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11-01-2010, 05:27 PM   #1
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Lens Correction: 15mm DA Limited (in-camera Pentax Kx processing or post-processing?)

My photography professor suggested shooting in RAW (duh) and to avoid any in-camera processing because there is nothing you can't do later in Photoshop or Lightroom.

Unfortunately Lightroom does not have a lens profile for the Pentax DA-Limited 15mm lens, and I'm wondering: In this instance should I let my camera handle distortion corrections or should I attempt it manually? This seems like an area where it might be best left to the camera to fix it, working with the assumption that Pentax cameras probably know how to handle correcting Pentax lenses.

My concern is that the camera will be making edits that can't later be undone, that the distortion edits will be baked into the RAW file as its captured and corrected.

Also how is all of this impacted by turning the camera vertically as opposed to horizontally?

Thank you for your feedback. I've learned a lot from these forums but still have so much to learn.

Thank you again.

11-01-2010, 06:23 PM   #2
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In my experience, the lens profiles for Lightroom yield results that are all over the map. Some appear to be quite accurate while others do some rather strange things to images. Mostly this concerns chromatic aberration either being correctly removed or, in some cases, made worse.

I understand, though, that you are talking about distortion. I own a K-7, not a K-x, but a co-worker does and he complained once to me about how long it took to review an image after initial shooting. I suggested that he turn off the built-in CA and distortion compensation. This made a huge difference in camera responsiveness. I would hate to find out you missed a shot because of camera lag. Orientation of the camera should not affect your results if you decide to try using the compensation.
11-01-2010, 06:31 PM   #3
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First I have used Light room a bit, and I should probably go ahead and get it, but that is another posting. From what I understand, you can create your own lens profiles for Lightroom....I am wondering out loud (since I have not tried it), if you could mount your camera on a tripod, and take two images of a "brick wall" (or similar "target"). One image with in-camera lens correction and the other one without in-camera lens correction. Then via the Lightroom lens profile creator, use the non in camera corrected image to correct it (in some way), to match the camera corrected image. If you can do this, then you essentially have a Lightroom lens profile that replicates the Pentax in camera correction.

Just a thought....
11-01-2010, 06:38 PM   #4
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QuoteOriginally posted by LowVoltage Quote
1: Mostly this concerns chromatic aberration either being correctly removed or, in some cases, made worse.

2: I understand, though, that you are talking about distortion. I own a K-7, not a K-x, but a co-worker does and he complained once to me about how long it took to review an image after initial shooting. I suggested that he turn off the built-in CA and distortion compensation. This made a huge difference in camera responsiveness. I would hate to find out you missed a shot because of camera lag. Orientation of the camera should not affect your results if you decide to try using the compensation.


1) I'm not sure I totally understand the difference between distortion and CA. I know that CA has something to do with the purple fringes you sometimes see around contrasty light/dark areas, but I also notice blurriness in similar examples. Does CA cause blurriness? I thought that might have been camera shake (which surprised me b/c I had a 1/30 shutter speed for 15mm *fast enough, right?) but now I'm guessing it might be CA.

2) The K-x is dreadfully slow with CA and lens distortion correction turned on. Like seriously painfully slow. But if it yields better images than Lightroom then for me it is worth it even if I miss some shots. Do you know if the in-camera processing for CA and distortion is baked into the RAW file or could the camera processing be "undone" via Lightroom? I never tried the CA correction on the K-x but I think they do have that in addition to the specific distortion correction.

11-02-2010, 09:03 AM   #5
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Shoot a straight RAW format with your camera. Then in Lightroom attempt to manually correct any optical issues using the sliders. You can always undo anything in Lightroom. Manual lens correction in LR is useful and fairly intuitive. It's also a good way for you to learn about the limitations associated with lenses, and to see how fine some are.

The 15mm Ltd is a very good lens; I haven't owned mine long enough to explore corrections (yet), but my semi-educated guess is that you won't need to "correct" things very significantly.

M
11-02-2010, 10:19 AM   #6
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I tried the distortion correction with the k-x (kit lens @18mm) and it seems that the raw image data itself is not corrected (the barrel distortion is still there). The embedded preview jpeg, however, is corrected, and this can give a false idea of what is going on. I would imagine that the raw file also gets a set of correction parameters added to it when distortion correction is on, and compatible software could use these to do the correction in PP. What happens with CA correction I don't know; this was not as easy to try out.
11-28-2010, 06:44 PM   #7
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I've been researching some of the KX modes and processors and found some great information at this site:
KX Optics Review
Go to the last half of the page

I don't know, if this has been posted before...or if it's even a reputable source, but I hope this helps.
11-28-2010, 08:18 PM   #8
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Will the supplied software process lens corrections or is this function limited to the camera?
The other thing is, can you make a Lightroom preset that will satisfy your requirement and just apply it as needed?

11-29-2010, 04:06 PM   #9
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QuoteOriginally posted by Wheatfield Quote
Will the supplied software process lens corrections or is this function limited to the camera?
DCU 4.31 can indeed apply the same lens corrections to your RAW images as the in-camera processing applies to the JPGs.

It's one of the good reasons to keep DCU 4 on your system.
11-29-2010, 04:41 PM   #10
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QuoteOriginally posted by rawr Quote
DCU 4.31 can indeed apply the same lens corrections to your RAW images as the in-camera processing applies to the JPGs.
[deleted]
I'm curious: are the lens corrections as applied to the RAW file permanent vs. Lightroom's non-destructive approach?
Thanks.

M
11-29-2010, 08:11 PM   #11
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QuoteOriginally posted by Miguel Quote
I'm curious: are the lens corrections as applied to the RAW file permanent vs. Lightroom's non-destructive approach?
They only apply on any output you generate from the RAW, unless you specifiy otherwise.
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