lamiaceae Loc: San Luis Obispo County, CA

Dear UHH'ers:

As you know I have been getting in to some rather technical Photography lately. I just got a nearly new Gossen Luna-Pro SBC Exposure Meter Tuesday from KEH in the mail, and it got me thinking. . .

Any of you Mathematically inclined Photographers or Engineers out there able to help me out and solve this equation.

D=(10*LOG10(N))+1

for N = ?

I can not seem to do it correctly in Excel, that is a base 10 Log not a natural log. What I was doing is making a "calculator" for converting ISO to DIN on a spread sheet. That works fine. But I would also like to go from DIN to ISO. I can not seem to figure out how to do it or Excels' cryptic math functions. It has been over four decades since I have taken any math classes. My education was in Biology, Art, and Teaching. I got as far as (D-1)/10=LOG10(N). Please solve this for N. Thank you.

twowindsbear

Follow this link to an instruction book for your light meter:

https://www.pacificrimcamera.com/rl/01256/01256.pdf

Scroll to Section VI, Appendix, for a table of Intermediate ASA&DIN Values.

Well, unless what you REALLY want to do is an exercise in using EXCEL.

According to the image on the front of the manual from the link above, the Gossen Luna-Pro SBC Exposure Meter also has a scale to directly set the ASA/ISO/DIN value into the calculator.

lamiaceae Loc: San Luis Obispo County, CA

Thank you. Yes, I was aware of the table in the owners manual. I DL'd a copy earlier this evening. I really wanted to play with it in Excel. As it turns out I finally figured out the equation and able to get it to work with Excel. I found both equations on a Wikipedia page about photographic exposure. It had all sorts of obscure historic exposure scales too. It seems Gossen has made all sorts of variations of their meters for different markets and years like car models. My particular Luna-Pro SBC does not have the DIN scale at all, only the ASA just before that was switched to ISO. Their older Luna-pro and Luna-six Cadmium meters also varied as to their film speed scales provided. Some what annoying I'd say for those looking for a used one and finding a so many that are virtually alike but still slightly different. Some only differ by their color schemes. I have been a fan of Gossen meters for decades. This is what KEH sold me! It seems to be in like new condition. Only missing the original box and the Instruction Manual.

Notice My Gossen Luna-Pro SBC Meter has no DIN scale, only an ASA (US ISO).

(Download)

rmalarz Loc: Tempe, Arizona

This might help without the need for the math.

https://rafcamera.com/info/imaging-theory/gost-asa-din

https://www.scribd.com/document/357114731/DIN-ISO-Standard-Conversion
--Bob

twowindsbear

Hmmmm Your meter is a bit different from the meter pictured in the link.

lamiaceae Loc: San Luis Obispo County, CA

Yes. And I am not surprised. Thanks for you input anyway.

lamiaceae Loc: San Luis Obispo County, CA

Hi pals,

It figures, a few minutes after posting my cry for help I re-read the Wikipedia article and finally understood it and its two pertinent equations. I was quickly able to figure out what I needed for Excel,
N=POWER(10,(D-1)/10), N and D being cells on the spreadsheet for N being ASA or ISO and D being DIN. One hogger suggested using 0.955 instead of 1 for better results. I was not actually trying to create a table, but a "calculator" for ISO to DIN and DIN to ISO. Some of you found ingenious ways of doing this and by iteration. Thanks everyone for helping. I should get back to doing some photography again, including focus stacking small subjects. Whence the need for an incident exposure meter. - Mike

fetzler Loc: North West PA

The Answer:

D=(10*LOG10(N))+1

Subtract 1 from both sides

D-1 = 10*Log10(N)

Divide both sides by 10

(D-1)/10 = Log10(N)

Take the antilog (raise to a power of 10)

10 ^ ( (D-1)/10 ) = N

lamiaceae Loc: San Luis Obispo County, CA

Yes, thank you. The last step there is what I did not remember how to do. I eventually found the equation in a document and was able to get it to work in excel. Thank you for actually answering the question the way I asked it and showed the steps.