A7 & A7R... could real-world low light performance be worse?

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mrbenji
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A7 & A7R... could real-world low light performance be worse?
6 months ago

I've had a NEX-5 for a few years now, and was planning to upgrade to a NEX-6 until the 7/7R announcement gave me pause. I'm not heavily invested in APS-C glass... in fact, I only have the 50/1.8 and 18-55... the rest of my lenses are some terrific Konica Hexanon and Minolta MD manual glass. I'm primarily a "papa-razzi" (i.e. mostly pictures of my kids) but have recently started doing some shoots for friends and am thinking of branching out into the occasional paid job.

I think I have a decent-enough understanding of the differences between APS-C and FF... and something has started nagging at me that I'd appreciate help clearing up.

Basically, unless I'm misunderstanding something, my fear is that the A7/A7R will represent a step DOWN in "real-world" low light performance. By "real world," I'm referring to handheld, indoor shots.

Let me see if I can express my concern clearly. Whenever I'm shooting, one of the things I'm considering is (of course) DoF. Say we're considering the same scene, shot with a NEX-5 + 35/1.8, and with an A7 + 35/2.8.

As I understand it, if I frame the shots identically (i.e. standing closer with the A7 than the NEX-5), and I shoot the NEX-5 at f2, shooting the A7 a stop slower at f2.8 will provide an equivalent depth of field. But as far as light gathering goes, f2 & f2.8 are f2 & f2.8 regardless of the sensor size, so achieving the same exposure on the A7 would require using half the shutter speed, double the ISO, or some mix of the two to compensate.

Then you consider the fact the 35/2.8 is unstabilized... Sony claims a 4-stop advantage from OSS! Even if that's wildly optimistic and the advantage is "only" 2 stops, you'd still have to QUADRUPLE your ISO again to achieve a shutter speed high enough to compensate!

If you were shooting the A7 with the 55/1.8 (or, more precisely, a hypothetical 52.5/1.8), you could use f2 from the same spot as the NEX-5 + 35/1.8 and get ~ the same FoV and DoF... but would the resulting output actually be better after you factored in a quadrupled ISO?

It would, of course, be nice to have greater DoF control in bright light (due to the FF FoV's effect on DoF *and* the 1/8000 shutter), but as is, in bright light I just slap a polarizer and ND filter on my 50/1.8... that blocks enough light that I can even shoot wide open in full sun if I want to! There's no equivalent way of physically compensating in a low-light, handheld situation.

In short, although have little doubt I'd get better detail & DR from an A7 (or A7R, of course) in broad daylight... or in a static, tripod-mounted, low light situation, I'm starting to wonder whether the downside on the low-light end isn't too big to justify the added cost. I'm beginning to feel like the omission of IBIS/OSS in the current lineup is a WAY bigger deal than Sony would like us to believe.

Thoughts?

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Sony Alpha NEX-5 Sony E 18-55mm F3.5-5.6 OSS Sony E 50mm F1.8 OSS +5 more
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