Mauro, There is much literature to suggest that what happens when the scope gets larger is that the image simply gets larger, making it more visible. Lots of literature suggests that the contrast ratio is the same in all scopes, so if color isn't visible in one scope it won't be visible in any. However,: 1) The contrast of an object with the night sky may be 1.1:1, making the object only 0.1 brighter than the night sky. Double the size of the telescope, and the ratio becomes 4.4:4, for a difference of 0.4 The contrast ratio didn't change, but the delta did. Perhaps our vision sees the delta and not the ratio, because it is definitely the case that fainter objects are more visible in larger scopes. 2) Bigger scopes do see more color. Period. That's empirical, not theoretical. I've looked through scopes of 3" to 32" on the same night, all targeting M42, and seen increased color in larger apertures. Whatever visual analysis says, it has to explain what is empirically verifiable. What I KNOW is true is that fainter objects and details are more visible in larger scopes, and deep sky objects have more color in larger apertures. Any argument to the contrary is simply false. So stating that "If a nebula is under cones threshold it will never get above whatever the size of the scope" is inadequate to explain what I have seen. If the cones are active enough to see color in larger apertures, then I should see it in smaller apertures is the implication, yet this simply is false and verifiably so. What is open to discussion is WHY that's the case. 3) a nebula filter makes a nebula more visible by increasing contrast. The nebula isn't any brighter with the filter in place, but the background is darker. However, adding a nebula filter to my 12.5" doesn't allow me to see any more of a nebula that can be seen without the filter in a 32" scope. Since the contrast ratio is the same in the big scope as it is in my smaller scope, and since the nebula filter increased the contrast in my scope, the 32" shouldn't have an improved contrast over the 12.5" with no filter, and definitely shouldn't have an improved contrast over the 12.5" with filter. Eppur su muove. And yet it does. Bottom line: a larger aperture mimics the contrast enhancement of a smaller aperture used with a filter.
This discussion has gone on over many years and many threads, and resurfaces periodically because the theory does an inadequate job of explaining the empirical facts. I suspect the issue is semantics rather than a hard disagreement, but, for me, it appears the spread of light quantities I mention in point 1 seems to have a significant effect on what is seen. The physico/psychological reason for it is, IMO, poorly explained in the literature, and I have read extensively on the subject. Clark's articles attempt to bring it to a mathematical explanation, but I am left unpersuaded. I SEE an improvement in brightness and contrast and color in larger scopes. Arguing that it doesn't happen gets nowhere.
-------------------- Don Pensack
12.5" Truss Dob, 5" Maksutov
Sustaining Lifetime IDA member, TeleVue junkie
Previous
Index
Next
Flat
Re: Is it possible to see the nebula with colour?
Edit
Reply
Quote
