Quote:
Originally Posted by mental4astro
What "loss of field of view" are you talking about?
There is an urban myth that using long focal 2" eyepieces in an 8" SCT will result in vignetting. People who say this ALL have NEVER tried this combo & are only repeating what they have heard.
I have used long focal length 2" eyepieces with not only 8" SCTs but also a 127mm Mak which has an even smaller bore in its primary mirror. I have gone out of my way to look for this vignetting & have never seen it. I have used all manner of ling eyepieces, including 30mm 82°, 38mm 70° & 55mm 45°, at night with stars & the Moon & with daytime viewing to make sure I wasn't missing anything & have never been able to see any vignetting.
HOWEVER, the image will vignette ONLY if you use an f/6.3 focal reducer-corrector with these long focal length eyepieces. But neat, without a reducer, no vignetting.
But please, tell us what this "loss of field of view" is that you mentioned. Using 2" eyepieces INCREASES the true field of view, not decreases it, with long fl eyepieces. By "loss of field of view", do you mean the AFOV getting smaller beyond a certain focal length? Or are you talking about some reduction in the TFOV? Because the two are not the same thing.
This is all with visual use of these scopes. I am not discussing imaging as your post is about visual.
Alex.
|
Obviously, some people are much less sensitive to a reduction in illumination than others. I could see vignetting in the 8" SCT with any eyepiece having a 38mm field stop of larger. It didn't bother me that much, but I could always see it.
The C8 was designed to fully illuminate a 1° field, according to the white paper, and anything larger would result in more vignetting than the 50% illumination at the edge that was designed into the scope. I found I could tolerate vignetting up to about 1.2°, but not larger. A 46mm field stop yields 1.3°, and vignetting was definitely noticeable 100% of the time.
I could also see it in my 127 Maksutov when the field stop was larger than about 25mm. I never used 2" eyepieces with that scope because vignetting would have been severe.
Some use no coma corrector at f/4. I found coma horrible at f/5 and bought a coma corrector the next day after getting the scope.
We all have different sensitivities.