Focusing manual lens - fine focus control and lock?

[michaelmorris]

I'm looking at getting a fixed focal length telephoto lens for astrophotography.  The commonly used Canon 200mm f2.4 L is beyond my budget, so I'm considering getting a manual focus SMC Takumur 200 f4 as a far cheaper alternative.  My only concern is making sure that I get really good focus and that it stays in focus during the imaging run.  The Teleskop Service micro-focusser seems to fit the bill as a solution.

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p3284_Microfocuser-and-focus-lock-fuer-camera-lenses-up-to-D-105mm.html

Is anyone using one? 

How good/necessary are they?

Are there any cheaper alternatives?

Thanks

[bogdog]

have never used the micro focusser so can't advise on that

super takamur are good lenses,i use the 55mm one on a nikon it holds focus fine,but at 200mm i guess you would want something to make sure you don't lose focus

[jnc71106]

the fine focus rings are very very good and are much better than trying to do it by hand alone, up until recently i used a set with my canon 200mm L with my CCD and they were awesome

[Alien 13]

The 135mm lens i have holds focus all night but may need a tiny tweek if the temp changes by more than a few degrees.

Alan

[Psychobilly]

They work a treat... I made my own and it's gone through several pairs of hands at SGL  starparties...

Peter. ..