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Author Topic: Adobe Camera Raw4 - Lens Corrections Tab  (Read 3097 times)

Dinarius

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Adobe Camera Raw4 - Lens Corrections Tab
« on: January 14, 2008, 12:27:36 pm »

This may be a silly question, but I can't quite work out what the difference between the two tabs is!

I am trying to do the following........

I have a gallery wall which has been evenly lit but which is displaying some discrepancy between the midpoint and the corners.

So, I do the following:

1. Using the Colour Sampler tool I take a reading in two, diagonally opposite, corners (actually a little in from the corner) and the middle of the frame. The red channel readings are 224, 239, 223.

2. I move the amount slider to the right and the low readings rise to 239/238 quite at about 62 on the slider.

But, if I move the slider only as far as, say, 55 and move the Midpoint slider to the left, i can achieve the same result.

And on a white gallery wall, I can't see any difference between both approaches.

So, what should I be doing to get the readings the same?

All Amount and no Midpoint?

A lot of Amount and some Midpoint?

A bit of both?

I can't find a decent explanation of this (wonderful!) feature anywhere.

Help!

Thanks.

D.
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JeffKohn

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Adobe Camera Raw4 - Lens Corrections Tab
« Reply #1 on: January 14, 2008, 12:59:18 pm »

Amount controls the strength of the correct, the Midpoint controls how far from center the correction starts. A large positive value for the midpoint setting means that the correction will start closer to the edge and transition more sharply, while moving the midpoint negative will begin the correction further into the image but with a more gradual transition.

If you set a large negative value for amount and then slide the midpoint between the extremes it should become apparent how it affects the image.
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Jeff Kohn
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Dinarius

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Adobe Camera Raw4 - Lens Corrections Tab
« Reply #2 on: January 14, 2008, 01:09:26 pm »

Quote
Amount controls the strength of the correct, the Midpoint controls how far from center the correction starts. A large positive value for the midpoint setting means that the correction will start closer to the edge and transition more sharply, while moving the midpoint negative will begin the correction further into the image but with a more gradual transition.

If you set a large negative value for amount and then slide the midpoint between the extremes it should become apparent how it affects the image.
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Jeff,


Thanks for that.

So, would I be right in thinking that if I want the gallery wall to be as even as possible, I should begin by setting the Midpoint to zero, and then moving the Amount to the right until the readings match?

It certainly looks good that way.

Thanks.

D.
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walter.sk

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Adobe Camera Raw4 - Lens Corrections Tab
« Reply #3 on: January 14, 2008, 08:44:14 pm »

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So, would I be right in thinking that if I want the gallery wall to be as even as possible, I should begin by setting the Midpoint to zero, and then moving the Amount to the right until the readings match?
[a href=\"index.php?act=findpost&pid=167101\"][{POST_SNAPBACK}][/a]
It seems to me either way is fine.  But if you find you are using the same settings over and over, I'm sure you can save them as a default.  If not on that tab, you could start with your default ACR settings, opening a typical image, and changing only the settings on the Lens tab.  Then go back to the Basic tab and save as your new defaults.
« Last Edit: January 14, 2008, 08:44:44 pm by walter.sk »
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