Sunday, 15 July 2007

The Hartblei 45mm Super-Rotator (Part 2)


Following my first piece about this lens and how it came to be, I thought it would be a good idea to describe the situations in which you would use a lens like this and something about what it is like in use. Those who have previously used large format cameras will be well aware of the application of camera movements, but for those who are unfamiliar, this may help. The lens is able to shift (that is to move the lens axis either up or down or to one side or the other) and/or tilt (change the angle of the axis of the lens). More about camera/lens movements can be found here.

Tilt movements change the angle of the lens axis. This in turn changes the angle of the plane of sharp focus (as well as the planes defining the limits of depth of field). This can be used to keep objects that are at varied distances in focus, or as is common in much contemporary commercial photography, to throw parts of an image out of focus. This approach can also be seen in the image of the church interior near the bottom of this piece. The roof is completely out of focus. The tops of the pews are sharp from near to far. The floor at the bottom of the frame is un-sharp. Even on such a small reproduction the impact of this treatment is quite clear. It shows up much better in larger images. The same technique was also applied to the shot of Denham Village used in an earlier piece.

The shift movements would often be used to overcome problems of converging lines, as might be found when photographing tall buildings from ground level. Aim the camera up and the sides of the building taper in towards the top. Shift the lens up while keeping the camera level (pointing horizontally) and the sides of the building stay parallel.

Shift movements can also be used for stitching purposes (no sewing skills required). If you have sufficiently large shift movements you can capture several frames whilst keeping the camera facing in one direction. Unlike panoramic photography where the camera is rotated, these images don't require special software to combine them. Any image editing program that supports the use of layers (layer masks are also useful, but not essential) will do the job. Shift and tilt movements can easily be used together, but where stitching is concerned it is probably wise to avoid using tilt unless you really need it. Having said that, it could produce some interesting results. I will have to experiment. The result is often very large images and equally large files.

Main controls for shift and tilt movements

The first thing that you notice about this lens is that it is quite big and heavy. There is no plastic used in the making of this lens - well, none that I could see anyway. Metal rules here (heavy metal at that). The next thing that you notice is that it has a lot of knobs and levers. Working from the filter thread back to the lens mount, these are the controls (see image just above): Large focussing ring, aperture ring with two little "tabs" attached - makes finding the aperture ring by feel very easy. A ring marked in millimetres for the lens shift. A tab that unlocks the rotation of the shift movement. A knob sticking out that applies tilt. A locking slider to release the rotation of the tilt movement. Behind that on my lens is the adaptor, which has a knob that is rotated for the extra 11mm of shift. The rotation of this movement is not locked, but clicks into a number of pre-set positions.

The lens is a fully manual lens in every way. There are no connections with the camera beyond the lens mount itself. Most lenses allow you to set the aperture you want to use for the shot but leave the lens open while framing the shot for a brighter viewfinder image. Not this one. Open the aperture wide to compose and (manual) focus, and then close it down as required for the exposure and depth-of-field. In use the lens is a dream to use. When I first started using it I was struck by how much I felt in control of the image in a way that I had not experienced since I stopped using a 5"x 4" camera. Being able to control perspective and focus (as in Scheimpflug) is something that users of rigid-bodied cameras don't normally experience to the full. But one solution leads to another problem. Critical focussing on a focussing screen designed for auto-focus isn't easy. I decided I needed to magnify the viewfinder image. I already had an angle finder, but bought one with a built-in magnifier (as seen on the first image in this piece). The magnified image doesn't give full frame coverage, but is useful just at the time of focussing. This worked well enough outside in good light, but I then found that the magnified image was significantly darker, and in the studio I needed a tungsten focussing light, as the modelling lights on the flash were not bright enough. It is not uncommon to do this, but I had never found the need before.

How you approach each shot will depend on the subject matter, but I will run through how the office building shot that accompanies part 1 of this piece was taken. Taking several frames to get one image may seem tedious, but it can be achieved very quickly. When shooting the office building I was standing in the road (there was no footpath on that side) and was keen to get out of the way as soon as possible. I had set up the camera and taken the four shots required in less time that it would have taken to get the Sinar 5x4 out of it's case.

The tripod was set up, and the head levelled. The camera was set in portrait format (RRS or Kirk "L" brackets are a nice refinement here). As already mentioned, the lens has no connection with the camera, so aperture settings are made on the lens (nor is any EXIF data recorded for this lens). The camera doesn't even know that there is a lens attached. It only knows how much light is recorded by the meter. The aperture was opened up for focussing and to give a brighter image in the viewfinder. The exposure mode was set to "manual" which is where it normally is anyway on my camera.

Full upward shift of 11mm was applied to the adaptor (lets call it "back shift") Then full shift of 12mm was also applied to the lens (for the purposes now called "front shift"). All movements on the lens are independently rotatable, so the front shift direction could be changed to give four different images (top left, top right, bottom right and bottom left) that together would make one larger image. Before taking the shot I checked that at the four rotation positions I wanted to use I could see all of the building that I wanted to include. The aperture was then set as required for the correct exposure and depth of field and four shots taken (using an electronic shutter release - but self timer would do). The resulting image is similar to one taken with a much wider angle lens with a much higher resolution camera with 11mm of upward shift applied.

That's it. I got off the road and packed away. The images were converted from RAW in DXO (with any auto settings being overridden) and put together in Photoshop. I tried Photomerge in Photoshop CS3 (under the "File - Automate" menu) and although it is now much better than previous versions, I still found some inaccuracies. It was easier to do it myself. Some of the bottom of the image was then cropped off as I didn't feel the need to see so much tarmac.


Limitations: Limited to stationary subjects - beware trees on windy days. Best with full frame cameras, as you can get access to more of the lens' image circle. Also, judging tilt movements on smaller viewfinders is not easy. Even with the reasonably large and bright finder on an EOS 5D critical focusing and application of tilt movements is hard to judge (I once worked with a photographer who shot on 10"x 8" rather than 5"x 4" purely because he preferred using the larger ground glass screen). Canon's cropped frame cameras are not noted for bright viewfinders. I'm not sure how Nikon viewfinders compare, but I gather that they may be a bit brighter.

Non-limitations: Surprisingly, the lens works quite well hand-held. Using tilt hand-held is good fun, rather like (and at the same time totally different from) using a Lensbaby 3G. Try doing multi-frame stitching with a Lensbaby.

A separate piece will be put up soon dealing with overcoming the problems of internal reflections. There will be a before and after example to show the extent of the initial problem of light reflecting between the sensor and the adaptor.

Part 1
Part 3

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