philip_pj wrote:
Agree with MAubrey's point here. Even expert assessments of MTF at infinity using high end equipment can have great variations, enough so that they are simply irreconcilable - making both series unreliable. LR's 22/10/2019 comparo of the Tamron-Zeiss-Sigma f1.4 35mm lenses being a case in point.
Unlike many LR results (esp. the field graphs), which can often reflect the cross-frame performance of Zeiss lenses as seen in CZ's own MTF data sheets, this one, the Milvus 35/1.4, looks like an entirely different (and rather poor) lens.
MAubrey wrote:
It isn't about tested vs. theoretical (thought the Nikon S addition is certainly theoretical!). It's about two entirely different systems for measurement that produce different results.
It's just not a responsible comparison.
This is so, so true and leads to so many useless arguments online. A quick summary of what you're looking at, annotated.
All manufacturers except Zeiss and Leica: Computer generated 'theoretic best possible' MTF at infinity.
Variables: which program used for calculations, what type of light used, frequencies calculated
Zeiss and Leica(in-house, not just labeled): actual MTF results done on Zeiss K-8 and K-9 machines at infinity, average of 20 to 80 copies of prototype lenses.
Variables: none
Lensrentals: Trioptics Imagemaster HR MTF bench at infinity
Variables: none
All other test results: computer analysis of target chart.
Prime variables: Imatest or DxO
Major variables: Target chart size, target chart resolution, choice of 'corner' and 'mid' targets (this is actually 24 choices using Imatest), lighting (a 20% variation in results possible), camera used, 'acceptable angle' standards, use of RAW vs JPG, RAW converter used for RAW images.
Any comparison between two sites using numbers is absolutely positively invalid.
Comparison within a site is generally valid, although with computer analysis sites you need to make sure methodology hasn't changed over time (changes in cameras or charts) or with focal length (many use different charts and lighting for wide-angle vs telephoto).
So it's never valid to say Joe shows the XRay 85 is sharper than Bill shows the Wonderbar 85 to be. It's never valid to compare Nikon's MTFs to Sigma's MTFs, etc.
It is valid to say the Nikon MTF charts show their 24mm is sharper than their 35mm.
It is valid to say Joe shows the XRay 85 is sharper than the Wonderbar 85.
And it's valid when someone else says Bill showed the Wonderbar 85 is sharper than the XRay 85.
And these days, when differences are slight, Bill and Ray could well have both shown the absolute truth. Not just copy variation, but Bill might be testing in-camera jpgs at 12 feet and Ray testing RAWs at 26 feet, both with different lighting.
As a bit of an illustration, this is an Imatest Chart (not all Imatester's use it). I've circled in different colors the areas that can be analyzed as 'Corner' by different testers. If a color is used twice, they average both those results. In a big circle, all of the results.
After that some average all 4 corners (they're always a little different) and use that number, others use best corner, or worst corner, or average of middle two corners.
Since none tell you what their 'corner' is, it should be pretty apparent why you can't compare two different tester's corner numbers.
RCicala wrote:
This is so, so true and leads to so many useless arguments online. A quick summary of what you're looking at, annotated.
All manufacturers except Zeiss and Leica: Computer generated 'theoretic best possible' MTF at infinity.
Variables: which program used for calculations, what type of light used, frequencies calculated
The nuance of what was said was being lost in the rush to state the obvious of how MTFs from different sources aren't precisely comparable. I compared your measured MTF results of the GM vs Sigma's published MTF results - this is comparing actual results (GM) vs the best-case possible (Sigma), and even with that the Sigma still lags behind the GM at 24mm, so I don't understand the point rehashing how MTFs aren't comparable when even in the best case the original point about the Sigma underperforming vs the GM at 24mm still stands. Not to mention how the relative performance between the center and edges/corners within each MTF could also be used and the Sigma still underperforms by that methodology as well.
snapsy wrote:
The nuance of what was said was being lost in the rush to state the obvious of how MTFs from different sources aren't comparable. I compared your measured MTF results of the GM vs Sigma's published MTF results - this is comparing actual results (GM) vs the best-case possible (Sigma), and even with that the Sigma still lags behind the GM at 24mm, so I don't understand the point rehashing how MTFs aren't comparable when even in the best light the original point about the Sigma underperforming vs the GM at 24mm still stands. Not to mention how the relative performance between the center and edges/corners within each MTF could also be used and the Sigma still underperforms by that methodology as well....Show more →
What's interesting about the Sigma 24-70/2.8 MTF graph is that the zoom actually performs better at 70mm than 24mm.. (at least at center). I've never seen a zoom performing better at the long FL. Perhaps Roger can comment on this...
Fred Miranda wrote:
What's interesting about the Sigma 24-70/2.8 MTF graph is that the zoom actually performs better at 70mm than 24mm.. (at least at center). I've never seen a zoom performing better at the long FL. Perhaps Roger can comment on this...
I think it's pretty common for zooms to be optimized at one extreme of the FL over the other and agree it might be more common that wide end gets optimized on midrange zooms. Sigma might have chosen to optimize the long-end as consideration for how the lens fits with users who shoot with their 14-24mm as well, the idea being they will use the 14-24mm for 24mm in preference over the standard zoom.
snapsy wrote:
I think it's pretty common for zooms to be optimized at one extreme of the FL over the other and agree it might be more common that wide end gets optimized on midrange zooms. Sigma might have chosen to optimize the long-end as consideration for how the lens fits with users who shoot with their 14-24mm as well, the idea being they will use the 14-24mm for 24mm in preference over the standard zoom.
The Sigma 14-24/2.8 DG DN definitely performs better at the wider range. It's really world-class at 14-18mm.
Although 24mm is its weakest FL, it's still great, performing similarly (actually better) than the 24/1.4 GM prime in terms of resolution/contrast, CA and astigmatism. https://www.fredmiranda.com/forum/topic/1609212/20#14997501
So, yes, perhaps Sigma optimized the lens knowing they already have the 14-24mm range covered with outstanding performance.
On the other hand, the Sony 24-70/2.8 GM is much weaker at 60-70mm and that could be the range the new Sigma outperforms it.
Actually the Canon 70-200mm f4IS II L performs better at the longer FL than shorter.
Fred Miranda wrote:
What's interesting about the Sigma 24-70/2.8 MTF graph is that the zoom actually performs better at 70mm than 24mm.. (at least at center). I've never seen a zoom performing better at the long FL. Perhaps Roger can comment on this...
Fred Miranda wrote:
What's interesting about the Sigma 24-70/2.8 MTF graph is that the zoom actually performs better at 70mm than 24mm.. (at least at center). I've never seen a zoom performing better at the long FL. Perhaps Roger can comment on this...
That was my finding, too, and it is a little unusual. I have been told by a designer (and I'm repeating stuff that's above my pay grade here, so I may be wrong) that zooms generally start design as focal length X and then the zoom is designed in to reach X + Y or X- Y. X will generally remain the best performing focal length. That would suggest the Sigma started out as a 70mm design, but I'm guessing.
snapsy wrote:
The nuance of what was said was being lost in the rush to state the obvious of how MTFs from different sources aren't precisely comparable. I compared your measured MTF results of the GM vs Sigma's published MTF results - this is comparing actual results (GM) vs the best-case possible (Sigma), and even with that the Sigma still lags behind the GM at 24mm, so I don't understand the point rehashing how MTFs aren't comparable when even in the best case the original point about the Sigma underperforming vs the GM at 24mm still stands. Not to mention how the relative performance between the center and edges/corners within each MTF could also be used and the Sigma still underperforms by that methodology as well....Show more →
Wasn't trying to roll over your comparison, Adam, I follow your logic here. I just get high-strung about people comparing numbers from two different sources.
I wonder how many people on this forum don't have 24-70 GM yet. It has been around for almost 4 years and I bet that anybody who needed one already has one. I guess there are new SONY E-mount shooters migrating from other brands, but even if Sigma is going to be better than GM - I'm not going to switch. 24-70 GM may not be the sharpest and best GM lens, but it works just fine for me even on A7RIV.
samosh wrote:
I wonder how many people on this forum don't have 24-70 GM yet. It has been around for almost 4 years and I bet that anybody who needed one already has one. I guess there are new SONY E-mount shooters migrating from other brands, but even if Sigma is going to be better than GM - I'm not going to switch. 24-70 GM may not be the sharpest and best GM lens, but it works just fine for me even on A7RIV.
I really like my GM, it works very well for me too. But I did order the Sigma because if I can possibly find a better lens...I figure it's worth a try. I'm expecting it to arrive before Christmas and like that due to the Holiday Shopping Season, B&H has extended the return policy to Feb. 1, 2020. This gives a little more time over the holidays to have both in hand and see which one I like better.
samosh wrote:
I wonder how many people on this forum don't have 24-70 GM yet. It has been around for almost 4 years and I bet that anybody who needed one already has one. I guess there are new SONY E-mount shooters migrating from other brands, but even if Sigma is going to be better than GM - I'm not going to switch. 24-70 GM may not be the sharpest and best GM lens, but it works just fine for me even on A7RIV.
I’m one that has never owned a 24-70/2.8. That will change once the Sigma shows up on the doorstep. Since I prefer shooting with primes and I don’t shoot for pay, the big zoom hasn’t been a temptation. Until now. If I can get 90% of the Sony GM for half the price, it’s a big win since I’ll now have a single lens travel solution when I don’t want to bring all the primes. I said in another thread that I’ve owned several f4 zooms and other than landscape they never got much use since they didn’t inspire me. Same reason why I haven’t considered the excellent Sony 24-105. It’s a fantastic lens but I know from past experience I wouldn’t use it since it wouldn’t inspire me like some of my primes. If this Sigma turns out to be excellent, it will find a solid place in my bag. I’m quite excited to see more reviews.
mudlake wrote:
I’m one that has never owned a 24-70/2.8. That will change once the Sigma shows up on the doorstep. Since I prefer shooting with primes and I don’t shoot for pay, the big zoom hasn’t been a temptation. Until now. If I can get 90% of the Sony GM for half the price, it’s a big win since I’ll now have a single lens travel solution when I don’t want to bring all the primes. I said in another thread that I’ve owned several f4 zooms and other than landscape they never got much use since they didn’t inspire me. Same reason why I haven’t considered the excellent Sony 24-105. It’s a fantastic lens but I know from past experience I wouldn’t use it since it wouldn’t inspire me like some of my primes. If this Sigma turns out to be excellent, it will find a solid place in my bag. I’m quite excited to see more reviews. ...Show more →
Agree 100%, same situation and same opinion!
Based on my use of the 14-24 dg dn and the 35 dg dn, im betting this lens will be (good enough).
RCicala wrote:
Wasn't trying to roll over your comparison, Adam, I follow your logic here. I just get high-strung about people comparing numbers from two different sources.
Thanks Roger. I was responding mostly to the original poster in response to claims the MTFs aren't comparable and that it wasn't responsible to do so, which kinda triggered me as well since it looked completely past the nuance of what was being conveyed.
