Do we still "need" fast lenses ?

Started 6 months ago | Discussions thread
nigelht Senior Member • Posts: 1,861
Re: Do we still "need" fast lenses ?

vyoufinder wrote:

JimKasson wrote:

nigelht wrote:

JimKasson wrote:

nigelht wrote:

vyoufinder wrote:

primeshooter wrote:

Raising iso lowers IQ much faster than my idea.

Your idea doesn't produce the same image. It's irrelevant. IF it were relevant, I would also argure that, no, it doesn't. The difference between f1.2 and f4 is as different as apples and oranges whereas iso 100 vs. iso 1200 is almost unnoticeable. I'll re-iterate though, it's not a matter of image quality, it's a matter of a different image entirely. One has depth of field and sharp focus while the other will not.

Right. You're going to shoot ISO 100, 1/1000, f4 in poorly lit high school gyms when folks are shooting ISO 6400, 1/500, f2.8 in the same conditions.

No. What are you talking about? I'd probably be shooting with something more like f4, 1/500th and iso 3200 if others were shooting at iso 6400 1/500 and f2.8.

You're shooting 1 stop underexposed when using an iso invariant camera and 2 stops normally if proper exposure is ISO 6400, 1/500, f2.8.

While many cameras are iso invariant you're down one stop of actual light and that's not recoverable since that's 1 stop less of actual signal.

That's NOT the same as exposing at iso 100 1/500 f2.8 vs iso 6400 1/500 f2.8 and using ISO invariance in your favor.

Regardless of whether you shoot ISO 100 and push or shoot ISO 6400 there's still the same amount of noise as ISO 6400 because there's only ISO 6400 worth of signal.

By using 1 stop slower aperture you just made it ISO 12800 worth of signal and increased noise.

Also 1/500 is a compromise. You still get motion blur. 1/1000 is good and can stop most human motion. 1/2000 is better as it can stop fast human motion (punches, spikes, etc).

More light means you can shoot at a higher shutter speed rather than the lowest you can sorta live with.

But you never know, maybe I'd be shooting at f1.2 and a much lower iso... you know, if I wanted to separate the subject more and didn't mind almost no depth of field.

You don't have f1.2 because according to you it's not necessary.

ISO doesn't matter within the natural ISO range. Light matters. f1.2 physically provides more light to the sensor. Light you can trade for faster shutter speed or less noise.

Light that will help the AF sensor.  That matters too.  Faster lenses provide the AF system more light.

These numbers don’t make sense to me. What is your point here?


The point is that he would be shooting terribly underexposed in the lighting conditions often encountered by sports shooters.

Your point is based on an incorrect assumption. It's pointless. See: "What are you talking about?"

Its not pointless as you don't seem to understand exposure, light and noise.

The fallacy that everyone has the option of starting at ISO 100 is common in these kinds of threads.

Just start at ISO 100 and push three stops. See! There's zero impact on IQ! There's no need for fast lenses! Modern sensors are ISOless!

Also not true.

Very true. Your example above started at ISO 100. Why not start at ISO 12800 and try to push three stops?

Because then you'd quickly realize that the upper end of the ISO range you stop being ISO invariant as you end up pushing into the extended ISO range because you have multiple stops of less actual light to work with.

primeshooters question was:

And when you are shooting a moving subject in lower light and are unable to use flash, sports, wedding...please explain how a slow aperture and vr would help and why "they are just for bokeh"

Your tediously narrow minded "I only care about how I shoot" answer was:

I'd adjust my ISO

Your answer is wrong. Sports shooters already adjust their ISO to 1600+ in these conditions even with fast lenses. Often we're at ISO 6400 for proper exposure. We could shoot at ISO 100 and push in post but we STILL need to be shooting wide open.

There is no substitute for faster glass in low light conditions when you need to stop action. Not iso invariance. Not IBIS.

That's why folks pay for expensive fast glass. Not "just for bokeh" but for more photons.

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