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MTF: Tangential and Sagittal
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PostPosted: Mon Jul 13, 2009 10:39 pm    Post subject: MTF: Tangential and Sagittal Reply with quote
One thing I'm not able to understand well in MTF tests is how tangential and sagittal curves relate.
Specifically, where on the lens does one measure tangential, and where sagittal?
And how can there be somtimes such big differences in the resolution and illumination curves between tangential and sagittal? How does this translate in practical terms on the performance of a lens? Example: say that at f/4 the 20lpm tangential and sagittal curves begin together in the centre of the lens, but when approaching the edge of the lens, the tangential curve remains more or less up to the same level, where the sagittal curve falls down: what does that mean, in concrete terms?

thanks


PostPosted: Tue Jul 14, 2009 7:16 am    Post subject: Reply with quote
http://doug.kerr.home.att.net/pumpkin/Astigmatism.pdf

or that, a bit easier to read, more pictures and more colorful:
http://www.normankoren.com/Tutorials/MTF1A.html

or if you prefer a Zeiss source, let the master speak - Dr Hubert Nasse, Chief of the Zeiss Optics Lab lecture about it:

part I
http://www.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/CLN_30_MTF_en/$File/CLN_MTF_Kurven_EN.pdf

part II
http://www.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/CLN_31_MTF_en/$File/CLN_MTF_Kurven_2_en.pdf


PostPosted: Tue Jul 14, 2009 8:03 am    Post subject: Reply with quote
Thanks, the first link was perfect to understand what I needed, while the Zeiss link is very interesting as a general reading.


PostPosted: Tue Jul 14, 2009 8:18 am    Post subject: Reply with quote
By the way, the Zeiss link explains well why 35mm film in theory is superior to digital cameras having resolution lower than 24 MP - I underscore in theory because it is my impression (and I might be wrong) that compared to digital cameras with a good resolution, the adverse effect of grain in film balances, and more, the adverse effect of the antialiasing filter of digital cameras.


PostPosted: Tue Jul 14, 2009 10:34 am    Post subject: Reply with quote
Fascinating links Klaus - Thanks


PostPosted: Tue Jul 14, 2009 10:39 am    Post subject: Reply with quote
Big thanks for the links, Klaus!

Regards,

Jes.


PostPosted: Tue Jul 14, 2009 12:49 pm    Post subject: Reply with quote
wrote:
Is color negative film sharper?
If you choose to believe manufacturer's data sheets, yes, they are sharper

it is also my experience, sensia 100 is not sharper than a 200 iso negative

Quote:
the Zeiss link explains well why 35mm film in theory is superior to digital cameras having resolution lower than 24 MP

even if 24MP dslr have in theory better resolution than negative they still are years behind
most wide are not telecentric and borders are awful on digital, my Zeiss 20:4 is superb on film and horrible on digital crop
all the problems like sensor bloom and magnified CA put digital in shame
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