EM-1 MK1 High FPS question

[AdzeCO]

Just noticed an interesting behavior on high speed sequential shooting on my EM1 mk1, using my ft 50-200 non swd lens.

In saf, hfps, mechanical shutter, fps set to 10. I notice a different maximum fps depending on whether I am in aperture priority vs shutter priority. I A mode the max fps is noticably higher, while in S mode it slows down. This is under the same conditions and adjusting for equal aperture and shutter speed. I asked a prevjous question here on reduced fps for FT lenses and understand that.

What I don't get is why in A mode I could shoot at a higher rate than in S mode, which is where I may typically want that advantage. Behavior didn't change by using larger or smaller aperture. Anyone else notice this?

 

[barry]

Hi, what shutter speed was set?

 

[AdzeCO]

I tried it at varying shutter speeds and apertures. from 1/60 to 1/500 and from f2.8 to f16 or so. There are so many settings that it could be somehting I'not aw a re of. for instance the frame rate, and or the IS settings. Just seems odd to shoot in Av at a high rate and then switch to Sv and see a noticabke decrease in fps.

 

[alex g]

One thing that affects fps with 4/3 lenses is the aperture setting. If the lens is wide open, the fps will generally be higher than if it is stopped down. The iris mechanisms are slow by modern standards — closing and opening them again for each frame takes a significant amount of time.

Turning IS off will increase fps too, but that's something different, of course.

 

[AdzeCO]

True, but what is confusing is that the only real thing I'm changing is going fro aperture priority to shutter priority. Making the aperture or shutter speed equal across modes. Just seemed to be a behavior that I wasn't expecting.

 

[alex g]

I don't personally have a copy of the lens you're using, so I'm not in a position to test it unfortunately. It would be interesting to know if there is a difference in fps between the following two settings:

1. aperture priority mode, lens @ 50mm, f/4.0, ISO 400
2. aperture priority mode, lens @ 50mm, f/2.8, ISO 200

My guess is that there will be, because in the first case, the camera has to wait for the iris to operate before and after each frame, while in the second case it doesn't, because you've manually fixed the aperture wide open.

However, in shutter priority mode, the camera adjusts the aperture dynamically in response to changing light levels. My guess is that it makes more sense to include the iris actuation routine in the timing of every cycle of the burst, even when the computed target aperture value is equal to the maximum aperture of the lens. In theory, there's no need to change the iris setting under those circumstances, so in the interests of burst fps, it might be feasible to have the camera recognise "wide open" as a special case and thus speed up the cycle by skipping the iris actuations. A drawback of that scheme would be that the burst rate would no longer be constant — it would slow down whenever the aperture wasn't wide open, and my guess is that, on balance, a comparitively slow, constant speed burst is deemed preferable to one that changes speed erratically on an apparently arbitrary basis.

Total speculation on my part though, I hasten to add.

How are you measuring fps, btw? it might be useful to have some actual numbers.

 

[ijm5012]

One thing that affects fps with 4/3 lenses is the aperture setting. If the lens is wide open, the fps will generally be higher than if it is stopped down. The iris mechanisms are slow by modern standards — closing and opening them again for each frame takes a significant amount of time.

Turning IS off will increase fps too, but that's something different, of course.

In the OP, he said he's using S-AF, not C-AF. So, the lens will not refocus between frames, as it'll lock focus based on the first frame. What you describe is only applicable when using C-AF.

 

[alex g]

In the OP, he said he's using S-AF, not C-AF. So, the lens will not refocus between frames, as it'll lock focus based on the first frame. What you describe is only applicable when using C-AF.

It won't refocus, I agree, but the iris will still close and reopen for each frame — even with the focus and exposure locked — which seems to be enough to slow the burst rate down significantly. The only case where the iris is inactive is with the lens wide open in aperture priority mode, which boosts the fps. At least, that's what happens with the four 4/3 lenses I have. Perhaps the 50-200 non-SWD behaves differently, it's possible!

 

[Phocal]

I just messed around with this on my 150/2 and 50-200 SWD. With both lenses and using shutter priority the fps will drop even with a wide-open aperture. It behaves just like they do when stopped down in SAF or when in CAF. @alex g is probably pretty close to what is going on with the lens in shutter priority. Guess I never noticed it before because I hardly shoot in shutter priority and when I do I am using CAF (which slows them down also).