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Archive 2015 · Great Stuff on Lenrentals .com Blog re MTF of Wides

  
 
Scott Stoness
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p.1 #1 · p.1 #1 · Great Stuff on Lenrentals .com Blog re MTF of Wides


http://www.lensrentals.com/blog/2015/07/variation-measurements-for-wide-angle-lenses

Unsurprisingly to me - the zeiss 15/2.8 does very well.And at f2.8. With little copy to copy variation.
The samyang 14/2.8 is not nearly as good as the zeiss but is consistent across. With much larger copy to copy variation. [And massive barrel distortion which is not shown]

My other favorite zeiss lens does well as well except at extreme edges. 25/2. Signifcantly better than the ts24. And at f2. But the zeiss 21/2.8 does better at f2.8.

Unsurprisingly to me - the ts17 does better than the ts24. Contrary to other reports. Every time i focus at 7x or 14x I am impressed by the TS17.

This confirms my favorite lens - TS17, Zeiss 25/2 (nightscape) and Zeiss 15/2.8 (nightscape)

Thank you very much lenrentals.com

If you could just add the 11-24 it would be complete.

Scott



Edited on Jul 20, 2015 at 02:56 PM · View previous versions



Jul 20, 2015 at 02:01 PM
dgdg
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p.1 #2 · p.1 #2 · Great Stuff on Lenrentals .com Blog re MTF of Wides


thanks for the heads up.

And also a 20% off rental sale this summer.



Jul 20, 2015 at 02:55 PM
kevindar
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p.1 #3 · p.1 #3 · Great Stuff on Lenrentals .com Blog re MTF of Wides


thanks for the link. I guess we all look at the data and take from it what confirms our own bias the most to some extent.

First thing of course is that many of this lenses are fast lenses. with the exception of nightscape photography, wide open resolution, esp corner resolution is not very applicable in the field. most of these lenses will be shot from f5.6 to f16. Unfortunatley the data is for lenses wide open. additionally, variance will be less of an issue as you stop a lens down.

The canon 14 2.8 II, which I have repeeatedly claimed to be the most ridiculously overpriced lens canon makes, has the same crap shoot variance score of 4 as the Rokinon 14 2.8, at over 5 times the price. and does not even turn in as even of a performance wide open. (of course more interested in f 5.6 MTF.



Jul 20, 2015 at 03:24 PM
snapsy
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p.1 #4 · p.1 #4 · Great Stuff on Lenrentals .com Blog re MTF of Wides


The consistency ratings are shockingly bad for many of the expensive lenses Roger tested. Sadly it matches my experience as well. Hopefully Roger's tests will light a fire under Canikon and Zeiss.


Jul 20, 2015 at 03:57 PM
Schlotkins
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p.1 #5 · p.1 #5 · Great Stuff on Lenrentals .com Blog re MTF of Wides


Yea it would be interesting to see these at f8 or f11.

I have both the TSE17 and TSE24. Given I have 24 covered with about 3 other lenses, I always think about selling the 24 and just using an extender on the 17 when I really need shift.

Chris



Jul 20, 2015 at 04:01 PM
wayne seltzer
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p.1 #6 · p.1 #6 · Great Stuff on Lenrentals .com Blog re MTF of Wides


Would be better to compare at f5.6 or f8 instead of wide open for both MTF and consistency.



Jul 20, 2015 at 10:43 PM
johnctharp
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p.1 #7 · p.1 #7 · Great Stuff on Lenrentals .com Blog re MTF of Wides


wayne seltzer wrote:
Would be better to compare at f5.6 or f8 instead of wide open for both MTF and consistency.


That's coming. But look at Canon's latest- 50/1.8 STM, 24/2.8 IS, 28/2.8 IS, and 35/2 IS leading the pack!



Jul 20, 2015 at 10:47 PM
snapsy
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p.1 #8 · p.1 #8 · Great Stuff on Lenrentals .com Blog re MTF of Wides


wayne seltzer wrote:
Would be better to compare at f5.6 or f8 instead of wide open for both MTF and consistency.

Copy variation is most obvious wide-open so it seems like the best way to ferret out the data. That said, the magnitude of copy variation might be different at smaller apertures so consumption-wise I'd agree, that data might be useful as well.



Jul 20, 2015 at 10:47 PM
snapsy
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p.1 #9 · p.1 #9 · Great Stuff on Lenrentals .com Blog re MTF of Wides


johnctharp wrote:
That's coming. But look at Canon's latest- 50/1.8 STM, 24/2.8 IS, 28/2.8 IS, and 35/2 IS leading the pack!


Would be interesting to know if the improvement in consistency for these newer designs are a function of manufacturing process improvements, or optical design improvements (including designing for manufacturability), or because they're simple lenses/designs to begin with. I know from personal experience that the 24-70 II has horrible copy variation.



Jul 20, 2015 at 10:51 PM
johnctharp
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p.1 #10 · p.1 #10 · Great Stuff on Lenrentals .com Blog re MTF of Wides


snapsy wrote:
Would be interesting to know if the improvement in consistency for these newer designs are a function of manufacturing process improvements, or optical design improvements (including designing for manufacturability), or because they're simple lenses/designs to begin with. I know from personal experience that the 24-70 II has horrible copy variation.


Honestly, it's probably a manufacturing process improvement. Particularly for the 50/1.8 STM which is a weaker design than Nikon's more modern 50/1.8G, it being an aspherical design with a ring USM motor, designing tight requirements into the lens manufacturing seems like an inexpensive route to optical competitiveness while maintaining a price/feature advantage as in the case of the stabilized primes.



Jul 20, 2015 at 11:20 PM
RCicala
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p.1 #11 · p.1 #11 · Great Stuff on Lenrentals .com Blog re MTF of Wides


The short telelphoto lenses are now up, and a table you can sort to look at various factors. I have to say I was totally disappointed in the 85mm lenses as far as variation.

http://www.lensrentals.com/blog/2015/07/variation-measurements-for-telephoto-lenses

And Scott, the 11-24 is on deck for testing next week.



Jul 21, 2015 at 09:34 AM
Toothwalker
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p.1 #12 · p.1 #12 · Great Stuff on Lenrentals .com Blog re MTF of Wides


RCicala wrote:
The short telelphoto lenses are now up, and a table you can sort to look at various factors. I have to say I was totally disappointed in the 85mm lenses as far as variation.

http://www.lensrentals.com/blog/2015/07/variation-measurements-for-telephoto-lenses


Interesting stuff. Keep up the good work.

Do you measure the variance on lenses new out of the box, or after numerous harsh rentals? And which focus criterion do you use for the MTF bench?





Jul 21, 2015 at 10:28 AM
RCicala
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p.1 #13 · p.1 #13 · Great Stuff on Lenrentals .com Blog re MTF of Wides


Toothwalker wrote:
Interesting stuff. Keep up the good work.

Do you measure the variance on lenses new out of the box, or after numerous harsh rentals? And which focus criterion do you use for the MTF bench?



Paul, we measured groups of lenses both ways (new and after rentals). I've done a number of comparisons over the years and we don't see a difference. But our protocol is all lenses are tested on arrival, bad copies (about 2-2.5%) are screened out and returned, then the lenses are retested after each rental. Any lens with detectible change from baseline is either fixed by us or returned to factory service if we can't do it. That's why we got into testing in the first place. This particular series were almost all lenses bought in April - June, so they've rented 3 to 4 times.

The bench we use checks on-axis focus in 20 steps over 50 microns, then chooses the best on-axis MTF as the focus distance. All points, on and off-axis are measured at that focus distance. The lens is refocused after each rotation (each lens is tested in 4 rotations, giving a total of 84 measured points for each lens).




Jul 21, 2015 at 11:21 AM
jcolwell
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p.1 #14 · p.1 #14 · Great Stuff on Lenrentals .com Blog re MTF of Wides


Thanks for sharing those test results, Roger.


Jul 21, 2015 at 11:24 AM
wayne seltzer
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p.1 #15 · p.1 #15 · Great Stuff on Lenrentals .com Blog re MTF of Wides


Roger, Great work! But I am trying to get a feel of what your consistency numbers mean besides a higher number being better. How much difference a score of 7 vs 4 means. Also breaking the number in two, one for center and one for corners.Most of the difference is coming in the corners for most lenses?
Also MTFs for f5.6 or f8 would be more interesting for the WAs.
Looks like you are keeping that Olaf guy very busy lately!

RCicala wrote:
The short telelphoto lenses are now up, and a table you can sort to look at various factors. I have to say I was totally disappointed in the 85mm lenses as far as variation.

http://www.lensrentals.com/blog/2015/07/variation-measurements-for-telephoto-lenses

And Scott, the 11-24 is on deck for testing next week.




Jul 21, 2015 at 11:35 AM
wayne seltzer
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p.1 #16 · p.1 #16 · Great Stuff on Lenrentals .com Blog re MTF of Wides


Roger, also in another thread here people were questioning how well built the Otus lenses are and if they are more delicate than other zeiss lenses?


Jul 21, 2015 at 11:39 AM
RCicala
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p.1 #17 · p.1 #17 · Great Stuff on Lenrentals .com Blog re MTF of Wides


wayne seltzer wrote:
Roger, Great work! But I am trying to get a feel of what your consistency numbers mean besides a higher number being better. How much difference a score of 7 vs 4 means. Also breaking the number in two, one for center and one for corners.Most of the difference is coming in the corners for most lenses?
Also MTFs for f5.6 or f8 would be more interesting for the WAs.
Looks like you are keeping that Olaf guy very busy lately!



Scott, it's just a relative number, sort of a mental summary. Doing center and outer 1/3 numbers would be better, but the graphs are better yet. I really recommend comparing those and now that The DIgital Picture is hosting them you can pull up the variation graphs for any two lenses and compare them side-by-side.

But basically if if the number gets down around 4 and you pixel peep, chances are pretty good you'll notice the variation. Either all the copies will tend to have a soft corner or with several copies you'll notice a difference in center resolution (the graphs will show you which, or if it's both). Lenses over 7 you'd be hard pressed to find a difference between two copies unless you get unlucky.

Stop down numbers for MTF are coming soon, and will be hosted in the same tool on TDP. But what we've posted so far is two months work. The stop down numbers will trickle out over the next couple of months.




Jul 21, 2015 at 11:45 AM
RCicala
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p.1 #18 · p.1 #18 · Great Stuff on Lenrentals .com Blog re MTF of Wides


wayne seltzer wrote:
Roger, also in another thread here people were questioning how well built the Otus lenses are and if they are more delicate than other zeiss lenses?


Wayne, they are very well built. They are also very complex. I mentioned in one of the posts that if you increase complexity, especially if you add things like double-sided aspheric elements, there's going to be a bit more variation. It can't be helped. People like to think that stricter quality control would eliminate variation but that's just not possible.

We only stock a few dozen Otus lenses so I don't want to say anything absolute about reliability, but they certainly seem to hold up at least as well as other high-quality lenses.



Jul 21, 2015 at 11:50 AM
Toothwalker
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p.1 #19 · p.1 #19 · Great Stuff on Lenrentals .com Blog re MTF of Wides


RCicala wrote:
Paul, we measured groups of lenses both ways (new and after rentals). I've done a number of comparisons over the years and we don't see a difference. But our protocol is all lenses are tested on arrival, bad copies (about 2-2.5%) are screened out and returned, then the lenses are retested after each rental. Any lens with detectible change from baseline is either fixed by us or returned to factory service if we can't do it. That's why we got into testing in the first place. This particular series were almost all lenses bought in April - June, so they've
...Show more

Very good. I assume you optimize the center MTF at a particular spatial frequency? Zeiss uses 20 lp/mm for focusing. The difference in focus between frequencies is small, but detectable with some lenses.





Jul 21, 2015 at 01:13 PM
RCicala
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p.1 #20 · p.1 #20 · Great Stuff on Lenrentals .com Blog re MTF of Wides


Toothwalker wrote:
Very good. I assume you optimize the center MTF at a particular spatial frequency? Zeiss uses 20 lp/mm for focusing. The difference in focus between frequencies is small, but detectable with some lenses.



We generally use the highest frequency with MTF above 0.6, usually 30 lp/mm on our bench.



Jul 21, 2015 at 01:22 PM
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