Fast lenses, and High ISO

Started Jul 18, 2014 | Discussions thread
EinsteinsGhost Forum Pro • Posts: 11,977
Re: "fast" is relative

bobn2 wrote:

EinsteinsGhost wrote:

bobn2 wrote:

EinsteinsGhost wrote:

So what? If the speed of `the lens is according to the shutter speed, then I've increased the speed of the lens by increasing the 'sensitivity' (I haven't, by the way) because I can now set a faster shutter speed, have I not?

Yes, you can change ISO and increase or decrease the shutter speed. What does it have to do with whether the lens is fast or slow?

You say that the speed of the lens is determined by the shutter speed it allows you to set. If you increase the ISO it 'allows' you to set a faster shutter speed, therefore under your definition, you have made the lens faster, because now you can set a faster shutter speed.

NO. You don't make a lens faster by increasing ISO.

So you keep saying, but that is not consistent with your definition of lens 'speed', that it allows you to use a fast shutter speed.

Nope. You simply don't get it. Unlike you, I won't run around screaming that my travel zoom is a fast lens when I use the camera at high ISO.

You reduce exposure time value by increasing "sensitivity" of the sensor/film.

You really don't The sensitivity of the sensor never changes. You reduce exposure time value by deciding to use a smaller exposure.

Almost there! Where you didn't want to trust my prediction we were going.

So, why do you shoot Auto ISO?

This is why people like to use the term "Exposure Triangle".

Many people get very misled by the 'Exposure Triangle'. Looks like you are one of them.

Actually the argument in favor of Exposure Triangle looks like this: "If you increase the ISO it 'allows' you to set a faster shutter speed"

Do you agree? I do. But, what is happening there?

Put it another way an f/2 at 200 ISO is as fast as an f/1.4 at 100 ISO because you can set the same shutter speed.

Shutter speed is as fast. An f/2 lens isn't any faster.

You need a new definition of 'fast' then, because you can set the same shutter speed with both.

And yet, you couldn't use a faster shutter speed because you claim having reached a limit on your lens being f/4.5 .

so the shutter speed can be twice as fast to achieve same brightness level in the image. Your change in exposure is only due to change in "sensitivity" of the media (we've discussed that several times before, haven't we? Funny though, you seem to be opposed to the idea of playing with exposure with ISO changes)

I don't know what you mean. I don't remember ever having expressed opposition to 'playing with exposure with ISO changes'.

Trust me, you will be going there sometime very soon.

Why should I trust you when you say I have said things that I haven't?

You don't have to trust me.

I trust you to be wrong.

You don't have a choice.

-- hide signature --


-- hide signature --


 EinsteinsGhost's gear list:EinsteinsGhost's gear list
Sony Cyber-shot DSC-F828 Sony SLT-A55 Sony Alpha NEX-6 Sigma 18-250mm F3.5-6.3 DC OS HSM Sony 135mm F2.8 (T4.5) STF +12 more
Post (hide subjects) Posted by
(unknown member)
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow