Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
First solid measurements of lens variance
#27
I consider a rental week to be worth about a buyer's month in a lens' lifecycle, so the failed copy of the otus is quite old.  The otus lenses have a particular design flaw; the hood is still a normal bayonette, yet users insist on grabbing the considerable heft of the lenses by the hood because it is visually so well integrated, and the torque backs off a screw in the front barrel, allowing it to wobble.  The optics are all inside their own cell, filled with more cells inside, but this is the type of thing that requires repair very often (and is a 5 min fix with $0 of parts, vs $hundreds from a manufacture to do the same fix). 

 

Different buyers rent different kinds of equipment.  The cinema equipment is rented more in a cashflow sense, so e.g the C300s and true cine lenses may go to one customer for a month and then return.  This type of customer will take better care of the equipment than for example someone renting a supertele for 2 days to go on a particular trip.  The cine stuff also ships inside hard cases by and large, though I do not think that is of particular value since IMO shock damage in shipping is more important than crush, and the foam in most hard cases is too dense to cussion shocks. 

 

Roger did testing beforeand there isn't much difference between new in box copies and copies in lensrentals' rotation.  For your typical Canon, Nikon, sigma "A / S", very new Tamron, etc, lens a failure means something coming loose entirely and optically the lens will look terrible.  More budget manufactures and ones with a cheaper construcion style (looking at you, micro four thirds) will be more subject to "slipping" over time. 

 

In terms of LR's checking - a recieving tech shoots each and every copy of every lens at full aperture on an ISO 12233 chart when it is returned, after which it is put into the stock waiting to be pulled.  A good tech can do about 80-100 lenses an hour in this setup.

 

If I pull lenses from that stock to test, they don't get any further screening by me and they get run - unless the results are an absolute trainwreck I read that copy into the database and move on with my life.  If the copy looks bad I will test it on a camera.  If it looks bad on camera, it gets removed from the db, repaired, and re-run later in the day.  It takes quite a terrible failure for a lens to fail on camera - a 70-200 IS II properly aligned for 200mm looks something like this - https://www.dropbox.com/s/ycq6824ryd4n77...s.pdf?dl=0 yet even a copy as bad as this https://www.dropbox.com/s/d5letwr5n7htfl...s.pdf?dl=0 which should show a bad corner looks A-ok.  This isn't us having a loose tolerance - honestly that corner looks maybe a tad muddy but if you didn't have 4 good copies to compare to you may think its normal.  There's a full mechanical check too, but I don't do that stuff - just write test software, do testing, and build things as needed to facilitate testing. 


If I pull lenses from the incoming shelves (on which there are about 500 lenses today) I screen them on OLAF, which is perhaps 5x as sensitive as a camera and is faster - it takes 10 seconds per copy.  A copy I deem as bad gets camera checked and if it passes, it gets tested.  The ISO 12233 method we use is at least as sensitive as what most camera manufactures are using, so I do not think we are setting the bar artificially low for them. 

 

Regarding copy age again - I can tell you that on average the 50 STMs included in this grouping rented 6 weeks more than the 50/1.8Gs tested here.  In fact, 8 of those Gs were never rented before. 

 

Regarding regional differences - the manufactures do not ship different batches to different regions or any of that nonsense.  The biggest regional differences are the level of service offered and the skill of those technicians.  If you are in Australia, CPS will not have as good a service as on east coast USA, for example.  The customer base isn't there to support it. 


If you return a lens to a manufacture, they will test it more thoroughly than it was tested on the production line.  If it fails a quick service attempt is made, if that does not work it will be scrapped for parts, the parts checked to be working individially, and working parts cleaned and returned to production lines.  Everything else is trashed. 

 

It is far faster to test many copies of the same model at once (minimal if any re-alignment between lenses) so with future lens releases we should be pulling 4-10 copies on arrival to test.  It depends on the focal length greatly - an 85 takes about 5 minutes.  A 14 takes about 20.  One ties up the copies all day, one ties them up for an hour. 

 

At this point we're talking about what we're going to do for the rest of the summer.  Primes are basically as done as I care to finish them (about 675 copies - 50+ models in the database - all of the ones lensrentals carries good stock of in EF or F mount completed) and we can either start zooms, or start stopped down data collection.  The 70-200 IS IIs took about 2 days, but I worked on a number of other projects and did not test them as fast as I could have.  Something like a 16-35 f4 IS would take the entire week, and god is it maddening to take a distortion profile for each and every copy to facilitate measurement. 

 

We are also working with a partner to put up a proper database online of the charts with a comparison tool as well.  As of now we are working with the MTF charts, but variance should be done as well.  Later the 3D plots I linked above are something we may do too.  I hope so, it took quite a bit of effort to program them.  I think they may make the data more intuitive for people who don't speak MTF.

 

It is essentially this:

 

https://www.dropbox.com/s/3e0l67u59p4981..._.png?dl=0


vs this+this:

 

https://www.dropbox.com/s/8ziuhp3yuhnwg9...O.pdf?dl=0


https://www.dropbox.com/s/iwc5ovnobivu7r...O.pdf?dl=0


Or, flat


https://www.dropbox.com/s/6d899z4dukebln...p.pdf?dl=0

 

https://www.dropbox.com/s/q0tp4cvbyc5f3d...p.pdf?dl=0

 

While we won't stick our foots in our mouths and state it officially and explicitly, the 10lp/mm chart does show contrast while the 30lp/mm chart shows the highest resolution that can be recorded by most FF cameras.  40 or 50 lp/mm would be needed for something like M4/3.

  


Messages In This Thread
First solid measurements of lens variance - by davidmanze - 07-14-2015, 03:33 AM
First solid measurements of lens variance - by Scythels - 07-14-2015, 03:56 AM
First solid measurements of lens variance - by davidmanze - 07-14-2015, 07:32 AM
First solid measurements of lens variance - by davidmanze - 07-14-2015, 08:11 AM
First solid measurements of lens variance - by Scythels - 07-14-2015, 12:48 PM
First solid measurements of lens variance - by davidmanze - 07-14-2015, 09:29 PM
First solid measurements of lens variance - by Scythels - 07-14-2015, 10:36 PM
First solid measurements of lens variance - by Scythels - 07-15-2015, 03:17 AM
First solid measurements of lens variance - by davidmanze - 07-15-2015, 06:35 AM

Forum Jump:


Users browsing this thread:
1 Guest(s)