I have built a couple
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First two very bad third good but I liked one already built in China (12inch)better... but if I had not built them I would not be prepared to pay big bucks for good ones now.. I appreciate the effort and the time and the stuff you must learn..
These days I think it would be cheaper all things considered to buy one already made... a dob is a great choice and they are cheap.. 6 inch to 12 inch and 16 inches are here or soon will be.
I use from 50mm and 80mm binos, and two 6 inch scopes for photos and a 12 inch dob for visual... in a dark site and there is little difference in many respects so dont think something can be too small... I can not believe the views thru 80mm binos are so good.. I reckon you get a better view of Orion..other will disagree but there is my view.
A dark site is the key...do not underestimate that in your consideration..if you have to travell to a dark site get a scope that will transport with ease.. this may mean the 4 inch is it...and there is nothing wrong with a 4 inch if you point it at the right object
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Still if you are set on building one give yourself about 6 months to read the stuff out there
.. you can melt and mold your own glass if you want
..grind a lens for a refractor, make your own mirror and even silver it
.. just goggle ATM or the like you will be busy
...I have seen such sites.. they tell you how to do everything
do you really want to or do you think it may be cheaper? it can be but you need to be cunning...
It is satisfying but time is more valuable than cash when you have small children.. the time taken by anything that means less times with them should be regarded with suspicion for they grow old far to fast as do all of us.
Buy a DOB and start grinding a 20 inch mirror
alex