Apodizing Screen RevisitedPosted By Michael Rowles |
Hi!
I know this is a five-year-old thread, but I had to put in my two cents. I have experience with an apodizing mask, know that they can work, and I know why they work. I made one for my 10" f/4.8 Newt. The mask improves contrast on bright planets, allowing more detail to be seen. Also, detail that was seen without the mask is seen more easily with the mask. Apodizing masks improve contrast by reducing the brightness and thickness of the first two diffraction rings and increasing the size of the Airy disk. This is what "apodizing" means. (From the Greek "a" without + "pod" foot: "without a foot.")
An apodizing mask does not work by reducing the aperture, it does not work by reducing the glare (though that is helpful on the Moon), and it does not work by drawing the eye toward the center of the field of view. An apodizing mask works because it changes the diffraction properties of the telescope, thereby increasing contrast, which in turn allows more detail to be seen in the object.
By the way, the idea about charging your eyes with white light before you view planets is a good idea. It works, too! The white light tends to reset your eyes to photopic vision, how your eyes see during daylight. Our eyes can see more detail with more contrast and a much greater color recognition when they are photopically adapted. Mesopic or scotopic (twilight- or dark-adapted) eyes will see less detail, less contrast and less color on planets than photopic eyes. When I'm looking at Jupiter or another planet, I stare at the reflection on a white sheet of paper from a white flashlight every 10 minutes or so to try to maintain my photopic adaptation. It works, and I've explained here why it works. Apodizing masks can also work, if they are constructed and used correctly and with a little patience.
Clear Skies,
Mike
I know this is a five-year-old thread, but I had to put in my two cents. I have experience with an apodizing mask, know that they can work, and I know why they work. I made one for my 10" f/4.8 Newt. The mask improves contrast on bright planets, allowing more detail to be seen. Also, detail that was seen without the mask is seen more easily with the mask. Apodizing masks improve contrast by reducing the brightness and thickness of the first two diffraction rings and increasing the size of the Airy disk. This is what "apodizing" means. (From the Greek "a" without + "pod" foot: "without a foot.")
An apodizing mask does not work by reducing the aperture, it does not work by reducing the glare (though that is helpful on the Moon), and it does not work by drawing the eye toward the center of the field of view. An apodizing mask works because it changes the diffraction properties of the telescope, thereby increasing contrast, which in turn allows more detail to be seen in the object.
By the way, the idea about charging your eyes with white light before you view planets is a good idea. It works, too! The white light tends to reset your eyes to photopic vision, how your eyes see during daylight. Our eyes can see more detail with more contrast and a much greater color recognition when they are photopically adapted. Mesopic or scotopic (twilight- or dark-adapted) eyes will see less detail, less contrast and less color on planets than photopic eyes. When I'm looking at Jupiter or another planet, I stare at the reflection on a white sheet of paper from a white flashlight every 10 minutes or so to try to maintain my photopic adaptation. It works, and I've explained here why it works. Apodizing masks can also work, if they are constructed and used correctly and with a little patience.
Clear Skies,
Mike
