Telescope Reviews: C14. Refractor Equal

The question here is how valid it is to compare planetary performance to deep sky performance. Clearly with bright objects like Jupiter, the improved contrast that a larger scope provides is very useful when looking at the fine scale, low contrast details on Jupiter's surface.

But Jupiter is very bright, the Ring Nebula is very dim. To resolve those faint, barely visible details of the ring, the eye requires that the scale of the detail be very large, highly magnified. The eye is not resolving those fine details on M57 because the entire image is barely visible, it is the added light gathering of the larger scope that allows the higher magnification and brighter image at the same time that allow for more details to be seen. But the telescope resolves more than the eye can see, the camera shows this.

I like your example of the M57. How does the ring nebula compare to Jupiter in terms of details resolved and brightness...

According to the Sky, Jupiter is currently 35 arc-seconds in diameter with a brightness of -2.2 magnitudes. M-57 is 2.5 arc-minutes in diameter and magnitude 9.0. Jupiter is 28,000x brighter and covers an area 1/18th of that of M57. Do the math, the surface brightness of Jupiter is 500,000x brighter than M57.

With an image this bright, there is enough light that the eye can see those fine details. 500,000x, most solar filters have an attenuation of 1/100,000. If my calculation is correct, that says that the ring nebula is dimmer than were I to view Jupiter through a solar filter.

Do the thought experiment, viewing Jupiter through a solar filter... no detail is lost, no contrast is lost, only brightness.... what would Jupiter look like through a solar filter?

I suggest that Jupiter would be barely visible and that the wealth of detail that is there to be seen at full brightness could not be seen, the added contrast of the fine details that the increased aperture provides would not be visible to the eye. Were it merely brighter or the eye far more sensitive, it could be seen.

The camera is instructive because it is an example of the contrast and detail visible in deepsky objects. Long integration imaging does not improve the spacial detail, it just makes the image brighter... The example of the fine detailed images of the deep sky that the camera provides which are not visible to the eye is merely useful to demonstrate that there is significantly more at the focal plane to see than the eye can see...

So my point is that factors that are important in providing the high quality planetary views are not in operation when viewing the faintest objects because the details are simply too small for the eye to resolve because there is just not enough light reaching the retina. Less light means the image at the retina must be larger.

This is why image intensifying eyepieces are so effective, they provide the brightness needed so the eye can resolve what is there to be seen.

So, I ask this question:

I make the calculation that from a brightness point of view, a C-14 has the through-put of a perfect 12 inch telescope. So, that means the C-14 is 4 times brighter than the 6 inch refractor.

Add neutral density filter with 25% transmission to the C-14 and look at the M57. How different would the images be, the detail seen, than if you were looking through the 6 inch? Were you looking at Jupiter, the larger scope would show significantly more.

Looking at M57, I just don't think the fine details that are enhanced by the improved contrast of the larger scope are visible to the eye.

Jon