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Does MTF describe a lenses accuratly

Mike

I agree with you that the colour theory is a deep subject. However, IMO that if we just forget about the theory, conduct the experiment, run it and see what happen.
Since no body can count these colour, we have to relie on computer software to do the counting. So as long as we are consistance with equiptment and software choices, then the test can be conduct fairily and objectively. and if there is something different can be pick up, hopefully it can pick up!

Ben
 
Hi Ben,

Thinking about it, if your goal is to find out the colour balance of the lens then there are some practical options. Starting with a white incandescent light source of a known spectrum, you could measure the spectral distribution of the resulting image. That would give you a chart showing the amount of absorbtion that occurs across the visible frequency range, which in turn could be used to work out the effective white point for a given type of film or sensor. The equipment necessary to measure the spectral distribution isn't commonplace however.

To make things easier, you could assume a fairly smooth and compatible response for the different film/sensor types, allowing you to work out a single white point that would hold reasonably well for most conditions. One way to measure this would be to use a DSLR to take a shot of a calibrated white card under controlled lighting then look at the numbers in the RAW file. This would certainly tell you whether the lens was a bit warm/cool/yellow etc.

-= mike =-
 
Good discussion. But the reason I went with Zeiss lenses was the quality of photos they produce. But it's difficult to find any one measure that captures all of a lens's attributes. So, if you're not sure what lens system to buy, you should spend time looking at photos. And the gallery section of this site has some fabulous ex&les of what CZ lenses can produce.
 
Mike, firstly, must thank you for pointing at the right direction in reading some of the artical about MTF, that something good to know. I know more about it (can't say that I understand it, guess with time will understand more).

I do agree with you that firstly produceing the standard white light will be technically difficult{impossible). Measuring these white light, and produce some readable table will be nightmare! I don't know if this is true or not, but the more we know, the more lost it seems to be (what the acient chinese use to say).

So what I am suggesting is more simple (don't know if it will work though), what we need to do is to get the computer and print a "standard" color referece (with all 64 bit or 98 bit) colour. Use the lens to take photo of the print (with a standard film), scan the film with a standard film scaner, and read it with a computer and see how many different colour captured by the lens. Repeat for a few times and get the mean. Collect data from different brand of lenses and compare. Will it works? All of these hardware are available, it is the colour counting software I am worry about (it may take forever to read with 64 bit colour!)

Using a DSLR may be another option, however, mounting all the lenses will be technically very chanlenging, and may cost you a lot of money.

Robert, there is no doult in the past Zeiss or leica produce the best lenses! However, and IMHO it true, according to the MTF, the other brand are catching up. looking at the MTF of Canon, the mean of their score in MTF chart are very close compare to CZ or Leica (sometime better). So if CZ/Leica's lenses do offer something extra, I think it is important that we could describe it, and let other to know! By using subjective word such as great, stunning, fabulous to describe it is simpily not enough! or otherwise, in the very near future (comming very fast! things do change fast these day!), more people will just use MTF to judge the lenses quilities and we will have no more CZ/Leica!
 
Please bear in mind that Zeiss is the only brand that is measuring the MTF in during the producting of the lenses. All others (Leica, Canon etc.) are publishing MTF data from s&les/ prototypes, which are not mandatory the same if if you start to produce them in large quantities.

So what you will experience is, that if you buy a Zeiss lens in Tokyo and the same one in NY, you will have two lenses with the same MTF's (within specific, very tight tolerances).

If you do the same for any other brand, you will see bigger differences. This is why tests in photo journals are meaningless, if the lenses are perselected and handchoosen by the manufacturer and then sent to the test team.

See for more details the Zeiss articles in our manuals section I have mentioned before.
 
Ben,

There are some things that are difficult to capture in a measurement. MTF is only one measure of a lens, and probably not the most meaningful, unless your only concern is resolving power. But, who knows. Maybe some clever person will figure out how to measure Bokeh.
 
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