Naptown Gaijin wrote:
Because a tilt shift lens has a changeable focal length as projected on to the sensor, I do not see how a photographer can use it for precise photogrammetry. I used to take photos of objects for use by people who would analyze the photo forensuration, the measuring of an object by calculating focal length, distance to object, etc. You have probably seen crime photos where an object of known length is included in a photo, usually a ruler or yard stick. By analyzing the length of the yardstick, you can, within parameters evaluate the densions of an object of hitherto unknown size. I used a 50mm f1.4 lens for photos of vehicles, and we could tell the size of the vehicle within small tolerances. Don't see how you can do that with a tilt shift lens as you are adjusting it so that the side of the building look straight.
In other words, you are making it look good, not taking a photo than can be used for measurent or mapmaking or intelligence analysis. Zoom lenses have the same problem, in that the precise focal length is unknown, except when you are at either end, though they can be used for a close approximation when the photo is taken at either end of the zoom range. There is always some distortion in ANY lens, the difference is in degree. Space telecopes have less, cheap binoculars have more.... same with camera lenses. Thisay be one reason why pros carry a bunch of fixed lenses rather than one long zoom....less distortion, in addition other advantages.
The OP needs an accurate method of reording densions for an excavation project; itmcould be for a nuclear power plant containment vessel, who know? In such a case, I am confident a tilt shift lens would not be used when precise meaaurents are needed.
Because a tilt shift lens has a changeable focal l... (
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Maybe we are thinking of different scenarios.
There are certainly many types of photogrammetry and many different types of scenes to be measured, which ultimately may require different methods for optimal use, but if you've cleared an area and made it reasonably flat, having a flat, undistorted image would allow easy measurements.
For instance, if you placed a rectangular frame with a meter stick on each end and then shifted a TS-lens so that the meter sticks on each end of the frame filled the appropriate side of the camera frame, you'd have an undistorted image that would make measurements not only simpler, but trial. In addition, by applying the correct tilt to the lens, you'd have better focus of the area. No distortion, no out-of-focus parts of the image.