KaStern_Former_Member
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Posts posted by KaStern_Former_Member
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Hello,
Some seem to think it's good visually and it looks like a reasonable planet hunter has anybody used one both visually and / or for photographing DSOs?
this scope has a quite big central obstruction.
Therefore the contrast transfer suffers, wich is most obvious for low contrast detail.
The scope is o.k. for lunar observation, where most detail is high-contrast detail,
but for planetary observation where many detail is low-contrast detail this scope is somewhat limited.
This scope was meant to serve for astrophotography. In this part it is good.
Due to the RC-Cassegrain Design it is free from off-axis coma.
And there is no colour aberration at all.
But there will be a bit astigmatism off-axis and there is field curvature too.
Please note that the RC must be well collimated!
Cheers, Karsten
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Altair Astro GSO 6" F9 Ritchey Chretien
in Discussions - Scopes / Whole setups
Posted
Hello ajohnson,
much depends on if you want to image or if you want to observe.
If you want to make images you definitely should chose the RC over a 6" SCT.
The RC does not have off-axis coma, the SCT does have a lot of it.
Off-axis image quality is much better with the RC.
If you want to observe this does not matter that much.
The eye is only capable of high resolution in a very small area of the retina, the fovea centralis:
http://en.wikipedia.org/wiki/Fovea_centralis
So you only see sharp objects when you look directly to them.
Therefore you will only notice off-axis unsharpness if you look directly to the object.
In theory the SCT should have a small on-axis advantage over the RC
because of its slightly smaller central obstruction.
But the obstruction is bigger than tthe secondary alone, the baffletubes cost additional obstruction.
And a telescope has to be collimated very well.
This is true for the SCT and the RC.
In practice the collimation can cause bigger differences than the obstruction.
Both SCT and RC are lightweight and compact.
But the SCT may have a slight advantage.
If you can manage this you should try to do a direct side by side comparison
between these two scopes.
Cheers, Karsten