Math for comparing APS-C to full frame?

Started Oct 15, 2013 | Discussions thread
Melbourne Park Senior Member • Posts: 2,683
Re: Crippling.

You can get too technical with all this.

Lets look at wide angle for a second. In A6000 etc, there is the Zeiss 12mm, which is an F/2.8 lens. It costs $1,200.

What's the equivalent from a light and width sense in the A7 range?

Well, as far as depth of field goes, you only need to get an F/4.3 lens ... so let be easy on APS/C Sony (actually a 1.53 crop) and say you need an F/4 lens.

What is in that range? Well, the 16-35 zoom from Zony would fit the bill. Depth of field wise, its shallower than the F/2.8 Zeiss prime. And its wider too - it only needs to be a bit over 18mm to be the same width, yet it is wider. And its longer too. So, it must cost a whole lot more. And it does too - its $1,348. So, for the extra $148, you get much greater width, and much greater length.

Lets try some primes then.

Let's start at the current best auto focusing portriat lens, the Batis 85mm, F/1.8 lens. It costs $1,199.

For depth of field, we'd need an A6000 lens that would be an F/1.18 - faster than an F/2.0 lens.

The focal length of the lens would need to be 55mm. Guess what - there is nothing approaching it that can auto focus.

Well, that simply did not work ... portraiture is better suited to full frame.

How about the classic full frame 35mm size? That equivalent to an A6000 with a 23mm lens. OK, the 24 is closest. Its the Zony 24mm f/1.8 ZA E-Mount Carl Zeiss Sonnar Lens. It costs $1,098. You need in full frame, for same depth of field, an F/2.8. The Zony Sonnar T* FE 35mm f/2.8 ZA Lens. It's $798. $300 cheaper ... and it weighs 120 grams, compared to the APS lense's 224 grams. And its half the length of the A6000 lens.

Hmm ... cheaper, more compact, lighter, but the same shallow depth of field and range.

Look at what the $445 28mm F/2 lens achieves ... with an A6000, you'd need an F/1.2 lens (well, F/1.3), and it would need to be a 22mm lens. Nothing comes close ...

Its only when you push full frame to fast lenses, to an area that is simply not available with A6000 lenses (and if it was available it would be terribly expensive) that things get costly. And such full frame lenses are often not costly when they are manual focusing (3rd party manual focusing lenses in full frame typically cost the same as they do with A6000 lenses but you get the sensor advantages from the full frame). You get stability for free too with series two Sony full frames. You get more colour depth out of the sensor too.

 Melbourne Park's gear list:Melbourne Park's gear list
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