How to handle/remove color cast of digital backs

[MichaelEzra]

Is there a version to try on 10.6.X?

I am a using Win7, but one of the main RawTherapee developers is using Mac (actually Emil wrote flat field correction on the mac:) )
Try one of these:

http://www.rawtherapee.com/releases_head/mac/

You should try the auto selection of the flat fields, just store them in a single folder and point to it using preferences.
Lens cast is fixed then with a simple checkbox selection (Flat Field auto select).
If flat field with exact aperture is not found, it will select the closest match for camera/lens/aperture combo.

[yaya]

I am a using Win7, but one of the main RawTherapee developers is using Mac (actually Emil wrote flat field correction on the mac:) )
Try one of these:

http://www.rawtherapee.com/releases_head/mac/

You should try the auto selection of the flat fields, just store them in a single folder and point to it using preferences.
Lens cast is fixed then with a simple checkbox selection (Flat Field auto select).
If flat field with exact aperture is not found, it will select the closest match for camera/lens/aperture combo.

No dice:-( both builds crash at launch...

[MichaelEzra]

I'll see if there is a tested recent build for your version of OSX.

[acg]

Yair, Do you have some recommendations on the diffuser filter? I could not figure out which one to buy. Many thanks!

No need for a computer.

Set the back's compression to "Lossless"
Shoot with a White diffuser filter (or a piece of white perspex) as John suggested. It is important to do one whenever you change aperture and to compensate by adding 2 stops of exposure time.

I'm assuming that no firewire port means it's a PC, so you have to use Capture One Pro:
Select the white image and in the lens tool tab, select Analyse from the LCC drop-menu, save it let's say with the f-stop number. Then select all the images that you've taken with the same aperture and apply this correction by selecting it from the same drop-menu

You can opt to apply fall off correction as well at the same time

Note that this function does not exist in Lightroom/ ACR so if you use these you will have to do the correction in Photoshop, which si time consuming and probably not as good.

Enjoy your new back!

Yair

[yaya]

I'll see if there is a tested recent build for your version of OSX.

We make a 100x100mm one, you can get it through your local dealer

[Doug Peterson]

http://www.captureintegration.com/store/leaf-accessories/

In addition to the manufacturer solutions I can also selflishly suggest our own LCC panel which is provided with a strap to hang on your camera and a little sleeve to keep it clean.

At the end of the day it's just a white piece of plexiglass thick enough to ensure full diffusion but not too thick to lose excessive light. But I like ours best :-).

Doug Peterson,
Head of Technical Services
CaptureIntegration.com
Phase One, Leaf, Mamiya Dealer and more

(while traveling)

[pixjohn]

i use the Leaf disc but have also used 2 plain white plexi doubled and held it against the lens.
I also point a light source directly at the disc. Do a search on LL and you will find lots of posts about lens correction.

[acg]

http://www.captureintegration.com/store/leaf-accessories/

In addition to the manufacturer solutions I can also selflishly suggest our own LCC panel which is provided with a strap to hang on your camera and a little sleeve to keep it clean.

At the end of the day it's just a white piece of plexiglass thick enough to ensure full diffusion but not too thick to lose excessive light. But I like ours best :-).

Doug Peterson,
Head of Technical Services
CaptureIntegration.com
Phase One, Leaf, Mamiya Dealer and more

(while traveling)

Thanks! That looks very neat indeed.

I ended up ordering an ExpoCap after some reading on LL as pixjohn suggested. I only have 1 Alpa lens for now and a 52mm ExpoCap seems convenient.

[yaya]

Thanks! That looks very neat indeed.

I ended up ordering an ExpoCap after some reading on LL as pixjohn suggested. I only have 1 Alpa lens for now and a 52mm ExpoCap seems convenient.

Their site doesn't state the thickness of the expocap. A good diffuser will require approx. 2 stops of compensation. Just remember to do it by changing the shutter speed and NOT the aperture!

[acg]

Their site doesn't state the thickness of the expocap. A good diffuser will require approx. 2 stops of compensation. Just remember to do it by changing the shutter speed and NOT the aperture!

Thanks! I will report back when I can try it out. I am not sure if it will work out or not, but my D700 has a 35F2D that can use the ExpoCap if it does not work out for LCC.

[fredjeang]

I'll see if there is a tested recent build for your version of OSX.

Michael, on Windows 7, I've never been able to install properlly Rawtherapee (previous versions also). In fact it works but the all folder is always located in the desktop and not where it should be. I don't really understand why but it's like the instalation is corrupted. So yes, I can run it from the desktop folder but this is not normal. Any idea?

[MichaelEzra]

Michael, on Windows 7, I've never been able to install properlly Rawtherapee (previous versions also). In fact it works but the all folder is always located in the desktop and not where it should be. I don't really understand why but it's like the instalation is corrupted. So yes, I can run it from the desktop folder but this is not normal. Any idea?

Hi Fred,

Here is a link to RawTherapee package (just compiled it on Win7) which does not require an install:
http://timelessme.com/temp/Postings/rt-win32-3.1A-b8ebac4184d4.zip  - 12.8 MB
Unzip it to any directory you like and run rt.exe from there (create a shortcut, if this is more convenient).
Let me know how t works for you.

[fredjeang]

Nope. It crashes all the time at launch. Very weired. Thanks for the help anyway.

[MichaelEzra]

Nope. It crashes all the time at launch. Very weired. Thanks for the help anyway.

This might be compiled for a non-generic CPU, sorry about that. I'll see what I can do.

[Bart_van_der_Wolf]

This might be compiled for a non-generic CPU, sorry about that. I'll see what I can do.

Hi Michael,

I tried it, and your compilation works fine for me. I'm on Win7 Ultimate, with an Intel Xeon processor, and an nVidia graphics card.
Maybe Fred's hardware is non-generic?

Cheers,
Bart

[fredjeang]

It is. It's something else. I know it because it worked for me in the past although I thought the installation not very orthodox, but it worked. I'm sure it is something stupid and easy as often.
If I find I post.
Cheers.

[MichaelEzra]

Thanks, Bart.
Actually, I compiled this rt.exe on Athlon-64 but for a generic CPU target.
However, I do find this particular build unstable on my other i5 machine.
The problem could be that I've packaged here shared libraries from another build,
as my local process for packaging builds for distribution is not yet tuned,
and these libraries may be in conflict with the rt.exe executable on a specific platform.

Fred, great to hear that it is working for you now. I am curious if you get a chance to use the flat field feature, how would it work for you.

[fredjeang]

Oh Michael, I'm sorry. It does not. It freezed again when I thought I got it. Nice try anyway.