[gary]

Originally Posted by OzEclipse

I have been working with Terry Cuttle on a series of articles about solar eclipses and the 5 Australian eclipses for the AAQ website.

I have mostly been doing a lot of proofing and editing of Terry's articles. Terry asked me to write a 3-page article on eclipse photography. Easy I thought. Well no as it turns out. I ran into what you might call "reverse writers' block," or perhaps, "writers' verbose diarrhoea."

My first draft was a whopping 17 pages. I viciously edited it down and I only got it down to 9 pages then I stalled and could cut no more.

So, I asked ChatGPT to write the article for me. So, I asked, "How do I photograph a total solar eclipse?

Hi Joe,

Here's a tip.

Rather than ask ChatGPT to write a one page original work on some very
technical esoteric subject, you will sometimes get a better result by
prompting it with, "Shorten the following report to a one page quick
technical how-to guide" and then copying and pasting what you have
written after that.

Now at 9 pages it is very likely that it will exceed the maximum number
of input tokens (essentially characters), but if your document was split
into multiple sections, you might be able to feed in a bit at a time.

Just like you yourself went from a draft of 17 pages down to 9 but balked
at being able to get it below that, it probably means your
essential facts to verbiage ratio was nearing unity and so ChatGPT may
do no better with a result missing important stuff.

Let's face it. Say you are sitting on a plane flying to West Australia
and some stranger asks if you are going on a holiday. You tell them
you are going to photograph a solar eclipse. They then ask, "Do you
need to do anything special to photograph them? How do you go
about that?" So you passionately launch into the full spiel including all
your hard won tips to "open up to f5.8-f8 where lens MTF is highest and
resolution sharpest" and so on.

Meanwhile, if you take notice, the stranger's eyes are starting to glaze
over.

When they asked, they were thinking, "Can I somehow snap this
with my phone?"

The reason I mention this is yesterday I wrote an overly long
post attempting to explain what is called the attention mechanism
within ChatGPT that attempts to keep it on topic.

A bit like the entry for "Earth" in the Hitchhikers Guide To the Galaxy
that originally read "Harmless" and was then revised to "Mostly harmless",
I guess it comes down to your target audience.

Believe me. Anyone who is serious enough to travel half way around the
world or cross a continent to get a great image of a solar eclipse will
not hesitate to read 17 pages. So my best tip of all is to keep it like
you have it. Besides, they have plenty of time to read it on the plane.

That hypothetical stranger on the plane was looking for totally
different advice.

Though trained on a large set of text, the current purpose of ChatGPT
was not to be the oracle of all knowledge but a demonstration of a language
model.

The other day I watched a builder using the lithium battery
out of his portable drill to hammer in a nail.

I mention it of course as reference to the old adage of the right tool
for the right job.

So hence as a language model ChatGPT is probably better at word crafting
what you as an expert had written than it is at hammering out an original
document of a technical nature. One day, maybe, but not now.

By the way, when I read the acronym you wrote of MTF, I had no idea
want it meant.

Having said it is not an oracle of all knowledge, it is amazing what
ChatGPT does know.

I asked ChatGPT :-

In the following sentence :-

"open up to f5.8-f8 where lens MTF is highest and resolution sharpest"

What does MTF stand for?

Originally Posted by ChatGPT

MTF stands for Modulation Transfer Function.

What does it indicate?

Originally Posted by ChatGPT

The Modulation Transfer Function (MTF) is a measure of the image quality of a lens. It indicates how well the lens is able to transfer the contrast of an object in the scene to the image. The MTF plot shows the relationship between spatial frequency and contrast, and provides information about how much of the original detail of an object is retained in the final image. A higher MTF value indicates that the lens is able to retain more detail, resulting in sharper and more detailed images.

Does it use a Fourier transform?

Originally Posted by ChatGPT

Yes, the Modulation Transfer Function (MTF) is calculated using a Fourier Transform. The Fourier Transform is used to analyze the spatial frequency content of an image and to determine how well the lens is able to transfer contrast from an object to the image. By calculating the MTF, lens manufacturers can quantify the performance of their lenses and determine the optimal aperture setting for the highest image quality. The MTF measurement is usually performed at different spatial frequencies and plotted as a graph to provide a visual representation of the lens's performance.

Is it plotted in the complex plane?

Originally Posted by ChatGPT

The Modulation Transfer Function (MTF) is not plotted in the complex plane. Instead, it is usually plotted as a graph with spatial frequency on the x-axis and contrast on the y-axis. The contrast is typically expressed as a percentage and is measured at different spatial frequencies. The graph shows how well the lens is able to transfer contrast from an object to the image as a function of spatial frequency, and provides information about the sharpness and detail of the lens. The MTF measurement can be used to compare different lenses and to determine the optimal aperture setting for the highest image quality.

So would something like a point spread function be utilized with the MTF Fourier transform?

Originally Posted by ChatGPT

Yes, the Point Spread Function (PSF) is related to the Modulation Transfer Function (MTF) and can be used in conjunction with the Fourier Transform to analyze the performance of a lens. The PSF describes how an idealized point source of light is spread out as it passes through the lens and is used to calculate the MTF. The MTF is the Fourier Transform of the PSF and provides information about how much contrast is retained at different spatial frequencies. By analyzing the PSF and the MTF, lens manufacturers can determine the sharpness and detail of their lenses and optimize the design for the highest image quality.

So in a sense the lens is acting as a bandpass filter at certain frequencies and this is less than ideal for uniform contrast?

Originally Posted by ChatGPT

Yes, that's correct. A lens can be thought of as a filter that selectively passes certain frequencies of light and reduces the contrast at other frequencies. The Modulation Transfer Function (MTF) provides a quantitative measure of this effect and shows how well the lens is able to transfer contrast from an object to the image. If the MTF is low at certain spatial frequencies, it means that the lens is not effectively passing the information at those frequencies and the contrast in the final image will be reduced. This can result in images that appear soft or have less detail. A higher MTF value indicates that the lens is able to retain more detail and provides a clearer, sharper image. In general, lens manufacturers aim to design lenses with high MTF values across a wide range of spatial frequencies to achieve the highest image quality.

Where a lens is selectively passing certain frequencies of light, fundamentally what is the physics of how that takes place? Is it at an atomic level?

Originally Posted by ChatGPT

The physics of how a lens selectively passes certain frequencies of light occurs at the macroscopic level, although it is influenced by the atomic-level structure of the lens material. When light passes through a lens, it is refracted, or bent, by the lens material. The amount of bending depends on the refractive index of the lens material, which is a measure of how much the speed of light is slowed down in the material. The refractive index also varies with the wavelength of light, which means that different colors of light are bent by different amounts. This results in chromatic aberrations, where different colors of light are focused at different points, and is one of the factors that can impact the quality of the final image.

In addition to chromatic aberrations, the shape and curvature of the lens elements also play a role in determining the MTF. The lens elements are designed to have a specific shape and curvature to control the way that light is refracted and focused. This allows the lens to effectively pass certain frequencies of light and reduces the contrast at other frequencies. The combination of the lens material, the shape and curvature of the lens elements, and the aperture setting all work together to determine the final MTF of the lens.

So ideally a perfect lens would allow 100% of light to pass through it at all optical frequencies and hence essentially be a unit transfer? Ideally a flat, linear response?

Originally Posted by ChatGPT

In theory, an ideal lens would allow 100% of light to pass through it without any loss of contrast or reduction in image quality at all optical frequencies. This ideal lens would have a Modulation Transfer Function (MTF) that is a flat, linear response with a value of 100% across all spatial frequencies. However, in practice, it is not possible to create a lens that meets this ideal specification. All lenses will have some level of aberrations, such as chromatic aberrations, spherical aberrations, and distortion, that impact the final MTF and result in a reduction in image quality. The goal of lens design is to minimize these aberrations and produce lenses with the highest possible MTF values across a range of spatial frequencies. This allows for the creation of lenses that produce sharp, detailed images with accurate color and minimal distortion.

Well, you can learn something new every day. Good luck with the eclipse.