BRIEF FIELD REPORT:

**Schneider 90mm XL f5.6 (ultra-wide angle)**
Theoretical covering power:  266mm

Background:                            Schneider Lens Data available here along with MTF charts

Front filter:                               standard 95mm (no mechanical vignetting observed with normal 95mm Heliopan filters

                                                  and/or with either the Sinar or Cokin X-Pro holder)
 

Test Camera:                           Chamonix Whole Plate.  Sinar mount lens board.  NB Wista lens panel users - rear element may not 

                                                  fit without disassembling rear element and retro-mounting via detaching bellows.
 

Groundglass:                          Groundglass viewing is very limited without darkcloth coverage in daylight.  With a 

                                                  darkcloth, the groundglass image is faintly discernible compared to a standard 180mm 

                                                  f5.6 or 300mm f9 lens.  Note the limitations of a non-wide-angle ground glass         

                                                  fresnel screen.  Corner to corner  illuminance is still difficult however the clip corners of 

                                                  the ground glass design facilitates checking for light-fall off 

 
Illumination:                            This lens possesses a remarkable across field illumination
                                                  throughout the image area of the whole plate negative. 

Centre Filter:                           No requirement for a centre filter [designation IVa]; a surprising finding in view of its
                                                 near edge-edge reliance on the image circle at f11 (image taken on monochrome negative

                                                 film - Ilford FP4+.  Colour slide users may find otherwise).

Focussing:                              Chamonix Whole Plate users:  1st front standard detent (100mm) to be used.  

                                                 90mm XL lens can be focussed without recessed board or simultaneous front/rear tilts.

Image characteristics:           Distortion and field characteristics can be seen here:  Full
                                                 negative with ragged edge scans shown.

Whole Plate cameras with fixed rear standards (such as the Chamonix Whole Plate) will show the technical limitations of such an ultra-wide field design: the lower 1/6th of the image shows the base rail of the front bed intruding into the image.  

Correction requires:

1. Front bed drop capability
2. Front + Rear standard horizontal axis tilt for field perspective correction
3. Sufficient covering power for front/rear standard axis tilts

Attempts at horizontal axis tilts reveal expiration of coverage from the 90mm XL lens from f5.6 - f32.  The measured diameter of the whole plate image (less than the diagonal of the 6/12 x 8 1/2 inch) is approximately 259mm, thus enabling around 7mm of movement for the 90mm XL f5.6 lens at f22.

In comparison to 4x5" format with a 47mm XL lens, the  90mm XL lens for 6 1/2 x 8 1/2 inch is not as extreme wide in its angle of coverage.  It does however possess superior field illuminance without the requirement for a 2 stop Centre Neutral Density Graduated filter for correction (obligatory for even field illumination on the 47mm XL lens).  The 90mm XL shows less mechanical vignetting issues with filters/holders.  Field distortion looks similar with peripheral evidence of barrel distortion.


Summary: 

1. The Schneider 90mm XL f5.6 lens possesses sufficient image coverage for the whole plate camera prior to movements.  It represents the  widest of the ultra-wide angle lenses available for whole plate format, however for format comparison, it is not quite as wide as a Schneider 47mm XL f5.6 lens on 4x5" format however is superior for filtration and filter holder usage than the 47mm XL assembly with a 3a Centre Filter.

2. Successful use of the Schneider 90mm XL f5.6 lens depends on the design of the whole plate camera; cameras with built-in front bed drop have less difficulty than cameras with fixed rear standards for utilising this lens.

3. In the case of whole plate cameras with fixed rear standards, front bed drop requires both front and rear horizontal axis tilts to avoid inclusion in the final image.  Indirect camera bed drop is possible however leads to an expired covering power of the lens.
 

4. The Chamonix camera design can surmount this difficulty, however it is practically very challenging due to the design of the vertical shift/rise  and tilt mechanisms being located on the same controls, in addition to the absence of a scale for degrees of tilt on both front and rear standards.  Other camera designs, such as the vintage Charten or Sanderson models; the modern Canham or Ebony cameras may surmount this issue by their respective designs.
 

5. Such an extreme wide-angle lens on the whole plate format has limited application for architectural purposes without the possibility of field perspective correction.  For cameras without direct front bed drop, there is a mechanical limitation for its use.   Indirect front bed drop is at best,  a compromise, leading to further coverage issues for the 90mm XL lens.  This is accompanied by even further barrel distortion of the field perspective which is not correctable within the limited 7mm of movement available for whole plate format.

6.  The design of the Schneider 90mm XL f5.6 lens when applied to a whole plate format, appears more useful as an ultra-wide angle lens for landscape purposes.

Other Schneider Lenses (require 259mm Image Circle to cover Whole Plate):

_____________________________________________________________________________________________________________________

Revisions and comments welcome.


RJ