Anatomy & Physiology of Nwtonian Reflector Scopes

[rabbithutch]

I read a lot of posts here that I don't understand and use them to direct my attention to trying to absorb enough basics to continue to extend my knowledge. Recently, there have been a number of posts about mirrors and coatings, for example. There are innumerable posts about EPs.

Here's my proposition. Can we have a thread that will tell those like me who don't know, how to go about examining and evaluating their scope or one they are considering?

I've been a member here for about a year. During that time I've learned more than I would have dreamed when I started. Last winter I found a used 8" dob (Orion of a '90s vintage) within my budget and purchased it. I had no idea how to examine it or question it. Since then, I have probably abused the scope moving it around. I've not yet learned collimation and my viewing thus far has been planets and Earth's moon. I suspect that the primary mirror in my scope needs cleaning and maybe recoating. The secondary mirror is mounted on a single vane. Is this good or bad? My focuser is NOT a crayford style (I don't know what to call the type that I have). I will not even go into the dobsonian mount so as not to complicate the discussion.

So, you see that I still have much to learn about the care and feeding of a scope. Anyone want to jump in and start a discussion about this subject? Let's start with the primary mirror? Is dismounting it a task that a reasonably sentient user could safely accomplish? What should one look for when inspecting the mirror? . . . its cleanliness? . . . its coating state? Where does one go (besides tapping the knowledge here) to learn about the mechanics of it all?

et cetera et cetera et cetera (in my best Yul Brynner voice)

[NGC 1502]

Hi from across the 'pond'.

This link gives lots of further links that may be useful to you -

newtonian reflector telescope - Eye of the Telescope

As to your question, removing the primary on almost all Newtonians can be done by almost anyone, with a bit of care, just basic tools required. When doing this, I've found that it's best to place the tube on a sofa, with the mirror end overhanging the end. That way, when the cell & mirror detach, then the tube doesn't do a sudden nose dive. Quite a lot a dust & crud on a mirror doesn't detract much from the views, so if you aren't certain that cleaning is needed, then best left alone.

If the coating looks ok, it probably is. Further evaluation can be done when the mirror is detached from the cell. Hold it up to a bright light, and look from the back.

Quite a few 'pinholes' in the coating are ok. I've even seen some on freshly coated mirrors. Loads of pinholes or bare patches mean that a recoat could be needed, but even then, the mirror will still be ok for a while, no need to panic. Another tip when handling mirrors (or any optical component) is to wear clean cotton gloves, if you make a mistake, and a finger strays onto the optical surface, you won't leave a fingerprint.

You mentioned the single stalk secondary mount. That probably means it's thicker than ideal. But I once had an "Astrosystems" 8.5 inch Newt with a similar thick single stalk secondary mount. It did make it harder to collimate, but once sorted, the rugged construction meant it never moved. It gave superb planetary views. I was daft enough to sell it. I wouldn't worry about the secondary mount you have.

The focuser is likely to be a rack & pinion. The Crayford is the 'in thing' at the moment. It does have some advantages, mainly less prone to the draw tube wobbling. But many regular R&P focusers have adjusters to sort that. A well made

R&P can be excellent, and an lesser one can be made to work ok, with a bit of basic maintenance.

Please come back for more if needed, regards, Ed.

[nicnac]

that link is naff NGC, came up as a google redirect that didnt lol

try this one

Eye of the Telescope

these is interesting too

http://www.telescope-optics.net/reflecting.htm

http://www.astro.caltech.edu/~george/ay20/reflecting-telescopes.pdf

http://www.lightholderoptics.com/optical.htm

dont know if this would be any use but.......

http://www.spectrum-coatings.com/Telescope-Mirror-Prices.htm

[NGC 1502]

that link is naff NGC, came up as a google redirect that didnt lol

try this one

Eye of the Telescope

Well the link works for me and yours takes me to another part of the same site. Thanks for the further links.

Regards, Ed.