Should I consider an SCT ;-)?Posted By Steve Lathrop |
"Perhaps the central obstruction and contrast degradation is a myth; for if it weren't, how then could these pictures be so contrasty and sharp?"
I don't know if it's a myth or not. I've never looked through an SCT either. I do know the pictures you are looking at on the web are not sharp. The originals might be, but not the ones you are looking at. Unless you have the freedom to zoom in to view microscopically small detail, your computer screen can not display sharp images, because its resolution is too coarse. With that exception, everything you see on a computer screen is inherently soft, and this can hide a multitude of sins.
To illustrate, the Legault website's most impressive image to my eye, by far, is the image of Saturn, and I think we would all agree it looks like a supurb image. On my screen that image is 4 inches across. I can see the Encke division, which shows that this is a high-resolution image. But I can barely see the Encke division, which shows that this is not a sharp image. A high resolution sharp image of Saturn displayed at that size should make the Encke division stand out much more.
Contrast is another issue. Moon pictures, particularly, almost always display harsh contrast. This is not the same as good contrast. The key is not whether the blacks look really black, and the whites look really white, but whether subtle, nearly identical shades of grey can be distinguished. If they can, especially in the highlight and deep shadow areas, then that's good contrast.
Conveniently, you have an excellent point of reference for both sharpness and good contrast with your TV-102. Just set it up next to someone's SCT on a night of good seeing and you will be able to find out all you need to know about these subjects in a few minutes.
You may also find out that the SCT has virtues that have nothing to do with sharpness and contrast, for which you could excuse some shortcomings in those areas. I'd like to find out more about the Celestron 9.25 myself.
Steve
I don't know if it's a myth or not. I've never looked through an SCT either. I do know the pictures you are looking at on the web are not sharp. The originals might be, but not the ones you are looking at. Unless you have the freedom to zoom in to view microscopically small detail, your computer screen can not display sharp images, because its resolution is too coarse. With that exception, everything you see on a computer screen is inherently soft, and this can hide a multitude of sins.
To illustrate, the Legault website's most impressive image to my eye, by far, is the image of Saturn, and I think we would all agree it looks like a supurb image. On my screen that image is 4 inches across. I can see the Encke division, which shows that this is a high-resolution image. But I can barely see the Encke division, which shows that this is not a sharp image. A high resolution sharp image of Saturn displayed at that size should make the Encke division stand out much more.
Contrast is another issue. Moon pictures, particularly, almost always display harsh contrast. This is not the same as good contrast. The key is not whether the blacks look really black, and the whites look really white, but whether subtle, nearly identical shades of grey can be distinguished. If they can, especially in the highlight and deep shadow areas, then that's good contrast.
Conveniently, you have an excellent point of reference for both sharpness and good contrast with your TV-102. Just set it up next to someone's SCT on a night of good seeing and you will be able to find out all you need to know about these subjects in a few minutes.
You may also find out that the SCT has virtues that have nothing to do with sharpness and contrast, for which you could excuse some shortcomings in those areas. I'd like to find out more about the Celestron 9.25 myself.
Steve