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Old Apr 20, 2005, 1:05 AM   #1
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The enlarged manual focussing display on the A200 is hard to get used to – it seems be overenlarged and it is hard to see when the image is really sharp.

But I think it should be used in a different way – when the image is in focus then it seems to shimmer with any slight movement of the camera.

So instead of trying to set to the sharpest picture, focus to the point where you see maximum shimmer.

It reminds me of the focussing technique I used on the microprism screen on my 30 year old Pentax Spotmatic.

Mike

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Old Apr 20, 2005, 3:08 PM   #2
stk
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Hi Mike,

I use the same technique. It's subtle but definitely there.

I also go half way between the points when the image starts to blur before and after the object and found that this shimmering is strongest around this point.

It also reminds me of my old SLR fresnel focussing (a minolta as well) - though personally I always found the split screen easier!

Cheers
Steve
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Old Apr 20, 2005, 3:19 PM   #3
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When you say maximum shimmer what exactly do you mean? The object flashes or flickers?? Does it happen with any type of lighting?

Please describe in little more detail. I find the enlarge picture more of an annoying effect but if there is way to use it usefully then i will take a second look



thanks

eqqmc2
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Old Apr 20, 2005, 5:21 PM   #4
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By shimmer or flickering I mean - contrasty points in the picture change in brightness rapidly.

This happens over a small range of focus dial positions - once I have determined the extremes where the shimmering stops, I set the focus dial between the these two extremes.

Mike
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Old Apr 20, 2005, 5:30 PM   #5
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I use it mainly in video mode as I use manual focus for this - especially as when using x4 digital zoom for video when my autofocus goes haywire.
In this mode the image doesn't enlarge. I think that the enlargement function always operates if digit zoom is not in use on stills.

Its rather difficult to describe.To me its a bit like the image is not blurred but breaks up a little. Focussing on grass gave quite a strong effect to me (to video a bird feeding).

I've just had a play with the camera and it seems like the shimmering is caused by sharp edges pixels when focussed. These seem to bemuch softer when not focussed.

Really quite subtle though and very difficult to describe. Its a bit like seeingone of these optical illusions, once you see it itssort of there!

Not sure if this helps. Maybe Mike has a better way of explaining it.

Cheers
Steve
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Old Apr 26, 2005, 8:21 AM   #6
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This effect is much stronger on horizontal lines compared with vertical lines (if holding teh camera in Landscape mode).

Set the camera to 200mm macro and manual Focus and hold the ribbed part of music CD case (at the left edge if you are looking at the large front cover) about 40cm away. Use a desk light so you have light coming in from the side so you get some shadowing.

With the ribs vertical, you can see some shimmering as you reach the focus point. With the ribs running horizontally there is strong aliasing and diagonal lines appear.

This shimmering only happens if -
- you have some high-contrast lines
- you are in manual focus with the image enlarged for focussing
- the camera is moving (it won't work on a tripod)

Mike
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