Lens Correction

[pharrael]

Hi,

I have a Panasonic FZ200 and I recently decided to try a little with shooting in raw mode. What I was surprised is that in raw mode, the shortest focal length (25mm equivalent I think) the image is distorted. Before I bought the camera I had read that at short focal lengths the photo really gets distorted. But when I saw my jpg pictures at shortest length I just assumed that value was not short enough to produce any distortion.

Well, seeing distortions in the raw photos, I came to conclusion that the camera was correcting the distortions before generate the jpg file, am I right?

I see in the software I use (aftershot) that there is a place where you can correct the lens distortion by giving three parameters (a, b and c). What I want to know is whether you generally use that feature or just let the photos get distorted and use lens with longer focal length to avoid distortion?

Is there some place where I get these values for my camera? The software has some presets for some cameras, but not for FZ200.

Thanks!

[Manfred M]

This is totally expected and is especially noticable with P&S or super-zoom cameras that have lenses with a very large focal range. The camera manufacturer has data on the amount and type of distortions (generally pin-cushion to barrel are most noticeable, but if you look carefully, you might detect chromatic aberation and vignetting (darkening of the corners of the image). These are corrected by your camera's software when outputing to jpeg.

The RAW converter producers establish camera / lens profiles and software like Adobe Camera Raw (ACR) or DxO Optics Pro. They have to come out with new versions as new cameras are rolled out. They tend to concentrate on current interchangeable lens cameras, but some more advanced super zooms and point and shoot cameras may be included. DxO Optics Pro 8 has the FZ200 profiles (I just checked). Adobe does provide the tools if they do not have your camera / lens combination if you have Photoshop / ACR.

[Mike Buckley]

What I want to know is whether you generally use that feature or just let the photos get distorted and use lens with longer focal length to avoid distortion?

I always use the focal length that produces the image that I envision before releasing the shutter. That means using the distortion-correction capability of my post-processing software. I could enable the software to automatically correct the distortion but I prefer to do it manually once the distortion is evident.

By the way, using a longer focal length does not always avoid distortion. Also, whether or not the distortion is noticeable depends on the scene, such as whether or not the scene contains strong horizontal lines.

[pharrael]

...but if you look carefully, you might detect chromatic aberation and vignetting (darkening of the corners of the image). These are corrected by your camera's software when outputing to jpeg.

Yes, I've already noticed that too.

DxO Optics Pro 8 has the FZ200 profiles (I just checked).

I use linux, so sadly I'll have to stick with Aftershot. I tried to adjust the values by myself, but I have the sensation the I could use the exact values to correct it.

Thanks for your reply, I've found very helpfull!

[pharrael]

I always use the focal length that produces the image that I envision before releasing the shutter. That means using the distortion-correction capability of my post-processing software.

I understand you and I agree.

I could enable the software to automatically correct the distortion but I prefer to do it manually once the distortion is evident.

Sadly the software I use can't do it automatically.

By the way, using a longer focal length does not always avoid distortion. Also, whether or not the distortion is noticeable depends on the scene, such as whether or not the scene contains strong horizontal lines.

I understand! Thanks for sharing your knowledge! I have learned a lot from everyone in this forum.

[revi]

(...)
I use linux, so sadly I'll have to stick with Aftershot. I tried to adjust the values by myself, but I have the sensation the I could use the exact values to correct it.

Thanks for your reply, I've found very helpfull!

In that case, you can use the Hugin tool set to determine lens correction parameters (there's a tutorial for that), which can be used directly by the lensfun library.
I don't know if Aftershot uses lensfun, though.

And there are several other RAW decoders available for Linux as well (Darktable or UFRaw are just two examples).

[Manfred M]

I use linux, so sadly I'll have to stick with Aftershot. I tried to adjust the values by myself, but I have the sensation the I could use the exact values to correct it.

I don't use either Linux or the RAW converter you do. I suspect that

The only work around I see for you is for you to photograph a test target at different focal lengths and then dial in those corrections into your PP process. Once you have them, you could apply these values to images you have taken going forward, based on the focal length used for the shot.

I'm not sure what capabilities GIMP plugins have; I seem to remember that they had a Linux version.

[pharrael]

In that case, you can use the Hugin tool set to determine lens correction parameters (there's a tutorial for that), which can be used directly by the lensfun library.
I don't know if Aftershot uses lensfun, though.

Thank you so much I'll try and I'll tell if it worked!

And there are several other RAW decoders available for Linux as well (Darktable or UFRaw are just two examples).

Again, thank you so much! I will try these software too.

[pharrael]

I don't use either Linux or the RAW converter you do. I suspect that

The only work around I see for you is for you to photograph a test target at different focal lengths and then dial in those corrections into your PP process. Once you have them, you could apply these values to images you have taken going forward, based on the focal length used for the shot.

Wow, how couldn't i have thought that?

I'm not sure what capabilities GIMP plugins have; I seem to remember that they had a Linux version.

Yes, I already use it. But if I am not wrong, still there is no raw support in GIMP.

Thanks!

[xpatUSA]

But if I am not wrong, still there is no raw support in GIMP.

Thanks!

I use a Sigma camera which has limited raw support also. People with that problem often use the RAW converter that is supplied with the camera (just to convert) then save as TIFF, 8 or 16bit, which can then be opened by almost every editing program available.

I have a Panasonic GH1 and usually use the JPEGs output, although the .RW2 files can be fun to play with

[inkista]

In that case, you can use the Hugin tool set to determine lens correction parameters (there's a tutorial for that), which can be used directly by the lensfun library.
I don't know if Aftershot uses lensfun, though.

Even if it doesn't, the Hugin optimizer will produce the a,b,c numbers the OP was asking for.

And don't know if this is any use, but googled up a way to add a lens to Aftershot Pro.

[Inkanyezi]

But if I am not wrong, still there is no raw support in GIMP.

UFRaw plugs with Gimp. I.e. when you have installed it, opening a RAW in Gimp opens it first in UFRaw before dropping the converted image in Gimp.

[revi]

Even if it doesn't, the Hugin optimizer will produce the a,b,c numbers the OP was asking for.

And don't know if this is any use, but googled up a way to add a lens to Aftershot Pro.

That's always useful, as it works both ways:
since Aftershot uses the PTlens distortion model, you can also use the data from Aftershot in lensfun and Hugin...

A general remark wrt to automatic recognition of lenses (one of the remarks in Kathy's link):
A lot of 3rd-party lenses use IDs that are already used by OEMs, so an ID provided by the lens can correspond to several different lenses.
So make sure that the program you use does select the actual lens used (or select it in the provided list) before applying the distortion corrections...

[pharrael]

I use a Sigma camera which has limited raw support also. People with that problem often use the RAW converter that is supplied with the camera (just to convert) then save as TIFF, 8 or 16bit, which can then be opened by almost every editing program available.

Interesting option, but at least in aftershot my camera is already supported.

I have a Panasonic GH1 and usually use the JPEGs output, although the .RW2 files can be fun to play with

Yes. I have had much fun working with raw too, but my raw shots aren't still much funny yet.

Thanks!!!

[pharrael]

Even if it doesn't, the Hugin optimizer will produce the a,b,c numbers the OP was asking for.

And don't know if this is any use, but googled up a way to add a lens to Aftershot Pro.

I will try to determine the values in Hugin and will try to add the lens to Aftershot.

Thank you so much!!!

[pharrael]

UFRaw plugs with Gimp. I.e. when you have installed it, opening a RAW in Gimp opens it first in UFRaw before dropping the converted image in Gimp.

Very interesting! I will try this too.

Thank you!!!!

[pharrael]

That's always useful, as it works both ways:
since Aftershot uses the PTlens distortion model, you can also use the data from Aftershot in lensfun and Hugin...

It seems that Darktable also uses lensfun, so I will try to add the lens in both softwares and play a little to decide which I'll use.

A general remark wrt to automatic recognition of lenses (one of the remarks in Kathy's link):
A lot of 3rd-party lenses use IDs that are already used by OEMs, so an ID provided by the lens can correspond to several different lenses.
So make sure that the program you use does select the actual lens used (or select it in the provided list) before applying the distortion corrections...

When I open the raw in aftershot it shows my camera model, but it says the camera have no preset yet.
Thank you so much!!!

[Glenn NK]

If you take a short visit to the M43 section of lens testing at photozone.de, there are some great examples of this distortion.

http://www.photozone.de/m43/846-olym...556iir?start=1

Check the difference between a camera JPEG (which has correction applied), and a non-corrected image.

This is the Achilles heel of the M43 system.

Glenn

[Manfred M]

This is the Achilles heel of the M43 system.

I would suggest that it is not a MFT problem, but rather the result of questionable choices made in lens design, especially at the wider end of the range. This is a fairly inexpensive, low end lens, so price point rather than optical performance likely drove these design decisions.

[pharrael]

If you take a short visit to the M43 section of lens testing at photozone.de, there are some great examples of this distortion.

http://www.photozone.de/m43/846-olym...556iir?start=1

Check the difference between a camera JPEG (which has correction applied), and a non-corrected image.

This is the Achilles heel of the M43 system.

Glenn

Sorry for the newbie question, but what is a M43 system?