Originally posted by David-C The lens: Pentax 1:4/200 SMC K-mount. It is a prime lens. Apparently fixed aperture?
There are two meanings. One applies to mirrors and other lenses without an aperture iris. Thus my 500/8 mirror is ALWAYS at f/8. The other applies to zoom lenses, which can have a fixed or floating MAXIMUM aperture. My Tomioka 55-135/3.5 has a fixed maximum aperture; an F35-70/3.5-4.5 has a floating maximum aperture. The term doesn't apply to a prime lens like your 200/4.
Quote: But when I went to use my camera this lens left me dumbfounded...
It has two sets of f-stop rings and neither moves.
What does it mean when the first ring has a big red dot at 32?
It would help to know just which lens you have there. Can you find it in the lens review database? (Click on LENSES near the top left of this page.)
Is there an A between the 32 and the red dot? Then the dot is a button that lets you shift the ring into or away from the A (auto aperture) position.
Quote: What does it mean when the second ring has a red diamond at 8?
The red diamond is usually an index mark for focusing.
Quote: Why does the lens have the name 1:4?
Because the maximum f-stop is f/4. An f-stop is the ratio between aperture diameter and focal length. We don't need to know that diameter; we DO need to know the ratio. The f-stop f/4 means the iris diameter is 1/4 the focal length; the ratio is 1:4. Depending on the lensmaker or the user or the continent, a lens may be referred to as
200mm 1:4 or
200/4 or
4/200 or
F 1:4 200 -- they all mean exactly the same thing.
Quote: From what I can gather on the net by sifting through info on zoom-digital type lenses, the lens will always maintain an aperture of f-4? Then why the 32? Why the 8?
Your lens' maximum (widest) aperture is f/4; its minimum (tightest) aperture is f/32. And f/8 is one of the midway stops. The f-stop sequence would go: f/4-5.6-8-11-16-22-32. Every lens with an iris (this excludes mirrors, projector and copy lenses, etc) has a variable aperture -- assuming it's not stuck, of course!
Quote: I am curious if there is any way to change the exposure time drastically on a prime-fixed-aperture as you would when changing f-stops on a lens with variable-aperture.
Only a no-iris (or broken) lens won't let you change apertures. That said, there ARE ways to slow an exposure. The easiest is to... stop-down the aperture! Or add a ND (neutral density) filter; or if shooting B&W, use some heavy-cutting filter like a Red or Blue; or you could make a Waterhouse stop (look it up) but that doesn't really apply here; or you could just dial-down the ISO as much as possible.
Quote: As an added question I have seen some macro lenses listed as 200/4... Is this not the same designation as my telephoto lens?
Exactly right. The differences are that 1) the macro lens focuses much closer; 2) the macro lens' optics are sharper; and 3) the macro lens costs much much more! That's a tele macro, good for field work, highly prized, highly priced.
Quote: Lastly, whats the point of fixed aperture?
I think I answered that above. Cheers!