lamiaceae Loc: San Luis Obispo County, CA

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.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

The formula in Excel will be [=(10*LOG10(N))+1].

I've attached a screenshot of a quick table I populated with the formula and incremented the ISO numbers in third stops.

The formula in Column C says to look at the value in Col B and do the math. That formula is copied down the column. A quick and dirty way to populate the ISO values is to start with a value of 100 in Col B (in my worksheet that would be Row 2), then in the next row beneath the row (Row 3) with 100 write the formula [=B2*1.333] which will take the value directly above it and multiply it by 1-1/3. In the next row write the formula [=B2*1.6667] which will multiply the value found two cells above it by 1-2/3, and finally in the next row (Row 5) write the formula [=B2*2]. Then select the cells in rows 3,4 and 5 - and with the mouse, hover over the bottom right corner of the selection until the cursor turns to a plus sign - then drag as far as you want to populate the cells with this sequence of formulas that will increase the values in thirds.

This took way more time to explain than it did to execute. But if you are not familiar with Excel, it could be a challenge. I've attached the worksheet for you to play with.

Hope it makes sense to you. I would format the cells in Col C to not have any decimal points (or as many as you like).

Attached file:
(Download)

BebuLamar

Using your formula I figure this formula will solve for N given D

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

The formula works but I am still not quite understand your formula and although it does work.

LLC Loc: Ontario, Canada

Fir conversion from DIN to ISO see attached PDF...

Attached file:
(Download)

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

MrPhotog

You might want to round or truncate your results to make them come closer to the numbers found on cameras and light meters

Looking at the previous chart you fan see that ISO 100 = 21 DIN, but ISO 200 = 24.0103 DIN. While the mathematics is precise, on the camera or lightmeter, you would see 24 DIN— a whole number with no fraction.

In that Excel list, As the ISO grows, so does that useless decimal fraction.

Going from ISO to DIN you can just truncate that. The problem gets a bit fuzzier when you translate in the opposite direction and go from DIN to ISO. 24 DIN is going to come out as some number under 200. 27 DIN will be something under 400, and so on. For anything over 100 / 21 you want to , round to the nearest 100, but that doesn’t work when the DIN is under 24.

ISOs of 80, 64, 50, 40, 32, and 25 were associated with various films in the past, and so they had corresponding DIN numbers that matched up. For example, You wouldn't want to get a close answer ( like 65) instead of that 64 if you fed in the DIN and tried to translate.

Have fun tweeking your formula.

BebuLamar

The way they round off ASA or ISO number (as well as how they round off f/stop and shutter speed) it would be very difficult to use calculation to come up with exactly they way they round them off.

lamiaceae Loc: San Luis Obispo County, CA

Exactly true. Same with shutter speeds and especially F-Stops. The square root of 2 raised to the n-th power does not yield all the same numbers we usually set our lenses too. Note you get 22.627... rounded to 23, which is not 22. Never seen a full or quarter stop of 23 on a digital or film camera.

lamiaceae Loc: San Luis Obispo County, CA

You have a point there but that would take an overly complex Excel spread sheet to test and adjust output, and well beyond my programming skills. That issue was posted by another person answering my initial question. Once I got Excel working to do what I wanted I set it to round off and only display zero digits after the decimal point so to have it display only whole numbers for DIN or ISO. The ones that come out wierd I have to adjust myself in my mind. Like ISO 398 for DIN 27. One fellow Hogger gave me an adjusted equation that yielded 402, but I found that no better. Thanks for trying to help in any case.

amfoto1 Loc: San Jose, Calif. USA

Why don't you just copy a spreadsheet that already exists?

All you really need is a simple list of the original ISO combines both ASA and DIN.... such as 25/15, 50/28, 100/21 and 200/24.

The left hand number is ASA or what we now call ISO, while the right hand number is DIN.

There's a complete list of ISO ratings from 1/1 to 4000000/67, in 1/3 stop increments, at: https://en.wikipedia.org/wiki/Film_speed

Today we only use the ASA part of ISO.

PhotogHobbyist Loc: Bradford, PA

I think that Gene51 gave you a good basis for your conversion. Starting at ISO/ASA 100 equals DIN of 21. ISO 200 is DIN 27 and each full stop increase of the ISO is a three step increase of DIN. To me this is obvious from Gene51's scale which he posted. Based on that, each increase of 1 to the DIN scale is a 1/3 stop of ISO or ASA. No real need to have a formula and mathematically figure it, unless you want to get the very small variances of the fractions or decimals.

lamiaceae Loc: San Luis Obispo County, CA

That actually could work for what I need. I knew about the 0.3 to 1/3 stop already.

lamiaceae Loc: San Luis Obispo County, CA

I really just don't want tables of photo data and also like the challenge of figuring out how to present it in a formula. The DIN data I probably will never use. I wanted to play with it essentially. Thank you for helping.

Badgertale Loc: Albuquerque, New Mexico, USA

Here is a discussion on another forum that you may find interesting. It is mentioned that a one to one conversion is impossible.

https://www.photo.net/discuss/threads/asa-din-iso-conversion.90750/

(Download)

lamiaceae Loc: San Luis Obispo County, CA

LOL, that discussion on that other forum is all screwy and wrong. Crazy meter dial that can be flipped around backwards. And the table is all of historic and long obsolete standards. It does not even include modern ASA, DIN, and ISO standards. The table is from that same long Wikipedia article that I too found. Thanks for your involvment.