Thanks for the additional info guys! As promised a little
review of my experience with the Tokina 11-20mm so far! (I'm working with a Nikon DX camera, so this is roughly 16-30mm range for a full frame camera).
A first pleasant surprise: the
box in which the lens came states that it's an
aspherical lens! Hadn't read that in any of the reviews or online specs, but aspherical lenses are supposed to be perfect for photogrammetry so that's great.
Secondly:
ultra-wide really does mean
ultra f*cking wide. I guess I theoretically "knew" that the angle was going to be very wide, but I didn't really grasp just how wide until I took my first pictures. You can literally photograph another person standing at arms length and have their entire body in that single shot, with plenty of ground and sky left along the edges. My first tests were on a square with a church, and I could easily capture the entire opposite side of the square with a single picture, whereas with my regular 35mm 'wide' angle lens I'd need at least 8 pictures (4 along the width of the square + a second row of pictures above that to get all of the facades).
In terms of
handling: the lens feels very sturdy, the zoom ring is quite "resistant to change", so you don't have to worry about it moving in our out without you actually meaning to do so, and the auto focus is fast and accurate.
Picture quality looks great (here's a
landscape shot I did, edited in DxO), the wide aperture allows for good shooting in low light and at F11 the images look sharp from corner to corner.
So my
first photogrammetry tests were on a city square with a church: I first recorded a statue and the bottom of a tree there. I then decided to push my luck and record a tunnel by just aiming the camera in the same direction as the direction of the tunnel (not the walls of the tunnel) and hope that because the view angle is so wide the entire thing would align. Finally I made some shots of the church on the same square. The images were a mix of 11mm, 16mm and 20mm. Total number of images: 173.
For my PhotoScan tests I decided to just align all images together, and wonderfully they aligned all at once, even though I made no attempt to make a good photogrammetry transition between the statue and tree on one side of the square, and the church at the other end of the square. Camera locations shown
here. The tunnel is the only part of the scene for which I built the
dense cloud in PhotoScan. I was really impressed that the
images of the tunnel aligned without problem, considering that none of the surfaces (walls / ground / ceiling) of the tunnel were ever in the middle of the pictures but only at the edges. The dense cloud shows the general shape nicely, and of course the resulting mesh has quite a lot of noise (since all pixels were captured at a very oblique angle, at the edge of the field of view of each picture) but as I said this was just an alignment test so that's fine.
In order to test what kind of quality you can get when the camera is actually angled perpendicular to the surface being recorded I also took 81 pictures of a house. The house is in a relatively narrow street but with the wide angle I had no problem getting the entire building in a single shot from across the street. Again
all images aligned without a problem and the resulting
dense cloud looks good. If we look at the
mesh it's clear the area of interest on which the cameras were oriented is cleanly reconstructed (with the exception of the windows because of glass) - a very large area around the area of interest is also reconstructed but this contains more noise.
So conclusion: I think the Tokina 11-20mm F2.8 AT-X PRO DX lens is a great price / quality purchase for photogrammetrists! The software didn't have any problem aligning the images even when taken at the widest 11mm and the wide angle allows you to significantly reduce the amount of pictures needed to completely record large or cramped spaces.
The only downsides compared to my regular
Nikon 35mm prime is that the Tokina is significantly heavier (you definitely can't shoot from just the wrist, you need two hands; that's all right for a couple of pictures but if you're taking thousands of a pictures in a day I can imagine your arm getting tired). You also have to remind yourself that even though an area at the edge of the field of view might be reconstructed, you also have to take images of that surface with the camera oriented perpendicular to the surface (nadir) in order to avoid surface noise. Finally the Tokina captures a lot of the scene in a single shot, but those pixels still have to share the same sensor space (in my case 24MP), so you can't expect the same mesh detail from 20 ultra-wide pictures as you'd be able to get with 160 less-wide closer up images of the same scene taken with another lens.
I hope this little "review" is helpful to someone - might write a more scientific review once I have some more time!
Topic: Ultra wide lens choice (Read 9972 times)
