Pentax spotmatic sp

Depth of field view/ stop down metering - what in the world is this all about ? The depth of field -all what i see happens is the finder gets

all dark - anyone can explain :) ?

Focus on something close to the camera (like 3-5 feet away), then stop down to like f11 and see how the background becomes clearer (more in focus) when you hit the stop down button on your Spotmatic. What you are seeing is the impact of greater DOF at F11 vs a wide open lens.

Most screw mount SLR had to measure light at shooting aperture so lenses had to be stopped down for metering.

Or, focus on the background, then stop down to like f11 and see how something 3-5 feet away becomes clearer (more in focus) when you hit the stop down button on your Spotmatic. What you are seeing is the impact of greater DOF at F11 vs a wide open lens.

 

You are seeing the actual depth of field as it will register on the film. Of course it looks darker. You are getting the light through a tiny f/11 aperture hole as opposed to a big f/2 aperture hole.

"...all what i see happens is the finder gets all dark"

 

I've heard those exact words before. At least I was around to explain. That may be why a lot of manufacturers stopped including a DOF preview button. I could still get DOF preview by releasing the lens and turning it slightly. That would cause the aperture blades to close down to the aperture setting.

Ok thaks i understand now . But what is the difference between the automatic a and manal b settings. I know with A it

aparture are wideopen when focusing but at B it is not?

<p>I suppose you mean the switch on the lens for auto or manual stop down. That switch is there because on some screw mount bodies there was no auto stop down lever on the camera or if the lens was used on manual extension tubes or a bellows, then you would switch the lens to manual.</p>

<p>The switch on the lens is needed if you use screw mount lenses via M42 to Pentax K adapter so the lenses can be used on bayonet mount Pentax bodies. Or if used on a Minolta camera with the M42 to Minolta SR adapter.</p>

<p>The automatic aperture on screw mount lenses works backwards from most other types.</p>

<p>If you take Nikon or Minolta, etc. bayonet lens in hand, and operate the aperture lever, the aperture opens and closes. It's automatic only when the camera's internal lever engages the lever in the lens, so when you put it on a manual extension tube, it reverts to manual.</p>

<p>If you hold an automatic screw mount lens in your hand, and operate the aperture lever, it remains automatic and the aperture remains open. It's manual only when the camera's internal lever pushes in the pin in the mount. Because of the screw mount configuration, a manual extension tube or other equipment without the requisite internals will not push in that pin. So you must switch it to manual mode to use it on extension tubes and the like. </p>

<p>You probably know this already, but just in case....Through the lens metering on most cameras is accomplished by computation. When you stop down an automatic lens, it remains open and the light hitting the meter does not automatically change. Instead, a coupling compensates the meter itself to simulate changed light. If you have a non-coupled lens on a Nikon, Minolta, etc. , you must stop down meter. On the screw mount, since there is no coupling, the only way for the meter to see a change in light is to stop down. </p>