Nikkor 25-50 AI f4 zone focusing

[anthony_semone]

Well, how does one zone focus with a lens body which does not have a complete set of data inscribed on it? that's the case with the 25-50. I've got it mounted via an mu43 to my E-P2.

any help greatly appreciated,

tony

[principe azul]

1. Google. Not being snide, but you'll come across pictures that will help better than I can.

2. DOF varies a lot, but for midrange focal lengths a good rule of thumb is a third in front of the focal plane and two thirds behind, so with a rangefinder (where I can't check DOF) I tend to focus a third of the way into the important stretch of the photo - I'm not worried if I don't hit it.

3. Use the aperture preview (dedicated button on GF1, don't know about E-P2).

4. A 25-50 f/4 becomes effectively a 50-100 f/8 on micro four thirds. You still gather light at f/4 speed, but because of the crop/enlargement factor, DOF effectively doubles. Effective f/8 at the wide end is good enough for most people.

5. You'll find what you're comfortable with. Most people will stop down to actual f/5.6, f/8 or f/11 and focus at a few metres (may need to turn off the autofocus). Depends on how much DOF you want, what focal length you have, how far your subjects are typically in front of you. DOF scales help (though will mislead with a film lens on M43), but I think most people end up doing it intuitively. It's not an exact science.

6. Google a picture of an old metal Nikkor 24mm and 50mm and see what you get.

[anthony_semone]

Very, very helpful, sir; thanks so much

tony

[principe azul]

You're welcome! As you have an AI Nikkor, you doubtless know a lot more than I presumed when I replied, so thanks for bearing with me!

Online DOF calculator: http://www.dofmaster.com/dofjs.html. Links down the side for printing charts/tables. It shows how my 1/3 - 2/3 rule of thumb falls apart very quickly! But always less DOF in front than behind, as far as I know. As you have the distance scale on the lens, you can zone focus quicker than I can with my Panasonic 20mm, which only has a red dot on the barrel!