E-M1 II / Panasonic 100-400 aperture randomly stops down in shutter priority

[wjiang]

I've been shooting with the E-M1 Mk II and Panasonic 100-400 for a little over a month now.

Something odd I've noticed is that while panning around at 400mm in Shutter priority with Auto-ISO enabled, the camera will randomly stop the lens down from f/6.3 wide open to f/7.1 to establish the metered exposure. While I would expect this behaviour at base ISO, this happens even with the ISO up in the thousands - instead of just dropping ISO, sometimes the aperture stops down to f/7.1 instead.

I've not noticed this behaviour with any other lens, including the 100-300 II. Has anybody else experienced this?

 

[wjiang]

real odd. Have you tried increasing the max ISO to see if it still happens?

That sounds like a firmware bug. Lens and body are both up-to-date, I expect?

Yip, all up-to-date. I'm only at ISO1600 or so, so I don't think raising maximum ISO matters (mine is set to 6400).

 

[User ID]

Sounds like nothing is really happening
exposure-wise. I'd guess that the body
is trying to read Panasonic signals via its
Olympus reader and it's just coming up
with f/6.7 ... as a slight read error. What
you see is merely the readout switching
back and forth from 6.3 to 7.1 as its way
of expressing f/6.7 as best it can.

I use a few lenses that do the same thing,
and only at max aperture. Also the exif of
the max aperture will read slightly oddly,
"f/1.6953125" instead of simply "f/1.7".

I've learned to not get fussy over details
like that.

 

[wjiang]

Doesn't make much sense since it's the body that tells the lens to go to a specific aperture, not the other way around...

 

[User ID]

Doesn't make much sense since it's the body that tells the
lens to go to a specific aperture, not the other way around...

No. The body never "tells the lens to go to a specific
aperture". The body only tells the lens to open up or
close down until the meter is satisfied. The body never
"thinks" that "f/6.7 is correct right now". The body only
"thinks" stuff like "OK, just enuf, not too much". The
numeric readouts are the user interface, nothing more.

 

[wjiang]

For automatic lenses in stills mode, the initial focussing and metering is typically done wide open (for focussing), and the body tells the lens to stop down to the desired setting for final capture.

I know this because I used to use a front mount C-180 teleconverter with the 45mm f/1.8. The exit pupil of the TC is slightly smaller than the front element of the 45mm, but thanks to the increase in focal length by 1.7x, rather than causing mechanical vignetting it actually limited the effective aperture of the combination to give an f/stop of about f/2.5.

The effect was that, between f/1.8 and f/2.5 set in camera, DoF and bokeh would not change with the TC mounted. With exposure metered at f/1.8 and set manually, no change in actual exposure occurs when you stop down by 1EV to f/2.5, even though the meter now thinks you're 1EV underexposed. In aperture priority, if you stop down, it would consistently overexpose, metering wide open thinking it was f/1.8, when in fact it was 1EV darker. If you then set the aperture to f/2.5, it would boost ISO or drop shutter speed by 1EV to compensate, when in reality f/2.5 was the effective aperture, thus overexposing by 1EV.

Based on that, I can only conclude that the body has no clue what the actual aperture on the lens is other than what the lens tells it. I also conclude that it performs exposure calculations for stopping down based on what is reported by the lens. Even if it's the body that tells the lens to stop down further (differential rather than absolute set point), it must be doing it off the reported lens data.

 

[RAH]

the camera will randomly stop the lens down from f/6.3 wide open to f/7.1 to establish the metered exposure. While I would expect this behaviour at base ISO, this happens even with the ISO up in the thousands - instead of just dropping ISO, sometimes the aperture stops down to f/7.1 instead.

This does seem a little odd, but when you have Auto-ISO AND shutter priority, it seems to me you are telling the camera to adjust one (ISO or aperture) to achieve the correct exposure.

So is there anything in the specs that says it will always drop the ISO to correct an over-exposure? I guess the answer is obvious (it uses either one) because of what you are asking about, but it doesn't seem all that unexpected to me.

Back in the early days when I used Program mode, which gives it leeway to adjust either aperture or shutter, it was hard to predict which one it would use, and, if I remember correctly, the exposure compensation dial could be used to adjust which one it used (I think; maybe this is on Canon).

So, in other words, unless it is stated in the specs, I think it is to be expected that when you give it TWO options (ISO and/or aperture) to adjust, there's no telling what you'll get. Myself, if you are determined to use shutter priority, I'd use a fixed ISO and just let it adjust the aperture as needed.

I suppose you are using Auto-ISO together with shutter priority in order to guard against reaching the limits of your lens' aperture (and therefore get a bad exposure), and I agree that this is prudent, but I think you are stuck with sometimes getting the ISO adjusted instead of the aperture. To me, this is a good reason to use aperture priority instead (just about always).

 

[wjiang]

I'm actually trying to ensure a fast enough shutter speed to avoid major motion blur for moving subjects, while keeping the ISO as low as is possible - I don't mind using the lens wide open as an ever slightly less sharp picture is better than one ruined due to unintentional motion blur.

I've mostly worked around it out in the open field - I just use full manual in that case. When there is partial shade it's tricky, that's where I end up using shutter priority in the manner I've described since there is not necessarily enough time to establish a manual exposure where a bit of action ends up occurring.

 

[RAH]

Yes, I understand that that is the primary reason someone would use shutter priority. But consider - using aperture priority, if you open your lens as wide as you deem prudent, the camera will ALWAYS give you the fastest shutter speed that gives a good exposure (at a given ISO).

This is the secret to using aperture priority - you ALWAYS get the fastest shutter speed (for a given aperture and ISO). In this case, open the lens as wide as possible, set your ISO as high as you dare, and use aperture priority - you will get the fastest shutter speed. Trying to FORCE a faster shutter speed via shutter priority will not yield anything faster and still get a good exposure.

 

[hoodlum]

You could try using aperture priority at f5.6 and then set a minimum shutter speed. I prefer this over shutter priority as good lighting will force the shutter speed to increase instead of changing the aperture. I do all of my birding in aperture priority with a minimum shutter sped

 

[RAH]

I know that some photographers prefer to use shutter priority for wildlife, where they set the shutter speed to what they want, and then rely on Auto-ISO to protect them against under-exposure when the lens inevitably is unable to open wide enough to get a good exposure. This is OK as a method, IMHO.

The danger in this approach is that you can wind up getting a really high ISO. You can set the ISO to some maximum, but then you run the risk of under-exposure again.

With aperture priority, you always get the appropriate and fastest shutter speed possible for the aperture and ISO you set, and essentially NEVER run the risk of an incorrect exposure.

The danger with that is that you might not notice when your shutter speeds have gone down too low because of dark conditions (meaning you'll need to boost your ISO or open your aperture if possible). But the way around this, of course, is to start with the highest ISO you can stand and a wide-open aperture. Then there is no worry - whatever shutter speed you get is the fastest it can be for those conditions.

 

[hoodlum]

The danger with that is that you might not notice when your shutter speeds have gone down too low because of dark conditions (meaning you'll need to boost your ISO or open your aperture if possible). But the way around this, of course, is to start with the highest ISO you can stand and a wide-open aperture. Then there is no worry - whatever shutter speed you get is the fastest it can be for those conditions.

Why not just use Aperture priority with Auto ISO and set a minimum shutter speed. In really good light the shutter speed would then just increase even higher than the set minimum shutter speed, while in poor light the ISO would increase. I was asking for a minimum shutter speed in Aperture mode for many years before Olympus finally introduced it on the Mkii.

Previously I was always changing custom modes on the GH3 depending on lighting (I didn't even bother on my G1/GH2). But that was challenging when shooting smaller birds that went in and out of good light. Now I don't need to think about it while knowing the camera is choosing the best setting for the specific lighting situation.

 

[wjiang]

You could try using aperture priority at f5.6 and then set a minimum shutter speed. I prefer this over shutter priority as good lighting will force the shutter speed to increase instead of changing the aperture. I do all of my birding in aperture priority with a minimum shutter sped

Something to try I guess. It's quite slow to change minimum shutter speed via menu though - I switch between birds on the ground versus in-flight at a moments notice and these call for different minimum shutter speeds. It's relatively easy to switch using a dial but I'd probably totally miss the shot if I had to menu dig.

 

[ibd]

Why not just do full manual (desired shutter speed, wide open aperture) + auto ISO? That would fix the things you want fixed. If you're wondering about exposure comp., that will also work with auto ISO (maybe needs to be enabled in settings).

 

[RAH]

These are all interesting suggestions. I've never had a camera that had minimum shutter speed, so I'm not familiar with it, but it sounds very helpful, for sure, and opens up additional options, as mentioned. As far as manual mode, desired shutter speed and wide open aperture and auto-ISO, I think I've never had a camera that would do that either. It also sounds interesting, although very similar to using Aperture mode and setting the ISO yourself as needed. I just bought an E-M5III a few days ago, so maybe some of these advanced options are available on it...

 

[hoodlum]

Something to try I guess. It's quite slow to change minimum shutter speed via menu though - I switch between birds on the ground versus in-flight at a moments notice and these call for different minimum shutter speeds. It's relatively easy to switch using a dial but I'd probably totally miss the shot if I had to menu dig.

I guess you could use different custom modes to manage this. I haven't checked if this is possible but maybe you could assign a Fn button to the min shutter speed.

 

[wjiang]

Why not just do full manual (desired shutter speed, wide open aperture) + auto ISO? That would fix the things you want fixed. If you're wondering about exposure comp., that will also work with auto ISO (maybe needs to be enabled in settings).

Yeah, I do this already sometimes. I'm not sure why I don't use it exclusively - maybe it's just familiarity from my old E-M1 that could not do this...

In any case, as far as the lens stopping down by itself... I guess just something to be aware of.

 

[tiago.ereira]

I have no idea of what can be the cause of the problem but I have the same behavior with the m.zuiko 75-300. Even if the maximum aperture is 6.7, when in shutter priority and auto ISO, most of the times the camera sets the aperture to 7.1. This is specially annoying with these lenses because we are always working on the limit and every 1/3 of a stop matters.

I normally go manual (auto iso) to avoid that.