How sensitive is your camera?

Has anybody else noticed this? If I put my K5 and Q cameras side by side, both in Av(Aperture Priority), framing the same shot, both with the same aperture and ISO the shutter speed on the K5 is twice as fast as it is on the Q, or 1 f stop.

The real surprise came when I checked my friends Canon 5D which was two stops slower!! The same as Sony (with their semi-silvered mirror robbing you of 2 stops), the K-01 and the Nikon D7000 were both the same shutter speed as the K5.

Is this just a one off? Has anybody else noticed this phenomena?

It means that if you shoot in low light, don't buy a Canon and you can use 2 stops smaller apertures on a Pentax (forgetting the DOF differences) and get the same shutter speed as a Canon which is quite a saving on wide aperture lenses.

No wonder the K5 has such a good low light performance. We should shout this from the rooftops.

This possibly due to light transmission through the different lenses rather than any body or sensor issues...

Also watch out that light coming in through the viewfinder can affect the metering
But it's an interesting point nonetheless...
Matt

Good point, but if I put my K to Q adapter on the Q and use the same lens on both cameras I get exactly the same result, pretty sure it's differences in the sensors, it's the only thing I can think of.

The test was done in Live View, though I hadn't thought of that.

You didn't say what aperture and LV anyway will stop the lens
down to make sure the LV picture isn't blown out wide open.
I seem to remember it uses alterenate f stops.

Lenses do vary slightly in transmission.

-

All the cameras I've tested (ongoing) give pretty much the same exposure at the ISO and aperture settings, but it seems different cameras need different shutter speeds (Av Mode where the variable is shutter speed), where possible the same (Pentax 50mm f1. lens was used. There is no sign of burnt out to white or blocked out to black pixels in any of the exposures.

I would agree that I need to set up a target with a known exposure value, may be an evenly lit mid grey screen so there is no variation in the tones that each camera may be seeing, but all the cameras were looking at, as near as I could, the same frame.

Also, some camera's ISO setting are kind of optimistic, according to some reports like DxO and a few others.

But then the lens has a different field of view which could also possibly alter aperture and shutter and ISO settings...

Metering technique, angle of view, metering pattern, all have a part to play. Different marques have a different reference point as well. Some use am 18% grey as the average, some use 10% grey, and no doubt others vary in their own particular ways.

Having said that, transmission should not be much of an issue between lenses, not in this day of high-tech coatings, but there could be expected variation of maybe 0.5 stop. Two stops would cause some concern and I would start to look into why that was.

That's correct Canikon don't tell you but they change the iSO
at f1.8 and the Pentax will under expose.

Try to use an f/2.8 or f/3.5/f/4 lens so that all the ISO's
remain the same.

To check light transmission set the lens at f/4 or f/5.6 at
a fixed shutter speed at the correct WB then see if all the
RGB values are the same should be about 118R 118G 118B for
middle grey, although that isn't all that important.

As I understand it ISO is not an absolute, there is no S.I. unit for ISO, shutter speeds and aperture are absolutes and should be the same for all cameras.

Angle of view is the same (same tripod position), all were in centre weighted metering, all were viewing the same frame as near as I could get, the only variable I can see to alter the shutter speed is sensor sensitivity.

Can anybody else do some tests too?

There is another factor that hans't been mentioned yet. Shutter speeds are not fixed at the value that appears in the display - they are infinitely variable. The display indicates the nearest pratical value.

Suppose the actual exposure was about half way between two shutter speeds. It would be possible with some modest variation for one camera to indicate one way and the other to indicate the other way. Hey presto, one stop difference indicated but actually maybe a tenth of a stop actual difference. Possibly.

Q and K-5 both pointed at the same evenly lit surface - both gave me exactly the same readout.

I would expect the K20D to show a faster shutter speed as its exposures are slightly darker than the current range.

No one has mentioned the metering options - I've had widely differing exposures from the same camera/lens when changing this.

regards
Bernard