Sky Watcher 250 goto dob

[spikkyboy]

Hi all. Just bought a used 250 SynScan dob with the three flex tube bars.

1 question. When setting up you loosen the 3 wing nuts and slide the top part of the scope up.

Pictures in manual show full extension all the way to the end.

My question is why are there 2 detent stops? This indicates that you could stop at the first detent and shorten the focal length thus changing the F ratio of the scope?

Is this correct. Does anybody have experience of that and what benefit would there be in doing this.

Thanks

[lenscap]

1 hour ago, spikkyboy said:

My question is why are there 2 detent stops? This indicates that you could stop at the first detent and shorten the focal length thus changing the F ratio of the scope?

Stopping at the first detent does not shorten the focal length or alter  the focal ratio of the scope.

It does push the focal plane further away from the OTA which may be necessary to enable some cameras to be correctly positioned for prime focus photography.