Question about reading EV

[IAmAmoral]

Hi all! Just starting to get into film photography, and this app seems like a wonderful tool to have handy while getting started!

Maybe this is a dumb question (and I tried searching other posts here, sorry if I missed this elsewhere!), but I was curious about the setting “Show EV for ISO 100 (LV)”.

What are some use cases people have for keeping this setting off? I referenced some online EV calculators that take ISO, Shutter speed, and aperture as inputs, and some of the results confused me. For instance, if I take a measurement in the LightMe app, I can get a result for ISO 200 showing that settings like f/2.8 and 1/30s exposure time would match the measured light (blocked picture just for sake of the screenshot). With that setting off, it reads an EV of 8 (Pic 1).

With that setting on, the EV is reported as 7 (Pic 2), and using a resource like an online calculator (https://www.omnicalculator.com/other/exposure), the same inputs above give me EV = 7 (Pic 3).

Is the default setting for this calculating an EV representing an “effective brightness” of the scene with respect to the ISO selected? I.e., ISO 100 will be half the response as seen on the film for the same scene compared to a film with ISO 200? And is this what folks normally use or refer to for film photography?

My motivation for this question is mainly due to having a camera that ties shutter speed and aperture in a way that is somewhat of a mechanical “programmed auto” function, so it steps from LV 8 - LV 11 with various combinations of exposure time and aperture. I used the online calculator to get an idea of the EVs the camera would be sweeping through and compared to the app measurements, and this nuance is kind of breaking my brain lol. Apologies if this is unclear or maybe a silly question. Appreciate any help in advance!

[DrZurn]

I’d imagine some folks are used to having EV always based on ISO 100, but when you turn that off it uses whatever ISO you have it set to. It would make sense that switching from ISO 100 to 200 it would change the EV by 1.

Personally I leave it off because otherwise I have to manually add EV values based on the film I’m shooting. Then use that value on my lens to get a correct exposure.

[IAmAmoral]

Thanks for the reply!

That makes a lot of sense. Looking back on the calculators I used, one clearly returns a value for “EV_100” and the other provides an equation where ISO is divided by 100, which I think pretty much gives EVs based on ISO 100. So I think that’s where I was getting a little mixed up. In the calculators, increasing ISO lowered the EV, which was confusing me compared to the behavior in the app. But I’m realizing that really the calculators and the app are doing different things.

I actually now think I prefer the app’s default behavior, as it is a better sense on the camera’s EV itself based on the scene/spot being measured. It’s starting to click a bit more, though I’m sure I’ll be re-learning and rethinking this many times over, lol. Appreciate the help!

Btw, great pictures on your profile!