Post by nobody on Oct 6, 2015 11:35:41 GMT -5
Hi Guys
Following the advice of enthusiastic members here I ordered the last 7" 180mm f/12 R35 lens through John Timmins of iStar Optical UK.
These lenses had been discontinued by iStar but my interest in obtaining one resulted in the last lens being sent over to me here in Europe.
I already had a 6" f/8 Celestron achromat but wanted more, with much less colour and hopefully, much better optical quality.
An 8" is a much bigger and heavier instrument, at any focal ratio, and needs to be mounted solidly on a huge mounting.
So I decided to build a [slightly] smaller 7" refractor instead.
Fortunately, iStar's R35 technology has allowed me to have the CA equivalent of 7" f/15 but which fitted in "only" an f/12 tube.
Even so, this tube length was probably pushing the limits of my 50 year-old, Fullerscopes MkIV mounting.
Though they have been used to support heavy 15" reflectors in the past.
So my OTA would have to be kept light to reduce the loading and leverage. [moment arm]
It would still be a rather large and heavy telescope with a focal length of 7' and a 10lb objective.
I already had my massive welded steel pier for my MkIV mounting which had easily shrugged off the 6" f/8 Celestron.
The problem was moving the massive pier around the garden to allow me to see the sky between the high hedges, even taller trees and my own house.
No point in building a new telescope if I could never see anything through it because of some local obstruction!
So the build had several important goals:
A bigger and better refractor but with a new level of mobility for the entire instrument.
It has to be manageable by me in weight terms for carrying the OTA from storage.
Then lifting it into the mounting rings at over 7' high.
I am well past retirement age and weight lifting is not amongst my many hobbies.
Though I do try to keep fit with daily walking, cycling, gardening and DIY.
The project also had to be built as cheaply as possible but without making any serious compromises.
So do not expect pictures of costly focusers, carbon fiber tubes, professional spray jobs or machined parts.
The entire project must be DIY and built with locally available materials with my existing tools.
I also wanted it finished and functioning yesterday. Or preferably the week before that.
I have used blogging as a personal ATM build diary.
Where I discuss my reasons [at very great length!] for doing everything during the build.
It is chronologically illustrated, with my own photos.
So I can look back on my obvious mistakes at a later date.
Typically of blogs it runs backwards to the future.
So you ought to start at the beginning.
Then keep pressing Newer Post when you get too bored with each "chapter".
There are 18 build posts altogether:
Far too much talking and probably not nearly enough pictures:
fullerscopes.blogspot.dk/2015/08/toobs.html
I'd like to thanks John Timmins of iStar UK for his professionalism, helpful advice and truly remarkable knowledge:
www.istartelescopes.co.uk/
And Ales Krivanek, the proprietor of iStar for his knowledge, help, advice and enthusiasm.
Here is the [still unfinished] result of several week's activity but without the full length dewshield.
The blue cords are just for security to ensure the OTA does not slide through the tube rings.
Skywatcher don't do an 8" 200mm tube ring so I had to pack out their 235mm size.
[With router-cut, 30mm wide, birch plywood rings.]
I originally padded the over-sized tube rings with thick foam but it was too soft to hold the weight of the OTA.
The tube slid downwards in the pitch dark while pointing overhead at Vega!
Luckily it was saved from potential damage by the security cords.
I now plan to use four tube rings with a carrying handle between the middle two.
Following the advice of enthusiastic members here I ordered the last 7" 180mm f/12 R35 lens through John Timmins of iStar Optical UK.
These lenses had been discontinued by iStar but my interest in obtaining one resulted in the last lens being sent over to me here in Europe.
I already had a 6" f/8 Celestron achromat but wanted more, with much less colour and hopefully, much better optical quality.
An 8" is a much bigger and heavier instrument, at any focal ratio, and needs to be mounted solidly on a huge mounting.
So I decided to build a [slightly] smaller 7" refractor instead.
Fortunately, iStar's R35 technology has allowed me to have the CA equivalent of 7" f/15 but which fitted in "only" an f/12 tube.
Even so, this tube length was probably pushing the limits of my 50 year-old, Fullerscopes MkIV mounting.
Though they have been used to support heavy 15" reflectors in the past.
So my OTA would have to be kept light to reduce the loading and leverage. [moment arm]
It would still be a rather large and heavy telescope with a focal length of 7' and a 10lb objective.
I already had my massive welded steel pier for my MkIV mounting which had easily shrugged off the 6" f/8 Celestron.
The problem was moving the massive pier around the garden to allow me to see the sky between the high hedges, even taller trees and my own house.
No point in building a new telescope if I could never see anything through it because of some local obstruction!
So the build had several important goals:
A bigger and better refractor but with a new level of mobility for the entire instrument.
It has to be manageable by me in weight terms for carrying the OTA from storage.
Then lifting it into the mounting rings at over 7' high.
I am well past retirement age and weight lifting is not amongst my many hobbies.
Though I do try to keep fit with daily walking, cycling, gardening and DIY.
The project also had to be built as cheaply as possible but without making any serious compromises.
So do not expect pictures of costly focusers, carbon fiber tubes, professional spray jobs or machined parts.
The entire project must be DIY and built with locally available materials with my existing tools.
I also wanted it finished and functioning yesterday. Or preferably the week before that.
I have used blogging as a personal ATM build diary.
Where I discuss my reasons [at very great length!] for doing everything during the build.
It is chronologically illustrated, with my own photos.
So I can look back on my obvious mistakes at a later date.
Typically of blogs it runs backwards to the future.
So you ought to start at the beginning.
Then keep pressing Newer Post when you get too bored with each "chapter".
There are 18 build posts altogether:
Far too much talking and probably not nearly enough pictures:
fullerscopes.blogspot.dk/2015/08/toobs.html
I'd like to thanks John Timmins of iStar UK for his professionalism, helpful advice and truly remarkable knowledge:
www.istartelescopes.co.uk/
And Ales Krivanek, the proprietor of iStar for his knowledge, help, advice and enthusiasm.
Here is the [still unfinished] result of several week's activity but without the full length dewshield.
The blue cords are just for security to ensure the OTA does not slide through the tube rings.
Skywatcher don't do an 8" 200mm tube ring so I had to pack out their 235mm size.
[With router-cut, 30mm wide, birch plywood rings.]
I originally padded the over-sized tube rings with thick foam but it was too soft to hold the weight of the OTA.
The tube slid downwards in the pitch dark while pointing overhead at Vega!
Luckily it was saved from potential damage by the security cords.
I now plan to use four tube rings with a carrying handle between the middle two.
