How sensitive is your camera?

Metering options change the way the camera measures the light level, so technique will have a bearing on this, especially with spot metering. The use of spot metering needs to be understood and it causes a bit of heartache sometimes for the unwary.

I'd imagine that there is light loss with the K/Q adapter much as there is with an extension tube.

The light loss you get with the different viewing angles of the various focal lengths is taken care of by f numbers. The light loss you get from extension tubes is because your magnifying the view and only getting the light reflected off a smaller area, doesn't apply when your just adapting a lens so it can focus on infinity.

I used centre weighted metering in my tests, but I've also used spot metering with the same results, it definitely seems that some cameras can select a faster shutter speed when in aperture priority and the aperture and ISO is the same on all cameras, the same field of view, the same position for the camera.

Surely the adapter just makes up for the difference in flange distances for the cameras. Total distance from lens to sensor will be the same either on a K mount DSLR, or an adapted Q mount.

When I was well into film photography it was said that you could try six different meters and get six different readings. The trick was to get used to your meter and interpret what it was telling you. I used a Gossen Lunasix III for many years.

i think you're right

Different makers have different factors of safety
(K values) for exposure. Canikon being Pro probably
use a smaller value than Pentax, although I seem to
remember that it wasn't very high. The idea is that
they aim for the highest percentage of success based
on their users level of competence/incompetence.
i.e. Can they tell the difference between freshly
fallen snow and a black horse


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The K value is the value alloocated to the meter, as mentioned previously usually 18% grey or 10% grey.

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Could you expand a bit on this John as I use spot metering a lot for my wildlife shots.
Dave

Spot metering, as the name implies, measures the light from just the very centre of the frame. A separate spot meter will measure from a 1 degree area, but the camera spot meter will be slightly wider than that.

It is ideal for measuring, say, the exposure of a spotlit subject, or measuring the darkest and brightest areas of a scene so that an average exposure can be worked out. This works best using manual exposure.

It doesn't lend itself so well to auto exposure techniques. Most of the trouble comes in where the spot meter ends up reading an inappropriate area of the image, so it's not the method for beginners.

Centre weighted metering offers a more easily reliable method, coupled with exposure compensation where necessary.

Hope that helps.

Metering from the camera position is always prone to error no matter which metering mode you use which is why there is an easily accessible EV compensation control on most cameras.

All meters see the World in B&W, they measure the Luminance, but metering from the camera position make no allowance for the tone of the subject, how reflective they are.

All they do is take an average of the metered zone (zonal, spot or centre weighted)and then set the exposure to make that Luminance level reflected off the subject a mid grey, in film days mid grey was referred to as 18% grey as film responds to light in a logarithmic way, digital sensors are linear so mid grey should really be referred to as 50% grey, but the old 18% grey term seems to have stuck.

It's easy to show this happening with a piece of white and a piece of black card, place them in a well, evenly lit area and fill the frame with the white card and take a picture then take another picture of the black using any auto mode (Program, Aperture Priority, or Shutter Priority) both exposures will be the same - mid grey.

This gives us the old problem with scenes that are predominantly light or dark toned, snow scenes tend to be under-exposed to give us a mid grey snow, and the ubiquitous black cat on coal will be over-exposed and give a grey cat on grey coal, hence the need for EV compensation.

I think given the decent dynamic range of modern sensors, John's advice above is sufficient. You can claw back up to 5 stops of under exposure on the K-5 so there's no problem in dialling in a not insignificant amount of negative exposure compensation to avoid clipping the sensor and getting whiteout regions in your image if you're in doubt.

Shooting digital is a little like shooting fast reversal film, there's not a lot of headroom in the exposure, a 1/3rd of stop can make a visible difference to the amount of data collected.

Maximising image quality with digital has as much, if not more, to do with the the A/D converter and bit depth as it has with sensor dynamic range.

http://www.luminous-landscape.com/tutorials/optimizing_exposure.shtml

Re-mapping Raw files in the Raw Converter may correct for an incorrect exposure, but it will not give you back any lost data caused by incorrect exposure, in extreme cases it will just give you a posterised image, blocks of colour with little detail.

When I read the title of this topic I thought to myself, I don't think I've made mine cry yet.

It's usual to talk of dynamic range of a camera as the dynamic range of the sensor/AD converter system as one unit.

In the early days Audio recording went through the equivalent of Expose To The Right [ ETTR} when AD convertors were still evolving. i.e advice was always record as hot as possible without clipping to maximise bits and keep digital quantisation noise to a minimum.

Nowadays digital audio is recorded leaving 2 or 3 bits of headroom by calibrating 0dB 9 optimal level ) as something between -12dBFS to -18dBFS on the digital scale.

More recently camera sensor/converters have evolved where there's no need to [i]always[i] implement meticulous ETTR and you can easily dial in up to a couple of stops ( 12dB ) of negative exposure compensation to avoid blowing highlights if the scene is very contrasty and well lit enough for a low ISO.


ETTR was certainly pertinent to exposing on digital cameras a few years ago, but were going to see dynamic ranges increasing in the coming years .... 16bits and even towards 24bits. By which time ETTR will be irrelevant.