The big lens resolution test on the AF101

A key part of the adaptation to shooting on a multi-lens camera, is knowledge of your lenses.

I bought an additional lens for my kit the other day, a Sigma 50mm f1.4. I was curious to see how good the sharpness was compared to my other lenses, and this led me to creating my own resolution test for all my lenses.

First off, this isn’t particularly scientific. It’s just for me to make a comparison. So the only control I had over the experiment, was to keep the resolution target (the image I’m shooting) the same, and to keep the lighting the same throughout.

I didn’t look at any of the manufacturers web sites for any tech details, I just used my eyes and summarised what I saw.

NOTE: In actuality, all these lenses produce nice results but it’s good to know the limitations of each lens to avoid disappointing results. Image quality is very subjective and depends on the what you are producing for. This test just represents my view of how these lenses perform to my eyes.

The Process

The chart used is an ISO 12233 resolution chart (downloadable here). This, I’m led to believe is as good as any in seeing the weaknesses of a lens. See this link for more information about the chart.

This was then printed onto A4 photo quality paper using a Canon iP4300 photo inkjet printer. You can buy expensive versions of this chart, but for the sake of cost and comparison, this inkjet version seemed adequate enough. In some of the finer areas of the chart, you can see the limitations of the printing process, but this is the best I could achieve using the tools available to me.

The chart was fixed to the wall and lit with a single light overhead. I framed up the test chart the best I could and then shot with the different lenses and different apertures to assess the difference between each lens – not to measure the resolution of the lens, only to see the differences.

The Lenses

I’m sure if I had more time (or less of a life) I could carry out a more accurate test of each lens. But this test was just for me to see where the differences lay between each lens.

The lenses I will be testing are:

Sigma 30mm f1.4 

Sigma 50mm f1.4

Sigma 50mm f2.8 Macro

Tokina 12-24 f4

Tamron 17-50 f2.8

Sigma 70-200 f2.8

So, as you can see, all fairly normal Nikon fit stills lenses. The AF101 has around a 2x crop factor with these lenses, so the focal lengths are effectively doubled. This has the effect of using the centre portion of each element in the lens and avoids the normal drop in resolution observed at the edges of the glass. This would be viewable in a full frame stills camera, such as the Canon 5D MkII. So I was curious to see how this looks in the real world.

The lens adapter I’m using (The MTF Nikon G to Micro 4/3rd’s adapter) doesn’t allow me to measure the aperture except for fully open and fully closed. Only two of the lenses have an aperture ring (the Sigma 50mm Macro and the Sigma 70-200 f2.8). So there are some approximate apertures in the test and these are indicated as such in the results.

Each lens was measured fully open, partially open (f2.8 for the wide aperture lenses) and also around f8-f11.

The Results

Sigma 30mm f1.4

f1.4		f2.8 approx		f11 approx

Sigma 50mm f1.4

f1.4		f2.8 approx		f11 approx

Sigma 50mm f2.8 Macro

f2.8		f11 approx

Tokina 12-24mm f4

f4.0 at 12mm		f4.0 at 24mm

f8 approx at 12mm		f8 approx at 24mm

Tamron 17-50mm f2.8

f2.8 at 17mm		f2.8 at 50mm

f8 approx at 17mm		f8 approx at 50mm

Sigma 70-200mm f2.8

f2.8 at 70mm		f2.8 at 200mm

f11 at 70mm		f11 at 200mm

Conclusions

The 30mm and 50mm f1.4 Sigma primes

The 30mm and 50mm Primes are sharper a couple of stops back from wide open. This is common knowledge I believe, but it’s good to actually ‘see’ it. They get even sharper as the aperture increases.

Chromatic aberration is present at wider apertures but is better controlled at smaller apertures. So if you are shooting high contrast things such as a leafless tree against a bright sky – watch out for chromatic aberration at wider apertures. Stop down to minimise.

In summary – expect softer results at f1.4 but get sharper results at f2.8 onwards.

The 50mm f2.8 Sigma Macro

The 50mm Macro is sharp at f2.8 and even sharper at f11. Quite a nice surprise for a cheap(ish) lens. Chromatic aberration at f2.8 is minimal and even less at f11. Nice.

In summary – this is a nice, sharp lens. Seems to have good optics for the price.

The Tokina 12-24mm f4 Wide Angle

Leaving aside the obvious barrel distortion at the 12mm end, the Tokina 12-24mm f4 exhibits quite a lot of blue diffraction at at f4 on the 12mm end but less so at the 24mm end at f4.

Additionally, when it’s stopped down, at 12mm, the aberration is blue and at 24mm it is pink. Weird.

In summary – this lens is quite sharp but exhibits chromatic aberration across the zoom range and throughout all apertures. Just be prepared for this.

The Tamron 17-50mm f2.8 Zoom

Nice lens this. It’s quite sharp throughout the zoom range. Perhaps a little softer at f2.8 at 50mm. Chromatic aberration is well controlled as well. The only thing of note is blue diffraction at the 17mm when stopped down.

In summary – this is my ‘go to’ lens as it is versatile and produces nice images for the money. Just be prepared for blue diffraction on the wide end when stopped down.

The Sigma 70-200 f2.8 Zoom

This is not the newer 70-200mm that Sigma now sell, so I’m sure there are better optics in that model. It’s also not the most expensive 70-200mm Nikon fit zoom lens out there. So I’m not expecting amazing results. And guess what, it’s not amazing. Principally, this lens seems to be quite soft at f2.8 with a fair amount of chromatic aberration. It’s especially soft at the 70mm end at f2.8. When stopped down the sharpness improves measurably as does the chromatic aberration.

Summary – try not to shoot at the 70mm end at f2.8.