Leaf Custom Gain Adjuster

[Streetwise]

Edit: This post was moved over to Med Format. Sorry for any confusion.

I own an Aptus 65 back and have recently purchased a Cambo DS Wide for it. As for lenses, I've been renting from a large company in Chicago, but they only stock the Schneider Apo-Digitar XL lenses. After my first batch of wide images, I was disappointed to see an odd color shift in the images from one side of the frame to the other. I did some research and found out about the "lens cast" and "centerfold" phenomenon with shooting ultra-wide. A call to Leaf America put me on to a utility called the "Custom Gain Adjuster".

What I would like to know, is exactly how do you go about using this software? I could not find a users guide, but I may have just missed it. I did not get a white piece of plexiglass with my back. Would any old piece of white plexi work?

Secondly, according to Leaf's May 2007 Tech bulletin, "Leaf Aptus Backs and Ultra-Wide Angle Photography", they state that the lenses noted for causing the worst issues are the Schneider Apo-Digitar XL lenses. They suggest the Rodenstock Apo-Sironar digital HR lenses instead. Do you know who rents these lenses in the U.S.? The firm in Chicago does not.

As for "Best Practices", here are my questions:

- Do you typically create your custom gain files in the field, or after-the-fact, in the studio (via strobes)? If so, is it just a matter of writing down the aperture and V/H shift settings so they can be duplicated in the studio?
- If you produce gain files in the field, how would that work? It seems that if you were to put a piece of white plexiglass in front of the lens, it would eliminate most of the light.... So a 1 sec f/8 field exposure would produce a very dark (unusable?) gain exposure assuming a piece of plexi was put in front of the lens to create the gain file.

I'm just trying to understand how you personally go about shooting and applying the Custom Gain Adjustment to your files, and also what lenses you are using.

Thanks,

David Anderson


Edit - I just realized that I should have posted this over at the Med Format forums. Could someone please move it over there? Sorry.

[Richowens]

David,

 Yes you will probably get more response in Medium Format than here. You can copy and paste this post to MF and no one will get upset with you    I think it will be to your advantage to do so.

 If you wish you can edit this post with a note that it is also in the Mf section.

 As far as your your question I have no experience in Digital MF so can't help you there.....sorry.

 Rich

[roskav]

Hi David

After a bit of messing around with "Leaf custom gain adaptor" program I have found that most wide angle shots really benefit from this part of my workflow.  For wide angle I use Rodenstock 35mm .. which also has its issues especially at any shift beyond 5mm.  As I use a gottschalt ds30 camera I have to make calibration files immediately in the field as the info can't be written down with the shift system. ie take shot .. change shutter speed by 3 or four stops (Don't change the aperture) and put the white disk (supplied with my Aptus 75) over the lens and take the calibration shot.  This normally results in a narrow enough histogram with a peak in the top third of the scale.  (I find if I over expose, the resultant adjusted file looses any benefit of the colour correction.)  The files are then side by side in Leaf capture.... I then start the "Leaf custom gain adaptor" program and make an extra folder for calibrated files ... do the calibration with an amount of fall off correction to suit the files.. then throw them back in the first folder to look at the original files beside them for reference.... tweak a bit .. then proccess.  This is really useful for very wide stitched files and really turns a wide angle shot into a great file for further tweaking... It's like you are given a file that has had a lot of time put into getting it a nice neutral stage.. perfect raw image.
I also found that it really pays to take the calibration shots at the same time as the original shots as there are always colour changes and light patterns (ie light coming from above into a dark stairwell) that you might want to take account of in your final set of images.  This uses up a lot of space, but with my business (Architectual photography) it just about fills up a 4GB card in a day's work. I don't shoot the calibration files for every shot.
I think any white opaque material will work ... try getting one that fits into a filter holder.

Regards

Ros

[Streetwise]

That's good information, Ros.

With the white material, I'm assuming that it's pressed tight up against the lens and not held out at any distance? A filter holder sounds like a good idea. Maybe I could even use a piece of tough-frost diffusion material?

Second question is on the creation of custom gain files:

Suppose that you took two shots to stitch together, shot at +5 and -5 H shift.  Would you create a separate gain file for each shot, or just center the lens and create a single gain file? I think I'm understanding the work flow better now.

I assume that you shoot untethered?

Thanks

Dave

[roskav]

Hi Dave am at home now but will post a screen grab tomorrow of a stitching example (seperate calibration files for seperate shots).. in answer to first question .. I think it should be as flat as possible against the lens ... or with a holder .. very little chance for light to reflect off the inner side of the white panel .. ie as close to the lens as you can get.

Ros

[rogerxnz]

How would I take a diffusion filter shot for a Hasselblad 30mm lens (on a 503cx)? Where would I get a "white disk" big enough? Would it matter if I could only hold some white plastic material about 20mm in front of the lens, because of the hood "fins"?

The 30mm lens has small internal filters (about 30mm in diameter). It would be pain to unscrew the lens in the field to put in a filter.

Would the effort be worthwhile?
Roger

Hi David

After a bit of messing around with "Leaf custom gain adaptor" program I have found that most wide angle shots really benefit from this part of my workflow.  For wide angle I use Rodenstock 35mm .. which also has its issues especially at any shift beyond 5mm.  As I use a gottschalt ds30 camera I have to make calibration files immediately in the field as the info can't be written down with the shift system. ie take shot .. change shutter speed by 3 or four stops (Don't change the aperture) and put the white disk (supplied with my Aptus 75) over the lens and take the calibration shot.  This normally results in a narrow enough histogram with a peak in the top third of the scale.  (I find if I over expose, the resultant adjusted file looses any benefit of the colour correction.)  The files are then side by side in Leaf capture.... I then start the "Leaf custom gain adaptor" program and make an extra folder for calibrated files ... do the calibration with an amount of fall off correction to suit the files.. then throw them back in the first folder to look at the original files beside them for reference.... tweak a bit .. then proccess.  This is really useful for very wide stitched files and really turns a wide angle shot into a great file for further tweaking... It's like you are given a file that has had a lot of time put into getting it a nice neutral stage.. perfect raw image.
I also found that it really pays to take the calibration shots at the same time as the original shots as there are always colour changes and light patterns (ie light coming from above into a dark stairwell) that you might want to take account of in your final set of images.  This uses up a lot of space, but with my business (Architectual photography) it just about fills up a 4GB card in a day's work. I don't shoot the calibration files for every shot.
I think any white opaque material will work ... try getting one that fits into a filter holder.

Regards

Ros

[Dave Carter]

I have an Alpa 12 TC and use the white plastic quite often.
I have a filter step-up ring on my Schneider lens that stays there all the time. It is quite a large step up - I forget how much and I am not at home to look.  But it is well above the field of view.  My white plastic is just like a lens cap, so just slip it on the step-up ring and snap another picture after dropping the shutter speed.

Do it in the field!  You can do this very quickly.  

Good luck,
Dave

[pixjohn]

I used translucent plexi in the past ,when the provided leaf disc was not big enough. It worked fine.