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I'm after a cassegrain reflector but I don't know which one to buy,
I have a celestron c5 and it worked wonders for all fields, I now want the same but twice as powerful as my final upgrade
I am looking at a c9.5 for £1350 or a c11 for £2000, My question is an extra 2.75" focal worth it for £750 more?
I will likely purchase one this week
I'm considering the 250PDS. The main use is visual, and the second is EAA (I currently use a zwo183mm).
What I'm hesitant about is the primary focus. since It's mostly for visual, I'm wondering on how much back focus it has compared to the standard Skywatcher 10" dobsonians? with the standard dobsonias with the same optics and focuser you already need an extension tube for most eyepieces...
Also, there's probably a "bigger" obstruction (bigger shadow on primary)?
Due to an unfortunate accident my SN10 primary mirror is broken. While it was an unwieldy beast and pretty much required a complete rebuild when I got it from the previous owner I really loved it.
My understanding, thanks to discussions between owners of this OTA, is that the SN10 used a spherical mirror. However Meade's representative did not wish to confirm this "proprietary information" after stating that they could not sell me a replacement.
So, I'm stuck with a bit of a quandary: do I roll the dice and attempt to get a spherical mirror constructed? (I doubt that non-parabolic mirrors are routinely manufactured and would probably come at a price-premium). I have read anecdotal discussions that the primaries are somehow "matched" to the schmitt correctors which, I must admit, makes no sense to me as I thought that a spherical mirror was manufactured with a uniform curvature. Thus, without more information, I'm thinking that this could be an expensive and ultimately unworkable solution.
Alternatively, do I cut my losses and replace it with something like a Skywatcher 250P?
Any other suggestions?
Many thanks for taking the time to read this and for any advice you can render.
Hi, I have changed the focuser on my newtonian but its too short.
I realise that I can just add an extension tube to it but I’m not sure if that is the best solution.
I also seem to have have a stray light problem (I’m getting a hazy image on a 5mm eyepiece).
A third problem is that I find it quite cumbersome that the focuser has to stick out so far (155mm+eyepiece).
I wonder if I might solve the stay light problem by extending the main telescope tube instead of the focuser and therefore getting the eyepiece closer to the secondary. And also maintain more precision in the focuser by not extending it.
As it stands the focuser would have to come out 265mm from the centre of the secondary mirror in order to focus. The secondary is 50mm wide. From primary to secondary is 950mm approx.. The primary is 200mm Thanks for reading. Any advice will be much appreciated.
I'm aiming for the best possible field illumination for my Explore Scientific PN208 f/3.9 imaging newtonian. The scope is 5 years old now and while doing maintenance I wanted to do something about the design flaws as well.
With the current secondary holder design it's impossible to center the mirror beneath the focuser. My question is: is this really an issue when the entire primary is visible? I read about optimal field illumination when the secondary is centered, but this isn't achievable with this telescope.
I attached an image showing the (very bad aligned and already degrading) secondary at the moment. This is as far down as I can go, I would need to replace the holder screws with longer threads to go further but I don't know if it would make any difference for field illumination?
Thanks in advance,