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# Thread: Square Wave Light Source or Transformer lens

1. ## Square Wave Light Source or Transformer lens

I started to read CTEIN book and at first page , there was an idea. He wrote square wave light is sharper.
Is there a square wave light source or a lens transforms the curvey psf to square.
This is possible with Radar.

Best ,

Umut
Istanbul

2. Are you referring to a mention in "Post Exposure" by Ctein? If so, could you direct me to where in the book this discussion takes place? I'm having a bit of trouble understanding this on a theoretical basis.

3. If you're referring to Ctein's _Post Exposure_, he is not writing about square wave 'light'. It's a discussion of acutance as one of the factors of perceived sharpness in a print. He's talking about sharp edges as opposed to blurry edges here (page 3 of my PDF copy of Post Exposure, 2nd Edition):

Ill spare you the math, which is beyond the scope of this book (it involves Fourier transforms, if you want to work it out for yourself ). The difference between a sharp edge and a fuzzy one (a square wave and a sine wave) corresponds to a difference in spatial detail three times finer than the line spacing.
He's talking about the density of ink on paper if you graph it, like a densitometer trace. Cross a sharp edge, and it looks like a square wave function. Cross a blurry edge and the density rises gradually, and could resemble a sine wave. "Wave" in this context, refers to functions he used in his mathematical derivation, not anything physical that relates to a lens, light source, or enlarger.

cheers,

Steven

4. rco3 and Steven K ,

I think square wave tema is the subject of wave optics and its a large ocean . I think there must be a breadboard laser or microchip fabrication physical application. May be lens point spread function can be calibrated in to square wave.
I will wait more answers.

Thank you ,

Umut

5. Originally Posted by Mustafa Umut Sarac
I started to read CTEIN book and at first page , there was an idea. He wrote square wave light is sharper.
Is there a square wave light source or a lens transforms the curvey psf to square.
This is possible with Radar.
Wrong.

1) It's on page 3.

2) ctein actually wrote: I’ll spare you the math, which is beyond the
scope of this book (it involves Fourier transforms,
if you want to work it out for yourself ). The difference
between a sharp edge and a fuzzy one (a
square wave and a sine wave) corresponds to a
difference in spatial detail three times finer than
the line spacing.

3) There is no mention of square wave light.

4) What is discussed is square wave edges in images. That means where the image (negative) presents an abrupt sudden change from light to dark or the reverse.

5) Since light is simply electromagnetic radiation, square waveform electromagnetic radiation would be possible, but it would not look like light, since only the fundamental frequency would be visible. The rest of the harmonics needed to actually produce a square wave would be up in the ultraviolet and x-ray radiation regions.

6) Light is a narrow band of wavelengths, basically from 400 nanometers (nm) to 700 nm. You need to comprehend this fundamental fact of great importance to understanding photography.

7) A study of the waveform harmonic characteristics of square waveforms shows that they are composed of a harmonic series of the odd integer harmonics. That means frequencies 3, 5, 7, ... times the fundamental frequency. When this is combined with point (6) above you have the reason for point (5).

6. You don't want a square, or rect, for your PSF. Ideally you'd want a dirac delta. Think about what would happen if you imaged a really thin line using your lens with a rect for a PSF. Would you still get that really thin line or would that line spread out to be the width of that rect?

7. Let me ask an question ,

Lets imagine contact printing with UV for PT PD. What would be the sharpness difference between square wave illumination and the curvey.

8. Originally Posted by Mustafa Umut Sarac
Let me ask an question ,

Lets imagine contact printing with UV for PT PD. What would be the sharpness difference between square wave illumination and the curvey.
Go back and study light. You won't get square wave illumination for the reasons explained above. Square wave electromagnetic illumination with a fundamental frequency in the visible spectrum would have radiative frequencies (in the harmonics) that are injurious to life and your eyesight. Don't attempt it. Until you understand that point you are wasting your time and the time of others kind enough to respond to you.

By the way, what do you mean by "PT PD"? Post-traumatic photographic disorder?

9. Originally Posted by Mustafa Umut Sarac
Let me ask an question ,

Lets imagine contact printing with UV for PT PD. What would be the sharpness difference between square wave illumination and the curvey.
None, if the light source was other wise the same. What may impact would be a diffused verses a colaminar, condenser, light source.

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