Olympus-OM
[Top] [All Lists]

Re: [OM] MTF Lens tests

Subject: Re: [OM] MTF Lens tests
From: frieder.faig@xxxxxxxxxxxxxxxxxxxxxxxxx
Date: Tue, 23 Jul 2002 00:17:41 +0200
On Mon, Jul 22, 2002 at 11:04:11AM -0700, Winsor Crosby wrote:
> >Hi,
> >

> 
> Terrific. Thanks, Frieder.
:-)

> 
> I still have trouble wrapping my mind around the meaning of MTF.  How 
> do you interpret the data?

Hmm, Higher is better :-)

MTF is determined with several test pattern (grids), consisting of line pairs 
(black and white, or respectively tranparent or not).
The lens is projecting such a  pattern on a sensor which is meassuring the
maximum and minimum brightness (contrast). 
This difference is compared with the min-max. difference of the orinal pattern. 
The MTF-value compares  the contrast (differences) of the orginal
pattern with the contrast of the projected pattern.

When the projected contrast is the same as the grid the MTF would be 100%.
A fine grid wich is not resolved any more appers as a even gray area:
No difference -> No contrast -> MTF = 0%.

A high MTF indicates that the lines are saturated black and white.
Lower MTF indicates that it is becoming dark and bright gray instead.

The pattern do have (5 lp/mm), 10 lp/mm, 20 lp/mm and 40 lp/mm.
(often refered as  frequency, eg. = 10 lp/mm) 
The value of 5 lp/mm (= line pairs per mm on the negative) was 
meassured only by Color Foto in the later test (4 lines per diagram!).

5 and 10 lp/mm describe the contrast of image structures. 
20 and 40 lp/mm rather indicate the resolution of the lens.
As reference. For dof-calculations 0.033 mm max. c.o.c. equals about 15 lp/mm

On the left side of the diagram (MTF-axis) you see the values of the
center, at 21mm image heigt the edge at the end of diagonal of the frame,
where you can see corner falloff.

Hmm, the values of the table are simply the average for a frequency
over the diagonal. No centerweighting like photodo does. I´ve used the
calculator an simply summed them together to one value.

I hope this is understandable and helps a bit.

Frieder Faig




 

> -- 
> Winsor Crosby
> Long Beach, California
> 
> ?
> 
> < This message was delivered via the Olympus Mailing List >
> < For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
> < Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
> 

< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >


<Prev in Thread] Current Thread [Next in Thread>
Sponsored by Tako
Impressum | Datenschutz