How to open 1/3 stop with ISO dial.

kbrede said:

I used 1/3 stop as an example, bad one I guess. I have other filters with larger filter factors that I want to apply what I learn here. Also some of my lenses only have full stops between clicks. With a camera that only has full stops for shutter and a lens with full stops on aperture, knowing how to change the ISO dial to compensate is something I'd like to learn.

Click to expand...

Changing the ISO on the meter won't magically make 1/3 or 1/2 detents on the aperture ring (Zeiss Ikon)

To clarify for OP... How the ISO dial links to camera behavior seems to be the point of confusion...

The Pentax ME Super doesn't have an automatic aperture. The f/stop you click is the one you get.

Some cameras override the aperture in program and shutter priority mode (OM-Program comes to mind). Pentax ME Super doesn't mess with your f/stop once you set it.

The camera has an electronic shutter. When using Auto - Automatic mode, shutter speed varies automatically and the speed will change by 1/3 stop if you make 1/3 stop change to the ISO dial. (But don't do that for filters since it reads the light through the lens).

When using M - Manual mode, you get the shutter speed displayed in viewfinder - the shutter does not change 1/3 stop when you change the ISO dial.

Going to the original plan: Setting meter ISO "B" to 125 is a good idea. Leaving the camera at 160 is a good idea.

Thanks all for your help and sticking with it, until I got it.

Setting the ISO (on the meter) to 125 is convenient as you don't have to apply the filter factor to the reading. However, if you lenses can only be set at full stop or 1/2 stop and your shutter speed at full stop then the meter at times will give you a reading you can not set exactly.