Hi Martin,
As per the other thread I've opted for a 8" (over the 10"). I went with Skywatcher over the Bintel/GSO and have the following comments:
- from what I've skimmed from various forums and timelines over the past few days is that the GSO apparently is more prone to flex issues, not the other way around. This was from older posts, mainly relating to dobs so maybe it's not 100% correct now. Tube weights might have something to do with it, but I've seen some variance in the listed weights, some are OTA only, some are OTA + accessories (finder, tube rings etc). It's not always clarified on which weight is listed.
- SW have Pyrex glass while the GSO have the BK7 which seems to need recoating after a period of time. Again, sourced from old posts. Manufacturing may have improved. To the average amateur can they even tell when they need recoating or just a wash?
- Black vs white: while black surfaces do absorb more heat than whites, they also emit it better than white surfaces. I would have rather a white scope to match the mount
- The current SW f/5 8" is a 200P-DS (or P200-DS) which has an upgraded 58mm secondary from around 2012 or so (with the dual speed focuser). Again, found this information on one forum and one shop website but nowhere else. Will confirm when I unbox mine. I've been playing with some secondary calculators and while there is a slight dimming in magnitude near the edge of field it wasn't significant enough for me to jump to the 63mm (58mm is definitely better than the 52mm that the 200p used to come with). This larger secondary may only be to offset that the primary is further up the tube. I was only estimating a range of distances in the secondary calculator.
- The Bintel/GSO has the cooling fan and slightly larger secondary, but I've picked up the SW for $495 vs the Bintel unit for $479 + $50 shipping, so the cost of adding my own fan is offset by the cheaper purchase price.
Anyway that's a brain dump of what I've found over the last few days. As with anything, don't take it as gospel, YMMV etc etc, but hope it helps. I'm certainly no expert. I'm sure either unit will be fine to use
.
Cheers