Determing the f/stop of a lens

[Bosaiya]

I was going to suggest putting the lens in front of an slr body to get a reading off the inbuilt light meter and then working back from that but you've already done something very similar...

given the exposure latitude of most films if you're correct to half an f-stop [or even a bit more] you'll never notice the error

I tried that towards the end as confirmation, but I blew it using a dSLR that had the lens coupled to the body (it freaked out without the lens attached). I was able to use my noggin and kept the lens on, focusing on the back of the LF lens. I'll run some sheets of film through tomorrow to see what I end up at.

It's sort of like an adventure.

[Andrew]

I blew it using a dSLR that had the lens coupled to the body (it freaked out without the lens attached).

there's something to be said for old technology...
if you'd used an older film slr it'd have just given you a shutter speed without tossing a hissy fit

[Bosaiya]

there's something to be said for old technology...
if you'd used an older film slr it'd have just given you a shutter speed without tossing a hissy fit

But then I'd miss out on the paradox of mixing ultra-modern with antique.

[jnantz]

the whole nodal point throws me for a loop too ...
i usually just measure from the rear element,
or s if someone suggests the iris ...

i have been not too far off ... and i never worried much about it
seeing i usually use these things with b/w film
(and i'm not too worried about exactness ... )

But then I'd miss out on the paradox of mixing ultra-modern with antique.

i LOVE that!

[Bosaiya]

I'm a file-to-fit kind of guy. I never stop learning. For example I keep learning that if I want to make one of something I need to buy enough for at least two - inevitably I will screw things up along the way.

[Ernest Purdum]

For focal length, if you ave enough bellows you can first focus at infinity, mark your rail or bed, then focus on a scale to get 1:1 on the groundglass. The distance moved is the focal length.

For aperture, it sounds silly, but it is the size the diaphragm seems to be when seen from the front that matters. There are several ways of getting a fairly accurate measurement of this and I'm sure you'll find them here by using the search.

The math is easy enough even for me. Just focal length divided by effective aperture.