SL metering with adapted lenses

[ramarren]

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I've been using almost exclusively R lenses on the SL since I brought it home, and did my share of lens tests with them. What I find is that, when you're using adapted lenses, metering accuracy and range limits come into play when the lens is stopped down to f/8 and smaller openings (sometimes earlier in relatively dimly lit circumstances). It affects straight Manual metering at fixed ISO settings, Manual metering using AutoISO, Aperture priority metering at fixed ISO settings, and Aperture priority metering using AutoISO a little differently; in other words, all modes of both metering mode and ISO operation are affected and need to be tested so you can predict how the meter is going to affect your exposures reliably. I found this doing lens quick-tests when stepping through the range of lens openings in the various exposure modes. 

 

The only way to get reliably even exposures at all lens openings in the same light with, say, an f/1.4 to f/16 lens opening range is to set the camera to Manual exposure, meter for anywhere between f/1.4 and f/5.6, and use those settings as a basis to set the correct exposure time for each lens opening manually. 

This behavior is absent when using the SL's native 24-90mm lens—all automation modes and manual metering produce perfectly consistent results until scene illumination and exposure settings drop to a much lower level and you truly fall off the metering range. 

BTW, this is no different from what I've found with adapted manual lenses on FourThirds SLR, Micro-FourThirds (both Olympus and Panasonic), and Sony A7 cameras. Each of them has its quirks with respect to metering behavior using non-dedicated lenses. 

By and large, in my usual picture taking where I'm usually setting from wide open down to f/5.6 or f/8 lens opening, Auto ISO with a range up to 3200, in modest to normal light, these metering issues rarely affect the exposures I get. It's when I'm stopping down more and/or the light has fallen off a bit that I find the need to take more care about metering properly and setting the right exposure with R or M lenses. 

 

​Has anyone else seen this in their testing and photos so far? 

[masquar]

Yes, I have experimented exactly the same and I did it since I was using my R lenses with the Canon 5D II. It also happened with the M240 (although much less than the Canon thanks to the EVF) and it happens also now with the SL. I'm afraid it's a price we have to pay because of the absence of auto diaphragm/full aperture metering :-(

 

Cheers

Massimo

[Jared]

It is just possible that when the R to T adapter comes out late this year that it will have auto aperture stop down with R lenses, so this problem will go away. I hope that's the reason for the long wait on that adapter--takes it from a simple mechanical adapter to something with a motor and various electrical contacts. If so, that would be great--and probably expensive. In the meanwhile, metering accuracy will necessarily be poor when stopped down under all but the brightest conditions.

 

- Jared

[ramarren]

It is just possible that when the R to T adapter comes out late this year that it will have auto aperture stop down with R lenses, so this problem will go away. I hope that's the reason for the long wait on that adapter--takes it from a simple mechanical adapter to something with a motor and various electrical contacts. If so, that would be great--and probably expensive. In the meanwhile, metering accuracy will necessarily be poor when stopped down under all but the brightest conditions.

 

 

Indeed, that's what I'm hoping for as well. I suspect there are some interesting technical challenges involved in creating an adapter of this capability. 

[scott kirkpatrick]

I was curious about the range over which I could meter accurately with my SL. So I set it up on a tripod looking at a dimly lit wall with its 35-70 zoom at 70 mm focal length and ISO 800.  The exposure was 4 sec at f/22, and it increased in even steps all the way up to f/5.6, with a half-step up to f/4 (some vignetting, perhaps?).  My old Gossen meter says that this is EV = 7.  Sunny 16 is EV = 18 at that ISO, so the range that can be metered is pretty impressive.  If you set it up to be a meter, of course.  I had turned stop-down simulation on for this experiment, which I believe means that the camera integrated for 4 seconds at f/22 to give me its reading.  The histogram showed a stable distribution of illumination at each f stop that I tested.

 

scott 

[Jared]

Actually, it probably wasn't integrating for four seconds as that would make the viewfinder virtually unusable if you weren't on a tripod. Likely it just pushes up the gain well above the set ISO value to give an "equivalent" view.

[ramarren]

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In aperture simulation mode, it closes down the aperture for a dedicated lens and pushes up the brightness of the display to compensate. 

 

In exposure simulation mode, it closes down the aperture then integrates the exposure for the metered exposure time or set time in manual mode. 

 

With adapted lenses, only exposure simulation mode provides useful,information, of course. 

[scott kirkpatrick]

Well, in the test I described, I was using a tripod, to keep the field of view constant as I moved the light level down.  But can one of you give a simple explanation of the difference between aperture simulation and exposure simulation when I have a lens with non-camera-controlled aperture on an adapter -- e.g. all the M and R lenses?  And what settings get you there?  I just set something in the "settings" menu long ago, and so now the histogram shifts when I half press the shutter, giving me a clue that I am going to be underexposed.  Or not.

 

scott

[scott kirkpatrick]

adding to the above.  The only setting that i have made is "exposure preview -- ON."  I'll look in the FM to see what it says about exposure and aperture simulation, but I do not expect enlightenment.

 

Also with several lenses I see the same pattern.  The shutter speed changes by a factor of two with each one stop change of the aperture except when I open up fully to the limiting aperture.  Then I get only a half stop change in the shutter speed. 

 

scott

[ramarren]

The EXPOSURE PREVIEW setting controls whether the viewfinder brightness is regulated to track the set ambient exposure when you half-press the shutter release. You normally leave it ON and on the half-press, it engages aperture simulation so you can see what the aperture setting does to the image before making the exposure. You turn it OFF for when you're using studio flash as the main light, because then the exposure will be gated by the flash units power settings. 

 

The FN button's commands cycle between normal display mode, aperture simulation, and exposure simulation by doing a short press on the FN button in sequence. 

 

• Normal display mode keeps the LCD/EVF bright and constant, without tracking exposure settings. 
• Aperture simulation mode is for use with the SL dedicated lenses. It forces the diaphragm to the taking aperture setting, doing what EXPOSURE PREVIEW does on the shutter half press, but persistent throughout focusing and framing. A green F with a dittie appears next to the aperture number in the viewfinder when it is enabled. It does nothing with adapted, manual lenses that the camera has no control over.
• Exposure simulation mode adds exposure time to the aperture simulation. A green S with a dittie appears next to the shutter time when it is enabled. It faithfully reproduces the actual exposure in the LCD/EVF, collecting light through the full exposure setting. 

Both simulation modes reset after an exposure or exposure mode change (A to M or M to A when using manual lenses). 

 

The live histogram always displays the exposure analysis as displayed in the viewfinder/EVF. This is important to remember: it is only truly accurate when the camera is in exposure simulation mode. It's "close enough" in normal and aperture mode if the light and settings used are above the metering range limit thresholds, but it cannot display the actual histogram once the metering has gone out of range due to the SL keeping the viewfinder bright for focusing and framing. 

[Jared]

As far as why your shutter speed is shifting full stops for each aperture except in the last clicks to the "wide open" setting... It's just that lens vignetting wide open on many lenses is so strong vs. one stop down that the light meter is adding extra exposure time to compensate and get a better overall exposure. Try spot metering near the middle of the frame and you should see this effect go away since the middle of the frame has no vignetting. Of course, metering for the middle of the frame is not generally a good way to pick an overall exposure, so just do this as a test, not a general practice.

 

- Jared