Advice on Orion Optics scope choice

[Dave In Vermont]

The Skywatcher tends to be Synta, while the Orion's here in the US are likely GSO (Guan Sheng Optics). As for the question of which is better? It swings like a pendulum - sometimes (years) it's Synta, while other times it's the GSO. I'd suggest finding the most recent reviews by end-users and stay informed. As for Bresser, I'm told these are from Meade Instruments. Meade tend to have excellent optics - whoever they're employing. But their mechanical skills are often quite in need of help.

Having re-done several Meade SCT's,

Dave

[Cornelius Varley]

7 hours ago, Dave In Vermont said:

The Skywatcher tends to be Synta, while the Orion's here in the US are likely GSO (Guan Sheng Optics). As for the question of which is better? It swings like a pendulum - sometimes (years) it's Synta, while other times it's the GSO. I'd suggest finding the most recent reviews by end-users and stay informed. As for Bresser, I'm told these are from Meade Instruments. Meade tend to have excellent optics - whoever they're employing. But their mechanical skills are often quite in need of help.

Having re-done several Meade SCT's,

Dave

Orion Optics is a UK company OrionOptics and has no association with the US company known as Orion Telescopes and Binoculars. 

[Piero]

1 hour ago, Cornelius Varley said:

Orion Optics is a UK company OrionOptics and has no association with the US company known as Orion Telescopes and Binoculars. 

Hi Peter, by "here", I guess Dave mentioned the continent where he is from (North America - US), not here in this thread.  

 

Anyway, to make things clear to the OP, there are two "Orion" suppliers, one in the US and one in the UK. 

The one in the US (Orion, http://www.telescope.com/) sells commercial telescopes with GSO mirror (see Dave's post above). The quality of these telescopes is broadly the same as for the Skywatcher' ones. 

The one in the UK (Orion Optics, http://www.orionoptics.co.uk/ ) sells specialised telescopes for a niche market. Some of these telescopes are specific for astrophotography, others (like the VX series you mentioned in this thread) are also bought by visual observers. The optics are made by them here in the UK. 

[Cornelius Varley]

3 minutes ago, Piero said:

Hi Peter, by "here", I guess Dave mentioned the continent where he is from (North America - US), not here in this thread.  

 

Anyway, to make things clear to the OP, there are two "Orion" suppliers, one in the US and one in the UK. 

The one in the US (Orion, http://www.telescope.com/) sells commercial telescopes with GSO mirror (see Dave's post above). The quality of these telescopes is broadly the same as for the Skywatcher' ones. 

The one in the UK (Orion Optics, http://www.orionoptics.co.uk/ ) sells specialised telescopes for a niche market. Some of these telescopes are specific for astrophotography, others (like the VX series you mentioned in this thread) are also bought by visual observers. The optics are made by them here in the UK. 

The telescopes of Orion Options UK are being discussed in this thread not Orion Telescopes and Binoculars which Dave mentioned and I do know the difference between the two.

[scarp15]

You have outlined some good plans Linda, will be interesting to follow what you decide upon. Might also, if you had not entirely ruled out all options,  be worth checking current UK sterling rates against the Norwegian Krone, as the pound has been weakening on international markets, combined with a possible 5% discount, OOUK might still perhaps be an option for consideration. 

[Linda]

44 minutes ago, scarp15 said:

You have outlined some good plans Linda, will be interesting to follow what you decide upon. Might also, if you had not entirely ruled out all options,  be worth checking current UK sterling rates against the Norwegian Krone, as the pound has been weakening on international markets, combined with a possible 5% discount, OOUK might still perhaps be an option for consideration. 

Yes, I see that the pound at this moment is relatively good compared to our currency. The Euro is still very high.

I have checked what a good quality mirror costs at Orion Optics and the price in pounds is about the same as a new Skywatcher in euros. So I think I will end up buying a Skywatcher at the German shop that tests the optics before selling it. Then at least I won't have a bad quality mirror. That shop also says that the standard Orion UK scopes are a little bit better than the Skywatcher, but not as much as the difference in price would suggest.

I asked the shop about the different quality in Dobson telescopes and they ranked them like this:

Orion UK

SkyWatcher
GSO

Orion US
Bresser
Omegon
ES

 

I am still a little in doubt though whether an open system like a Dob of Newton is smart. I saw some information about (not) cleaning the primary mirror. It should not be done often and is a lot of work to do and a lot can go wrong. So I'm also thinking if a closed system is not a better idea. But all alternatives are more pricy and my hubby might start objecting. He didn't seem too upset about the Dob, as I explained it cost less than my current scope.

[scarp15]

I wouldn't worry about cleaning the mirror, particularly if you will be buying as new a solid tube and if the caps are kept on when not in use and stored somewhere clean, warm and dry ought not be a concern. If eventually there came a time that the mirror might benefit from a clean, an 8" primary is easy enough to handle. 

[cs1cjc]

Now, I would not buy a Newtonian in the F/4.5 to F/5.5 range, though I have two...  This a middle ground where collimation is quite tight, you will get quite a wide angle view, but the secondary obstruction is becoming an issue and a coma corrector will make a significant difference to the view even though most observers do without.

If you go shorter than this, then the need for a coma corrector and precise collimation become facts of life, but you get a nice wide field of view. 

Longer, then for visual use, no coma corrector is needed.  You do not get a very wide field of view but the secondary obstruction will be small and for a given eyepiece magnification will be relatively large.  An F/6 200mm Dobsonian is not bulky and from OO is lightweight. 

Second hand instruments can be very affordable.

 

[John]

18 minutes ago, cs1cjc said:

Now, I would not buy a Newtonian in the F/4.5 to F/5.5 range, though I have two...  This a middle ground where collimation is quite tight, you will get quite a wide angle view, but the secondary obstruction is becoming an issue and a coma corrector will make a significant difference to the view even though most observers do without....

 

 

The secondary obstruction is 21% on my 12" F/5.3 which I believe is a decent figure for high resolution observing. I only see a tiny amount of coma right at the field stop of my 21mm Ethos - I don't use a coma corrector.

 

 

[Linda]

Buying second hand is difficult here in Norway. There is very little on sale other than toystore scopes. And what is on sale is very overpriced, often more expensive than a new scope imported from abroad + import fees. And buying second hand abroad requires visiting the seller to check the quality. It's really not that easy, or I would have done it already.

[ollypenrice]

Like John, I find (and so do my experienced guests) that the TeleVue Ethos and Naglers give a decent edge of field without a coma corrector, and in my case that's at F4.1. Nobody using our scope has ever requested or advised that I go for a CC. One or two were surpirsed to hear that there wasn't one in place already. Of course, the edge of field isn't perfect but nor is it a distraction.

I prefer open truss to closed tube. Now that it has thoroughly settled down over time our 20 inch truss rarely needs collimating and then only by a small amount. The genuine Serrurier design is very clever and allows fllexure only in the most harmless plane. It doesn't build or retain tube currents and it doesn't retain spiders' webs, autumn leaves and assorted detritus which fills up a closed tube. (Host of robotic instruments speaking here!) With an open tube you can keep things clean and do a minimalist intervention from time to time to clean off a suspicious looking deposit on the mirror without dismantling.

And a truss design makes you feel like a miniature professional!

Olly

[Linda]

4 minutes ago, ollypenrice said:

I prefer open truss to closed tube. Now that it has thoroughly settled down over time our 20 inch truss rarely needs collimating and then only by a small amount. The genuine Serrurier design is very clever and allows flexure only in the most harmless plane. It doesn't build or retain tube currents and it doesn't retain spiders' webs, autumn leaves and assorted detritus which fills up a closed tube. (Host of robotic instruments speaking here!) With an open tube you can keep things clean and do a minimalist intervention from time to time to clean off a suspicious looking deposit on the mirror without dismantling.

Tja, that is a new perspective on things. A closed tube is indeed much more difficult to clean, but I hoped it was not necessary to do it regularly.

In the category stupid questions: can you hold a reflector upside down without the mirror falling out?  To empty it for the autumn leaves...

[Dave In Vermont]

My F/4 Newt is closed-tube. Rich-Field we used to call them. On the rare occasion it needs a brush-off of the mirror, etal, it's not an issue to me. I've actually come to enjoy collimating Newts. Pretty weird? Weird is a specialty of mine!

Your milage may vary,

Dave

[Mr Spock]

Being a planetary observer, if I had to choose a Newt it would be long focal length with the best possible optics.

Long focal length comes with a smaller secondary and therefore better contrast; the central obstruction is what lowers contrast in Newts, SCTs etc., so smaller is better. A longer focal length Newt is also easier to collimate - perfect collimation is essential for best image quality.

Good optics to take advantage of better moments of seeing. With higher grade optics less of the light is pushed out into the diffraction ring and so make images crisper.

[Linda]

32 minutes ago, Mr Spock said:

Being a planetary observer, if I had to choose a Newt it would be long focal length with the best possible optics.

Long focal length comes with a smaller secondary and therefore better contrast; the central obstruction is what lowers contrast in Newts, SCTs etc., so smaller is better. A longer focal length Newt is also easier to collimate - perfect collimation is essential for best image quality.

Good optics to take advantage of better moments of seeing. With higher grade optics less of the light is pushed out into the diffraction ring and so make images crisper.

That is my conclusion as well. I see that the Skyliner Dob is an F6, which should be a minimum f-ratio for me. I also looked at the Vixen VMC 200L which has F9,8 for an 200 mm scope. But again the cost is 3 x as high as the Skyliner Dobson. So I still think it will be a Dob. Still looking at the Newtons as well, as I think a tripod will be more stable than a stony parking place than a Dobson. But then were talking heavy mount tripod and that is not grab & go at all. I still think the 8" solid tube Dob is easy enough to transport in two bits and a good bargain. But difficult to clean on inside.

I will also keep thinking about a bigger suitcase trussdob, but that is so definitively not cheap...

[brantuk]

" In the category stupid questions: can you hold a reflector upside down without the mirror falling out?  To empty it for the autumn leaves... "

Yes you can - the central mirror and spider assembly will stop it falling all the way out lol

[scarp15]

7 hours ago, Linda said:

 But difficult to clean on inside.

You might consider adding some flocking material to the inside (opposite the focuser) but that would be it - keep the inside to fill up with star light and not autumn leaves. 

[John]

I've owned my solid tube 12" F/5.3 dob for around 2 years now and I've had the mirror out just once to blow some dust off it. No leaves though and I did look carefully

 

 

[Scooot]

37 minutes ago, John said:

I've owned my solid tube 12" F/5.3 dob for around 2 years now and I've had the mirror out just once to blow some dust off it. No leaves though and I did look carefully

 

 

Me too. Had it since end of 2011, never touched the mirror, and no leaves either. I just looked especially, and it looks remarkably clean and tidy. I keep it indoors so I suppose that helps.

[cs1cjc]

This is I guess slightly off topic, but I thought I would respond on the issue of coma.  Coma robs the image of contrast and indeed brightness long before it becomes visible to the the human eye as a distinguishable aberration.  The diffraction limited, strehl of better than 0.8, sweet spot of a perfect Newtonian is small, with a diameter approximately as follows:

F.4 1.4mm

F/4.5 2mm

F/5 2.8mm

F/6 4.8mm

F/8 11mm

F/10 22mm

For reference the field stop of an 8mm Tele Vue plossl is 6.5mm.  It can easily be seen that why collimation, getting the sweet spot in the centre of view, is so important.  The telescope still has to be well collimated with a coma corrector, but the sweet spot is enlarged considerably and there is a real difference at the eyepiece.  Let me know if you would like to borrow mine...

As to the size of the secondary obstruction.  It can be made smaller but you lose brightness towards the edge of field. Mel Bartels has a nice web page here that shows the illumination for different sized secondary mirrors:  http://www.bbastrodesigns.com/diagonal.htm.

The OO 200mm scopes have a secondary of 63mm for the F/4.5 (over 30% which will surely reduce contrast) and 50mm for the F/6. 

 

 

 

[ollypenrice]

The 'leaves business' concerns robotic instruments at my site which are operating on maybe 20 nights per month, so maybe 240 nights per year - and since that's photographic it means all night when possible. This is much less of an issue if a scope is out for two or three hours for six nights a month, and in the company of a human being who knows when all sorts of stuff is blowing around!

Olly

[Scooot]

On 23/03/2016 at 15:10, cs1cjc said:

This is I guess slightly off topic, but I thought I would respond on the issue of coma.  Coma robs the image of contrast and indeed brightness long before it becomes visible to the the human eye as a distinguishable aberration.  The diffraction limited, strehl of better than 0.8, sweet spot of a perfect Newtonian is small, with a diameter approximately as follows:

F.4 1.4mm

F/4.5 2mm

F/5 2.8mm

F/6 4.8mm

F/8 11mm

F/10 22mm

For reference the field stop of an 8mm Tele Vue plossl is 6.5mm.  It can easily be seen that why collimation, getting the sweet spot in the centre of view, is so important.  The telescope still has to be well collimated with a coma corrector, but the sweet spot is enlarged considerably and there is a real difference at the eyepiece.  Let me know if you would like to borrow mine...

As to the size of the secondary obstruction.  It can be made smaller but you lose brightness towards the edge of field. Mel Bartels has a nice web page here that shows the illumination for different sized secondary mirrors:  http://www.bbastrodesigns.com/diagonal.htm.

The OO 200mm scopes have a secondary of 63mm for the F/4.5 (over 30% which will surely reduce contrast) and 50mm for the F/6. 

 

 

 

http://www.bbastrodesigns.com/The%201974%20Telescope%20Secondary%20Experiment.html

This was an interesting read about secondary sizes in the link you posted. I don't have enough experience comparing to judge myself, but the author gives the impression at the end, that other factors might be more important when choosing a scope?

[Ricochet]

On 21/03/2016 at 12:43, Linda said:

I asked the shop about the different quality in Dobson telescopes and they ranked them like this:

Orion UK

SkyWatcher
GSO

Orion US
Bresser
Omegon
ES

If that is true then the skywatcher mirror must be significantly better than the bresser because everything else is better on the bresser IMO. Does the shop you spoke to sell all of the different brands or have they just happened to suggest that the one they do sell is almost as good as one costing three times as much and better than all the competitors in the same price range? 

[Linda]

On 23.3.2016 at 21:44, Ricochet said:

If that is true then the skywatcher mirror must be significantly better than the bresser because everything else is better on the bresser IMO. Does the shop you spoke to sell all of the different brands or have they just happened to suggest that the one they do sell is almost as good as one costing three times as much and better than all the competitors in the same price range? 

They sell many brands. The Bresser 8" costs 60 euros more than the Skywatcher 8".