Fast lenses, and High ISO

Started Jul 18, 2014 | Discussions thread
EinsteinsGhost Forum Pro • Posts: 11,977
Re: "the light"?

bobn2 wrote:

EinsteinsGhost wrote:

bobn2 wrote:

EinsteinsGhost wrote:

bobn2 wrote:

EinsteinsGhost wrote:

Great Bustard wrote:

EinsteinsGhost wrote:

Great Bustard wrote:

Albert Silver wrote:

tko wrote:

Remember that F4.0 is considered kind of slow on FF, but is equal to F2.0 on M43rds, which is considered "fast."

That's not entirely accurate. You are describing the depth of field equivalence, from one sensor to the next, not the light. f/2 on a m43rds may have the depth of field of f/4 on a full-frame, but the light will still be f/2.

What do you mean by "the light will still be f/2"? For a given scene luminance, shutter speed, and lens transmission, the density of light (exposure) projected on the sensor will be the same regardless of format, but not the total amount of light projected on the sensor.

Total light does not matter for correct exposure. It does not change the time value for which an exposure is made for a specific aperture value.

A competent mFT photographer with an EM10 + 12-40 / 2.8 shoots a scene at 25mm f/5.6 1/100 ISO 400. What settings would result

in the "correct exposure" if they had instead been using FF with a 6D + 24-70 / 2.8 VC?

For same exposure, any competent photographer would use f/5.6, 1/100 and ISO 400 on ANY format.

Would a competent photographer always use f/5.6, 1/100 and ISO 400 then?

No. The choice depends on scene. We're talking about a comparison of exposure here (don't deflect).

I'm not deflecting. The issue is how a competent photographer would select exposure.

And, a competent photographer would know that f/5.6, 1/100 at ISO 400 indicates a set of exposure parameters that is not bound by format.

That's not an answer. The photographer could choose f/2.8, 1/100, ISO 200; f/2.8, 1/50, ISO 100; f/11, 1/100, ISO 800; f/11, 1/200, ISO 1600 etc. Different exposures which lead to the same final image brightness. So which one should the competent photographer be choosing?

Same exposure as f/5.6, 1/100s, ISO 400.

No, they are all different exposures, one stop apart.

So, we should drop ISO from this argument, because it only defines final outcome, not exposure itself. In other words, exposure entails: Shutter Speed and Aperture Size. So, how in the world do you now manage to speed up a lens without using a larger aperture? Until now, you (and those few from the collective you've apparently impressed) have been claiming you can a lens becomes faster if you increase ISO.

Make up your mind, to enable a more coherent argument.

In fact, that is exactly what you arrived at with several possible combinations

As I said, they are all different exposures. So, your problem here is arguing from ignorance. You won't get much further unless you learn some photographic basics.

f/2, 1/200s and f/4, 1/50s are same exposures. Why would you disagree?

(something you don't seem to get in your own arguments above). Instead, there you claim, only one set of values provides you with "maximum" exposure.

Only one set here does give 'maximum' exposure, f/2.8, 1/50 ISO 100.Why wouldn't you use that?

As someone who you accuse to be ignorant of photography, allow me to educate you:

f/2.8 and 1/50s will give you the same exposure as f/4 and 1/25s. If you use a slower lens that goes to f/4 max, your best option is 1/25s for shutter speed. Now, if you want to bring in the concept of Exposure Triangle, that you can increase ISO to compensate for aperture and/or time, be my guest.

We don't have enough information to know - maybe not enough DOF at f/2.,8, maybe too much camera shake at 1/50 - assuming that the competent photographer chose f/5.6, 1/100 for a good reason. Still, maybe you should go and learn some basic photography before we continue. First, what 'exposure' means.

The topic is: Exposure.

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