In the previous post, I used a torque gauge to measure the amount of torque generated on a camera and lens under windy conditions. From this, we then directly calculated the amount of tripod stiffness necessary to hold the camera steady. While this is great, it is still a theoretical calculation made after many borderline egregious approximations. We thus want to do a real world test of image sharpness and see how well those calculations correspond to reality. The root of science is in experiment and testing. We don’t want to stray too far down the theoretical rabbit hole without grounding ourselves in data for the actual thing we care about.
To make a real world test, I have chosen four tripods of varying stiffness to go along with the three different focal length lenses (45mm, 110mm, 250mm) used in the torque measurements of the previous post. The yaw stiffness’ of the four tripods are calculated below:
These four tripods were chosen primarily to provide a large spread in stiffness. Very roughly, there is about a factor of two in stiffness between each of the tripods with a total span of 14x between the highest and lowest stiffness. This is about the largest spread in stiffness I can get with the current equipment I have. The Gitzo could be made stiffer by not using it at full height, but its already not the limiting factor at that level of stiffness. The manner in which the Fuji GFX camera is mounted to the tripod, via a lens foot or the RRS L-bracket is less stiff than the tripod, so there is little point in going stiffer from there.
Next, lets bring in the results from the previous post. The second row of the table below, underneath each lens, shows the amount of tripod stiffness required based on the torque measurements to keep the camera and lens steady enough in the wind for sharp images. The second column is the tripod + head yaw stiffness. The body of the table is then the ratio of the tripod stiffness to the stiffness required for the camera and lens.
Where the tripod stiffness is more than sufficient, the table is color coded in green. Less than sufficient is in red. So, we should actually expect to achieve sharp images with any of the tripods when using the 45mm, and with none of them while using the 250mm.
To test the results of the above table, I took 10 images with each lens and tripod combination under the same wind conditions . Now, this isn’t really enough images to draw precise conclusions, but I wasn’t going to spend the time taking a hundred images at each setting. The lenses were set to F/16 and 1/30s shutter speed on the camera. This is by no means long exposure, but I forgot to bring an ND filter that day so it was the best I can do without stopping the lens down even further. The shutter is long enough though that a tripod is necessary to achieve sharp images (without image stabilization). Wind of course is also inconsistent, building and dying off in gusts. Now that I have gone into all the reasons why this test isn’t ideal, here are the results:
The table shows the percentage of shots that appeared to be sharp by my eye when viewing them at 100% on screen. Any one of the images that I considered sharp I would be happy to print to a reasonably large size. Since we are using the lenses at F/16, the definition of ‘sharp’ is somewhat relative since no image taken at F/16 is truly razor sharp. Motion blur causes a distinctive pattern and is fairly easy to distinguish between other sources of image softness. Naturally that is what I am screening for here.
The results certainly don’t perfectly match what we calculated in the second table. There are definitely discrepancies and I won’t go into discussing each and every one of them. More broadly, the wind is variable and lulls can result in sharp images even when we should get them. Most of the shots with the 250mm showed motion blur, as expected, and most of the 45mm shots were sharp, also as expected. I am surprised that only 6/10 of the shots with the 110mm were sharp when using the stiffest tripod. The Gitzo GT 5533LS should have been more than stiff enough to hold the camera steady. As suggested by CarVac in a comment to a previous post, I suspect that the answer is in the stiffness of the connection between camera and the L-bracket.
The stiffness tests account for the connection between the arca swiss plate and the clamp, but they don’t account for the connection between the plate and the camera. When using a tripod as stiff as the Gitzo GT 5533LS, it quickly becomes apparent that the weakest link is in fact this connection between the camera and the plate for the Fuji GFX 50S. I am using a RRS custom L bracket, so I don’t believe that the problem is with the bracket itself, but with the stiffness of the camera body.
This brings up an awkward dilemma. If the body of the camera is the limiting factor in stiffness, what is the point of acquiring a big, heavy, expensive, high performing tripod? There may not be a point. This only really applies for the largest, stiffest tripods. On the travel tripod end of the spectrum, the camera is by no means the limiting factor, and so every bit of stiffness is still useful. Of course, the stiffness of each camera body and lens foot will be different, placing different limitations on the maximum useful tripod stiffness. I am not going to attempt address this additional layer of complication for every camera, as I have neither the time nor funds for such an endeavor. I am sure that there are cameras out there with significantly stiffer frames. I just don’t know which ones they are or how to systematically test camera stiffness. Naturally this leads into an open call for camera manufacturers to build stiffer frames into their products. While we’re at it, lets wish for some built in Arca style dovetails.
Overall, this test has been a success. We are seeing a realistic correspondence between the measured torques on the camera and the amount of tripod stiffness required to keep the camera steady for sharp images. More testing is clearly going to be required to confirm this with different wind speeds, and hopefully different camera systems as well. I believe that some themes will remain constant though. Namely that tripods are not stable enough to support any kind of long exposure with long telephoto lenses in windy conditions. There is too much torque, optical magnification, and lack of stiffness from the lens foot. Ultimately, our goal will be a table showing approximately how much tripod is necessary for a given focal length and wind speed. We aren’t there yet.