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Author Topic: 50mm Lens Comparison Wide-Open & Does Canon Boost ISO Sneakily?  (Read 5784 times)

neuroanatomist

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Re: 50mm Lens Comparison Wide Open & Does Canon Boost ISO Sneakily?
« Reply #15 on: July 13, 2013, 05:14:12 AM »
Hmm...right, it's a 1/2 stop, sorry.

No it is 1/3 stop!

The 1/3 stop steps are: 1.0 1.1 1.2 1.4 1.6 1.8 2.0 .........
No, it's both, or if you prefer, neither.  On the half-stop scale, f/1.2 is 1/2-stop wider than f/1.4, but on the 1/3 stop scale, f/1.2 is 1/3-stop wider than f/1.4.  See the wikipedia page on f/stops

Mathematically, f/1.2 really is closest to a 1/2-stop, since 21/2x0.5 = 1.1892), whereas 22/3x0.5 = 1.2599, which personally I'd round to f/1.3.
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Re: 50mm Lens Comparison Wide Open & Does Canon Boost ISO Sneakily?
« Reply #15 on: July 13, 2013, 05:14:12 AM »

CharlieB

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Re: 50mm Lens Comparison Wide-Open & Does Canon Boost ISO Sneakily?
« Reply #16 on: July 13, 2013, 08:31:58 AM »
Very good point about the sensor acceptance angles.  I'm also wondering if periferal illumination correction also might have had an effect in this case.

Fleetie

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Re: 50mm Lens Comparison Wide-Open & Does Canon Boost ISO Sneakily?
« Reply #17 on: July 13, 2013, 09:27:12 AM »
Very good point about the sensor acceptance angles.  I'm also wondering if periferal illumination correction also might have had an effect in this case.
No, because I always leave it switched off. And I just turned on the camera to double-check, and it was, and is, off.

The jpgs are SOOC, too.
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Mt Spokane Photography

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Re: 50mm Lens Comparison Wide-Open & Does Canon Boost ISO Sneakily?
« Reply #18 on: July 13, 2013, 12:42:13 PM »
The 50mm 1.4 is a old lens (1993) designed for film, so the effects of light drop off at the edge of a digital sensor are not compensated for.  Newer lenses do a better job of collimating the light so it comes in at a steeper angle, and the effect is less.
 
http://www.nikonians.org/html/resources/nikon_articles/body/FF_vs_DX_sized_sensors/

I don't think it's possible to collimate the light and still end up with a sharp image. There's urban-legend BS at work in that link.

I think you are right, now that I think about it, its nonsense, there would be no fixed distance to the sensor focal plane for collimated light.
 
I've revised my post.

rs

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Re: 50mm Lens Comparison Wide-Open & Does Canon Boost ISO Sneakily?
« Reply #19 on: July 13, 2013, 01:14:04 PM »
As higher pixel density sensors and faster lenses seem like a bad combination according to this, I wonder if it makes small sensor high MP bodies such as the OM-D E-M5 with lenses such as the SLR Magic 50/0.95 hyperprime not all as advertised?

With the pixel density of a 16MP m4/3 body (pixel pitch equal to a 64MP FF body) it is probably a long way off the f0.95 light capturing levels it claims. Could this effect make it nearer to f2.8?
« Last Edit: July 13, 2013, 04:55:39 PM by rs »
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Dylan777

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Re: 50mm Lens Comparison Wide Open & Does Canon Boost ISO Sneakily?
« Reply #20 on: July 13, 2013, 03:34:56 PM »
Hmm...right, it's a 1/2 stop, sorry.

No it is 1/3 stop!

The 1/3 stop steps are: 1.0 1.1 1.2 1.4 1.6 1.8 2.0 .........
No, it's both, or if you prefer, neither.  On the half-stop scale, f/1.2 is 1/2-stop wider than f/1.4, but on the 1/3 stop scale, f/1.2 is 1/3-stop wider than f/1.4.  See the wikipedia page on f/stops

Mathematically, f/1.2 really is closest to a 1/2-stop, since 21/2x0.5 = 1.1892), whereas 22/3x0.5 = 1.2599, which personally I'd round to f/1.3.

Thanks Fleetie for the data.

Thanks Neuro for providing the math formulas - I'm going to pretend that I know how to calculate those formulas and simplify the math so an ave Joe could understand:

 
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WillThompson

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Re: 50mm Lens Comparison Wide Open & Does Canon Boost ISO Sneakily?
« Reply #21 on: July 13, 2013, 04:13:17 PM »
Hmm...right, it's a 1/2 stop, sorry.

No it is 1/3 stop!

The 1/3 stop steps are: 1.0 1.1 1.2 1.4 1.6 1.8 2.0 .........
No, it's both, or if you prefer, neither.  On the half-stop scale, f/1.2 is 1/2-stop wider than f/1.4, but on the 1/3 stop scale, f/1.2 is 1/3-stop wider than f/1.4.  See the wikipedia page on f/stops

Mathematically, f/1.2 really is closest to a 1/2-stop, since 21/2x0.5 = 1.1892), whereas 22/3x0.5 = 1.2599, which personally I'd round to f/1.3.

Not on a canon camera that actually uses 1/6 stop increments, when setting exposure.  The camera uses the standard 1/2 stop nomenclature but uses actuall 1/2 stop increments when set to 1/2 stop steps and the same goes for 1/3 stop steps so the steps will be exactly 1/3 or 1/2 depending on the camera setting.

This means that the difference between a setting of 1.2 and 1.4 will be different depending on camera settings.

In the real world there is 1/3 stop difference as apposed to the representational of 1/2 stop steps!
« Last Edit: July 13, 2013, 04:31:56 PM by WillThompson »
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Re: 50mm Lens Comparison Wide Open & Does Canon Boost ISO Sneakily?
« Reply #21 on: July 13, 2013, 04:13:17 PM »

Aglet

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Re: 50mm Lens Comparison Wide-Open & Does Canon Boost ISO Sneakily?
« Reply #22 on: July 13, 2013, 04:51:18 PM »
@Fleetie - thanks for doing the test.... I'll take a bow :)
(IMO) This is a swindle that's perpetrated to persuade people to continue buying fast glass.

Thanks guys, I've actually learned something. :)
Knew about the acceptance angle issues of pixels but didn't know a sensitivity tweak was happening w-o me knowing about it when using a very wide aperture setting.
It's not a shooting scenario I often use, typically at f/2.0 or smaller aperture.  But now I know about it if necessary.

neuroanatomist

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Re: 50mm Lens Comparison Wide Open & Does Canon Boost ISO Sneakily?
« Reply #23 on: July 13, 2013, 05:39:19 PM »
Not on a canon camera that actually uses 1/6 stop increments, when setting exposure.  The camera uses the standard 1/2 stop nomenclature but uses actuall 1/2 stop increments when set to 1/2 stop steps and the same goes for 1/3 stop steps so the steps will be exactly 1/3 or 1/2 depending on the camera setting.

This means that the difference between a setting of 1.2 and 1.4 will be different depending on camera settings.

In the real world there is 1/3 stop difference as apposed to the representational of 1/2 stop steps!

Fine, but that doesn't address the original issue, which was about the difference between an f/1.4 and an f/1.2 lens.

Quote
@Drizzt321 - wide open an f/1.2 lens collects (1.4/1.2)^2 = 1.39 times as much light as a f/1.4 lens. This corresponds to 0.47 stops (not 1 stop.)

That difference is best represented as 1/2-stop, whether or not the settings of the camera result in that complete 1/2-stop being used.
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WillThompson

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Still only 1/3 stop difference! (When using 1.3 stop steps)
« Reply #24 on: July 14, 2013, 02:07:52 PM »
That difference is best represented as 1/2-stop, whether or not the settings of the camera result in that complete 1/2-stop being used.

Still not correct.


With a 1/2 stop setting f1.2 is actually f1.1892.

With a 1/3 stop setting f1.2 is actually f1.2599.

With both a 1/2 & 1/3 stop setting f1.4 is actually f1.4142.


This difference is why the 1/2 stop setting between f1.4 & f2.0 is f1.7 not f1.6 or f1.8 as it is less confusing due to larger numbers allowing better numeric distinction between settings.

On a side note,

Is a f1.2 lens actually 1/6 stop wider when set to 1/2 stop increments when shot wide open???
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neuroanatomist

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Re: Still only 1/3 stop difference! (When using 1.3 stop steps)
« Reply #25 on: July 14, 2013, 04:32:46 PM »
That difference is best represented as 1/2-stop, whether or not the settings of the camera result in that complete 1/2-stop being used.

Still not correct.


With a 1/2 stop setting f1.2 is actually f1.1892.

With a 1/3 stop setting f1.2 is actually f1.2599.

With both a 1/2 & 1/3 stop setting f1.4 is actually f1.4142.


This difference is why the 1/2 stop setting between f1.4 & f2.0 is f1.7 not f1.6 or f1.8 as it is less confusing due to larger numbers allowing better numeric distinction between settings.

On a side note,

Is a f1.2 lens actually 1/6 stop wider when set to 1/2 stop increments when shot wide open???

Who are you, DxOMark, unable to consider a lens independent of a camera?  ;)  Forget about the camera for a moment.  Compare an f/1.4 lens vs. an f/1.2 lens, just the lens - how much faster is the f/1.2 lens?  Well, neither exactly 1/2 nor exactly 1/3 stop, but 1/2 stop is a better approximation. 

To answer your question, 1D X with 85mm f/1.2L II, illumination constant, camera locked down, VF shutter closed, AV mode, ISO 100:

1/3 stop increments: f/1.2, f/1.4, f/1.6, f/1.8, f/2, metered shutter speed 1/50, 1/40, 1/30, 1/25, 1/20 s

1/2 stop increments: f/1.2, f/1.4, f/1.8, f/2, metered shutter speeds 1/45, 1/45 (no change from wide open), 1/30, 1/20 s

1 stop increments: f/1.2, f/1.4, f/2, metered shutter speeds 1/60 s, 1/30 s, 1/15 s
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WillThompson

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Re: Still only 1/3 stop difference! (When using 1.3 stop steps)
« Reply #26 on: July 14, 2013, 11:12:59 PM »
A EOS lens is only functioning to specification when powered up with a body.

The aperture setting is not a passive but an active device!

Is that metered manual or auto exposure?

In auto the camera can skew both settings by 1/6 or is that multiple 1/10's of stops with no indication of f-stop or shutter speed change. (Not sure of the sub step values that Canon uses 1/10 vs 1/6, It has been a long time since I went to Canon school)

So answer me this, how many stops difference is f1.2599 from f1.4142??????
« Last Edit: July 14, 2013, 11:31:19 PM by WillThompson »
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Re: Still only 1/3 stop difference! (When using 1.3 stop steps)
« Reply #26 on: July 14, 2013, 11:12:59 PM »