Hello I use 758Dr ( newly purchased ). I am stuck with the reading jargon. The aperture is shown always with a fraction and another number. It is stops and the extra number. Light meter is on 1/10 or full stops, and camera can handle only 1/3 or 1/2 stops. So how can I fully use the power of handheld meters? I tried to custom set function in Sekonic, but still fractions are shown.

  • I am trying to calibrate the camera to meter, which I could not get succeffully. To add problems, the sekonic data software always ask the 1/10 of steps while adding pictures. – Bineesh Dec 27 '16 at 14:32
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    I'm unclear on the problem. Can't you just round to the nearest third or half stop? – mattdm Dec 27 '16 at 16:36
  • @mattdm my only problem is actually rounding . – Bineesh Dec 28 '16 at 9:56
  • While there are several great answers on how to find a 1/3rd stop based on 1/10th stop readings... the answer by @user67154 is going to be the easiest solution. You can switch the Sekonic 758DR to read in 1/3rd stop increments (the default is 1/10th stops) – Tim Campbell Jul 8 '19 at 18:23

There is a chart of Tenth stops at http://www.scantips.com/lights/fstop.html (down low on page)

But a third stop is 0.333 stops. Two thirds is 0.667 stops. A half stop is 0.5 stops.

So if your meter shows f/8 plus 0.7 stop, that is approximately 2/3, or virtually the same as 0.667 stops. So merely open 2/3 clicks above f/8, or 1/3 click below f/11. Either way, this is about f/10.

Tenth stops are not particularly useful outdoors in ambient light, since we cannot set the camera directly in tenth stops. We would just set it as close as possible, the difference is minor, and your only choice.

But tenth stops are extremely useful for metering multiple studio flash. We can set their differences more closely. But the overwhelming advantage of tenth stops is when pondering fill level for that lighting ratio - how much is one and a third stop less than f/10? It is about f/6.3, but who knows that? But if we read these two values as f/5.6 plus 3/10 stop vs. f/8 plus 6/10 stop, then in our heads we easily know 1.3 stops difference, immediately (in use, that is really a big deal for lighting ratio).

Most Sekonics have switches to set it to read Full stops (which is tenths) or third or half stops. Check the manual for your switches.

  • This is very clear. So how we translate f/8 plus .8 stops or f/8 plus .6 stops into 2/3 system ? – Bineesh Dec 28 '16 at 9:50
  • A little late seeing this, but f/8 is stop #6 in sequence 0, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, etc. So f/8 plus 6/10 is sqrt(2) to power of 6.6 = f/9.85. f/8 plus 2/3 is sqrt(2) to power 6.66667 = f/10.08. See scantips.com/lights/fstop2.html for procedure. – WayneF Aug 10 '19 at 13:21

There is a great demo of setting the Sekonic 758DR light meter Custom Setting function #3 to display full or 1/10 (default: 0), 1/3 f-stop (value: 1) and 1/2 f-stop (value: 2) aperture values: https://youtu.be/3Yuw00sCFvY?t=2m30s

With the light meter turned off:

  1. Hold the "MODE + POWER" button to turn on the meter in Custom Function setting mode
  2. Turn the jog wheel counter-clockwise until setting number 3 is selected
  3. Press the "MODE" button to cycle through the values to select either 1 (for 1/3 stop) or 2 (for 1/2 stop) increments.
  4. Hold the "POWER" button to power off then again to power back on

The Custom Setting instructions can also be found in the L-758 user manual, with Advanced Functions on page 44-45. http://www.sekonic.com/downloads/l-758_english.pdf


The aperture reading is indeed in 1/10 stop increments. I deem it impossible, except under laboratory conditions, to use the 1/10 f-number setting. Say a 50mm lens is mounted and set to f/8. The working diameter of the iris is approximately 50 ÷ 8 = 6.25mm. Opening up 1/3 f-stop, the revised f-stop is 7.1. Now the approximate working diameter of the iris increases to approximately 50 ÷ 7.1 = 7.0mm. Such slight changes are mechanically achievable. However, changes to the iris diameter finer than 1/3 f-stop will be challenging. To achieve, the price of the lens will escalate beyond the reach of the average photo enthusiast.


I found a really useful post on http://www.photographymad.com/pages/view/what-is-a-stop-of-exposure-in-photography

From this i understood that on most cameras ( set to 1/3 stops ), 3 clicks means 1 stop. 2/3 clicks means 2 clicks ( of dial ). To alter 1/10 system reading, eg= 0.7 (7/10) multiply 0.7*3 which will give 2.10 ie 2 ( cut fraction here ) and make 2 clicks ahead. You will get the 1/3 steps value of f

To get 1 step ahead in 1/3 steps, multiply original f with 1.41

  • That is a good article, and you are right about clicks, but I'm not sure where you are getting that math — it is not in the article, and it is very, very wrong. – mattdm Dec 28 '16 at 11:52
  • I see what you are looking for, though, and I'll post an answer when I get a chance to write it all up. – mattdm Dec 28 '16 at 11:52
  • @mattdm yes there was a mistake. I already corrected it. Thank you for insight. – Bineesh Dec 28 '16 at 12:04
  • Wayne says that f/8 plus 0.7 stops is about a third-stop below f/11. That is because f/11 is the next whole stop on the standard scale, and 0.7 is close to 2/3 (0.666666...). But, your formula is even more wrong at other apertures, because (as the article you found says!) the scale is exponential and you can't just add a linear offset. – mattdm Dec 28 '16 at 12:04
  • @mattdm you gave an insight to my calculation formulae, i have corrected it. Yet i assume my solution is simple and usable. Please comment. – Bineesh Dec 28 '16 at 12:07

enter image description herehello i have my own system of converting the tenth of the FM to the thirds of the Aperture scale. lets set f5.6 as an example: f5.6.o or .1 or .2 = no change f5.6

f5.6.3 its exactly 1/3, so plus one click from 5.6 = f6.3

f5.6.4 or .5 you are in the middle, same distance from all so it can be plus 1 or 2 clicks from 5.6 = f6.3 or f7.1

f5.6.7 is exactly 2/3 so its plus 2 clicks from 5.6 = 7.1

f5.6.8 or.9 its closer to f8 so its 3 clicks from 5.6 witch is a full stop = f8

enter image description here

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