# A7RII F1.2 Exposure Comparison?



## 9VIII (Aug 28, 2015)

I don't have the camera or an ultra fast lens, but maybe someone else around here who does also has the same curiosity?

The backside illuminated sensor on the A7RII is supposed to clear up a lot of space on the sensor for light gathering, and supposedly a lot of that circuitry on regular sensor designs gets in the way with wide apertures.

One of the biggest questions I've had ever since hearing about this camera is whether or not it produces the same exposure values at f1.2 as older sensor designs (or if you have an f1.0 lens to test that would be even better).
Apparently Canon uses a digital profile to adjust ISO accordingly and compensate, so ideally there should be no communication between the camera and the lens (an extension tube or taped pins should do the trick).

It would be amazing to see if the A7RII actually gets around this classic limitation of digital sensors, as it would open the industry for the possibility of making f1.0 lenses again.


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## bwud (Aug 28, 2015)

Is 1.4 wide enough? If so I could shoot on the R II and 5D3. I highly doubt ISO settings are equivalent, though, and don't know how to mitigate that.

Edit: never mind, per DXO's measurement they are only apart by 6 at base ISO (100=80 on 5D3, and 100=74 on a7R II). That must be practically indistinguishable.

If 1.4 is wide enough I'll set up some controlled lighting.


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## 9VIII (Aug 28, 2015)

Here's the article I'm basing this off of.
http://www.dxomark.com/Reviews/F-stop-blues

So I guess pixel pitch is also part of the equation here, the 5D3 having much larger pixels it should suffer from the effect less.
I'm guessing it would be about the same as the 1Ds3 or 1DMk4 at a light loss of around 0.4 stops (first chart).
According to the chart I would expect a 40MP camera to lose closer to 0.6 stops, so even if it matches the 5D3 then theoretically that's an improvement, though it would certainly be much less exciting.

But we really have no idea what's going to happen so yes, f1.4 should work.

If you have a crop body around it might be worthwhile to throw in as well.


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## Mt Spokane Photography (Aug 28, 2015)

You can't compare with a Canon lens, since the adapter puts it back and changes the angle. Sony does not have Native f/1.2 lenses, so you won't get a answer as far as a native lens.

Placing a lens further from the sensor should help with corners and edges. You would have to use a MF lens and adapter with a 5D MK III to get any sort of apples to apples comparison.


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## raptor3x (Aug 28, 2015)

Mt Spokane Photography said:


> You can't compare with a Canon lens, since the adapter puts it back and changes the angle. Sony does not have Native f/1.2 lenses, so you won't get a answer as far as a native lens.



This isn't true, you can see this effect quite clearly with an adapted lens (on an A7R at least). Just mount and f/1.4 or faster lens on an adapter without engaging the contacts and meter the scene. Engage the contacts and meter the scene again and you'll see a significant change. Alternatively, set the exposure parameters manually and take shots with and without contacts engaged and compare the histograms.


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## 3kramd5 (Aug 28, 2015)

Mt Spokane Photography said:


> You can't compare with a Canon lens, since the adapter puts it back and changes the angle. Sony does not have Native f/1.2 lenses, so you won't get a answer as far as a native lens.
> 
> Placing a lens further from the sensor should help with corners and edges. You would have to use a MF lens and adapter with a 5D MK III to get any sort of apples to apples comparison.



The sensor to rear element distance is the same between canon on canon and canon on Sony. How isn't that apples to apples?


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## Mt Spokane Photography (Aug 29, 2015)

raptor3x said:


> Mt Spokane Photography said:
> 
> 
> > You can't compare with a Canon lens, since the adapter puts it back and changes the angle. Sony does not have Native f/1.2 lenses, so you won't get a answer as far as a native lens.
> ...




Its pretty obvious that if a lens has no communication with the camera, the exposure will be change once it tells the camera what aperture its using. Canon cameras assume f/1.0, for example when the lens is disconnected.

What you see may happen, but you do not know what is happening because you do not know what aperture the A7R is assuming when the lens is disconnected.


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## 9VIII (Aug 29, 2015)

If Canon actually changes ISO values when you shoot with a manual lens, then just check the exposure at f4 first to calibrate.


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## raptor3x (Aug 29, 2015)

Mt Spokane Photography said:


> raptor3x said:
> 
> 
> > Mt Spokane Photography said:
> ...



None of what you're saying is true. A canon body absolutely does not assume an f/1.0 aperture. Try an experiment, it shouldn't take you more than 30 seconds. Attach something like an f/2.8 or slower lens. Pick a shot and meter with the lens connected. Now untwist the lens slightly and meter the scene again. You'll see the aperture reads 00 but the metering won't change. Now try the same with an f/1.4 or faster lens, you'll see that the metering changes by ~1/3 stop for an f/1.4 lens or ~2/3 stop for an f/1.2 lens. It's the same on an A7R. If your idea was correct, then the f/2.8 lens would change the metering by 3 stops while the faster lenses would show less change. 

EDIT: I just rechecked this with a 1DX and some lenses seem to consistently meter 1 stop under exposure when disconnected (24-70ii, 70-200ii, 100L) while the 135L didn't change at all between connected and disconnected. Unfortunately I don't have any f/4 lenses to test with but this is pretty interesting because I never saw this behavior with my 5D3. That said, keeping exposure constant you can still see the effect we're talking about in the RAW histograms where the camera boosts the ISO behind the scenes when using fast lenses. In addition, if you try the above experiment with an A7 body, I know for sure you'll see exactly what's been described. The question is whether or not the BSI sensor of the A7RII eliminates the need to secretly boost the ISO speed in the backgorund.


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## Sporgon (Aug 29, 2015)

raptor3x said:


> Mt Spokane Photography said:
> 
> 
> > raptor3x said:
> ...



Actually you might get a change in reading - if you had the camera set to matrix metering (pattern) mode. When you disconnect the lens the camera automatically switched to average metering, so when you do this with the lens connected properly make sure you change your camera's metering mode to 'average' - that's the one with no markings in the ikon. 

However you are quite right; with no contacts the camera switched to stop down metering mode - with an average reading.

Quite why Canon were good enough to supply us with this feature so we can use old, manual focus lenses via an adapter and still meter correctly via a stop down mode I have no idea, but it's great to be able to use some classic old lenses like the Takumars on the modern Canons.

And yes; it is pixel pitch that is the issue. If you want your f/1.2 lenses to work at f/1.2 without (too much) electronic jiggery pockery, get an old 5D.


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## sdsr (Aug 29, 2015)

9VIII said:


> It would be amazing to see if the A7RII actually gets around this classic limitation of digital sensors, as it would open the industry for the possibility of making f1.0 lenses again.



They haven't really stopped - among others there's a f/0.95 ff Sony E-mount 50mm made by Mitakon (and rather nice it is, too), Voigtlander makes several f/0.95 lenses for m43, and Ibelux makes a f/0.85 in various mounts. If I find the time this weekend I'll compare the Mitakon on a7rii vs a7r & a7s (before the a7rii showed up I believe I read comments to the effect that it behaved more like f1 or f1.2 (I forget which); I never bothered to compare it to my various f1.2 lenses in this way).


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## 9VIII (Aug 29, 2015)

raptor3x said:


> Unfortunately I don't have any f/4 lenses to test with...



Hold down the Depth Of Field preview button while unscrewing the lens. The aperture will stay closed to whatever you set.
(an old trick usually used for Macro shots with extension tubes)


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