Fast lenses, and High ISO

Started Jul 18, 2014 | Discussions thread
bobn2 Forum Pro • Posts: 55,085
Re: "fast" is relative

EinsteinsGhost wrote:

bobn2 wrote:

EinsteinsGhost wrote:

bobn2 wrote:

Fine. That's what I said too. What determines how fast a shutter speed?

"Sensitivity" of the media, scene brightness and aperture. Nothing to do with media size.

That's a strangely abstract way of determining your shutter speed. Do you have a table of available shutter speed against media, scene brightness and aperture? As I remember, my camera allows me to set 1/8000 for any scene brightness, 'sensitivity' and aperture, why should I not?

Glad that you have a camera you know how to turn dials of. Now, let us try something more with it. For that matter, let us use one of your images with EXIF:

So, why did your camera, or you, choose 1/250s, f/4.5 at ISO 100? Your response will help you get my point, on why you can't just turn the dial to 1/8000s just because you happen to have it.

Can't remember why I chose that exposure at that time. I was just trying out the camera anyway. But if I reconstruct my thinking. I aim for the largest exposure that I can get, subject to my pictorial constraints. This was hand held, and I was trying to avoid shake, so I set a shutter speed of 1/250 for 85mm and f/4.5 is the largest aperture that lens has at 85mm. Does that answer your question?

That was my original post. With high ISO do we need lenses with larger apertures just to allow more light when high ISO can achieve it for you with lesser light.

The only thing 'ISO' achieves is applying a given exposure to brightness function so that the image taken with your chosen exposure looks right at the end.

Which is the point of exposure, to achieve a specific brightness level.

But, you can achieve that specific brightness level with a different exposure just by setting the ISO differently. Does that make exposure pointless?

Yes, you can. In fact, I recall that being a major issue with a collective that I've often argued against.

You keep on saying this, but I can't remember myself or the 'collective' ever having an issue with setting the ISO differently.

But, since you seem to believe that you can't take ISO out of the equation when considering exposure, would you prefer lowest possible ISO if you can use it? Or, does it not matter?

As I said, I aim for the maximum exposure that I can, subject to my pictorial constraints.

Which ISO is your particular favourite?

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