APSC vs FF

Started 5 months ago | Questions thread
blue_skies
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Re: APSC vs FF
In reply to chr68, 5 months ago

chr68 wrote:

It looks like the apertures of the FE mount lenses that are available are ~1 stop lower that what we could get on a classic APSC camera.
The 24-70 does only open at 4. It is easy to find the equivalent on APSC opening at 2.8. ...

This limitation seems inherent to the low distance we have between the sensor and the lens that makes optical corrections much more complex to implement.
I'm wondering then what the benefit would be to have a FF camera like the A7 compared to an other APSC.

Of course I know that with adapters you can set lot of third party lenses.
Concerning the size, if you compares the A7 with an APSC camera, the benefit is less evident.

What are the optical and Image Quality advantage of the A7 full frame camera compared to APSC?

Using f/2.8 'super' zoom (wide-to-tele) lenses would quickly evaporate the 'compactness' factor of the A7/r cameras. Going with f/4 OSS lenses is a better choice.

I'd rather carry an f/4 OSS zoom lens with a faster prime, than having to use the large f/2.8 OSS zoom all day long. The same argument can be made for the APS-C cameras - even for APS-C, f/2.8 results in a sizable lens.

Consider that the FE2470Z/4.0 lens is similar in size & cost as the m43 12-40/2.8 Pro lens - you'll realize that even smaller format cameras pay a hefty price for fast zoom lenses.

You can adapt f/2.8 non-FE lenses quite easily, so you have plenty of options.

Mind you, there is no image box, so wide-angle lenses do not grow to artificial large sizes because they have to rear-project the image from a distance. Rather, they can come much closer to the sensor (except that the extreme case, UWA RF, causes magenta shift and smearing issues in the corners on the FF sensors).

If lenses are larger than the cameras flange distance, e.g. at around 55mm, the benefit of mirrorless disappears, as the lens for a mirror-box based DSLR and the mirrorless cameras reach about the same distance from the sensor in each format. (DLSR using a shorter lens - that needs an adapter on mirrorless).

As to the FF versus APS-C trade-off, the FF sensor is more than twice the area of the APS-C sensor. This requires lenses to project a larger image circle, which will grow lenses in girth: at the same FL, the FF lens will be heavier/wider. With such a lens, your sensor receives over twice the amount of light, and can have much larger pixel sites at similar resolutions, which all results in the larger sensor having higher dynamic range, producing lower noise levels at higher ISO settings, and capturing more fine detail for a lower resolving lens (as the lp/mm actually goes down for the larger sensor).

With the A7, you'd gain: noise-free, high ISO, shallow DOF (control), sharper images (with lp/mm limited lens), but the cons are: heavier lenses, needs more precise focus, larger camera body.

With the APS-C Nex, you'd loose roughly a stop wrt/ noise, ISO, DOF control, and you would need higher IQ lenses for the 24Mp sensors (Nex-7, A6000). But the lenses would be smaller & lighter, focus can be quicker (fewer steps), and the camera bodies are tiniest.

I would recommend carrying a zoom and a prime. If they are both OSS, you are also covered for video with either. The A7/r does not have OSS prime lenses yet, so video with a prime will be choppy, unless you use a stabilizer or video tripod. Of course, an f/1.8 prime on the A7 is a full stop beyond the f/1.8 prime on the Nex, resulting in more DOF control and lower noise output.

If you use the A7/r mostly in stopped down aperture mode (e.g. to gain more sharpness), then the better choice would be an APS-C camera, unless you have a lot of legacy glass. With legacy glass you have the choice to use a focal reducer (speed booster) on the APS-C or use the A7/r FF. In both cases, the lens will be back to its intended use (wider FOV than just APS-C crop).

Sometimes, using a straight adapter, narrowing the FOV by the crop factor, can be beneficial. E.g. if you have a fast 35mm/f1.8 lens, then with both straight and speed booster adapters you effectively get two lenses: 35/f1.4 and 50/f1.8. (Note, the lens is made 'faster', but effectively, since you are using a slower sensor, it is the same as using the lens on the A7/r).

On the A7/r, you can achieve the same by using 'crop-mode', but the pixel count drops to 10.5Mp for the A7 and 15Mp for the A7r.

If you use tilt and shift adapters, than only the APS-C has low cost solutions. On the A7/r you'd have to get a TS lens, which are quite expensive.

Look at pictures that you typically take - what type of lens, what type of lighting, what type of exposure. If you have lots of high-ISO images with stopped down aperture, just get a faster prime lens. But if you have lots of high-ISO images with a fast lens, you may want the A7/r FF sensor. If most of your ISO is at 1600 or below, you'd be happier with APS-C cameras.

(Be careful with the Nex-7, it is ISO 1600 limited, that is a stop slower than the other Nex cameras at ISO 3200).

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Cheers,
Henry

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