Good make of 254/1250 Newton for DSO

[Gerry Casa Christiana]

Hello all

Just a quick question. I'm looking to upgrade my scope to a 10" but F5 Newtonian. Just wondered if I missed any online apart from Skywatcher GSO Orion. I've kind of been hoping for a carbon fibre but they tend to be expensive. I was also considering building one but that seems just as expensive. 

Any options I've missed? I would like to spend under 900 quid if possible. 

Cheers 

Gerry

[alacant]

You have the mount, yes? This one has a rigid aluminium tube, a decent fat focuser and a secondary sized for AP. The SW doesn't;)

HTH

Edited May 27, 2018 by alacant

[John]

You should be able to get a pre-owned Orion Optics 10" F/4.8 for well under that price. You can nearly afford a new one - the VX10 with a 1/10th wave mirror upgrade costs £955.20. Delivery to Italy might push that up a bit. The Orion Optics newtonians weigh a bit less than the Chinese made ones.

 

[25585]

10 minutes ago, alacant said:

You have the mount, yes? This one has a rigid aluminium tube, a decent fat focuser and a secondary sized for AP. The SW doesn't;)

HTH

I have the Bresser in that link. It has the best Dobsonian mount, big rockers, easy assembly and good optics for F5. The focuser takes heavy eye pieces. I bought mine from Telescope House. @FLO sell the 8 inch & I am sure get the 10 if you asked them.

Carbon tubes are nice & don't dent. Teleskop Express sell Newts with them. 

 

Edited May 27, 2018 by 25585

[Gerry Casa Christiana]

53 minutes ago, alacant said:

You have the mount, yes? This one has a rigid aluminium tube, a decent fat focuser and a secondary sized for AP. The SW doesn't;)

HTH

Yes the secondary on the SW is 65mm? Or 60 I forget. Better for planets. Yes I have eq6. Do you have this scope Alacant? 

[alacant]

Just now, Gerry Casa Christiana said:

Do you have this scope

No, but I wish I did. I have a SkyWatcher 250. I needed to upgrade the -hopeless- single speed focuser to the -equally hopeless- dual speed Crayford, replace the 60mm secondary with a 70mm and I also needed a 50cm dovetail to prevent tube flex. The Bresser reflectors I have are head and shoulders above it.

Cheers and HTH.

[25585]

Just now, alacant said:

No, but I wish I did. I have a SkyWatcher 250. I needed to upgrade the -hopeless- single speed focuser to the -equally hopeless- dual speed Crayford, replace the 60mm secondary with a 70mm and I also needed a 50cm dovetail to prevent tube flex. The Bresser reflectors I have are head and shoulders above it.

Cheers and HTH.

Reduced to €420 the Messier is a bargain! 

[Gerry Casa Christiana]

2 hours ago, 25585 said:

Reduced to €420 the Messier is a bargain! 

 

2 hours ago, alacant said:

No, but I wish I did. I have a SkyWatcher 250. I needed to upgrade the -hopeless- single speed focuser to the -equally hopeless- dual speed Crayford, replace the 60mm secondary with a 70mm and I also needed a 50cm dovetail to prevent tube flex. The Bresser reflectors I have are head and shoulders above it.

Cheers and HTH.

Hi Alacant

I think I'm almost sold. Do you have some pictures done on your Bresser. What about the focuser any good. I notice the tube weight is 13kg seems light? No problems with flexure? I'm guess I'm asking what will I need to change!  

Thanks 

Gerry

[25585]

12 minutes ago, Gerry Casa Christiana said:

 

Hi Alacant

I think I'm almost sold. Do you have some pictures done on your Bresser. What about the focuser any good. I notice the tube weight is 13kg seems light? No problems with flexure? I'm guess I'm asking what will I need to change!  

Thanks 

Gerry

No pix at present but the only things I did were replace the puny 6x30 finder with a Telrad sight & an Altair RACI 60mm finder. I also bought a couple of Astrozap 10 inch tube covers from FLO. 

[Gerry Casa Christiana]

16 minutes ago, Gerry Casa Christiana said:

the 60mm secondary with a 70mm

Also the bresser has a 74mm secondary does that introduce any probkems? 

 

[John]

18 minutes ago, Gerry Casa Christiana said:

Also the bresser has a 74mm secondary does that introduce any probkems? 

 

Thats quite large for an F/5 250mm

Orion Optics use a 63mm one with their 250mm F/4.8.

[Gerry Casa Christiana]

3 minutes ago, John said:

Thats quite large for an F/5 250mm

Orion Optics use a 63mm one with their 250mm F/4.8.

I'm not sure if it represents a problem or not? The Bresser is 254mm? Been looking online doesn't seem to be anyone who puts these on a equatorial and uses them for astrophotography at least from what I can find. 

 

[Gerry Casa Christiana]

Anyone heard of the TS PHOTON? 

https://www.teleskop-express.de/shop/product_info.php/info/p2765_TS-PHOTON-10--F5-Advanced-Newtonian-Telescope-with-Metal-Tube.html

[alacant]

1 hour ago, Gerry Casa Christiana said:

some pictures done on your Bresser

Here's one with the 8" f4, the 6" f5 and the 6" f8. All white tube Bressers.

HTH

[alacant]

1 hour ago, John said:

Orion Optics use a 63mm one with their 250mm F/4.8

IIRC, not enough to get all the light reflected from the primary at the focal plane of a dslr. Not an issue if you're visual or don't mind vignetting.

Cheers and clear skies.

 

[25585]

1 hour ago, John said:

Thats quite large for an F/5 250mm

Orion Optics use a 63mm one with their 250mm F/4.8.

Shorter focal length the reason perhaps? Or a typo possibly, maybe it's 64 mis-typed. 

I think there is a Gary Seronik page about secondary sizes. At least less worry about losing light from slight misalignment. In reality does about 1cm make much difference for visual use. 

The benefit of that Bresser is, as for OO UK dobs, their OTAs can be removed from the rocker assemblies completely, allowing mounting on equatorial etc. 

 

[wimvb]

2 hours ago, Gerry Casa Christiana said:

Anyone heard of the TS PHOTON? 

https://www.teleskop-express.de/shop/product_info.php/info/p2765_TS-PHOTON-10--F5-Advanced-Newtonian-Telescope-with-Metal-Tube.html

Have been looking at those. The carbon fibre versions are almost twice as expensive as the steel tubes. But more stable, and less weight. 900 "quid", that's a bit over 1000 €:

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p5032_TS-Optics-UNC-200-mm-f-5-Newton-Teleskop-mit-Carbon-Tubus.html

TS market all kind of variations of these scopes; from TS Photon to UNC to ONTC to N-AG (Astrographs). Differences between these scopes may be in the thickness of the carbon tube, mirror quality and material (quartz, pyrex or BK glass) and the quality of the focuser.

[alacant]

10 hours ago, 25585 said:

page about secondary sizes

This explains the problem with the small skywatcher secondary. The size of the secondary is smaller than its physical size; there's a bevel.

HTH

Edited May 28, 2018 by alacant

[John]

12 hours ago, alacant said:

IIRC, not enough to get all the light reflected from the primary at the focal plane of a dslr. Not an issue if you're visual or don't mind vignetting.

Cheers and clear skies.

 

My 300mm OO F/5.3 has a 63mm MA secondary (21% of the primary diameter). I'm stricly visual but I don't get any vignetting even with the Ethos 21 and Nagler 31 eyepieces

The scope was used successfully for imaging by a previous owner - this chap:

http://kevwildgoose.co.uk/

 

[Gerry Casa Christiana]

11 hours ago, wimvb said:

quartz, pyrex or BK glass

Let's try and whittle this down. So which of these is best as a mirror? 

[alacant]

9 hours ago, John said:

I don't get any vignetting

You won't be able to see it, but a camera frame will. E.g. A flat frame with the 60mm secondary took 3.0s. With the 70mm and same light panel, it took 2.0s. That's a significant gain in light.

Another feature of the SkyWatcher was the alarming amount of light which simply misses the secondary altogether; point it at the sun and you can burn paper with the focused light exiting the open end of the tube with it. With the 70mm secondary, no light is allowed out of the tube unless via the focuser.

I'm sure it doesn't matter that much, but the OP wants DSOs.

Cheers and clear skies.

Edited May 28, 2018 by alacant

[John]

30 minutes ago, alacant said:

You won't be able to see it,.....

 

I can't and I don't image so thats OK. I seem to do pretty well on DSO's with my scope, visually

With Orion Optics, you can specify a different diameter secondary if thats what you want.

[wimvb]

5 hours ago, Gerry Casa Christiana said:

Let's try and whittle this down. So which of these is best as a mirror? 

Depends on who you ask. I have a thread going just about that. The concensus is that optically it doesn't matter which type you have, since glass only carries the reflecting surface. But thermal properties are important. (Quartz has the lowest thermal expansion.)  And thermal properties affect optical performance.

 

[wimvb]

Btw, Lacerta offers a photo newton with quartz mirror. It costs 300 € more than the non-quartz version, and is marketed as "zero expansion". With a carbon tube, it's supposed to be veeery stable. That may very well be true.

[alacant]

6 hours ago, John said:

Orion Optics, you can specify a different diameter secondary

Great idea. Get two? One for looking and one for snapping. Perfect.