next PZ lens test report: Carl Zeiss Vario Tessar T* FE 16-35mm f/4 OSS ZA - Printable Version +- Opticallimits (https://forum.opticallimits.com) +-- Forum: Forums (https://forum.opticallimits.com/forumdisplay.php?fid=4) +--- Forum: Sony (https://forum.opticallimits.com/forumdisplay.php?fid=14) +--- Thread: next PZ lens test report: Carl Zeiss Vario Tessar T* FE 16-35mm f/4 OSS ZA (/showthread.php?tid=1235) |
next PZ lens test report: Carl Zeiss Vario Tessar T* FE 16-35mm f/4 OSS ZA - Brightcolours - 02-27-2015 Quote:I'm no expert in this but could you really bump resolution figures without knowing if the lens is the limiting factor? And what does Photozone's "excellent line"mean (which the Canon lens never passes outside the center).There is another factor to take into account. Photozone uses sharpening in the MTF images workflow, which skews results somewhat. The A7r is AA-filterless, which will mean it will introduce some fake sharpness which the MTF software can't discern. To, don't put too much weight in small differences in he results, there. Don't put too much weight on vignetting figures either, they are measures from JPEGs I believe, and tend to differ from different cameras. This is what PZ says about that in case of Nikon (D3x) vs Canon tests: "We're performing our vignetting analysis based on (uncorrected) JPEGs straight from the camera. The JPG engine of the Nikon D3x features a rather flat gradation curve, thus has a moderate contrast characteristic, resulting in comparatively low vignetting figures - the corresponding Canon figures are roughly 40% higher due to the more aggressive default contrast setting." http://www.opticallimits.com/nikon_ff/447-nikkor_afs_1424_28_ff?start=1 Most probably, the Sony lens indeed has more vignetting. But without comparing them on the same body, in PZ's testing methods, we can't know for sure. CA is significantly better, but the imatest software is not really very good at testing the CA (sometimes it gives clearly wrong results). next PZ lens test report: Carl Zeiss Vario Tessar T* FE 16-35mm f/4 OSS ZA - Scythels - 02-27-2015 I wouldn't be so quick to dismiss imatest. Even Optikos' MTF bench has software that goes awry every 20-30 minutes, yet it gives some of if not the best MTF measurements you can get. And it's about $250,000-$300,000 =) 1-2px max in the edge of the frame is pretty consistent with the sample images. next PZ lens test report: Carl Zeiss Vario Tessar T* FE 16-35mm f/4 OSS ZA - Faketastic - 02-27-2015 Quote:Scythels IS an expert and has given a very detailed and rational reply to your question to which your mind-boggling reaction is to snidely accuse him of an irrational bias. And you accuse me of being a newbie.. You say: 1) You really can't compare system results "number by number" 2) Trust protozone's scaling with poor-ex rating I just see the Sony spend more "time" in the ex range than the Canon lens. So, either PZ or Scythels is wrong then? And a lens is worse because it's sharp in the center and not as even? CA (if kept reasonably low) is not relevant with todays SW correction. The same goes for distorsion. next PZ lens test report: Carl Zeiss Vario Tessar T* FE 16-35mm f/4 OSS ZA - Faketastic - 02-27-2015 Quote:The change to resolution figures are to attempt to remove some of the sensor - the accuracy I would say is +/-10% as there really are no terrible sensors these days.Thanks for the clarification. But my question remains; how can you be sure that scaling actually holds and that the system is not limited by the lack of "resolution" of the lens? next PZ lens test report: Carl Zeiss Vario Tessar T* FE 16-35mm f/4 OSS ZA - Scythels - 02-27-2015 Quote:Yes. Photozone results include three large-scale variables: * test chart * imaging sensor * lens You are trying to extract the lens but the raw results include other variables, so you cannot tell anything from raw results. Tests exist which extract pure lens performance but they are extremely expensive and much more time consuming than IMATEST which is used by photozone (honestly, imatest is certainly good enough for any photographer's purposes). These tests fall into two categories that I am aware of but more may exist: * interferometer (most accurate, +/-1.6nm precision) * MTF bench testing The former requires about $500,000 in equipment to begin testing and a further $20k or so for each focal length "class" you wish to add. The latter has many variants, each having their own merits. The MTF bench I have experience with is Optikos' Lenscheck VIS system. This puppy: http://i.imgur.com/unzdZFK.jpg http://i.imgur.com/BK2uvbd.jpg This setup is really shitty, the lens needs to be better coupled to the bench... something like this: http://i.imgur.com/ni1Sm4B.jpg The machine applies six compensations to its results in order to extract "pure lens performance". The basic premise of the machine is that it takes a fiber optic light source and shoots it into a collimator and beam expander. In between the two are two wheels, the test wheel and the filter wheel. The filter wheel has a couple of options: * open/clear * 546nm bandpass - very narrow range green light * green additive * blue additive * red additive * IR Cutoff + two empty slots for user requested filters The test wheel has a bunch of options, off the top of my head: * crosshair * 11um pinhole * 29.5um pinhole * 101um pinhole * 300um pinhole * 1mm aperture * 3mm aperture * 1951USAF chart After the collimator you insert the Lens Under Test (LUT). It images the light coming out of the collimator, behind it lies a microscope objective which images the spot formed by the lens. Inside the machine a fourier transform of the spot is taken to break it into its various frequency components. This allows the machine to measure resolution down to extremely fine spacial resolutions, far far finer than any photographic lens has any real resolution (over 1000lp/mm) The machine applies compensation curves for: * the microscope objective (user inputs microscope objective data, machine computes it out) * the sensor behind the microscope (fixed, one of two sensors) * the filter * the test object/thing (typically the 11um pinhole) * tilt of the image plane * the optics of the collimator and beam expander. Here is a test I did today with this machine of a customer's lens. I can't give you any info on the lens because it is a prototype other than the fact that it is extremely high resolution, nearly diffraction limited in the center. The diameter of the spot is about 1 micron, or 1/6th the width of the average full-frame sensor pixel. This lens can handle the sensor in your phone flawlessly and far "outresolves" a FF or APS-C or 4/3 camera sensor. https://gyazo.com/ce6f6bf560e3613cb30681ee3b9115a6 MTF bench tests are very far removed from results obtained with a camera. All factors other than the lens are computed out and importantly there is no coverglass so results are not super correlated to what happens with a real camera. Not only is such a tool fiscally unwise for PZ to use, it gets away from what the aim of this website is to do (provide lens tests "grounded" to photography). The poor-ex scale used by PZ is correlated to what the best lenses are capable of on that particular test camera. The results loosely (+/- 10%) correlate to similar pixel count camera in similar situations (i.e long vs short flange) but must be adjusted to compare between systems. This is how you would convert from MTF bench numbers to a camera sensor very loosely: * calculate nyquist frequency of the sensor (5D2 - 5600/36/2 = 77.7lp/mm) * discount by some "sensor loss" factor. Anywhere from 60-80% is normal. 66 is a decent starting point (now at 51.33lp/mm) * compare lens MTF to nyquist. All lenses > 50% MTF at nyquist are approximately equal because that is the threshold where two airy disks may be distinguished (Rayleigh criterion) Using this customer's lens for example, MTF is > 75% at 50lp/mm so the lens would resolve exceptionally well on the 5D2. This is also in the corner and wide open... The lens in the center could handle about 135lp/mm of resolution so we are looking at a would-be 136*1.5*2*36 = 14688px long full-frame sensor, give or take. This is the axial MTF data... http://gyazo.com/352613adf684f8ccc5cbec31e7552fa9 ---- Quote:You lose resolution to correct CA and distortion, they're still very relevant. Quote:You can't, that's why you use margins. +/-10% is arbitrary but is pretty safe. The system is lens-limited whenever the image doesn't look "perfectly clear." This is a situation where the system is absolutely sensor-limited (300/2.8L II on 1Ds3) http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=739&Camera=453&Sample=0&FLI=0&API=0&LensComp=917&CameraComp=0&FLIComp=0&APIComp=0 This is a border case: http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=917&Sample=0&FLI=0&API=0&LensComp=917&CameraComp=453&SampleComp=0&FLIComp=0&APIComp=0 There is some astigmatism in the corner (vertical resolution a bit weaker than horizontal). This is a more common lens-limited case: http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=403&Camera=453&Sample=0&FLI=0&API=5&LensComp=917&CameraComp=453&SampleComp=0&FLIComp=0&APIComp=0 This is a severely lens-limited case: http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=403&Camera=453&Sample=0&FLI=0&API=0&LensComp=917&CameraComp=453&SampleComp=0&FLIComp=0&APIComp=0 The 16-35L is more or less neck-and-neck with the detector so scaling is reasonable - http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=949&Camera=453&Sample=1&FLI=0&API=0&LensComp=917&CameraComp=453&SampleComp=0&FLIComp=0&APIComp=0 next PZ lens test report: Carl Zeiss Vario Tessar T* FE 16-35mm f/4 OSS ZA - Brightcolours - 02-28-2015 Quote:I wouldn't be so quick to dismiss imatest. Even Optikos' MTF bench has software that goes awry every 20-30 minutes, yet it gives some of if not the best MTF measurements you can get. And it's about $250,000-$300,000 =)I am not talking about this specific test, in the past there have been results on PZ with much too low imatest CA "measurements" (I do not know the reason for why the test shows that, obviously. Perhaps it can be focus distance related?), where the images show way worse CA performance. |