1. ## Lens Aperture vs Meter Reading

Not a burning topic, just one I've been thinking about my whole professional life and never thought to ask about. Maybe the answer is obvious, but it's eluded me thus far.
I only use digital incident meters, so this question isn't pertinent to some.

Let's say I have a lens of maximum aperture f/6.8 and I want to shoot at f/6.8.
My meter reads in whole stops, then in 1/10 f-stops, for example f/5.6 plus 3/10s, or as it's displayed: "5.67"

f/4.5 is easy to correlate on the meter, it's 4.05.
But I also have f/3.2, f/9, and f/6.3 to figure out. Is f/6.3 6/10 of a stop more than f/5.6? 9/10? I don't know.

Where would I find f6.8 to correspond with what the meter is capable of displaying? Where's f/6.8 on the meter?
Is there a scale somewhere that gives the equivalents to these odd maximum apertures?

TIA

2. ## Re: Lens Aperture vs Meter Reading

If you want a scale, get a broken Weston Master V meter.

3. ## Re: Lens Aperture vs Meter Reading

Originally Posted by Dan Fromm
If you want a scale, get a broken Weston Master V meter.
There ya go; obvious to most, but I had no ideer.
I'll take that to mean that f/3.2 on my digitized meter is f/2.83; f/6.3 is f/5.63 on the meter, and f/9 is f/83 on the digital meter.

Thanks, now I can get on with the rest of my life!

4. ## Re: Lens Aperture vs Meter Reading

I would think of those in terms of either 1/2 stops or 1/3 stops. Of course I shoot negative film, not digital, so close enough works sufficiently. In your example, I would take f 6.8 to be close enough to a half stop down from f5.6, or a half stop open from f8, and apply the meter reading in tenths accordingly. I have a meter that I use for medium format that displays tenths, and if the lens has half stop clicks I go with the nearest half or full stop. As to the exact f number for a half stop between f5.6 and f8, I’ll let someone else explain why it’s often given as f6.7, while the lens in your hypothetical is f6.8.

5. ## Re: Lens Aperture vs Meter Reading

Thanks, David; that's as good an explanation as any.
I use the stops and meter readings pretty much the same way you describe, though I've been doing so blindly for years, not making the correlations.
But my metering has always been close enough, even for slide film, and I'll often add or subtract a half stop anyway, depending on the type of film being used.

6. ## Re: Lens Aperture vs Meter Reading

This chart give stops in halves and thirds for aperture, shutter, and ISO. Maybe it will help.
https://www.flickr.com/photos/41681212@N02/5373674086

8. ## Re: Lens Aperture vs Meter Reading

Thanks Alan, thanks Michael.

9. ## Re: Lens Aperture vs Meter Reading

I find tenths both annoying and unnecessary. I set the configuration of my meter to display in either thirds or halves.

10. ## Re: Lens Aperture vs Meter Reading

All of my meters are set to read in n1/3 stops, and of course I still have my trusty and working Weston Master II to rely on.

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