Medium Format Lenses with the Pentacon Six Mount
A comparative test
by TRA

Results of tests with a Tilt Lens


While shift lenses have a clear major advantage in architectural photography, perhaps tilt lenses are particularly useful in close-up work – although we shall see below the benefits of also being able to shift a tilt lens, and others have demonstrated the power of tilt lenses in general photography, both to increase and to decrease depth of field.

Three factors reduce the depth of field (the area of acceptable sharpness) of a lens:
  • the aperture: the larger the aperture (the smaller the aperture number), the shallower the depth of field;
  • the focussing distance: the closer a lens is focussed, the shallower the depth of field;
  • the focal length: the longer the focal length, the shallower the depth of field.


The 45mm Hartblei Super-Rotator Tilt/Shift lens has a very short focal length (for Medium Format), and therefore an inherently extended depth of field, so I decided to exploit the other two factors that give a shallow depth of field by taking some close-up pictures and using wide apertures, to see if using the tilt facility of this lens would increase the in-focus range for me.
 

Here is the set-up for the test.
Photographs shot on Fuji NPS 160, which also enabled me to use wider apertures than might have been possible with faster film.  Illumination was provided by natural daylight from a north-facing window on a bright day.


45mm Super-Rotator fully tilted
[C471-25A.jpg]
The first shot is with zero tilt and zero shift.  Because the subject is at approximately 45° to the camera back and we are working at maximum aperture, the area of sharp focus is extremely shallow.  As with all lenses, the sharpness decreases gradually in front of and behind the area of sharpest focus, which in this photograph is right in the middle of the photograph.  What is considered acceptable sharpness is principally dependent on two factors:
  • the intended degree of enlargement
  • the intended viewing distance.
In this photograph, approximately one quarter of the height of the image might in some circumstances be considered acceptably sharp.  That zone of acceptable sharpness extends across more than three-quarters of the width of the image at that point.  Why does it not extend across the whole of the width of the image in the plane of sharpest focus?

That is because there is of course another factor in the first two test shots here: they have been shot at maximum aperture, to enable the effect of tilting the lens to become obvious to the maximum.  No-one would normally shoot an image such as this one at maximum aperture.  In fact, the aperture that gives the sharpest image for the lens would normally be used.  This is normally between f/8 and f/16, depending on the lens.

With any lens, at maximum aperture there is a marked decrease in sharpness away from the centre of the image area, and this is inevitably obvious with this image, too, if we look to the left and right of the in-focus plane.  Note in particular the lack of sharpness of the right-hand part of the red banknote.

Incidentally, the fall-of in brightness at the bottom of the image is a consequence of the set-up and the ambient lighting, as will be observed from the top picture on this page.



Zero tilt, zero shift, maximum aperture: 1/125 f/3.5
[C472-14/15]
When the lens is tilted down, the image moves up in the viewfinder and so it is necessary to change the angle of the camera on the tripod.  It is also necessary to re-focus.

In this image, even though the lens is still at its maximum aperture of f/3.5, the tilt has increased the depth of field tremendously, but much more in front of the point of focus than behind it.  I focussed on the central area of the blue banknote, just below the lady’s chin.  I need to re-try, with the focus set further back.  Naturally, the fall-off in resolution towards the edges of the image on each side of the area of acceptable focus has not been changed.

But note that the degree of vignetting that occurs when the lens is fully tilted is massive.  I need to re-run this test, adding an upward shift to see if the vignetting can be eliminated.  This where a tilt and shift lens should score over a lens that only offers a tilt facility.



Full tilt, zero shift, maximum aperture: 1/125 f/3.5
[C472-16]
It is of course in any case not normal to shoot “still-life” or close-up pictures at full aperture – or most other pictures, either, unless differential focus is important.  Here I have stopped down the lens to a more normal aperture for such a subject.  This has, as expected, sharpened up the image across the full width of the frame, and has of course likewise extended the zone of acceptable focus further back (and further forward, though that was not needed), bringing the rear-most coins into acceptably sharp focus.  This sharpening of the edges of the image and increase in depth of field at smaller apertures is of course a normal feature of all lenses.  As is to be expected, the smaller aperture has also sharpened up the boundary of the vignetted area.

As a result of running these tests, I would recommend using the magnifier head (scroll down) on the camera, or the angle finder on the prism, as both of these give a magnified image than facilitates the evaluation of the area of sharpest focus.  I do not recommend the use of the “focussing telescope” (scroll down) for use with tilt lenses, as it only magnifies the central area of the image.



Full tilt, zero shift, smaller aperture: ¼ sec f/16
[C472-17/18]

 

The quality achievable can be appreciated in this larger version of the final picture in the series, which has been rotated slightly.
With a natural crop that suits the composition, the vignetting disappears.

 

Full tilt, zero shift 8 sec and a slightly larger aperture: f/11
Again, a crop appropriate to the subject matter has eliminated the vignetting completely.  I clearly need to focus further back when using the tilt feature, or to adjust the tilt angle more accurately.
[C472-13]

To go back to the section on Other Accessories, click here.

To go on to the next section, click below.
Next section (Introduction to Macro photography)

To go back to the beginning of the lens data section, click here.

To go on to Schneider macro lenses, click below.
Macro lenses

To go back to the beginning of the lens tests, click below and then choose the focal length that you want to read about.
Back to beginning of lens tests

Home

© TRA September 2009
Latest revision: February 2017