Unexpected results when testing the X Vario light meter

[BAASCH]

Advertisement (gone after registration)

Having noticed that my (wonderful) new Vario tends to overexpose more often than I'm used to, I decided to test the camera's light meter using the Sunny/16 rule. Using a high quality 18 percent grey card in direct sunlight, I made a series of measurements that raise more questions than I myself can answer, so I'm hoping some of you may be able to help.

 

The idea is that the camera, using aperture priority, should pick a shutter speed equal to the ISO value. Instead, with spot metering, the shutter speeds are double the expected value:

• ISO 100 : 1/200
• ISO 200 : 1/400
• ISO 400 : 1/800
• etcetera

With centre-weighted metering the results are different (though they should be the same, having taken care to fill the frame with the grey card):

• ISO 100 : 1/160
• ISO 200 : 1/320
• ISO 400 : 1/640
• etcetera

Now to make things even more complicated, I found that in manual mode, the on screen exposure meter reads zero at a third set of values:

• ISO 100 : 1/125
• ISO 200 : 1/250
• ISO 400 : 1/500
• etcetera

With this final test, there was no difference between spot and centre-weighted metering, which presents us with yet another riddle...

 

Can anyone explain this? Or try to replicate these results with their Vario, just to rule out that I have a faulty item? Also, I'd welcome advice about adjusting exposure strategies in light (pun intended) of these irregularities. I use spot metering most of the time, and my thinking about exposure is largely in terms of Adams' Zones. 

Edited May 4, 2016 by Mandemaker

[pop]

First of all, Sunny16 is a rule of thumb which is not legally binding for digital cameras. It's certainly fine for photographing on film and it's perfectly good for an informed guess.

 

You say that your camera overexposes with respect to what you expect, given the Sunny16 rule. However, the exposure times you name indicate an underexposure by one f-stop. 1/200sec admits half as much light as 1/100sec.

 

The different values the camera arrives at between spot metering and center-weighted metering do not - in practice - matter much, being much less than a third of a stop. I have no idea as to the cause of the difference. When I do similar tests in my office, I see no difference in the metering results. However, I take great care not to change my position with respect to the light source and the grey card (which is the door of a cupboard in my case). Just moving by a few centimeters will result in a quite different reading.

 

I can't explain the difference you obtain between manual and automatic exposure, either, as I can not reliably reproduce it. Again, the position of my body with respect to the light source and the gray card has the largest influence.

 

On the whole, I'd think your X Vario performs perfectly well. When trying to apply the zone system, I think you'd to well to perform a few tests in order to determine how much light the sensor needs for rendering zone X.  That's IMO the most important thing to determine so as not to blow your highlights. That's commonly called ETTR, "Expose To The Right".

[Advertisement]

The Leica Q3 is available for pre-order at B&H Photo Video and Adorama

[BAASCH]

Thanks. Maybe I was unclear: I first noted too many shots were overexposed, when what I saw on the exposure meter while shooting made me expect differently, and then I decided to test the meter using the Sunny/16 rule. I think what happens is that the exposure meter displays values more or less consistently ⅔ stop lower than they should be, while the camera when in aperture priority mode does somehow choose the right shutter speed. In other words, the visible exposure meter 'undermeasures'. I find that if I try to read the meter bearing in mind that its reading is ⅔ stop too low, I get more predictable results.

 

By the way, ETTR is not a viable approach in full manual mode with this camera, because the histogram is then quite useless. Instead, measuring the brightest important part of the scene (now adding ⅔ stop) and placing it in the appropriate zone does work.

 

Incidentally, unless the cupboard catches direct sunlight and is painted exactly 18 percent grey, and very matte, the method you used does not seem reliable.

[pop]

Incidentally, unless the cupboard catches direct sunlight and is painted exactly 18 percent grey, and very matte, the method you used does not seem reliable.

The cupboard test was not designed to test the accuracy of the light meter within the camera. It was designed to test the light meter for consistency and it does exactly this.

[mikeodial]

Having noticed that my (wonderful) new Vario tends to overexpose more often than I'm used to, I decided to test the camera's light meter using the Sunny/16 rule. Using a high quality 18 percent grey card in direct sunlight, I made a series of measurements that raise more questions than I myself can answer, so I'm hoping some of you may be able to help.

 

The idea is that the camera, using aperture priority, should pick a shutter speed equal to the ISO value. Instead, with spot metering, the shutter speeds are double the expected value:

• ISO 100 : 1/200
• ISO 200 : 1/400
• ISO 400 : 1/800
• etcetera

With centre-weighted metering the results are different (though they should be the same, having taken care to fill the frame with the grey card):

• ISO 100 : 1/160
• ISO 200 : 1/320
• ISO 400 : 1/640
• etcetera

Now to make things even more complicated, I found that in manual mode, the on screen exposure meter reads zero at a third set of values:

• ISO 100 : 1/125
• ISO 200 : 1/250
• ISO 400 : 1/500
• etcetera

With this final test, there was no difference between spot and centre-weighted metering, which presents us with yet another riddle...

 

Can anyone explain this? Or try to replicate these results with their Vario, just to rule out that I have a faulty item? Also, I'd welcome advice about adjusting exposure strategies in light (pun intended) of these irregularities. I use spot metering most of the time, and my thinking about exposure is largely in terms of Adams' Zones. 

I have been shocked in my now three months with the camera how good the light meter is. After playing with my tenedency to "underexpose" a little (I have Sigma cameras and always trying to avoid blowing the highlights), I have come to trust the X Vario implicitly. The only change I like is a little extra shapening on the color RAW images when needed. 

So perhaps you have a problem with the camera; again I am not an expert, but there is seems very little you have to do with an X Vario image if correctly exposed. 

 

BTW I shoot manual ALL the time.