Full frame demands inclined planes

After just a short while working with full frame, high resolution DSLRs the need for tilt lenses has really come home to me. Most lenses deliver their best results at fairly wide apertures like f8, it’s easy for detail to begin to look soft and lacking impact if you are forced to stop down to f22 to get everything sharp. Tilt adaptors and tilt lenses solve the problem.

Most dedicated tilt lenses are also shift lenses. The PC-E Nikkor and TS-E Canon designs have a rising or cross front for architectural correction, and a tilt action for Scheimpflug plane of focus adjustment. Both come from the factory with the axes of these movements crossed, which is not how they are best used in real life. When ordering a Nikon lens, you can ask to have it modified so the tilt is in the same direction as the shift. One type, the Hartblei Super Rotator series, allows tilt and shift to be freely aligned to each other and the whole to be rotated relative to the image area.

Here is an acutely-angled studio view without tilt, taken on the Nikon DX3 with 45mm PC-E Nikkor f2.8 lens, shown above, at f11:

If you click to open full size 24 megapixel image and view it at 100%, you’ll quickly see that the zone of truly sharp focus is minimal. The Elinchrom BXRi flash units used are at minimum power, and it would be possible to get down to f22 or f32 with no problems, but the sharpness of detail would suffer and unwanted details in other zones of the image would be rendered as sharp as the subject plane.

Here is the same image taken with maximum tilt of 8 degrees, and a near-optimum aperture of f11:

But how would the owner of a Sony Alpha 900 cope with this problem? The system has no tilt-shift lenses at all, and no-one makes independent 24-28/45-50/85-90mm (the usual range) perspective control designs in the Alpha mount.

The answer, though not a complete solution, is to buy a Ukrainian tilt adaptor by ARAX or a similar supplier, and a Pentacon fit lens. Here is a vintage 50mm f4 CZ Jena Flektogon lens mounted on an ARAX tilt adaptor to the Alpha 900:

This lens certainly has the sharpness needed, but it is an early non-multicoated version (costing £100 s/h) and I may after trying it go for a later MkII black knurled grip multicoated design, as this lens does create a sensor reflection you can just see in the resulting image:

You will see it more easily in the full size file, just click to open; it is a patch to the right of the instrument’s nut (the instrument is a Canarian timple, a Canary Island relative of the ukulele). The overall focus is slightly different, despite a similar 8 degree tilt, as judging the focus and tilt angle on the focusing screens of these DSLRs is next to impossible for reasons we explain in this article.

A truly wide set of focus points with manual focus confirmation, selectable, or the use of Live View (not provided on the Alpha 900) could make fine tuning focus and tilt less of a hit and miss visual operation. Even so, study the images; the Pentacon lens has much lower contrast and warmer colour, and its lack of a lens shade probably allowed it to pick up too much light from the directly facing 60cm Elinchrom soft box. But it’s pretty sharp where the focus plane lies.

Outdoors, a fox had got some of our chickens, and made a very neat job of dining on chicken breast. I decided to test both the lenses at f8, an even better aperture for theoretical performance. If you don’t like such graphic documentary photography, abandon ship now, but it’s well worth studying these full size to see just how sharp the Pentacon rig is (the total cost was £240 including the tilt adaptor, compared to just under £1,000 for the Nikon lens).

Here’s the Nikon result, which did appear to be sharp right to the wings on-screen, but turns out to be a little closer focused:

This was at the minimum height of my Slik tripod, so the Sony result with the slightly longer 50mm lens is a tighter crop. It was interesting to note that the PC-E Nikkor, when tilted, darkens significantly to one end of the frame and the focus zone shifts along with image position, calling for tripod head adjustments. The ARAX tilt with 50mm Pentacon causes no image position shift or main focus point shift, or indeed any darkening. To get equal ‘centre field’ imaging from the Nikon, the factory modification to allow shift in the same direction is needed. Then you can restore the optical axis to aim at the centre of the sensor.

Here is the Sony result at f8:

The Sony needed 1/4 second exposure, compared to the Nikon’s 1/8, but as my other tests so far have shown, the Nikon is about 1/3rd stop faster in true ISO speed when set to the same nominal ISO 100. The Pentacon lens displayed fairly unequal divisions between f-stops anyway, and probably has a light transmission inferior to the Nikkor.

All these images are in-camera JPEGs, so not the theoretical optimum. The Sony has been criticised for poor in-camera JPEGs, but this mainly applies to high ISO results. I think that at ISO 100 there’s nothing to choose between the JPEGs, but the Nikon files are slightly larger indicating they are of higher quality and with more detail. I have resaved all files here to Level 10 CS4 quality for pBase storage.

While a 50mm lens is pretty good for general and studio work with tilt, both longer and shorter options are desirable. Nikon and Canon both offer them. Longer Pentacon lenses can be fitted to the ARAX tilt adaptor, and I have one Kiev ARSAT 80mm f2.8 which is nothing like as good as the Pentacon. Nothing shorter than the Pentacon is available except the Arsenal factory 45mm f3.5 (much inferior) and 30mm fisheye (an interesting idea); several longer lenses including 120mm and 150mm can be found from both the old Pentacon line-up and the later Kiev designs. I also have an ARAX type shift adaptor, but in practice you rarely need a medium or long focal length with shift, the optimum is probably a 24-28mm, and no optic exists which I can fit into the adaptor.

The only conclusions drawn here are that Sony needs to match Nikon and Canon, and make dedicated TS/PC lenses for the Alpha system; that the Ukrainian adaptor works pretty well, for any popular SLR mount including Nikon and Canon; that Live View with magnified local focusing could really transform tilt-lens adjustment accuracy; and that some older medium format lenses can definitely deliver on full frame DSLR.

And the chickens need to caged, as they now are of course, until we catch that fox!

– David Kilpatrick FBIPP Hon FMPA

3 thoughts on “Full frame demands inclined planes

  1. Pingback: Canon EOS 5D MkII, Nikon D3X, and Sony Alpha 900 compared | dPhotoexpert

  2. Frank, I don’t think Nikon will chicken out of the battle with Sony. Right now, you get what you pay for. The Sony A900 pitches real exposures much darker in raw than the Nikon in order – as far as I can tell – to allow Apical’s DRO Advanced IRIDIX chip to do its work. This results in much more noise, but gives them a chance to slope the highlights into a very gentle shoulder curve. And it leaves Nikon, despite their non-IRIDIX based D-Lighting, ahead of the field for noise levels.