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Setting Back-Focus Without A Focus Chart

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Jeff Coffman
Setting Back-Focus Without A Focus Chart
on Apr 20, 2011 at 1:51:13 am

I just got the XS8X4AS-XB8 wide angle lens. I've noticed that the back-focus must be set every single time the lens is removed and put back on (the stock lens doesn't appear to need this). If you are caught out in the field without focusing chart, maybe if the release lever accidentally is pulled up, releasing the lens, is there some frame to try and shoot (certain contrast or line characteristic) that is best for setting the back-focus without a chart?

Thanks

Jeff


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Michael Palmer
Re: Setting Back-Focus Without A Focus Chart
on Apr 20, 2011 at 4:31:08 am

This lens is so forgiving on the EX camera I just zoom out to the longest focal length and focus on something at infinity, then pull back wide and adjust (if needed) from there.

Good Luck
Michael Palmer


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Jeff Coffman
Re: Setting Back-Focus Without A Focus Chart
on Apr 20, 2011 at 6:03:34 pm

When I put the lens on, the backfocus is so off that the lens will not achieve sharp focus at it's widest point at all, unless I reset the backfocus.
That's why I want to know about being caught without a chart.


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john sharaf
Re: Setting Back-Focus Without A Focus Chart
on Apr 20, 2011 at 8:05:45 pm

Jeff.

A bulls-eye chart is nice to set back focus, but not necessary. zIt can easily be set as Michael says, BUT always set the iris at wide open to shorten the DOF as much as possible so that you can make the most accurate setting.

So, set iris wide open, zoom in and focus on an object 10' or more away, resize to widest focal length and set backfocus to sharpest focus on same object/distance. Repeat.

Voila, backfocus is set. It's not that unusual to have to reset each time you mount a new lens, in fact it would be foolhardy not to check the backfocus every time you do so.

JS



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Jeff Coffman
Re: Setting Back-Focus Without A Focus Chart
on Apr 20, 2011 at 8:35:17 pm

I see. You guys seem to be saying there's a different way to set the back focus than what I'm doing. I'm using the auto back focus function in that extra menu of the EX3. The one where you put the camera on full auto and it takes about 15 seconds to execute. How do you set that back focus otherwise.


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john sharaf
Re: Setting Back-Focus Without A Focus Chart
on Apr 20, 2011 at 8:47:13 pm

Jeff,

OK, that's first mention of EX3! Yes, that camera usurps control of back focus and automates it. You have no choice but to use the auto function. I don't know of any other camera that does it this way. The process I described it the universal method for every other type of camera that has a manual BF setting on the lens.

JS



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Jeff Coffman
Re: Setting Back-Focus Without A Focus Chart
on Apr 20, 2011 at 8:55:10 pm

I'm sorry I thought this forum was just for the EX3. My mistake. So when using this auto back focus what's the best frame to get if you don't have a chart? Thanks!


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john sharaf
Re: Setting Back-Focus Without A Focus Chart
on Apr 20, 2011 at 8:57:44 pm

Anything with intersecting horizontal and vertical lines or fine, contrasty detail, like a sign or chart with writing on it. Try it, tells us if it works.

JS



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