Lens Aperture vs Meter Reading

[Ari]

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

[Dan Fromm]

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

[Ari]

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!

[David Schaller]

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.

[Ari]

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.

[Alan Klein]

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

[mdarnton]

https://www.google.com/imgres?imgurl=https://s3-us-west-1.amazonaws.com/lazy-rama/uploads/2012/01/f-numbers1.jpg&imgrefurl=https://www.distantfuturejosh.com/posts/12-13-14-stops/&tbnid=pqB0Rzd-oWVF_M&vet=1&docid=We-g_5YSmfz3_M&w=804&h=1299&q=f+stop+chart&source=sh/x/im

[Ari]

Thanks Alan, thanks Michael.

[BrianShaw]

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

[Jim Noel]

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.

[Ari]

Thanks Brian and Jim; my meters (all tiny digital Sekonics) can only display 1/10 stops.

[mitrajoon]

I wonder is someone can comment on the following exchange with a representative of Sekonic (I added the bolding):

Hi everybody who has followed this thread, I contacted Sekonic and they kindly emailed me back with the following explanation, Explanation of 1/10th numeral on Sekonic L-758


Thank you for your inquiry.
I am Minoru Oda(Mr) from Sales Operation Sec.
of light meter in Sekonic Corporation in Japan.

As you already know, the numeral to the right of the aperture value in aperture priority mode is one tenth of the shutter speed.
If you would like to set this shutter speed into camera, it is better to set closer shutter speed including one tenth of the shutter speed.
For example, When L-758D is set full step of increments of shutter speed, if the desired F stop is 5.6, and Ｔ is indicated as 1/60s, and one tenth of the shutter speed is indicated as 9, it is better to choose 1/125s for suitable shutter speed. Please set f: 5.6 and t:1/125s into your camera.
Because "5 to 9" of one tenth of the shutter speed is closer to next step of shutter speed than this step of shutter speed.
Of course, if the desired F stop is 5.6, and Ｔ is indicated as 1/60s, and one tenth of the shutter speed is indicated as "0 to 4", it is better to choose 1/60s for suitable shutter speed. Please set f: 5.6 and t:1/60s into your camera.

It was easy to understand it, if one tenth of the shutter speed had been in the right of the shutter speed on the LCD display.
We would apologize for difficulty of your understanding because of restriction of LCD design.

Does it answer your question?
If you have any question, please kindly let us know.

Sincerely yours

Minoru Oda
Sales Operation Sec.

This is the link to the above comment: https://www.ephotozine.com/forums/topic/sekonic-l-758d-107041

[Ari]

Makes sense, thank you.

[Havoc]

I'm going to read the manual fo my L-758 again. This is not as I understood it to be.

[BrianShaw]

If I read it correctly, he describes simple half-stop rounding of shutter speed. Personally, I’d have the meter display the aperture in tenths, rather than shutter speed, if I needed that level of resolution and adjust the aperture accordingly. But with L-758, just like my L-558, it’s way easier to reconfigure the readout if tenths are not needed.

... but I’m kinda like Jim and often rely on either a Weston III or Gossen Luna-Pro because they are a lot easier to use than the Sekonic... unless 1-degree spot metering is needed.

[R.K]

In accordance with Seconic manual the decimal scale displays in 1/10th of a stop. Not time, not aperture, just a stop. So when Seconic measure 5.6 & 5/10 or 4/10 it will be yours 6.8 aperture. Because 6.7 is 1/2 of a stop down from 5.6. So if you visually divide the distance on the lens aperture scale in 1/2 or 1/3ds and round your Seconic measured tenths of a stop to 1/2, 1/3 or 2/3 of a stop you will be very precise. Let say Seconic indicate aperture 8 & 2/10 of a stop. Divide distance on the lens aperture scale between 8 and 11 on 3 equal parts and place aperture lever near the the 1/3 after 8 and it will be absolutely correct placement.