Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Focus reliability
#1
As there are some doubts in this thread about AF reliability and as well PDAF (phase detection AF) vs CDAF (contrast detection AF) I thought best to open a new thread, run some tests and find out what’s on in AF business.

 
First, the concerns are reasonable - PDAF is just spray and pray, sometimes a happy hit and soemtimes a crappy sh.. . But: That’s only valid for fast lenses or long focal lengths at short distances. Most lenses at f/2.8 or slower and  under 100 mm might just have enough depth of field to make the shot look good.
 
There was also a debate in this thread, that Sigma lenses focus worse than genuine Nikon lenses (can’t speak for Canon, others might run a test, too).
 
The setup was a D750 on a sturdy tripod pointing towards a target I print out from Reikan’s website. For the lenses between 35 and 105 mm the distance was 3 m, the 300 mm lens was too close at 4 m (but I only wanted to check focus reliability, not AF adjustments) and the 20 and 24 mm lenses were used with distance of 1.7 m, just to make it easy to spot the target. All lenses were AF calibrated before. Disclaimer: It’s not test about general quality Nikon vs Sigma - those are only my lenses. To make such a test with a wider conclusion, I’d need a lot more lenses and since I’m aware or convinced that AF with PD will never be as precise as CDAF in LiveView, I leave that statistically relevant test to others.
 
The setup made automatically 10 shots, and put a graph of the different sharpness results. At the end I got a number for those 10 shots. The next ten shots would give another number, just saying… It’s not about probability, it’s more how often were the shots very close to each other and if not, how much, was the difference. I don’t know the exact formula of this process. At the end I got 14 PDFs with 18 pages each for each lens and that number is only sometwhat abstract, a shot of a moment. Also, this test is only for static objects. Focus reliability with AF-C (continuous focusing until shutter release) is impossible to check or at least very difficult to compare.
 
In short, here are my results:
 
Sigma
 
20/1.4 98.3 %

24/1.4 99.7 %

35/1.4* 96.8 %

50/1.4 98.8 %
(another ten shots came up with 99.3 %
)
24-105/4 @ 90mm 97 %

24-105/4 @ 105mm 99.6 %

 
* I suspect the 35/1.4 needs a service, there’s a kind of akward sound in the lens. If it has to be repaired, I’ll repeat the test.
 
Nikon
 
14-24/2.8G @ 24 mm 99.6 %

85/1.4G  96.3 %

300/4 G 98.6 %

70-200/4 @ 105 mm 99.3 %

105/2.8 Micro 99.5 %

 
Here are three charts of those rows:
[Image: i-hwzhM6H-M.jpg]
70-200/4
 
 
[Image: i-W5msfkK-M.jpg]
85/1.4G
 
 
[Image: i-WDcXqrb-M.jpg]
24/1.4 Art
 
Now, I don't see a real big advantage from Nikon over Sigma. The 35mm appears to be far off and more a candidate for guessing, but as I wrote, I need to have it checked.
 
I also tried a row with Fuji XE-2 files - but this JPGs are not supported by FoCal Sad
#2
Thanks for your stats of AF repeatability JoJu,  I hope you realize I don't want to go down the road of Sigma vs Nikon reliability  pe se,  It looks like you are getting a very high success rate with both Nikon and Sigma personally I would be very happy with that!

   One thing though is the reported miss-focus shots all came from a distance of more than three meters, more from 5 mts to infinity, but rest assured I won't ask you to test those scenarios.

 

Here is a typical thread,

 

http://www.dpreview.com/forums/thread/3502775

 

 

 My point is just calling attention to the amount of complainants and general observations, I cannot say anything constructive beyond that, other than I have taken on board the PDAF vs PDCDAF debate.

 

  Just to add to the débâcle, here's Jason Lanier's video of the Metabones adapter and the Canon 70-200mm F2.8L on the Sony A7RII.

 

 If I was younger and richer, if...I would probably go there!

 

https://www.youtube.com/watch?v=1rz4T44GTWE

#3
Into the pool?  :lol:

 

I had not so much fun... thanks vor the vid. Very tempting, an A7II with the metabones adapter  :wub:

 

The reliability test is somewhat hypothetical, I mean, who takes 10 pictures and checks them for the sharpest? And all shots in AF-S, not helping to blow up the keeper rate if bird in flight are just too speedy for AF. As I said, I would not dare to compare anything like Sigma vs Nikon. It's alright, I guess and 100% is very impossible.

 

I could also check the "quality of AF points" but if I see how reliable PDAF with my combinations is, I think I better save some time and take pictures. At the end of the day it doesn't matter how high the reliability is if the one picture that matters, is off.

#4
Not sure what happened to your PD AF performing badly, though?

#5
Quote:Not sure what happened to your PD AF performing badly, though?
 

 I  think the short distance was favourable for the Sigma at least, no complaints from users at close distances!
#6
I really would like to see how a Nikon 200-500 performs along, with and without converter - that thing also changes a lot. The range of AFMA for the 150-600 appears to be huge. I'm still not certain how to deal with it: Redo the tests, which would be hours of work with uncertain results? Set up the values and try? Leave it and use LiveView? Use the Fuji with an adapter? At least, that LiveView is faster.

 

[Image: i-kM69WbW-M.jpg]

#7
JoJu,


I'm surprised by the vast range of different AFMAs that are needed for your Sport, my Tamron gets along fine with just -2 at all distances and at all focal lengths for "nearly" all the images...... when there is a miss, it's more to do with a bird (and it's usually is a bird) that was flying past fast or erratically, anything stationary is fine.


.....There is only one general exception and that is when the object is black against a bright sky. I also zoom in to 100% on birds etc. probably a maniac habit.....yes there are a few misses here and there, but I've rechecked with similar shots to find they were just a few outliers.


The more I've read, be it forums or utube user reviews, the more I see frustrated photographers having trouble with Sigma lenses especially the Art range. It makes me wonder if that "is" why they introduced this USB dock...... don't get me wrong, I think it's a great idea, but it should resolve issues and many are finding that they spend endless hours "twiddling" with fine tuning whilst ending up still having mis-focuses......

Others find fewer problems, but there seems to be a large gamble in the final outcome and it is at best uncertain.



My findings from pure reading and watching is that Sigma's optics are first rate but their AF is not yet without too many errors. Frankly I dare not buy an Art lens in case I find myself in the same boat...... and it's a pity!
#8
Don't tell me about fiddling around... IMO it starts earlier, with finding a quick and precise method to see if it's back- or front focus and then adjust AFMA. I tried LensAlign, lately I'm using more FoCal which is more convenient. In theory, both applications should find the same values - in real life it differs quite a lot. For LensAlign, I'd need a longer ruler, but Michael Tapes was not responding to a request. No ruler, no tele adjustments.

 

All results for the 150-600 should be taken with huge grains of salt. At first, how to focus 600 mm to infinity? Which kind of target? Most of the time infinity is beyond a huge wall of dust, mist or other things. I've seen the graphs and the spread of the shots. A value of -20 could as well be -12, it depends... The target for closer distances I printed out but the prints have slightly softer edges (in my eyes) than the professionally on plastic printed target of Michael tapes.

 

Honestly, dave, I do not believe that the Tamron would really be fine with one AFMA for all distances and all focal lengths, but if you get sharp shots with -2, then you get sharp shots Smile and I have no reason to talk you out of this. If you don't want to get a Sigma Art lens, leave it - there are other fine glasses as well. Those Tamron 35 and 45 are also getting very good reviews.

#9
The bottom line is........ I'm really not needing AFMAs at different FLs and different distances, one size fits all!

<a class="bbc_url" href="https://www.flickr.com/photos/124690178@N08/">https://www.flickr.com/photos/124690178@N08/</a>
#10
Roger at lens rentals has done some work on this:

 

http://www.lensrentals.com/blog/2012/07/...t-accuracy

http://www.lensrentals.com/blog/2012/07/...old-vs-new

http://www.lensrentals.com/blog/2012/07/...non-lenses

http://www.lensrentals.com/blog/2012/08/...on-cameras

 

really quiet an interesting read. 

  


Forum Jump:


Users browsing this thread:
1 Guest(s)