[JJ_SO]

So-so: Sigma 24-70/2.8 Art:

 

https://www.lensrentals.com/blog/2017/07...ess-tests/

 

(Actually, I was tempted to write "another mediocre 24-70/2.8" but it would be an insult to "mediocre", apparently the Sigma is a bit less than average and far away from excellent)

 

Closer to excellent and apparently quite yummy: 14/1.8 Art, therefore oho:

 

https://www.lensrentals.com/blog/2017/07...g-hsm-art/

 

Which should be interesting for Astro-stuff.

 

However, I still would like to see how it catches up with Irix lenses.

[stoppingdown]

24-70 is really an unlucky range...

[JJ_SO]

For me it's okay - I don't even remotely need to think of replacing my 24-105/A Art against this shorty 

 

But the 14/1.8... Maybe I'll try to get my hands on a Irix 15 or 11 mm although none of them is offering f/1.8 but then, f/2.4 is also not bad.

[Klaus]

So as expected.

[Rover]

Soon to be found in the Photozone's lab, innit?  The Lenstip review of the 14/1.8 is inspiring, though I'm not going to get this lens any time soon, and its f/2.8 predecessor is going to serve for quite a while still...

[borisbg]

Looking at lenstip sample images I see good sharpness even at 1.8.

Size and weight seems to be justified.

[JJ_SO]

The sharpness is one thing. To manage to get it on the sensor with all the limits of DSLR AF (in terms of narrowing the single AF focuspoint) is a different story. Sigma needs to simulate non-existing lenses and tell the AF-unit a more or less correct acceleration.

 

Although this lens is great for sure, the pleasure of using it with a DSLR will be limited. The wider a lens (in double sense, here it is "wide aperture" and "ultra-wide-angle"), the more difficult it is to AF. Using that lens in lowlight situations wide open should not be done with too high expectations and best be done with LiveView. It's a perfect lens for Sigma's own mirrorless sd quattro/-H (which totally sucks in lowlight...) but the DLSRs will have to chew on that one.

[davidmanze]

    I had trouble believing the Sigma 24-70mm would actually be that average.   It's the right moment then for Tamron and the announced  G2  version of the standard FF zoom.

 

   If their recent track record is anything to go by Tamron may be the obvious choice........we will see when it arrives!

[JJ_SO]

I did not want to start a new thread or put a comparison between Nikon AF-S 14-24/2.8 G ED and Sigma 14/2.8 DG Art into a thread about the test results on Canon. As I already mentioned in this post, I'm wondering about a 4 ★ rating of the Nikkor and a pretty low one with 2 ½ ★ of the Sigma Art on Canon. Now, I don't like to just throw out my opinion but also see, if that opinion at least has some truth in it.

 

When I was trying to find a setup which can show differences of the 14 mm prime (close to the price of the zoom, btw.) and the zoom @ 14 mm, I didn't want to go for charts or brick walls, these are not my main subject with one of these lenses. In particular I wanted to find out how bad the borders and corners of the Sigma are wide open and at f/2.8.

 

Now, there was the first question: If I ever need to emphasize a border or a corner of a flat pane then where and how to focus? The difference of a point in the center of a pane and (if that point is exactly 1 m from the sensor away AND the sensor is aligned perfcetly parallel in to the pane) to a corner is roughly 66 cm farther from the sensor than the center of the picture. The horizontal border is 53 cm farther away from the sensors center - I didn't calculate, I used a laser distance meter.

 

That makes it clear, that I have to use LiveView to get the sharpness I would want. A big difference to focus on a chart, see what works best for center and hope the corners will catch up. They won't. Not even the most expensive DSLR lenses do so. So to me it makes a lot sense to put the sharpness where I need it to be. And that didn't end up bad for the Sigma - or well for the Nikkor.

 

Samples? I was hoping someone would ask. But here's the next thing: waterdrops on a window might not be the best subject to seek for sharpness? I agree, partly because it's difficult to focus manually at their low contrast. I don't do focus bracketing, so this might also be an issue. I didn't because the results to me are clear enough. The one with the yellow dot is always the Nikkor, the blue one the Sigma. See for yourself:

 



 

Both lenses wide open, lower border, more or less center of it.

 



 

Corners wide open - of both pictures there's a "f/2.8 vs f/2.8" version, with declasses the Nikkor very much - in this tiny crop and in this not very realistic situation. If someone wants to see, I post the f/2.8 versions as links, as the number of pictures per post are limited:

Border

Corner

Sieve

 



 

This sieve I took as something more structured than waterdrops. However, it does show another flaw of the Nikkor at 14mm and f/2.8. The fringing of the highlights is a bit more annoying than the Sigma, no?

 

Now, what did I learn?

• Don't trust ratings only (but that one is common knowledge at PZ/OpitcalLimits)
  
• A zoom still can have 4 ★ and being outstanding as a fast ultra-wide-angle zoom - at the extremes, no wide-angle zoom scratches the merits of great primes.
  
• But it's also true, it can't beat a great prime.
  
• In that case, the prime is even faster and stopping it down from f/1.8 to f/2.8 doesn't improve things for the zoom
  
• The Nikkor has more distortion than the Sigma (although the latter also shows a fair bit), but after switching the correction off in Capture One, the sharpness improved a little. And the distortion was much worse.
  

In my opinion, tests like here on PZ/OL should always only help if comparing more or less the same components.

 

• A chart stays the same - but lenses usually are corrected for ∞ . With a 50 × fl (50 × 14 mm = 700 mm) as a distance to the chart, one has to run into problems such as more vignetting and distortion at closer range.
  
• Also, the correction of panes must be difficult. In general as well but particularly at a close range.
  
• But all that is valid as well for the Nikon zoom, so why the huge gap? Difference in MP? 24 MP vs 50 MP?
  

I don't say, the Nikon zoom is worse than the Sigma prime - too much apples and pineapples... But I do say, my Sigma 14/1.8  prime is wide open in center, border and corner performance better than the Nikon zoomed out to 14 mm, has less distortion and CA. The big question remains: Will field curvature give a disadvantage the prime? To me, it's too much effort to test and not enough value in the result. I never use a wide open lens to reproduce a painting or drawing - and stopped down, things will become even.

 

But I saw the Sigma prime being better than I was hoping for - and that's not bad to find out after the purchase  ^_^

[mst]

Let me be the one to spoil the party: what I see in the Nikkor shots is not PF, but LoCA, IMO. So, to me, the Nikkor shots look out of focus.

I didn't quite get how you focused. Did you use LV to focus on the corners, or especially the crops you're showin? And did you do some focus bracketing or stacking to see if you hit best focus?