Digital back lens cast problem

[hendrikm]

Hi there,

we just face a problem: The set mainly consists of shades of white and grey and for the desired perspective we need to use an old 90mm f4.5 Grandagon N. The lens cast CAN´T be removed completely by LCC in Capture One   , in fact, the image is still unusable.

First question: If we rent one of the new "digital" lenses, would they show less lens cast?
Second question: What is your experience with this lenses (except that they give you wideangle back)?

Thanks, Hendrik

BTW: We use a P25 on Sinar, studio setting with flash as light source.
Sorry for crossposting to the phaseone forum, but I just want to reach as mucg knowledgeable readers as possible.

[jonstewart]

... Sorry for crossposting to the phaseone forum...

[a href=\"index.php?act=findpost&pid=139768\"][{POST_SNAPBACK}][/a]

That's the first time I've seen it called that. I suspect a LOT of people are going to be a  little offended!  

[Henry Goh]

Hi there,

we just face a problem: The set mainly consists of shades of white and grey and for the desired perspective we need to use an old 90mm f4.5 Grandagon N. The lens cast CAN´T be removed completely by LCC in Capture One   , in fact, the image is still unusable.

First question: If we rent one of the new "digital" lenses, would they show less lens cast?
Second question: What is your experience with this lenses (except that they give you wideangle back)?

Thanks, Hendrik

BTW: We use a P25 on Sinar, studio setting with flash as light source.
Sorry for crossposting to the phaseone forum, but I just want to reach as mucg knowledgeable readers as possible.
[a href=\"index.php?act=findpost&pid=139768\"][{POST_SNAPBACK}][/a]

Would it be possible to post a down-sized or cropped 800x600 pixels version here?  Thanks.

[DavidP]

I would think the lens cast would not be as bad with that lens as it is not all that wide for the P25 chip size. I have been using a similar set up with a 65 grandagon and not had too much trouble. Although I always have to use the lens cast tool with the view camera. more so with a 35mm and less, but still needing it with a 120.
Are you using some extreme movements? that will increase the lens cast problem. Maybe you could try and reset the camera movements. also if you have the back shifted way over to the side of the image circle it will be worse.
When using the lens cast tool, they recomend adding a stop or two to the exposure. I usually raise the ISO up in the software to get the extra exposure so I do not have to adjust the camera. you just have to remember to reset it back.
If you apply the lens cast setting to itself, in otherwords once you have made the setting, apply it to the original blank image you used to make it, it should even out the color and you can check it that way. It does not seem to me that the digital lenses are much less prone to the lens cast, they are just sharper and optimized for digital and the smaller size image circle.
I think Phase also supplies a profile called "easy gray" which is for shooting on neutral color seamless. It may desaturate things a bit but may also help.
good luck
David

[hendrikm]

Would it be possible to post a down-sized or cropped 800x600 pixels version here?  Thanks.
[a href=\"index.php?act=findpost&pid=139773\"][{POST_SNAPBACK}][/a]

Here´s a full resolution of the upper half (it´s intentional out of focus as the product is on the lower half):
www.kakaotrinker.de/ausgang/test-111.jpg

It´s 500K big. You see the lens cast: green, magneta, green

[hendrikm]

Are you using some extreme movements? that will increase the lens cast problem. Maybe you could try and reset the camera movements. also if you have the back shifted way over to the side of the image circle it will be worse.
[a href=\"index.php?act=findpost&pid=139795\"][{POST_SNAPBACK}][/a]

Yes, there´s some movement involved - but it is needed, we can´t take it back.

I think Phase also supplies a profile called "easy gray" which is for shooting on neutral color seamless. It may desaturate things a bit but may also help.
good luck
David
[a href=\"index.php?act=findpost&pid=139795\"][{POST_SNAPBACK}][/a]

Í´ll have a look into this tommorrow. Thanks!

[ericstaud]

I would guess that in most any case that a failure of the LCC tool is caused by user error.  It is important to have a good working knowledge of this tool before needing it on a job.  It has never failed to 100% remove lens cast in any of the hundreds of shots I've made with Phase One backs.

it is important to read the Phase One instructions for LCC which can be found in their support section....

http://www.phaseone.com/KBFiles/1557/1/LCCMac.pdf

You should always contact your dealer first when you run into these kind of problems with Phase.  Phase One requires your dealer to be the front line in providing you with tech support and know-how.  If your dealer is good you should take advantage of this.  If they are not helpful, let Phase One and your dealer know, and do your next upgrade through another dealer.

Also, don't believe that you can shoot an image and then used a previously made LCC correction, or that you can make a LCC capture and correction later.  Shoot the white plexi for every setup you do.  Even small changes in swing, tilt, f-stop, or focus can render the LCC correction you are using invalid.

If you did not make a good capture of the white plexi for the LCC tool, then you are on to Photoshop to fix this image.  Try using a Hue/Sat layer and de-saturating the magenta and green, then invert mask, and just paint in the correction where there are problems.

[BJNY]

I would say try an Aptus 75 at I.S.O. 50.
Never once did I encounter any color casts using it on a Fuji GX680III with maximum movements (every lens from 50mm to 150mm) on photographic situations where it would show up (a lot of gray backgrounds).