# Sagittal Tangential Petzval Terms

• 06-22-2013, 10:43 AM
Mustafa Umut Sarac
Sagittal Tangential Petzval Terms
I want to clarify these terms in my mind. Erwin Putts tells that an image is a combination of these three. I saw at MTF tests , first two but not the third one. Do all aberrations spread in to these three or does it spread on more on one or two ? How do them to form a combination for better plasticity ?
Is there any computer simulation examples for each image characteristics to understand them better ?
Is there any way to effect each one to create a different combination ? Is there a way to separate each one ?

Umut
• 06-22-2013, 12:01 PM
E. von Hoegh
"Sagittal" and "Tangential" are terms relating to astigmatism . http://www.astrosurf.com/luxorion/re...errations3.htm

"Petzval" is a type of portrait lens, http://www.antiquecameras.net/petzvallens.html or the Petzval sum, http://books.google.com/books?id=kS9...%20sum&f=false

Mustafa, do you ever try to look things up yourself?
• 06-22-2013, 12:13 PM
Mustafa Umut Sarac
I found the same at wikipedia. Does it mean MTF tests only explain the amount of astigmatism ?
• 06-22-2013, 12:20 PM
E. von Hoegh
Quote:

Originally Posted by Mustafa Umut Sarac
I found the same at wikipedia. Does it mean MTF tests only explain the amount of astigmatism ?

No. MTF = Modulation Transfer Function. Think of it as a combination of resolution and contrast, since all aberrations effect both. http://spie.org/x34298.xml

If I could google this, so can you.:pouty:
• 06-22-2013, 01:01 PM
Mustafa Umut Sarac
But MTF tests have two curves , tangential and sagittal and we found that two relates to astigmatism. But your latest post and I have read in books says MTF shows the combination of all aberrations.

Whats going on ? I could not get it. Is it telling the aberrations in astigmatism ? By the way , I found a reference about the authors who got their prescriptions from ELCAN archive and conduct tests on Summilux , f:1 one and Summicron 50 f:2. They analysed mandler designs and the double gauss ones.

All they found , there is virtually no aberration record at summicron , but for others all aberrations are so low but one single abnerration is 10 times more. I never heard that one in any book.

IMHO , If they would put under MTF test , they would be worse than Zeiss or Nikon. But it does not say the all story.
• 06-22-2013, 03:24 PM
alanrockwood
Two of the Seidel aberrations are closely related, namely field curvature and astigmatism.

Field curvature is where the best focus of the image lies not on a plane but on a curved surface.

Astigmatism is where the tangential rays and sagittal rays do not focus at the same point. The tangential rays focus on a curved surface and the sagittal rays focus on a different curved surface.

There is an equation that provides a relationship between the radii of these three surfaces. I don't recall what the formula is, but it can be found on line. However, as I recall, one consequence of the formula is that it is impossible to correct for astigmatism unless one also corrects for field curvature.

There is also a theorem that relates field curvature to the refractive indexes and curvatures of the lens surfaces.

One other thing. Astigmatism contributes to the MTF curves, as do the other aberrations. As a result, the MTF curves in two directions are not equivalent, so one needs to MTF curves.
• 06-22-2013, 04:10 PM
Mustafa Umut Sarac
Can We say or not ,the balance between sagittal and tangential curves responsible for plasticity ?