Skywatcher 9x50 finderscope FL

[AlistairW]

Hello,

Anyone certain of the FL of the Skywatcher 9x50 finderscope ? - I seen 162mm and 180mm .....

Thanks

Alistair

[laudropb]

Is this the straight through or RACI version?

[gnomus]

Hi Alistair

I tried finding this out some time ago without any success.  Do you want to know because you have been asked to enter this information in PHD, or something similar?  If so, I wouldn't worry too much about it.  Just enter one of these numbers and let PHD calibrate - it should sort itself out as part of the calibration routine.

(I'm sorry but I cannot remember what number I ended up putting in when I was using my 9x50 to guide.) 

[AlistairW]

Yes straight through, and also yes need it for PHD, as I have turned it in to a Finderguider.

Thanks

Alistair

[gnomus]

The consensus seems to be that your Skywatcher has a focal length of 180mm - https://stargazerslounge.com/topic/251831-sw-9x50-finderscope-focal-length/  (I found a similar figure given on Astrobin.)

As I say though, so long as PHD calibrates successfully you should be OK.  

[Grierson]

24 minutes ago, gnomus said:

The consensus seems to be that your Skywatcher has a focal length of 180mm - https://stargazerslounge.com/topic/251831-sw-9x50-finderscope-focal-length/  (I found a similar figure given on Astrobin.)

As I say though, so long as PHD calibrates successfully you should be OK.  

I agree. I have mine set up as 180mm within PHD2 and from my novice perspective it works perfectly. -John

[Ben the Ignorant]

I measured the focal length in japanese and taiwanese 50mm finders, it was 180mm. When I looked at spare parts over the years, the 50mm short doublets were always f/3.6, thus the 180mm focal length seems to be standard. Not sure to remember perfectly, but cheap 50mm binocs I took apart also had that 180mm distance between the doublet's center and focal point.

[AlistairW]

Thanks all for the replies