There are occasions where 2000 lines in a capture aren’t enough. Large repro sizes where we need to render fine detail are common targets where the 2000 lines in the T2 chip won’t do. What are our choices? Always, there is film, which we should never forget. While it is time consuming and difficult to accurately measure, it does work. There is another alternative that may work for the occasional large repro. Taking the line scan idea, where the chip makes successive captures which are assembled to make a large image, you can make more than one capture with the T2 and hand assemble the captures in Photoshop.
There are two keys to the tiling process, consistency of the 3 pass strobe exposures and the need for the lens to remain stationary while the chip moves in an overlapping motion with respect to the proportion of the repro proportion. We are assuming that the capture is a three dimensional reflectance (two dimensional reflectances are far more tolerant of different lens perspectives when multiple captures are “stitched” together to form a single, unified image). Tiling three dimensional reflectances requires the flexibility of a modular view camera, which can allow the chip to move and leave the lens stationary. The chip needs to slide along the image plane, making sure the lens to image plane distance does not change. If your tiles can occur with no swings or tilts, any view camera with vertical and horizontal displacements will work. If the image calls for a swing or a tilt on the rear standard, you’ll need specific design in the construction of you camera’s rear standard. For upper and lower chip positions (a vertical tile), a base tilt camera provides the ability to facilitate a tilt and make the vertical displacement accurately along the image plane. For laterally displaced chip positions (a horizontal tile), a camera whose shift is built above the swing will allow the swing movement in the image tiling process and still move along the image plane.
Plan your tiles by considering how many tiles you need for the final repro size. Consider the efficacy of Photoshop’s extrapolation process (see topic on Enlarging your Images), if you can interpolate successfully, do it. Don’t make the tiling process any more involved than you need to, unless you are interested in exploring the limits of your view camera. From your lens you will need an image circle that will contain the number of tiles you’ve decided upon. You’ll probably want to use standard 4X5 focal lengths when choosing lenses. The T2 chip is 31 millimeters square and the 4X5 image is for practical purposes 90 X 120 millimeters (that’s the 9x12 size you see on European groundglasses). That allows a maximum of three tiles along the shorter axis and 4 tiles on the longer axis, if your camera and the movements you’ve chosen will allow that many tiles. Practice making a few composite images from multiple tiles. The technique can come in handy on those occasions where you need a little extra file size.
For an experiment, shoot two overlapping images. Try to overlap in an area where it’s easy to see that you’ve overlapped perfectly, tangent and spherical reflectances work well. Printed type is particularly good. Save the two files, labeled A and B or 1 and 2. Open both in Photoshop. Crop out the black mask at the edges of the T2 captures. Choose one of the images and extend its length with an Image>Canvas Size command. Double the dimension in the direction you’re interested in adding to. Copy the second file to ram by choosing Command+C and paste the image into the extended canvas area of the first image. Use Photoshop’s move tool to drag the second image toward its proper location. Zoom in enough to see what’s happening at the pixel level where you can use the arrow keys on your keyboard to move the image one pixel at a time. This is where preplanning the overlap area can be useful. Once you’ve got the images properly placed, flatten the image, perform any final cropping, and save it as a new, larger file. Don’t forget to change the name to avoid overwriting one of the tile captures.