Sel 50mm 1.8 Oss vs Fe 55mm 1.8

Started 5 months ago | Discussions thread
philip pj
Contributing MemberPosts: 698
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Re: Sel 50mm 1.8 Oss vs Fe 55mm 1.8
In reply to pixee, 5 months ago

It will depend on what 'much better' means to you, and what usage and aperture range you want. Let's look at the FE55 alongside two Nikkors of around the same focal length, the 50/1.8G and 50/1.4G to assist the decision (and to illustrate some other things for interested readers).

50s tend to be regarded as all rounders but the OOF quality and overall 'sharpness' are definite yardstick measures. Much better than a summary number such as DxO is the spread of performance across the frame at particular apertures. I like slrgear charts for this reason and it so happens they have tested all three of these lenses.

Aperture

You can't really expect even performance wide open on a planar subject to tell you much about resolution as your image at this aperture will be typically dominated by out-of-focus data, so quality of bokeh assumes much greater performance.

While it's not true that all lenses are equally good at f8 this is the best each generally can give for overall performance, if corner definition matters. To assess performance at one aperture for sharpness f5.6 is a good choice, but we must be aware of the rate of improvement on stop down from f2 to f5.6, because often you want very good results without surrendering more than a stop or so from wide open. Lets look at how these fare at f2, just one third - one stop down from open.

Nikkor 50mm f1.8G:

On a 24Mp sensor, this one has very uneven performance, up to 4 blur units = poor corners and substandard drawing of subject matter. Might have QC problems, I hope so.

Nikkor 50mm f1.4G:

On a 24Mp sensor also, a very centre-focused image with very poor corners, 3-4 blur units, fast drop-off of performance from the very small centre.

Sony 55mm f1.8:

On a 36Mp sensor - much tougher test! - very even and very good performance across the frame, very little loss of contrast/resolution from mid-frame to far corners. around 2 blur units.

Since it delivers superior results even with a challenging 36Mp sensor, on a 24Mp a7 the FE55 would be extremely good at f2. As you see above, it is still no contest with the two Nikkors. BTW, it is even worse for the $1700 Nikon 58mm f1.4, a supposedly refined 'bokeh' lens that is much less 'sharp'.

[You may wonder why lens review sites choose to test Sony lenses on the toughest test in full frame - the a7r - yet test Nikon's and Canon's lenses on five year old camera bodies, a far easier test of lens performance.]

The step up from 20-24Mp to 36Mp is exactly why lens makers are rushing to update designs, as we see with the Sigma ART 50mm f1.4. Unsuitable on the a7 cameras for other reasons - bulk and weight - that lens is almost double the weight of the a7r!

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