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04-23-2010, 01:59 AM   #16
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QuoteOriginally posted by blende8 Quote
I think focus bracketing would be a desirable thing.
That is an intriguing idea!

The big question then is how to implement that. How do you suggest it would be done?
What would be the delta parameter? If it is absolute distance, like # of feet/meters, the effect would be quite different depending upon the subjects distance to the lens.
Or could it be percentage of subject distance? Like: +/- 0.1% to +/- 0.5%?
Should it be relative to the aperture as well, since depth of field is also something to consider.

- Bert

04-23-2010, 03:01 AM   #17
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Well, it could be anything.
It depends on the accuracy of the AF motor.

I could imagine that you have several options for the delta:
e.g. the smallest possible step for obtaining optimum focus.
(focus once and then bracket 5 times in both directions with as small steps as possible.)

or larger steps for creating stacked images with Helicon Focus or CombineZP, which are sharp from the foreground to the back.

I wonder why nobody has implemented this already. It is not that difficult.

Last edited by blende8; 04-23-2010 at 11:20 AM.
04-23-2010, 03:47 AM   #18
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Some thing like this? Light Field Photography with a Hand-Held Plenoptic Camera
04-23-2010, 04:45 AM   #19
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QuoteOriginally posted by siva.ss.kumar Quote
Or how about this lens: GBO Lens - VIT Imaging Technology
How does it work, any ideas?

04-23-2010, 11:15 AM - 1 Like   #20
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QuoteOriginally posted by blende8 Quote
Well, it could be anything.
It depends on the accuracy of the AF motor.
Well, focus bracketing is something seriously missing.

When I first discovered exposure bracketing I almost phoned Pentax support because I couldn't find the setting to enable focus bracketing. To me, it seemed to be the first thing to do with exposure bracketing being second

As for focus stacking: I don't think you want to do it that way. The magnification would change too much. You'll use a m-button equipped positioning slider for that. At least, this is what I do.

As for hunt for perfect focus. I assume we all pixel peep if we use this feature. So, the most natural focus bracketing step is that between zero and 1 pixel focus blur. The firmware can easily compute it, based on aperture.

If you go through the DoF formulas at small magnification, you'll find that the required bracketing step is fairly universal und independent on focal length or distance, actually:

focus-shift = N*CoC where N is the f-stop number.

E.g., with CoC=5m (for 1 pixel confusion step), focus-shift is 20m at f/4. If you allow for perfect focus to sit between 1 pixel confused images, the focus step is 40m.

So, a focus motor accuracy of 10m is desirable and of 50m is mandatory.

I fear that both figures are only possible for unidirectional moves. I.e., the focus bracket starts at one end and runs thru to the other end.

At f/1.4, focus step is 7m and the desired focus motor accuracy is as low as 3m.

Seems like a new business model for precision-crafted Zeiss AF lenses


To contrast the focus precision with the entire focus:

15mm 60cm: 0.4mm (40x 10m)
50mm 45cm: 5.5mm (550x 10m)
300mm 2m: 45mm (4500x 10m)

The smallest move visible to the naked eye of the focus scale (1/10mm at 70mm diameter and a 180 turn focus drive) is a 1/1000th "step". So, the necessary focus bracket steps on a tele lens wouldn't be visible to the naked eye anymore.
04-28-2010, 05:03 AM   #21
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For the benefit of the other posters I'd like to point out that the OP may have an AF adjustment issue with his DA* 300/4. He is currently looking into it. Maybe the infinity problem is related.
04-28-2010, 09:28 AM   #22
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Quite likely. Mine needed +4 to achieve tack sharp autofocus.
04-29-2010, 09:55 AM   #23
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QuoteOriginally posted by jbinpg Quote
Quite likely. Mine needed +4 to achieve tack sharp autofocus.
Glad to see someone made AF adjustments on his gear.
Is this the same setup as mine: DA*300/4 + K7?
Did you make the tests inside/outside?
What type of target(s) did you use: charts? other objects?
What distance did you use (camera-subject)?

Thanks for the reply.

JP

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