With digital SLRs it has become very easy to combine or stitch multiple pictures together to create high resolution images. For example, the picture below shows a composite image of the Conservatory of Flowers in San Francisco stitched together from three source images.
The three individual source files were taken with my Canon 5D mk II and are roughly 21 megapixels in size (5616 x 3744). However, they can be combined in software to create a 40 megapixel stitched image (7229 x 5623). Right now, the only way to get 40MP images without stitching is to buy a medium format digital camera like the Hasselblad H4D where a starter kit will run nearly $20K. Jack Dykinga, a well known large format photographer claims the quality achieved by this process is similar to that achieved with 4×5 film (Outdoor Photographer, Jan 09).
There are two main ways of stitching or combining multiple images to get a high resolution composite:
- Using a special panoramic head to rotate the camera and lens while taking multiple overlapping images
- Using a tilt shift lens and take several shots at different shift settings.
In this article, I’m going to discuss the second method, using a tilt shift lens, for making high resolution images.
What is a tilt shift lens?
A tilt-shift lens allows one to use camera movements typically only found in 4×5 (or larger) view cameras on a 35mm based (or medium format) based camera. There are two movements that can be made:
- Tilt the front of the lens. This allows the photograph to manipulate focus and is typically used in landscape images to make everything from a few feet to infinity in focus. The same technique can also be used to create selective focus and just have a narrow range of the image sharp.
- Shift the lens up/down (or left/right) relative to the film/sensor. This function is typically used in architecture to take pictures of buildings without having to point the camera upward. Basically you would point the camera at the horizon and then to get the building in the frame, shift the lens upward.
For stitching we are going to be relying on the shift function. The key to understanding the shift is to recognize that lenses often project an image circle that is larger than the sensor. By shifting you can move the sensor from the center of the image circle and capture a wider scene. The three images in Figure 2 were created by shifting the lens to the left, center, and right.
Both Nikon and Canon have an excellent set of tilt-shift lenses. With Nikon you can get the 24mm, 45mm, and 85mm lenses as well as an older 35mm PC (shift only). With Canon you have the option of 17mm, 24mm, 45mm, and 90mm. In my personal kit, I use the Canon 24mm TS/E II, Canon 45mm, and Nikon 85mm TS (with an adaptor).
Capturing Images for Stitching
Stitching with a tilt shift lens and DSLR is a very simple process:
- Zero all movements (shift/tilt on the lens). I list this as a first step because it’s very easy to forget settings used from previous pictures.
- Setup the camera on the tripod. For horizontal picture I set the camera vertically and shift left and right. For a vertical picture set the camera horizontally and shift up and down.
- Set the focus, exposure, and white balance manually.
- Take the center picture.
- Shift the lens all the way to the left (top) and expose.
- Shift the lens all the way to the right (bottom) and expose.
While at first this method seems a little complicated, with very little practice the entire process becomes very quite quick and taking the 3 exposures can be done in a matter of seconds.
Note that technically to avoid all parallax errors you should keep the lens fixed and move the back of the camera. You can do this by moving the camera in the ballhead clamp in the opposite direction of the lens shift. However, I’ve found this to be unneccessary as the software for compositing CS5 photomerge has never had any problems with the very small amount of parallax error introduced (even when there are close objects)
Post processing the Images
Post processing the images for stitching is very easy. I use the following steps:
- Import the images into Lightroom (or your prefered program).
- Adjust one image of the series for exposure, color, white balance, saturation, etc.
- Copy adjustments to other images.
- Send images to CS5 photomerge for stitching with the reposition only option.
Using CS5 photomerge should provide a file with three layers and masks to produce a final image. The stitching has always worked extremely well for me and I’ve never had to make adjustments to the masks. The entire stitching process takes about about a minute on my Mac Pro.
When I create composite images with a T/S lens I generally use one of the following two setups:
- Position the camera vertically with shift left/right which yields a horizontal image with roughly a 4:3 aspect ratio.
- Position the camera horizontally with shift up/down which yields a vertical iamge with roughly a 4:3 aspect ratio.
However, there are several alternative ways of shifting the lens to get different final dimensions. For example, you could set the camera horizontally and shift left and right to create a horizontal panorama with aspect ratio of 1:2.4 (similarly you could create a vertical panorama). Generally, I do not use tilt-shift lenses for making panoramas and prefer to use a dedicated pan head. The main reason is that the number of vertical pixels is small and edge performance often degrades on T/S lenses when shifted in the long dimension.
Advantages over stitching with Pan heads
Stitching with tilt-shift lenses provides a number of advantages over using a panorma head.
- Quick and easy capture. I make stitched images using both tilt-shift lenses and panorama heads. However the Tilt-shift approach is much faster in capture than pan heads as you don’t need to spend any time leveling the base or adjusting the nodal rail.
- No post processing glitches. Photomerge stitches images very quickly and I’ve never experienced any problems. In contrast, using a panorma head I sometimes struggle with issues such as distortion or registering common points between images.
- No extra equipment required. The tilt-shift lens is all you need. Admittedly tilt shift lenses are expensive and often cost more than a panoramic head.
- Rectilinear projection. Using tilt-shift preserves the rectilinear projection of the lens. Practically, this means that straight lines remain straight in the composite.
- Precise framing. You can achieve very precise framing with tilt-shift lenses as you can preview the final image by simply shifting the lens while looking through the viewfinder. This lets you compose with objects near the edge of the image and accurately set the amount of border space.
- Consistent image size. Because you are always making three images with a set amount of shift, the final composite comes out with a very consistent image size. This is very important for a photographer that sells stock or fine art prints and who wants to have identical sizes for their images.
- Can use tilts. With tilt shift lenses you can apply tilt for a near-far composition and then use shift for stitching. The image of the Conservatory of Flowers used tilt to ensure that both the flowers and building were in focus.
- Limited lens selection. With a pan head you can use any lens in your kit including zooms. With tilt/shift you are limited to three or four (nikon has 24,45,85 ts, canon has 17,24,45,90)
- Price. Tilt/Shift lenses are expensive and run from $1000 to $2000 USD each. Some inexpensive pan heads can be just a few hundred dollars and it’s even possible to make your own head with a little ingenuity.
- Less flexibility in image dimensions. With a tilt-shift lens you are limited to only a handful of image dimensions (without cropping). with a regular pan-head you are essentially limited only by how many pictures you want to take.
- Image Quality. There are two factors that can lead to increased image quality with a pan head. First, with a pan head you can make composite images from any number of pictures. So far example, instead of using a 45mm TS lens with three pictures you could use a pan head, 90mm lens and take 12 images to cover the same scene. Second, with a T/S lens you may be using more pixels at the extreme edge of the image circle projected by the lens. Naturally, this will result in an image that is less sharp and with more chromatic abberation compared to using the center of the image. To some extent this is mitigated by the fact that the T/S lenses are all very high quality and stopping down improves performance.
Stitching with tilt-shift lenses has become a core part of my image making process for two reasons. First stitching delivers image quality that rivals pictures from digital medium format cameras costing tens of thousands of dollars and may even match 4×5 film quality. Second, stitching with tilt-shift lenses is extremely convenient and fast both in terms of the image capture and the post-processing required. In the field, I simply set the exposure and focus manually, and then shoot off three images in quick succession. In post-processing, I combine the files with CS5’s photomerge and it works beautifully to produce a perfect stitch with no intervention or manual inputs required.
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