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Author Topic: Shooting the target for Lens Correction Profiles  (Read 2528 times)

Hening Bettermann

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Shooting the target for Lens Correction Profiles
« on: December 19, 2014, 07:14:12 am »

I have difficulties to follow Adobes advanced math.
The AdobeLensProfileCreatorChartShootingQuickStartGuide advises to shoot the target at 1x, 2x and 5x the minimum focus distance of the lens. At the same time, it advises to make the target fill about 1/2 to 1/4 of the image frame. Well, the latter will only be possible for 1 of the 3 focus distances...or??

dwswager

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Re: Shooting the target for Lens Correction Profiles
« Reply #1 on: December 19, 2014, 04:02:12 pm »

I have difficulties to follow Adobes advanced math.
The AdobeLensProfileCreatorChartShootingQuickStartGuide advises to shoot the target at 1x, 2x and 5x the minimum focus distance of the lens. At the same time, it advises to make the target fill about 1/2 to 1/4 of the image frame. Well, the latter will only be possible for 1 of the 3 focus distances...or??

If I recall, that is for prime lenses.  I would use the 1/4 of frame as a minimum requirement.  They offer PDFs of the targets n 4 or 5 different sizes.
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Hening Bettermann

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Re: Shooting the target for Lens Correction Profiles
« Reply #2 on: December 19, 2014, 05:06:03 pm »

> If I recall, that is for prime lenses.
Well it is per focal length, prime or zoom.

> They offer PDFs of the targets in 4 or 5 different sizes.
Ooops! That's the parameter I overlooked: you have to use targets in different sizes!

Thank you for your reply.

AFairley

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Re: Shooting the target for Lens Correction Profiles
« Reply #3 on: December 19, 2014, 08:42:05 pm »

Personally, I don't bother with short distances since I never shoot at the minimum focus distance anyway.  I get the target printed and mounted on 24x36 gator foam and shoot it at the farthest distance that will cover the frame in a set of 9 or 25 shots.  Seems to work fine for me.
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Hening Bettermann

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Re: Shooting the target for Lens Correction Profiles
« Reply #4 on: December 20, 2014, 12:36:51 pm »

Thank you AFairley. I'm in the same situation as you, I only shoot at infinity. Maybe I will modify your idea to the end that I will settle with just 5x the minimum focussing distance of each lens, to feed the algorithm something that it exspects. (I am shy to blindly mess with math that I don't understand).

It will leave the task of calculating the size of the target for every given focal length at  that shooting distance. Would anybody know how to do that? How to calculate the target size for a given focal length and shooting distance to make that target fill 1/2 of the frame?

But even if that can be calculated, I see a problem.
E.g. the minimum focussing distance for my 24 mm Zuiko is 0.25 m, that would mean 1.25 m is the farthest distance that the algorithm exspects. Well that is still very far from infinity. Can this really work?

After all, the project will require considerable resources. I will have to have these targets printed and mounted, and then find out what is the cheaper procedure of these two: a- buy 2, maybe more softboxes to illuminate these targets evenly; my 2 Solux lamps can with some effort cover a max of A4 (210x294 mm). Or b- have a pro with a studio shoot the targets for me. I refuse to mess with ever shifting daylight for this task.

As I write this, I get the feeling that it will be easier to correct CA manually in ACR... (It is CA that I'm primarily concerned about).

Rhossydd

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Re: Shooting the target for Lens Correction Profiles
« Reply #5 on: December 20, 2014, 02:03:46 pm »

the project will require considerable resources...... I refuse to mess with ever shifting daylight for this task.
Really ?
I think you may be worrying too much about the process.
I built a profile for my 14mm Samyang a while back and it didn't seem much bother at all and it performs excellently.
From what I can recall, print out the target on some A3 matt photo paper, stick it to a wall on an overcast day, shoot away then just pass the files to the profile building software and that's all. The software seems particularly clever and compensates for all sorts of shooting inaccuracies without needing any help. It's definitely one of Adobe's little free gems, like the DNG profile builder, great utilities with ease of use to make very useful end solutions.

Just go for it, all you've got to loose is the cost of a couple of sheets of A3.
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Hening Bettermann

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Re: Shooting the target for Lens Correction Profiles
« Reply #6 on: December 20, 2014, 02:42:34 pm »

Thank you, Rhossyd. That sounds encouraging. - If daylight can be used, that leaves the question of the target size and shooting distance.

AFairley

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Re: Shooting the target for Lens Correction Profiles
« Reply #7 on: December 21, 2014, 12:13:28 pm »

Just use whatever distance lets you cover the frame with 3 or 5 images across (with some overlap), just make sure that the grid size you use is such that the squares are 20-40 pixels in the files.  The program is not at all finicky.
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Hening Bettermann

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Re: Shooting the target for Lens Correction Profiles
« Reply #8 on: December 21, 2014, 12:59:35 pm »

Thanks again, AFairly. I see it is a pretty large image you use. If your 24x36 means inches.

AFairley

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Re: Shooting the target for Lens Correction Profiles
« Reply #9 on: December 22, 2014, 11:35:24 am »

Thanks again, AFairly. I see it is a pretty large image you use. If your 24x36 means inches.

Yes, but I used to use target printed on 17x22 inch paper and those seemed to work fine also.  Don't sweat it.
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Hening Bettermann

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Re: Shooting the target for Lens Correction Profiles
« Reply #10 on: December 22, 2014, 02:34:13 pm »

Thank you. So this will be my good intention for the new year.
Merry Christmas and a happy new year! 
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