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09-28-2013, 12:46 PM   #1
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How to read these MTF charts from my mystical lens ?

Created separate thread for these charts to hit more people who might know how to read them. These are from a lens that is a total mystery to me and many other fellow pentaxians as the lens has no branding on it, yet performs seriously better than average.

here is a link to the thread with my attempt to identify the lens : Please help to identify this 135mm f2.8 lens

I thought however, that would be worthwhile to actually ask others how to read these famous resolution charts we see all over the net. Called MTF - - no idea why, still a mystery to me. If someone could be kind enough and have a look at these shots below. Were they taken good enough to be a credible source of any resulting informations ? How you actually read these ?

Thanks in advance!

Ok, here are the charts - to examine please click on each image to see full photo.
Each photo is 100% uncropped and unmodified - only description has been added. Images where shoot JPG in camera.

Click on the photos if you want to see the full frame - here are only small portions of each shot!

2.8

4.0

5.6

8.0


I tried to take as accurately framed shoots as possible and I know that it is possible to actually somehow "read" these lines and marks - but I have no idea how. Please somehow comment .

Thanks

09-28-2013, 05:22 PM   #2
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This is what I understand by MTF charts and how to read them: http://photographylife.com/how-to-read-mtf-charts
The photographic technique (as in your images) allows you to get a feel for sharpness and contrast by eye. Both clearly improve between 2.8 and 8 looking at the right hand side horizontal and vertical fine lines in particular. There are other charts using converging lines which enable the reading of line pairs per picture height which will give an estimate of resolution in relation to the theoretical Nyquist limit but I think that has more to do with aliasing.
You seem to have a good lens there by these images. Is it "better" than some other 135/2.8? Well, you could shoot the same chart with similar lenses and see how they stack up. Or you could go out and take some real world images. Other factors, such as real world colour rendition are probably going to be more important than an exact MTF number in determining how much you use the lens. But it looks like a great find.
09-28-2013, 05:41 PM   #3
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You got me curious, so I looked up what "MTF" actually stands for: Modulation Transfer Function.

From Wikipedia:

QuoteQuote:
While optical resolution, as commonly used with reference to camera systems, describes only the number of pixels in an image, and hence the potential to show fine detail, the transfer function describes the ability of adjacent pixels to change from black to white in response to patterns of varying spatial frequency, and hence the actual capability to show fine detail, whether with full or reduced contrast.
So "resolution" is the camera's potential to resolve detail, and "MTF" describes how well the lens utilizes that resolution.
09-28-2013, 08:22 PM   #4
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QuoteOriginally posted by manntax Quote
I thought however, that would be worthwhile to actually ask others how to read these famous resolution charts we see all over the net. Called MTF - - no idea why, still a mystery to me. If someone could be kind enough and have a look at these shots below. Were they taken good enough to be a credible source of any resulting informations ? How you actually read these ?
What you have here are not MTF charts as such,
but rather photographs of a test chart
designed to help you quantify the contrast/resolution of your lens.

Here are links to fuller explanations:

ISO 12233 Test Chart

About ISO 12233 Chart Data and Sample Images

Here's an ImageJ plugin to get actual MTF charts:

Slanted Edge MTF

Here's the wiki for ImageJ itself:

ImageJ - Wikipedia, the free encyclopedia


Hope this helps.

09-29-2013, 12:44 AM   #5
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Guys many thanks! I briefly went through all the links and all are great help to understand these charts!
Looks like there was a lot of confusion in my understanding (or lack of it ) - and I certainly agree that the real world performance counts far more. These images were simple part of a test I put my lens through in order to recognize it's quality - extraordinary good as for an unknown and unbranded lens.

Hopefully others will find these links provided the same helpful as I do
Thanks!
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