when using the Canon 15mm f/2.8 Fisheye on the Canon 5D Mark III in Autofocus and AI-Servo, the camera seems to deliberately slow down its maximum frame rate to 3fps instead of its potential 6fps.
I have tested numerous lenses incl. the cheapest and slowest plastic fantastic Canon 50mm f/1.8, which all work at the camera's maximum frame rate of 6fps. Only with the 15mm fisheye, the camera seems to restrict the frame rate.
Why is that? And how can I avoid this from happening? Is this a deliberate software restriction?
On other Canon cameras the 15mm Fisheye works at full speed.
I know the old fish is not the fastest and most reliable autofocus lens in Ai-Servo but for me it works most of the time, especially for underwater sports. Even if it misses, half the time you get something super quirky! 🙂
Don't know the answer but I'd guess AI servo has a hard time through the fish eye lens. I'd really like to see some samples of your underwater sports stuff though (diver here).
I had the same issue with my 40D, 7D and 5D Mk III. There is no way around it, and it should also happen with all other Canon cameras that shoot faster than about 4 fps. You probably just didn't notice it.
The slowdown in AI Servo is caused by Arc Form Drive AF lenses that autofocus and stop down the diaphragm sequentially rather than simultaneously. Newer lenses are designed to do this simultaneously and will give you the full 6 fps in AI Servo.
Chuck Westfall describes it here: Chuck Westfall - Digital Journalist (scroll down to the comments section)
Chuck Westfall −
Except for the EF80-200mm f/2.8L and EF20-35mm f/2.8L, all other EF lenses with AFD (Arc Form Drive) focusing motors were designed in such a way that autofocusing and diaphragm operation (via the Electromagnetic Diaphragm, or EMD for short) were carried out sequentially rather than simultaneously. This has no impact on continuous sequences in One-Shot AF, because no autofocusing occurs after the initial AF lock in this mode. But in AI Servo, both the focus and the diaphragm are operated for each photo, and consequently the camera's framing rate decreases.
For what it's worth, AFD motors were phased out of the EOS system for all new lenses introduced from 1990 onwards.
Best Regards--Chuck Westfall
Hey Mike, thanks for your reply. That makes sense.
Though, I can tell you that I have been shooting with this exact lens for the last few years with the Canon 1D3, 1D4 & 7D and all of those cameras shoot at their maximum FPS capabilities in Autofoucs + Ai-Servo, which is far beyond 3fps or even 6fps.
I have countless image sequences here that show that.
I haven't had a chance to try it on the 1Dx, but I'm sure it will shoot at its max fps with this combo too.
I suspect Dual Processor cameras make the difference here?
I also had the 7D and I can't remember if I ever tried 8 fps in AI Servo with an Arc Form Drive Lens. Is it possible you were in AI Focus instead of AI Servo?
I would be curious to see if the Dual Processor 1Dx works with AFD lenses. Chuck Westfall's answer was written in 2008 yet he doesn't mention the Dual Processor 1D Mk III camera which came out in 2007.
I've just double checked and pulled up a few "rapid fire" sequences in Lightroom to make sure I'm not tripping.
7D with 15mm Fisheye, Autofocus + Ai-Servo @ 7fps
1D4 with 15mm Fisheye, Autofocus + Ai-Servo @ 9fps
Imho it would be the dual processor that manages to shoot faster frame rates with that type of lenses.
Try stopping down the lens and switching to manual focus.
A fisheye even slightly stopped down will hardly need any focusing at all, thanks to depth of field. Unless you are working with extremely close objects, you can pretty much just use scale forusing, set it and forget it.
I don't know that this will increase frame rate... but wouldn't be surprised if it did.
Hi amfoto1, yes manual focus does work at 6fps but it doesn't work for me as I shoot in the water behind a dome port above and below the surface. Below the surface the lens needs to focus extremely close due to the virtual image.
If I go manual I can either set things up for either above- or underwater, which is quite annoying when you rely on doing both all the time.
Sounds like I'll be forced to buy the 8-15mm.
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