1.25" / 2" focuser setup weight comparison

[Alfian]

I have a TS 80mm f7.5 achromatic refractor  which came with a standard synta style  r&p 1.25" metal focuser. A simple focuser but pretty smooth, quite adequate and with a 32mm plossl would give almost 2.8 degrees fov. For some reason that I can't quite recall I decided this was not enough and having seen a 2" r&p synta style metal focuser of just the right size going begging, I duly fitted it and all was nearly well. To enable the scope to focus I had to cut 25mm of the tube and because the new focuser plus 2" diagonal etc made the scope tail heavy I needed to rig up a counterweight to get it all to balance. In this instance I chose to use a longer dovetail with a weight bolted to the "far" end. All done it worked very nicely and I have to say that with a litlle bit of tinkering the 2" focuser is very smooth.  With my 2" 35mm Rigel EP I now had a wonderful nearly 4 degrees fov.

In recent weeks I have been attempting to put together a lightweight setup to use and store at a caravan we have tucked away in darkest Galloway so I thought I would revert the TS 80 back to its 1.25" focuser status. This required a small 1.25" extension but that was OK. Given the very noticeable differences in size and weight out of curiosity I thought I would weigh each component. It worked out as follows:

1.25" focuser Setup:

Tube/Objective -855 gms

 1.25" focuser - 512 gms 

1.25" Circle T prism diagonal. - 99 gms

205mm dovetail - 190 gms.

Tube rings - 281 gms.

1.25" extension/adapter - 45 gms

(Total - 1982 gms)

 

2" Focuser Setup:

Tube/Objective -855 gms

2" focuser - 685 gms

Skywatcher 2" dielectric diagonal - 404 gms

2" - 1.25" reducer - 119 gms

305mm dovetail - 283 gms

Counterweight - 346 gms

Tube rings - 281 gms

(Total -  2973 gms)

As near as matters 2 Kgm vs 3 Kgm if you accept the necessity of the 1.25" extension and the 2"-1.25" reducer for practical purposes.  I was surprised that the last item alone weighed more than the Circle T prism diagonal. What price a very wide field of view! This does not prove much other than maybe on reflection, in terms of weight considerations it wasn't the best idea in the world. However its made me wonder why, especially, on short wide field refractors such as the 500 mm Startravel  which at f4.9  is going to mean EPs longer than 25mm or so is into big exit pupils, whats the point? A 1.25" 24mm/68 EP gives a nice 3.25 degrees.   Also given that some nice small ED/Apo  refractors have useful 2" dual speed focusers I wondered why no one makes 1.25" dual speed focusers or do they?

As a postscript to this ramble and just to show how plans can get derailed or at the least branched off I have recently acquired a Celestron Nexstar 6/8SE mount -with a 4SE ota - (thanks Gus) that the TS80 (2" mode) sits on very nicely. I just need to find a space for it now in the 'van.  

 

 

[nightfisher]

You did a lot of work on the TS80, but they are nice scopes for the cost, i am in process of sorting my small/travel scope, the opticstar AR90 and now have an AZ4 heading my way, this will be the third AZ4 i have bought, i better keep this one

[Alfian]

Yes, the az4, apart from a little bit of "stiction" which can be addressed, is a good solid practical mount. The 90mm will sit on that with no problem Jules.