[blackest]

Hi
I was thinking about the exif data when using a manual lens
The focal length you can set when you turn on with sr on but it is a problem that the camera doesn't record the f-stop.

Of course there is no way it can know or is there?

Pentax very cleverly designed the ka system to be compatible with the km to do this they designed a system of insulated and non-insulated contacts on the mount.
Basically 2 pins give the smallest f stop and 3 give the maximum
This works pretty well ka lenses with aperture rings have a pin that extends in A mode and the camera sets the aperture by moving a lever proportional to the fstop.

So what happens if we short the A contact?
well the camera now thinks its in A mode and trys to read the contacts but there isn't any contacts just the metal bayonet which means the camera see's 111A11 which is code for f22 - f1.2. In aperture priority mode and manual mode you can select the aperture you want to use sort off.

The km aperture lever isn't proportional to the f-stop so you are not going to get the f-stop set automatically correctly. chances are your lenses are not all f1.2's however you can manually set the aperture to what you want with the aperture ring.

So if you select f4 on the aperture ring and set f4 on the settings when the camera releases the aperture ring the lens will close down to f4.
Of course you could set the aperture to 1.2 and use the f3.5 maximum you actually have, that would probably fool 99% of people in to thinking you have expensive glass

I'm not sure what will happen with metering in Av mode will the camera adjust the shutter speed to the actual circumstances or assume its stopping down x number of stops from f1.2

Anyway at least now you will have the missing exif data and it will record what you say it is and hopefully you will set the aperture ring to what you said you were going to use.

I can not see a reason why you shouldn't keep the A pin set all the time. Every lens from a ka upwards will set it anyway, now all the km lenses will report an f-stop and its up to you to match it with the actual aperture you use. Even if you don't its still an improvement over f--

Ok so whats the problem with this? Pentax must have made the A pin for a reason. Is this going to break anything?

[Ole]

The A pin (and the contacts) were invented to enable the camera to set the aperture to the value calculated by the light meter. As you correctly write, that cannot be acieved with an M or K lens (even with your work around).

[blackest]

The A pin (and the contacts) were invented to enable the camera to set the aperture to the value calculated by the light meter. As you correctly write, that cannot be acieved with an M or K lens (even with your work around).

My work around does no magic turning a k into a ka, however what it does do is allow the exif information for f-stop to be written to the camera, obviously its up to the user to make sure that the f-stop recorded is the f-stop used.

The Exif can be a useful learning tool.

It does leave me wondering what made pentax decide to include the A pin on later bodies, it doesn't seem to do much other than remind people if they have the aperture ring out of the A position.

It also could be useful to macro photographers using extension tubes as depth of field is very small it would be handy to see which apertures worked and which were too shallow.

[stevebrot]

My work around does no magic turning a k into a ka, however what it does do is allow the exif information for f-stop to be written to the camera, obviously its up to the user to make sure that the f-stop recorded is the f-stop used

I'm not sure what will happen with metering in Av mode will the camera adjust the shutter speed to the actual circumstances or assume its stopping down x number of stops from f1.2

Your approach has been suggested in the past and does provide Av mode functionality if both the lens and body are set to the same aperture. The main risk is that the actuator lever may not have adequate travel at wider apertures to actually trip the stop-down mechanism on some non-A contact lenses.

Steve

[blackest]

Your approach has been suggested in the past and does provide Av mode functionality if both the lens and body are set to the same aperture. The main risk is that the actuator lever may not have adequate travel at wider apertures to actually trip the stop-down mechanism on some non-A contact lenses.

Steve

Thank you for that, I knew I couldn't be the first person to consider this option, I just used some foil to bridge it with a small ball to make the a pin contact work. When I change the lens the body will be facing down so if it falls it will fall out of the camera. I may well make it semi at least permanent.