Summary
It is important to use lenses that produce a wide enough image circle to accomodate the back's CCD and/or CMOS sensor.
In-Depth
Example:
Lenses with 70 mm image circle: (will barely cover the area of P 65+/IQ160/IQ180 and not allow for any shift)
Lenses with 60 mm Image circle (will barely cover the P 45+ / P 25+)
Sensor sizes:
IQ3 100 and IQ4 150 sensor size is 53,4 x 40 mm
IQ280/180, IQ260/160 and P65+ has sensor size 53,9 x 40,4 mm
IQ250, IQ140, Credo 40 and P40+ has sensor size 44 x 33 mm
Lens samples:
Lenses with 90 mm image circle:
Schneider Kreuznach 47mm XL
Linos Rodenstock 40mm HR
Linos Rodenstock 23mm and 28mm HR
Schneider Kreuznach 24 mm XL
Furthermore the P 65+/IQ160/IQ180/IQ 260/IQ 280/Credo 60/Credo 80 is not recommended with extreme wide non-retro focus lenses like the Schneider Kreuznach 28mm XL, Schneider Kreuznach 35mm XL and in some cases Schneider Kreuznack 47 mm XL.
Even though these lenses has more than 70 mm image circle, they are producing a very steep angle incoming light along the edges. This can result in uncorrectible lines and color casts in the images.
Instead we recommend similar Rodenstock HR lenses which have a retrofocus design.
For the XT camera we use the Rodenstock lenses with retro-focus design lenses. As a sidenote a lens with retrofocus design is a lens with one or more extra lens elements close to the sensor, that decrease the angle of light and thereby cause less colorcast in an image, as the light will be less reflected from the pixel wells. The CMOS sensors are designed differently and are less sensitive to colorcast however they still has a fall off in case of too much shift!
Here is an example of an uncorrectable shot made on an IQ180 and a Schneider 28mm XL lens
Sometimes wide angle lenses will produce a pattern of repeated lines in an image brcause of reflection from the sensor electronics next to the pixel wells. Here is an example at 100%
In most cases these lines can be corrected by enabling "Wide Angle Lens with Movements" when creating an LCC
Here is the result after LCC correction:
NOTE: In general we advice to use lenses from Rodenstock when large sensors and shift are used and use lenses from Schneider Kreuznach with smaller sensors or less wide lenses and less or no shift!