A couple of pluses and minuses of the Schmidt Cassegrain Telescope: Plus: The "folded light-path" of the Schmidt Cassegrain gives you get the equivalent of a longer telescope in a shorter tube. Shorter is better in that it will experience less wind load and the motors will require less torque to keep it aligned. A longer telescope would require more powerful and more costly motors. Minus: Because of the internal design of the Schmidt Cassegrain, some of the aperture is blocked by a secondary internal mirror (approximately 35-40%). That's a big reduction. When comparing an 8 inch Dobsonian with an 8 inch Schmidt Cassegrain, the brightness difference is quite surprising. Through the Dob, Jupiter makes me want to squint. Yes, its THAT bright. Excellent video as always!
Bob, you didn't use the term "trade-off", but that's what came to mind when you were describing changing the focal length or aperture, or both. The old phrase about using the right tool for the job at hand is so appropriate. You choose the best specifications to produce the results you want. I think covering these details is important, so thank you for sharing your experiences.
Very nice Bob. A couple of minor comments. The first element that the light encounters in a telescope is usually referred to as the objective, objective lens or mirror. Of course you might have a different experience. Unless you know that there is a protective hard coating on an optic you need to be very careful if you touch or clean it. Bare aluminum coatings on mirrors are quite soft and some of the old antireflective coatings on lenses can also be easily damaged. Some of these coatings can also be damaged by water so keeping dew off them is important. Water can react with any dust or other material on a optic so it's just all around bad to let them get wet. The magnification, plate scale, is not a difficult calculation. There are a number of places on the internet that will show you how it is derived. Basically it's Plate scale (Arc sec/mm) = 206265/D * f# = 206265/F Where D = diameter of the objective (lens or mirror) in mm F = focal length in mm f# is the f number at the focus F# = F/D of course I think I got that correct.
It is most important with looking at the moon, a relatively close 3d object. With distant objects, your images will be blurry until you are right at the correct focus with a fast, f/2.2 telescope, with the slower scope correct focus is a little harder to nail down as there is very little difference noticed when you are getting close and still making adjustments. Pro hint for focusing- once you have the donuts gone (stars will have a bright ring about a dark central spot when out of focus), increase the magnification of the image and check again. As you go to 100%, 300% and even 800% you might start seeing the dark center spot again. Reduce the steps (or use the fine focus knob) to tighten it up until the spots go away.
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I hope you're putting half a drop of homeopathic lens improver on each exposed surface.
A couple of pluses and minuses of the Schmidt Cassegrain Telescope: Plus: The "folded light-path" of the Schmidt Cassegrain gives you get the equivalent of a longer telescope in a shorter tube. Shorter is better in that it will experience less wind load and the motors will require less torque to keep it aligned. A longer telescope would require more powerful and more costly motors. Minus: Because of the internal design of the Schmidt Cassegrain, some of the aperture is blocked by a secondary internal mirror (approximately 35-40%). That's a big reduction. When comparing an 8 inch Dobsonian with an 8 inch Schmidt Cassegrain, the brightness difference is quite surprising. Through the Dob, Jupiter makes me want to squint. Yes, its THAT bright. Excellent video as always!
I'll discuss many of those points in the next videos.
Bob, you didn't use the term "trade-off", but that's what came to mind when you were describing changing the focal length or aperture, or both. The old phrase about using the right tool for the job at hand is so appropriate. You choose the best specifications to produce the results you want.
I think covering these details is important, so thank you for sharing your experiences.
Trade off is a very good term and comes into play in the next video
Very nice Bob. A couple of minor comments. The first element that the light encounters in a telescope is usually referred to as the objective, objective lens or mirror. Of course you might have a different experience.
Unless you know that there is a protective hard coating on an optic you need to be very careful if you touch or clean it. Bare aluminum coatings on mirrors are quite soft and some of the old antireflective coatings on lenses can also be easily damaged. Some of these coatings can also be damaged by water so keeping dew off them is important. Water can react with any dust or other material on a optic so it's just all around bad to let them get wet.
The magnification, plate scale, is not a difficult calculation. There are a number of places on the internet that will show you how it is derived. Basically it's
Plate scale (Arc sec/mm) = 206265/D * f# = 206265/F
Where
D = diameter of the objective (lens or mirror) in mm
F = focal length in mm
f# is the f number at the focus
F# = F/D of course
I think I got that correct.
Thanks and great points. I've used the term before, but for this video I had it stuck in my head. Objective Lens is the correct term.
Why is depth of field important in a telescope since you are not looking at nearby objects?
It is most important with looking at the moon, a relatively close 3d object. With distant objects, your images will be blurry until you are right at the correct focus with a fast, f/2.2 telescope, with the slower scope correct focus is a little harder to nail down as there is very little difference noticed when you are getting close and still making adjustments.
Pro hint for focusing- once you have the donuts gone (stars will have a bright ring about a dark central spot when out of focus), increase the magnification of the image and check again. As you go to 100%, 300% and even 800% you might start seeing the dark center spot again. Reduce the steps (or use the fine focus knob) to tighten it up until the spots go away.
I hope you're putting half a drop of homeopathic lens improver on each exposed surface.
spit?