[Bauie]

OK, I know this is a weird one but here goes. I'm attaching P67 close up tubes to a KX digital body via a P67-K mount adapter. I'm getting nice results but am curious, when I attach it and turn the camera on it asks me to input a focal length. I'm using a P67 90mm lens. also, is there a chart for the exposure compensation when using these tubes on the P67?

[Ivan]

You must enter the same 90 mm.I may be wrong, but you will still have to correct the exposure.Even if there is such a table, cameras measure differently.If I understand you correctly.

[johnha]

The TTL metering should account for the extension as it's through the lens. If using a handheld meter or manual flash, you'd have to make a correction. It depends on the camera to subject distance amongst other factors.

You'll need to use stop down metering (lens auto/man switch on man).

[photoptimist]

The TTL metering should account for the extension as it's through the lens. If using a handheld meter or manual flash, you'd have to make a correction. It depends on the camera to subject distance amongst other factors.

You'll need to use stop down metering (lens auto/man switch on man).

Exactly.

If you are using an external light meter or lighting calculations (e.g., sunny f/16 or aperture calculations based on a manual flash), the correction formula isn't too bad

Just multiply the "no-tubes" aperture by F/(L+F) where L is the length of the tubes and F in the focal length of the lens. Thus, if you are supposed to use f/16 and have 45mm of tube on a 90mm lens, the lens aperture needs to be 16 * 90 / (90+45) = 10.7 which is close enough to f/11 for government work.