Sekonic L-28 - meter scale question

[Area51Resident]

I have a Sekonic L-28 (L-28C2 to be precise) but no manual.

On the "incident light" scale there are two sets of markings where the needle swings. The red on silver scale is for direct readings with the appropriate slide and the upper scale (silver on black) shows measured light level for using the exposure calculator wheel. I know how to use the meter so that is not the issue. I'm looking for what the "upper scale" is calibrated in.

The L-398 series meters measure in foot-candles on this scale. The numbers on the L-28 do exactly not match so I assume it isn't in foot-candles. The L-398 measures 0-1.25K full swing and the L-28 measures 1-1M(illion) full swing. Both use a selenium cell and lumisphere and slides are interchangeable, so I assume they have the same sensitivity to light and should read the same under the same conditions.

The Sekonic site doesn't have the manual and Google has not found a source of information to answer my question.

Anyone have a copy of the L-28 manual or know what units that scale is calibrated in?

TIA,

JB

 

[jstraw]

I ran to get mine but it's an L-248. Sorry.

 

[Area51Resident]

Thanks anyway. I appreciate the effort.

 

[Helen B]

There was a calibration constant change between the L-28 series and the L-398 series. That means that there is about a third-stop difference in the correlation between foot-candles and exposure. The constant for the L-28 was 270 and it is 340 for the L-398. In theory the exposure (ie the aperture scale on these meters) that corresponds to 250 FC on the L-28 should correspond to about 320 FC on the L-398 (that is at f/8 on my L-398). I don't have an L-28, so can't check it for myself. As you have both meters, does that correlation happen in practice?

Best,
Helen

 

[Area51Resident]

Helen B:

I don't have a L-398 meter, just the L-28. Here is a snip from the L-398 manual on www.sekonic.com.

http://www.sekonic.com/images/files/L-398M_Quick_Guide.pdf


On the L-28 the F8 mark lines up with 125 on the outer scale, but reads 160 footcandles on the L-398. Is this the one third stop difference in calibration constant you mentioned?

Cheers,

Jason...

 

[Helen B]

Jason,

Yes, that is because of the approx third stop difference in calibration constant, but the numbers look wrong. As I mentioned in my previous post, on my L-398 the f/8 mark roughly lines up with 320 FC, not 160 FC.

Best,
Helen

 

[Area51Resident]

Helen:

My error in misreading the scales. On the L-28 f/8 mark is at 250 on the outer scale and on L-398 f/8 is at 320 FC. I was looking at f/5.6 on the scale (dead center) but wrote f/8 in my post.

I think the difference between 250 FC and 320 FC is 1/3 stop, or is my math wrong?

Thanks,

Jason

 

[Helen B]

Yes, you are correct - near enough. It is similar to the arithmetic ('ASA') ISO film speed series. You multiply by the cube root of two (1.26) for a third-stop increase.

Best,
Helen

 

[Area51Resident]

Helen:

Thanks so much for your helpful posts. A small mystery solved.

Cheers,

Jason...