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Old December 2nd, 2008, 06:38 PM
Asher Kelman Asher Kelman is offline
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Join Date: Apr 2006
Posts: 34,727
Thumbs up Imatest™ SFRplus a revolutionary advance it lens testing

We are approaching a time when we can evaluate lenses and sensors in ways never imagined previously.

First let me present the latest Imatest lens testing software. Imatest™ has just announced

"Master 3.2.4 with SFRplus, a new capability that automatically identifies regions of interest (ROI) and helps you rapidly complete a wide range of image quality tests, including sharpness, lateral chromatic aberration, lens distortion, gamma (contrast), tonal response, and color uniformity. This capability is enabled through use of Imatest's new SFRplus test chart, which offers significant advantages over commonly used charts such as the ISO 12233, including:
  • less wasted area
  • the ability to produce a map of sharpness over the sensor surface
  • better measurement accuracy due to lower contrast
  • full automation of region selection.

Details can be found at"

We often have to wade through the lens MFRS specifications about their lenses. A lot of what is shown in advertisements are setup with some of the best photographers who could do as well with anything better a broken coke bottle!

Lens testing is now possible with Imatest software that requires almost no user input apart from inserting a file name! The new Imatest™ software is called SFRplus.

Imatest™ SFRplus test chart

It requires purchase of a newly designed test chart. The picture is illuminated according to easily followed instructions and pictures are taken with the camera mounted on a tripod.

One cycles through different apertures and each picture is loaded in to the software and then leave it to the software. It can automatically locate areas of interest on the test chart and then the calculations are performed without need for further input.

Automatic location of points of interest

"Imatest™ SFRplus measures image sharpness and several additional image quality factors, including Lateral Chromatic Aberration (LCA), noise, distortion and tonal response, using a special test chart that provides a high degree of automation."

"The primary sharpness indicator is MTF50, the spatial frequency where contrast drops to half its low frequency value."
This software, "Spatial Frequency Response (SFR), also known as Modulation Transfer Function (MTF), and other aspects of lens and image evaluation are explained" on the Imatest website here.

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Old December 2nd, 2008, 07:08 PM
Doug Kerr Doug Kerr is offline
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Join Date: May 2006
Location: Alamogordo, New Mexico, USA
Posts: 8,558

Hi, Asher,

Originally Posted by Asher Kelman View Post

"The primary sharpness indicator is MTF50, the spatial frequency where contrast drops to half its low frequency value."
Ah, the 3 dB rolloff frequency, beloved of electronic and telecommunication engineers! Now that makes sense.

Overall sounds like a fascinating package. Thanks so much for the excellent overview.

Best regards,

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Old December 3rd, 2008, 09:49 AM
Bart_van_der_Wolf Bart_van_der_Wolf is offline
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Join Date: Jun 2006
Location: Netherlands
Posts: 4,054

Originally Posted by Asher Kelman View Post
We are approaching a time when we can evaluate lenses and sensors in ways never imagined previously.
Yes, measuring MTF is a good method of learning a lot about the characteristics of the lens. One should however not underestimate the interaction of all elements in the optical path. The lens, the optical low-pass filter (OLPF, AKA anti-aliasing filter), the microlenses, and the sensels, all shape the final MTF curve. Each element has an influence on the total system performance.
So results for one combination, may not be exactly the same for another camera model, even if we use the same lens.

Testing lenses is not a trivial exercise though, even if Imatest does make the evaluation a lot easier. Even something as simple as focusing on the chart, isn't as simple as it might seem: .

And there are other factors involved in defining image quality besides the MTF, luckily many of those are also covered by Imatest. It's a rather complete image quality test suite, and it uses several industry standard testing methods, so it allows to exchange results with others in the industry.

I've been using Imatest since it's early (beta) years, and it became even better as time went by. It is highly recommended for those who want to do some serious evaluations.

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