iso 50 on 20d, can i do it?

If you crank in ISO "L", it doesn't go for ISO 100 and "proper exposure", it essentially does 1 stop EC, and then adjusts the sensor site values down in internal PP to "undo the EC", so it's actually a 2-step process.

Jon wrote in post #2294567
If you crank in ISO "L", it doesn't go for ISO 100 and "proper exposure", it essentially does 1 stop EC, and then adjusts the sensor site values down in internal PP to "undo the EC", so it's actually a 2-step process.

Same thing really. ISO100 and proper exposure = ISO50 overexposed at the same shutter speed/aperture then cranked back down.

No - it meters and shoots as if it were at ISO 100 with EC+1, which isn't proper exposure, then cranks that back down to get the values more within range before writing the file(s).

Jon wrote in post #2294610
No - it meters and shoots as if it were at ISO 100 with EC+1, which isn't proper exposure, then cranks that back down to get the values more within range before writing the file(s).

Err yeah. Brain fart (seriously - I do get it!) Overexposure at ISO100...but that automatically blows highlights unless the scene is totally neutral. Turning it back down after the fact won't save the highlights. I'm failing to see how you could ever possibly save your highlights other than intentionally underexposing "ISO50", since that would be ISO100 either barely overexposed or properly exposed (this is where that term was coming in) but underexposed at ISO50.

Am I asking in a way that makes sense?

Shoot at ISO 100 and put a 1 stop neutral density filter on the lens. I assume you want ISO 50 in order to get a slower shutter speed. The neutral density filter does the same thing.

ScottE wrote in post #2294648
Shoot at ISO 100 and put a 1 stop neutral density filter on the lens. I assume you want ISO 50 in order to get a slower shutter speed. The neutral density filter does the same thing.

That's not the discussion.

Yeah - but that's where you lose a stop of DR. The highlights peak out at 4095 recorded; the camera halves that value to get things back down to ISO 50 equiv from the 100 that the sensor was running at, so the camera records that as 2047. So your tonal range is from 0-2047 instead of 0-4095 (11 bits/pixel instead of 12).

Jon wrote in post #2294660
Yeah - but that's where you lose a stop of DR. The highlights peak out at 4095 recorded; the camera halves that value to get things back down to ISO 50 equiv from the 100 that the sensor was running at, so the camera records that as 2047. So your tonal range is from 0-2047 instead of 0-4095 (11 bits/pixel instead of 12).

So I'm NOT crazy in thinking it's rather...stupid.

cdi-ink.com wrote in post #2294675
So I'm NOT crazy in thinking it's rather...stupid.

Only if you don't need it . . .

Or shooting wide open in really really really bright light.

I dunno, I'm stuck at ISO200 as my lowest "natural" ISO.... never using ISO100. I've never ran into maxxing out my shutter (but then again, it's at 1/16,000 )

cdi-ink.com wrote in post #2294542
... I can understand ISO3200 because sometimes you're just desperate for shutter speeds...but why would you need ISO50? JUST for waterfalls?

I never really shoot waterfalls, but I'd LOVE to have a real iso50 or even 25. Those really bright afternoons in the summer (when all brides seem to schedule their photos for) when you have maxed out your flash sync speed at 1/250 and have to use F/22 to avoid blowing things out.
HSS sucks as you gotta wait a few seconds between each shot.

Jon wrote in post #2294660
Yeah - but that's where you lose a stop of DR. The highlights peak out at 4095 recorded; the camera halves that value to get things back down to ISO 50 equiv from the 100 that the sensor was running at, so the camera records that as 2047. So your tonal range is from 0-2047 instead of 0-4095 (11 bits/pixel instead of 12).

I've noticed that my 20D (and my XT prior to that) have a highlight recovery of about 0.7 stop. So while you might not get the whole DR on a ISO 50 tweak on these cameras, ISO 75 is granted. In fact, shooting ISO 100 EC +0.5 (ISO 75) would increase DR, because you'll have to underexpose later in the Raw converter by 0.5. That would mean pushing cleaner data into the deepest shadows.

Ronald S. Jr. wrote in post #2294541
ISO 50 is achieved by an in-camera software trick. Not sure if 3200 is a trick as well. that's why they're called "H" and "L" instead of 50 and 3200.

Thanks Ronald, that's what I was trying to say.

cdi-ink.com wrote in post #2294653
That's not the discussion.

No, but it is the answer. Putting a one stop neutral density filter on the lens has exactly the same result as lowering the ISO from 100 to 50. Since the camera has no ISO 50 setting you have to do it some other way.

I am aware of two ways to accomplish the same result, both of which have been suggested.

1) Shoot RAW at ISO 100, over expose by one stop and post process to reduce exposure by one stop. That works as long as you don't blow the highlights, which will happen sometimes.

2) Neutral density filter. That does not risk blowing the highlights, but unless you use a high quality filter it can affect colour balance or add distortion or softeness. It also makes the viewfinder darker, which is usually not a problem if you have to use ISO 50 in bright conditions.

If you don't understand the fundamentals of photography, please don't criticize those who are trying to help.

ScottE wrote in post #2295591
No, but it is the answer. Putting a one stop neutral density filter on the lens has exactly the same result as lowering the ISO from 100 to 50. Since the camera has no ISO 50 setting you have to do it some other way.

I am aware of two ways to accomplish the same result, both of which have been suggested.

1) Shoot RAW at ISO 100, over expose by one stop and post process to reduce exposure by one stop. That works as long as you don't blow the highlights, which will happen sometimes.

2) Neutral density filter. That does not risk blowing the highlights, but unless you use a high quality filter it can affect colour balance or add distortion or softeness. It also makes the viewfinder darker, which is usually not a problem if you have to use ISO 50 in bright conditions.

If you don't understand the fundamentals of photography, please don't criticize those who are trying to help.

I do understand the fundamentals. You were suggesting a solution that was outside of the discussion. I agree that a filter would be better, but I was discussing the ISO50 in-camera methodology, not getting around it.