Two issues are here conflated: product QA and validity of MTF performance measurement. Zeiss (and Zeiss alone, according to many sources) report actual MTF of an actual lens used in white light, rather than a calculation of MTF taken from, well, almost thin air a.k.a. the marketing division ;-)
QA of photographic lenses is quite ineffective from some user reports, even for high end lenses...but given the propensity of bad news to travel quickly (however dubious the source), picking up intensity as it goes, and since it is unreasonable to expect makers to air dirty laundry in public by publishing various lens fault failure rates (which they of course would/should know from their QA measures), who knows for sure?
Finding faults in lenses by end users, whether sample faults or optical design faults, is a cottage industry in these days of 1920x1200 monitor resolution and facile 100% image viewing, with predictable consequences. How many such disgruntled reporters apply the same standards to their capture methods?
Zeiss almost certainly select several production line samples for final MTF data assessment to validate what they know from earlier stages of development, beginning with prototyping design candidates, through material selection, assembly methodologies, and so on. So not like John West's salmon!
Tariq Gibran wrote:
Somehow, I find it difficult to believe that Zeiss actually test every single lens they sell and reject those that do not meet their MTF charts. Has Zeiss ever officially stated this somewhere?
Yes, I am certain. Here they say that 20% of their employees work in quality assurance department. With 20% staff only inspecting lenses, I don't doubt that it is possible to check every lens, including MTF. They claim that their MTF testing system is real-time, so it is not very time consuming.
I find the following official statement to be very interesting, because it is easy to see which manufacturers they target with both parts:
"Zeiss is the only lens manufacturer to use these MTF systems in
lens production to tune every single lens to maximum performance.
For other manufacturers, MTF systems are either too slow for their
mass production or too expensive for the small quantities of lenses
they produce."
"In this way, Zeiss achieves 100% quality assurance, with every lens
being tested exactly for more than 100 different criteria during its
production. Carl Zeiss does not rely on statistical process control
and/or spot inspection, like it has become the cost saving standard
in mass producing industries.
Zeiss rather performs a 100% quality control, like it is done for
airplane components and other very demanding industrial products."
With testing going on all the time I doubt that Zeiss or Leica reject many lenses following the FINAL tests. All problems are discovered earlier.
Jan 17, 2011 at 09:09 PM
Lars Johnsson Offline • • • • • • • Upload & Sell: Off
sebboh wrote:
actually i'd like it to have the same size and weight as the leica summilux pre asph.
in all seriousness, i'm much more sensitive to the size of lenses i want to use for shooting people than i am to the size of lenses i use to shoot wildlife. at a certain point people begin to worry that i'm pointing a canon at them.
Yes I'm sure people begin to worry when you point a 35mm lens at them They get really upset when you point that 12 cm lens at them. And they only expected a 8-9 cm lens
I was shooting street and people shots all day in Bangkok/Nonthaburi with my 200/2 lens yesterday. None of those hundred people I aimed that big lens at begin to worry
trdonja wrote:
Yes, I am certain. Here they say that 20% of their employees work in quality assurance department. With 20% staff only inspecting lenses, I don't doubt that it is possible to check every lens, including MTF. They claim that their MTF testing system is real-time, so it is not very time consuming.
I don't doubt it either. Having 20% of your workforce devoted to QC is really quite a lot. By any measure that is a large, very intensive effort.
trdonja, not to doubt you, but context is very important and often not obvious. Can you provide a link to the second statement please, the 'official statement'. The fist can be read for the comany as a whole but is found on a page dedicated to spectacle lenses. TIA, Phil
trdonja wrote:
Yes, I am certain. Here they say that 20% of their employees work in quality assurance department. With 20% staff only inspecting lenses, I don't doubt that it is possible to check every lens, including MTF.
That 20% figure is for their eye glass division. your link specifically states "spectacle wearer" so those are not photographic lenses in this instance.
Here is the actual quote:
"About 20% of all staff are employed in quality control and quality assurance to ensure that Carl Zeiss can always provide the spectacle wearer with the best possible product."
philip_pj wrote:
trdonja, not to doubt you, but context is very important and often not obvious. Can you provide a link to the second statement please, the 'official statement'. The fist can be read for the comany as a whole but is found on a page dedicated to spectacle lenses. TIA, Phil
Sure, here it is. Second part of the document is interesting read for me as well, describing the whole process. They explicitly say, that in case of a glass element not being perfect, they will simply make a new one.
There are other issues to note WRT CZ modern lenses related to QA, and I know it is off-topic somewhat. CZ's ZA 16-80mm zoom, selling for quite a lot of money for its target market ($800), is pretty much universally regarded as having a poorly designed and sloppy zoom action and dubious QA. I see this complaint in many web fora, e.g. here is a reliable photographer's experience: http://www.photoclubalpha.com/1680/1680.html http://www.photoclubalpha.com/1680/problemlens.html
It seems to be quite inconsistent with the talk up in the statement just posted as the 'official line'. Maybe the 20% of staff doing QA were out to lunch on that assembly line, or work only on non-ZA lenses!
Segueing back to the topic at hand, maybe CZ are toughening up their high end lenses with more mass to prevent problems arising. 850 grams gives it the dubious heavyweight champ award for fast 35mm lenses, and I find the arguments given in favour of the extra 250 grams 'needed' over its competition far from compelling. Thanks to theSuede and denoir for a(nother) mine of information and analysis.
trdonja wrote:
Sure, here it is. Second part of the document is interesting read for me as well, describing the whole process. They explicitly say, that in case of a glass element not being perfect, they will simply make a new one.
Thanks for that link. Not many japanese in the photos in the lens production area, likely because the images are of their german facility and not Cosina's in Japan, where the majority of Zeiss lenses are made today.
There can be no doubt Zeiss have some of the best quality control in the industry but I do wonder how cost-cutting has affected it in more recent years.
philip_pj wrote:
There are other issues to note WRT CZ modern lenses related to QA, and I know it is off-topic somewhat. CZ's ZA 16-80mm zoom, selling for quite a lot of money for its target market ($800), is pretty much universally regarded as having a poorly designed and sloppy zoom action and dubious QA. I see this complaint in many web fora, e.g. here is a reliable photographer's experience: http://www.photoclubalpha.com/1680/1680.html http://www.photoclubalpha.com/1680/problemlens.html
It seems to be quite inconsistent with the talk up in the statement just posted as the 'official line'. Maybe the 20% of staff doing QA were out to lunch on that assembly line, or work only on non-ZA lenses!
Segueing back to the topic at hand, maybe CZ are toughening up their high end lenses with more mass to prevent problems arising. 850 grams gives it the dubious heavyweight champ award for fast 35mm lenses, and I find the arguments given in favour of the extra 250 grams 'needed' over its competition far from compelling. Thanks to theSuede and denoir for a(nother) mine of information and analysis. ...Show more →
Of course the ZA Zeiss lenses are made by Sony just as most of the other Zeiss lenses are made by Cosina, both in Japan. Zeiss QA techniques, special equipment and oversight are all supposedly employed in these situations, just as they were when Kyocera made Zeiss Contax lenses.
Here they say that 20% of their employees work in quality assurance department. With 20% staff only inspecting lenses, I don't doubt that it is possible to check every lens, including MTF. They claim that their MTF testing system is real-time, so it is not very time consuming.
Does it include Cosina?
I am a bit skeptical about this. Main reason being that I received 50/2 MP and it was a dud. Should not happen with "100% QA". But there are other reasons as well - for example, why are the cine lenses (and not only Compact Primes) so much more expensive?
Lars Johnsson wrote:
Yes I'm sure people begin to worry when you point a 35mm lens at them They get really upset when you point that 12 cm lens at them. And they only expected a 8-9 cm lens
I was shooting street and people shots all day in Bangkok/Nonthaburi with my 200/2 lens yesterday. None of those hundred people I aimed that big lens at begin to worry
i'm actually more concerned with shooting my friends and family. when you point a big camera with a big lens at them it suddenly seems like a serious picture that should be posed for not just a snapshot. shooting random people on the street without disturbing them is easy, especially with a telephoto (even one as big and short as a 200/2). in more intimate settings things are different. things are also different in different countries - i would imagine high density asian cities to be the easiest to shoot in without disturbing anyone.
sebboh wrote:
i'm actually more concerned with shooting my friends and family. when you point a big camera with a big lens at them it suddenly seems like a series picture that should be posed for not just a snapshot. shooting random people on the street without disturbing them is easy, especially with a telephoto (even one as big and short as a 200/2). in more intimate settings things are different. things are also different in different countries - i would imagine high density asian cities to be the easiest to shoot in without disturbing anyone.
In the current environment in the US, I hope this statement is not read out of context....
;-)
sebboh wrote:
yes, perhaps i should choose my verbs a bit more carefully. i'm sure i just raised a red flag with some homeland security/fbi search algorithm.
OH Great, now they are going to come visit me again! Just kidding.
Which characteristics of the mtf curves determine how much lateral and longitudinal CA the lens will have?
How can you tell if the lens transitions to OOF faster?
What does the divergence of the sag and tag lines in the corners indicate?
Jan 17, 2011 at 11:51 PM
Lars Johnsson Offline • • • • • • • Upload & Sell: Off
sebboh wrote:
i'm actually more concerned with shooting my friends and family. when you point a big camera with a big lens at them it suddenly seems like a serious picture that should be posed for not just a snapshot. shooting random people on the street without disturbing them is easy, especially with a telephoto (even one as big and short as a 200/2). in more intimate settings things are different. things are also different in different countries - i would imagine high density asian cities to be the easiest to shoot in without disturbing anyone.
So now even you camera gets bigger when mounting the new Zeiss 35 lens on it Don't tell me that your family & friends are easy to shoot with the 35/2 but very difficult if you use a 35/1,4
it would be interesting to know how much more heavy/larger you would expect the new 35/1,4 lens to be compared to the 35/2 lens. The 35/2 is about 530gr. what did you expect from a f/1,4 then ? I suppose you like it to be good build in all metal and sharp wide open.
Lars Johnsson wrote:
So now even you camera gets bigger when mounting the new Zeiss 35 lens on it Don't tell me that your family & friends are easy to shoot with the 35/2 but very difficult if you use a 35/1,4
it would be interesting to know how much more heavy/larger you would expect the new 35/1,4 lens to be compared to the 35/2 lens. The 35/2 is about 530gr. what did you expect from a f/1,4 then ? I suppose you like it to be good build in all metal and sharp wide open.
ha, no i don't have the 35/2. i was planning to get the c/y 35/1.4 instead (it's smaller than the Z* 35/2 incidentally), but figured i'd wait to see what the new 35/1.4 is like. for the record, there is a noticeable difference in reaction to my canon 55/1.2 (not that small of a lens itself) versus 24-70/2.8, don't ask me why.
It is interesting to compare both of those MTF charts, WO and at f4 with this one.
Obviously field curvature is less severe, but apart from that it looks very similar to me.
Edit: Tangential and sagittal lines are very important for bokeh quality and since WO they have identical positioning, I expect bokeh from both of these lenses to have similarities. It also gives me hope that 85/1.2 is in production. They will add 500 grams more for total of 1400 grams just to clear those corners and we will have 80 Jahre 85mm 1.2.
Lars Johnsson wrote:
So now even you camera gets bigger when mounting the new Zeiss 35 lens on it Don't tell me that your family & friends are easy to shoot with the 35/2 but very difficult if you use a 35/1,4
it would be interesting to know how much more heavy/larger you would expect the new 35/1,4 lens to be compared to the 35/2 lens. The 35/2 is about 530gr. what did you expect from a f/1,4 then ? I suppose you like it to be good build in all metal and sharp wide open.
I don't really fuzz too much about "metal" or "non-metal". When NASA uses plastic in their shuttles, I think I can live with my lenses having some plastic alloys. I know that some thinks that an all metal build is "be all, end all", but for me, that is just not it. Also, my nikkor 35 1.4 ai-s is metal/rubber, and weighs in at far less than this... :P (with far less optical performance though).
More importantly, Nikon just released a 35 1.4 af-s with AF that comes in at 83 x 89.5mm, and when they managed to release a lens with the performance that it seems to have in a such small package, it is tempting to ask why the zeiss is so gigantonormous.
Bottom line: Trying to make fun of those commenting on the size, when it is a valid point, is bad form. For some of us, size/weight are important. If it is not for you, that is great. Just don't patronize those of us that actually think it is important.
They get really upset when you point that 12 cm lens at them. And they only expected a 8-9 cm lens 
Don't tell me that your family & friends are easy to shoot with the 35/2 but very difficult if you use a 35/1,4