Sekonic L-758DR Question

Started Nov 20, 2010 | Discussions
Stan Prevost
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Sekonic L-758DR Question
Nov 20, 2010

I just got my new light meter and can't quite figure out one thing.

Just to the right of the f-stop numeric field on the display, there is a single digit, smaller, that the manual describes as 1/10 stop. Apparently it associates with either the time value or the aperture value depending on mode. But I don't know what it is telling me. If I have the meter set to use 1/3 stops for time and aperture, what does the 1/10 stop number tell me?

For example, if I have the meter set to available light, 1/3 stops, shutter speed priority mode and 1/100 second, take a measurement, and the f-stop shows as 5.6 with a small 2 to the right, what does that mean?

Stan

Peter Berressem
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Re: Sekonic L-758DR Question
In reply to Stan Prevost, Nov 20, 2010

Stan Prevost wrote:

f-stop shows as 5.6 with a small 2 to the right, what does that mean?

It shows 5.6 + 2/10... what is simply about f/5.6 1/3. Also, 5 increments equate 1/2 f/stop. Basically you have to transform the digits to fraction numbers.

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cheers, Peter
Germany

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Stan Prevost
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Some Data
In reply to Peter Berressem, Nov 20, 2010

Thanks, Peter. What you describe may be correct but seems odd that it doesn't display the closest value.

I just performed two experiments, using a simple arrangement in which I could vary the light on a surface. I should have done this before posting, or in lieu of posting.

First, I set the meter to ambient, reflected spot, aperture priority, 1/3 stop increments on time and aperture.

(Sorry for poor formatting, my formatting did not take effect)

Increasing light top to bottom.

Shutter Speed 1/10 stop reading
2.5 sec 0
2.5 1
2.5 2
2.2 0
2.2 1
2.2 2
1.6 0

In the third entry, the meter is telling me to use 2.5 seconds shortened by 2/10 stop. It seems odd to me that it would not tell me to use the closest value available in my chosen 1/3 stop setting space, which would be 2.2 sec. In full stop mode, I suppose it could tell me to use some value shortened by 9/10 stop.

Now the meter is set to shutter priority. Light increases top to bottom

Aperture Value 1/10 stop reading
3.6 2
4.0 0
4.0 1
4.0 2
4.5 0
4.5 1
4.5 2
4.5 3
5.0 0
5.0 1
5.0 2
5.6 0
5.6 1
5.6 2
6.3 0
6.3 1
6.3 2
6.3 3
7.1 0

These numbers are repeatable. I could never get a 3/10 reading except where shown, and I could get the shown 3/10 readings every time I tried.

Let's take the (4.5, 3) entry. The meter is telling me to use f-number 4.5 increased by 3/10 stop. Well, 3/10 stop is awfully close to 1/3 stop, so why doesn't it tell me to use the next 1/3 stop value of 5.0? I had to increase the light further to get 5.0. I don't know how much, since my simple method was not calibrated.

[Edit: I used a small range of data when eaking the aperture priority data, and never saw any 3/10 readings. After taking the shutter priority data, I did some more aperture priority looking, and also found some 3/10 values. Too lazy to take another data set and post them.]

I have learned that the 1/10 stop numbers are EV values. For shutter speed, a 1/10 reading of 2 means to shorten the time by 2/10 stop, and for the aperture, a 1/10 reading of 2 means to increase the f-number by 2/10 stop.

Wierd.

Stan

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Peter Berressem
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Re: Some Data
In reply to Stan Prevost, Nov 20, 2010

Ah, you've set the reading to 1/3 f/stops in the custom settings...what I described refered to the 'full f/stops' setting when the meter displays e.g. f 8 plus 1/10 increments.

Well, in your case the meter shows e.g f8 PLUS 1/3 f/stop PLUS any increments in 1/10 steps .

Being the mathematical dummy that I am, I admit that I use the simpler standard full f/stop plus 1/10 increments, as were used in the pre-digital days where cameras didn't offer logarithmic aperture and shutter speed steps
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cheers, Peter
Germany

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Stan Prevost
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New Data
In reply to Stan Prevost, Nov 21, 2010

I now have more definitive data on behavior of the L-758DR.

I made measurements over a not quite two stop range, in 0.1 EV steps. In the table you can see the EV, f-number and shutter speed given by the meter. For Aperture Priority mode, I used f/8, and for Shutter Priority mode, I used 1 second.

I took the displayed numbers for f-number and shutter speed and corrected them by the displayed 1/10 stop number, shown as the "Corrected f-number" and "Corrected Shutter Speed". This meter expects you to mentally perform that calculation to come up with the f-number or shutter speed to set in your camera. If you don't perform that calculation, you can have an exposure error of up to 0.9 stop (with the meter in full stop mode).

The "Ideal f-number" is calculated from the one second shutter speed and the measured EV. The "Ideal Shutter Speed" is calculated from the chosen f/8 setting and the EV. The other columns are attempts to decipher the math used in the meter.

I cannot fathom why the meter was not designed to directly show the closest values of f-number and shutter speed for the mode the meter is set to (full, half, or third stop) so the correct numbers are immediately available for setting into the camera, rather than requiring a mental calculation of using one number to correct another. It is not so immediately obvious how to adjust an f-number of 5.6 by an amount of 0.7 stop, and is a distraction, workload increaser and error generator in the middle of a fast and furious job.

There is not a word in the poor instruction manual about this. The small number to the right of the f-number is identified as a 1/10-stop number, but nowhere is there any mention that the f-number should be increased by this factor (and it is not just an additive correction) or that the shutter time should be decreased by this factor.

The table shows data only for the 1/3-stop mode, but for full stop mode, the 1/10-stop correction values range from 0 to 9.

This is the only thing I have found (so far) that detracts from this being a superb meter. Firmware is updateable in this meter, and it ought to be.

Stan

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andispiderweb
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Re: New Data
In reply to Stan Prevost, Jun 2, 2013

Hi, I'm a beginner who just bought the L-758D.

Regarding this L-758D, I would like to copy the this tutorial by Mark Walace (in the end of the video) http://www.youtube.com/watch?v=PijtJFw7B44 for the dyamic range image.

I'm using nikon D7000. I don't know where I can have the dynamic range data for my camera and how to calibrate this with the sekonic.

Furthermore, what Mark Walace did was taking some spot readings and put on memory, but then what he does with all these memorized data to get that great image? Did he calculate all those measurings himself and decide the aperture? Or He changed the lighting setting by flags etc to cover certain parts?

Thanks for insight!

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CraigBennett
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Re: New Data
In reply to andispiderweb, Jun 3, 2013

andispiderweb wrote:

Hi, I'm a beginner who just bought the L-758D.

Regarding this L-758D, I would like to copy the this tutorial by Mark Walace (in the end of the video) http://www.youtube.com/watch?v=PijtJFw7B44 for the dyamic range image.

I'm using nikon D7000. I don't know where I can have the dynamic range data for my camera and how to calibrate this with the sekonic.

Furthermore, what Mark Walace did was taking some spot readings and put on memory, but then what he does with all these memorized data to get that great image? Did he calculate all those measurings himself and decide the aperture? Or He changed the lighting setting by flags etc to cover certain parts?

Thanks for insight!

To calibrate your meter to your Dynamic Range of your camera, you must use Sekonic's software and a test target, such as their target or the xRite's Colorchecker Passport target.  If you go to Sekonic's site, they have tutorials on how to do this.

Since his meter was calibrated to his camera and lens combinations, when he was taking spot readings, he was comparing the actual light readings from his subject to what his camera is capable of capturing.

Regards,

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DecibelPhoto
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Re: New Data
In reply to Stan Prevost, Jun 7, 2013

There is nothing wrong with the way the meter works, you just need to learn to read the information it is displaying.

The meter isn't supposed to show you what setting to use, it's supposed to show you how bright the light is, and using that information you can infer how to set your lights as you please.

To show you the correct setting, with whatever 1/10-stop variance exists, it would have to display a negative number (i.e. f/8 -0.1).  It would be very easy to miss the negative sign in the reading, and then you would be off by a meaningful amount.

On the other hand, if you learn that f/9.5.4 means f/11 -.01, then you know to set your camera to f/11.  (My meter is set to half stops, so these numbers may be foreign to you).

I actually think that it is easier to have the meter set to full stops, I've been meaning to change mine.  Then you see f/5.6.9, you know you are 1/10 below f/8.  Then set camera accordingly.

Obviously it is pretty damn confusing, but when have aperture numbers not been?  Truthfully I use a variety of meters frequently, from different manufacturers, all of which work differently, and I never get confused anymore.  They all work pretty much the same in principal, and once you get used to it, you don't think about it.

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