bringing it up as an idea.

01-27-2007, 06:24 PM   #24
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QuoteOriginally posted by Dana G Quote
Has anyone considered that the higher resolution of the 10 megapixel sensor might reveal focus errors that were not visible on the 6 megapixel sensors?

I'm not saying one way or the other, just bringing it up as an idea.
Not to get into a film vs. digital debate but 10MP isn't all that detailed. I get over 10MP out of Provia on my home film scanner and I'm not even touching the tip of the iceberg in terms of resolution the film is capable of.

Provia can get about 30MP so focus errors would show up on a good film as well.

People have been complaining about focusing for the last 8 models (or something like that) but neither of my 2 DSLR's have had this issue (D and K10D).
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