Skywatcher vs GSO f/4 Newtonians

[riklaunim]

I'm looking at a f/4 12" Newtonian, mostly for Solar System imaging. Skywatcher has Quattro, while GSO has their own much cheaper f/4. The question is - which one is better, more rigid, that do not flex/bend? Older GSO like the 8" did commonly flex.

[Chris]

I've got to ask Rik, if it's for solar system, why not the cheaper, more stable, longer focal length 300pds f/5?

[riklaunim]

10 minutes ago, Lockie said:

I've got to ask Rik, if it's for solar system, why not the cheaper, more stable, longer focal length 300pds f/5?

To fit it reasonably on  a balcony DK build will likely fail and my other options are either Newtonians or second hand GSO RC. I don't want to go back to SCT as their closed OTA doesn't handle local night temperature drops efficiently.

[Chris]

1 hour ago, riklaunim said:

To fit it reasonably on  a balcony DK build will likely fail and my other options are either Newtonians or second hand GSO RC. I don't want to go back to SCT as their closed OTA doesn't handle local night temperature drops efficiently.

I see where you're coming from, the only thing with the steel tube f/4's is that temperature fluctuations effect collimation, and the sweet spot for an f/4 is tiny compared to an f/5 or f/6. If you're going the f/4 route I'd go for a more temp and flexure stable carbon fiber tube. Also, the faster the mirror, the more tricky it is to get a decent figure, so expect a lower Strehl for a mass produced fast mirror.

I'd go for a 10" f/5 over a 12" f/4 in your shoes, yes the 12" will have more resolution, but the image is more likely to be soft due to chasing collimation.

Also trying to focus the steep light cone of an f/4 can be very tricky.