Originally posted by jonhock Thank you Paul,
Yes, I can narrow that down a bit.
It is an SMC Takumar 1:1.4 50mm lens on an Asahi Spotmatic F.
As long as we're at it, I'm not familiar with doing a Depth Of Field preview either. I do know what a "depth of field" is and how to obtain a longer one using the shutter speed (slower) and the aperture (smaller using higher number), just not how the DOP thing works unless it just means to see if the in focus and out of focus zone is a short turn on the focus ring or a little longer turn.
I'm writing what I think I'm thinking hoping that what you read is what I mean or at least what I want to think is what I am writing. Whew!
Depth of Field refers to the range of distances from the camera that are in focus. It varies, depending on focal length and aperture.
A lens is only truly in focus at one precise distance from the camera. This is called the critical focus point. However, some distance in front of and behind the subject are in "acceptable" focus. This range is called the depth of field.
Have you ever seen a portrait, in which the person's face is in sharp focus, but the background is very blurred? This is shallow depth of field. On the other hand, you have probably seen pictures in which both the subject and background are in very clear focus. This is a deep depth of field.
Depth of field is affected by a couple of factors. The shorter the focal length of a lens, the more depth of field it inherently has. The longer the FL, the less DOF it has. For any given focal length, the wider the aperture, the less DOF; the smaller (larger number) the aperture, the more DOF.
On the Spotmatic F, the slide switch on the camera lets you stop the lens down to the selected working aperture. You will notice that the viewfinder gets considerably darker. If you look closely, you'll also see that things (not the principal subject) that were out of focus, suddenly snap into focus, even though you haven't touched the lens' focusing ring. That's depth of field. Not all 35mm SLR's had a provision for DOF preview. This is a somewhat desirable feature, even today, with digital SLR's.