K10 manual metering question.

Chris,....

I am aware of the other thread thats why I posted this one,...so as not to confuse issues too much.

"........ without stopping hte lens down, the camera has no way of knowing what the aperture ring has been set to....."

Exactly the reverse of what I'm trying of get at,.......will the meter simply give a shutter speed for whatever light it is presented with,...why does it need to "know what the aperture is"...? For example, when using a non Pentax lens via adaptor. When you use a separate exposure meter you are simply measuring light levels and getting a quantitve reading,..what settings you then use is your business. The separate meter does not need to know any of your working criteria to read the light other than film speed (and not even that in a good meter)

Mongoose,......thanks for your reply but even I can work out that the 'M' on the dial means 'manual' adn that the fancy wheels can adjust aperture and shutter (although aperture ring and shutter dial always worked ok for me!).....the problem with K10 is that for all of it's tricks and gimmicks the meter does not really work with older lenses. I'm just trying to find out how this might be in practice.

With the camera in Manual mode, with A-series lenses (set to A) or later, yes. With whatever aperture and shutter speed you have selected, there's a display in the viewfinder and on the top LCD panel that shows you how much over/under exposed you are. Move the camera around, and this changes as the meter sees different light levels.

Press the green button, and it sets the shutter speed for correct exposure (or the aperture for a chosen shutter speed if you choose an alternative option in the menu).

However, with M series lenses, it does not do this. There's no over/under display in manual mode.

With these, to get any reading at all in manual mode, you have to press the green button, which stops the lens down, and sets a shutter speed. The wrong one, usually.

However, in aperture priority or program mode, it does meter the light, and it does set a shutter speed. Since it's metering with the lens wide open, presumably the shutter speed can only be right if you leave it wide open.

viewfinder, sorry if my reply seemed patronising, I think I understand what your problem is now.

The cameras meter takes a reading of the light coming through the lens and assigns a shutter speed accordingly. Since we have an open aperture metering system, this light does not correspond to the amount of light which will hit the sensor when you trip the shutter, unless the lens is being used wide open.

In older cameras, there was a cam on the side of the K mount which engaged with another cam on the lens allowing the camera to determine the position of the aperture ring. This information allows the camera to adjust its selected shutter speed by the correct amount to compensate for the lens stopping down.

Unfortunately in recent years (starting with the budget MZ-50) Pentax have seen fit to remove this cam, presumably to save on manufacturing costs since it is only required for lenses at least 25 years old. I believe the MZ-6 was the last camera to be introduced with the cam, the entire *ist and KD series lack the ability to read the aperture ring.

Without the cam, the camera cannot tell how much to compensate exposure to get from wide open to the shooting aperture. The *istD and KD series have the option of circumnavigating this problem by stopping down the lens to shooting aperture to take the light reading. This works wonderfully on the *ist series, but for some reason it completely messes everything up on the K10D as discussed in another thread. This is the only serious flaw in an otherwise dangerously close to perfect camera.

Why Pentax cannot follow Nikon's lead in this and at least restore aperture ring support on the top of the range models I fail to understand. It's a feature which I for one would pay extra for.

this was true on the MZ-50, but the digital bodies are cleverer. They don't actuate the stop down mechanism unless they are in M mode or the lens is in "A"

On a *istD or KD digital camera setting anything other than M with an M series lens attached results in Av mode locked at wide open aperture (regardless of where the aperture ring actually is).

So it does!!

You're quite right.

Thanks both for your patience......

So, just to double check as this could be very important to me;

I could use K10 with my CZ Sonnars plus adaptor by simply adjusting shutter speed as light thru the lens drops/changes....?

A couple of thoughts.

First, if you use a screw thread lens then whatever aperture you set it to (set the A/M switch on the lens to M) the camera will have to accept that as open aperture and Av should work just fine.

With a K or M bayonet lens you need to use optical stop down (on the collar around the shutter release button) to stop the lens down and activate the meter in M mode.

Don't forget to set the custom function to permit use of aperture ring.

The use of the green button in these cases may prove to be a red herring...

yes you can, however the metering on the K10 is not very reliable with non-A lenses. If these lenses are very important to you then you are probably better off with a *ist series DSLR.

I have used my CZ Flektogon and Sonar with my *istDL2 with great success but on the K10D I have to take the metering with a grain of salt.

not quite sure what you mean by this John, as discussed elsewhere there are issues with K10 metering with non-A lenses, but these are every bit as real when using the DOF preview to stop down as they are when you hit the green button.

Only meant that the instruction book doesn't actually say the green button will work, but refers us to page 210 which describes quite clearly how and where exposure errors may occur. The answer seems to be Manual setting, and via the optical stop down switch.

Unfortunately I can't test the point as I have now moved over entirely to A series or later lenses.

So red herring in the sense that Pentax don't appear to have ever claimed it would work....

:

PS If I'm right in this, I'm not surprised there is confusion because the wording of the manual is, IMHO, atrociously vague.

I've also hunted through the manual and the Pentax web site in search of such a claim, and failed to find one.

However, it seems clear that they at least intended it to work, even if there's no actual claim to that effect. Otherwise, why would the green button stop the lens down and set a shutter speed at all? It only has this behaviour in manual mode, and with pre-A lenses (or A lenses in non-A mode), AFAICT.

If they'd really intended the K10D to be unusable with pre-A lenses, I wouldn't have expected them to make it do that at all.

interesting, now its my turn to , having assumed that since it does (sortof) work it was intentional. Must admit my scrutiny of the K10D manual was not as thorough as it was for my DL2.




If they had intentionally made the K10D incompatible with old lenses, why make all the fuss over all K mount lenses being usable?

If they'd said non-A lenses were incompatible and I had discovered that they work as well as they do then I'd have been happy.