Dobsonians . Skylwatcher vs revelation ?

[rory]

Having previously owned a 8" skywatcher dob that I was happy with until I needed emergency funds and do sold it along with my maxvision e/p's

. I now plan on getting another set up sometime in the near future , and I've been somewhat torn on which way to go.

I initially thought of a heritage 130 for great grab and go opportunities , plus as it's cheaper I could get it sooner. Down side is having already used a larger aperture I might find it a little underwhelming .

So I turned my attention to the 8" and 10" skywatcher dobsonians .

Now I carried out some popular mods on the dob last time out ( namely the lazy Susan and milk carton trick , bobs knobs and flocking) which in itself can be an enjoyable part of the hobby.

But now I've discovered these revelation dobs that are in the same price brackets , infact the 8" revelation can be had slightly cheaper than the Skyliner at the moment .

The revelation has roller bearings as opposed to Teflon pads , but I also notice it has a dual speed focuser which made me sit up and take notice.

So I guess I'm asking is there a reason that the Skyliner should still be in the running ? Am I missing a trick maybe .

Also interested to hear about the collimating adjustment on the revelations , are they the same as skywatchers ( I.e , daft alen keys and screwdrivers ) ?

Your input is much appreciated .

[John]

This is a personal opinion, of course, but I reckon the Skywatcher scopes, on average, have better optics in them. I've owned 2 GSO dobs (GSO make the Revelations) in 8" and 12" and 2 Skywatchers in 8" and 10". 

I'm not impressed with the claims of 1/12 wave optics for the Revelations as that is a RMS figure that translates to just about 1/4 wave PV which will just about meet the diffraction limited requirements. There will be some variation but my feeling is that Synta / Skywatcher do a bit better than this.

In the past the overcoatings on Revelation mirrors have been either poor or non existent but I'll give them the benefit of the doubt and assume that they have addressed that with the current versions.

I'll run for cover now before the GSO / Meade / Revelation dob owners catch me ! 

It is my honest opinion though, for whatever it's worth 

[Luke]

I've had three Skywatcher dobs and the optics in them in my view are a touch better than my GSO. That's just my experience having spent a lot of time looking through my scopes.

However, it's not a simple win for the SW for me, as I prefer the mechanics of my GSO. Also, using a Paracorr 2 has tidied up the optics a fair bit in my GSO. So I am not so sure I would swap it for a SW! I would tie them and be very happy with either.

I rebalanced the GSO tube easily using the mechanism for that and it can take a Paracorr plus 21mm Ethos without the need for weights, even on targets towards the horizon. It moves so super smoothly and the locks work well.

So I think there's a lot to like either way. For me the dual speed focuser on the 880 Deluxe was a big plus, as my other half often has to refocus just a small amount. I'd got a bit fed up of buying focusers and the one on my GSO can take a fair weight and for me it good enough that I am not tempted to replace it.

[rory]

Thanks for the info both. The sceptic in me made me wonder. What do you mean by the balancing mechanism Luke ? I had a magnetic knife rack on my Skyliner , is that something I won't need with the revelation / Gso then ?

[rory]

Thanks for the info both. The sceptic in me made me wonder. What do you mean by the balancing mechanism Luke ? I had a magnetic knife rack on my Skyliner , is that something I won't need with the revelation / Gso then ?

Actually I searched and found your unboxing thread which answers my question regarding the balancing. . Thanks Luke

[rory]

after reading johns reply and trying to understand the  1/12 wave comment . I googled and TRIED to read up on mirror measurements.

 after pages of "raliegh limit , rms measurements,peak to valleys "  im none the wiser,way above my intellect  .

 but I have noticed skywatcher uses pyrex glass while gso/revelation goes for bk7 glass .

not sure if any in particular is preffered for a specific reason , perhaps another google search is on the cards. 

[John]

There is not a lot of significance in the Pyrex v's BK7 thing as far as I know. I believe Pyrex keeps it's shape a little better as it cools but once cooled there is no difference as far as I know. I've never understood why Skywatcher used Pyrex just for the 10" F/4.7 

[rory]

There is not a lot of significance in the Pyrex v's BK7 thing as far as I know. I believe Pyrex keeps it's shape a little better as it cools but once cooled there is no difference as far as I know. I've never understood why Skywatcher used Pyrex just for the 10" F/4.7 

 thank you john .

 I come across this page that was informative  but simple ( what I like  )

http://www.oldham-optical.co.uk/Glass.htm

[AlexB67]

The way I recall it, BK7 has  higher heat capacity and lower thermal expansion rate, this translates to BK7 taking longer to cool, but also how much it distorts from its ideal shape across a temperature range.  Once cooled and the scope is stable there is not much in it as far as I recall.  The whole BK7/Pyrex debate is of more consequence to mirror makers, I forgot where I read this, but it did make sense. In a nutshell, time is money, the longer you got to wait for mirrors to settle,  the more they fluctuate with temperature, the more of nuisance for the makers to do a precise job in the shortest time possible.   

On a side note, All the talk about diffraction limited optics is easy to get hung up about, but, there is another factor, for the 10 inch scopes, the GSO is f/5, the SW is f4.7. For most of the field, and without a coma corrector as well, you will not be enjoying a diffraction limited field anyway. If you are a fan of the drift method and let planets drift across the view, the f ratio may be more of an issue than the differences in these two mirrors, assuming both collimated optimally and cooled. 

Hard to say,  but I expect if you do the sums for say 50%+ off axis for a of both f/4.7 and f/5 you may well be thinking the difference between the finish of the mirror are less of a concern where other aberrations will dominate.

In any case, both would be a great scope I feel, as such it is not a case of one blowing away the other, I'll qualify by saying that I've never used a GSO though.  In my situation,  had not been down to the flextube design being of importance for transport by car, it would have been  a hard call between the two, I'd be inclined to go GSO perhaps if it had been the solid tube.

[Luke]

My two cents is that if you place optics first, go the SW. If you place mechanics first, go GSO. If you are not sure, toss a coin and be happy either way

[AlexB67]

My two cents is that if you place optics first, go the SW. If you place mechanics first, go GSO. If you are not sure, toss a coin and be happy either way

Overall that is the way Iooked at it, the construction of the GSO the focuser as well, all the extras pull it over, it is only the question over the mirrors perhaps with GSO being a lesser known quantity that made me question them at times.

Depending what eyepieces you already own and or plan to buy, the f ratio is perhaps not to be ignored either, it may not seem like much, but the difference between f/5 and f/4.7 is quite appreciable  when you want to use FOV eyepieces over 65  - 70 degrees or so, at least to my eyes that is sort of my limit I'd be happy without a Coma corrector.  Personally I am happy with that amount of FOV anyway, however,  the GSO at f/5 could afford some maxvisions 82 degrees for example at a similar percentage of the field at a steal price, (rough estimate ), that increase in f ratio mounts rapidly.