Newtonian and 3" focuser/coma corrector

[Bobinius]

Hi everyone,

 

I am thinking about  investing in a Newtonian probably a 10" f4 https://www.teleskop-express.de/shop/product_info.php/info/p5647_TS-Optics-10--f-4-ONTC-Carbon-Tube-Newtonian-telescope---fully-customizable.html, 

Various options exist for the focuser and the coma corrector. I was wondering if the 3" is worth it. Its advantage would be less vignetting and stability? I am planning to shoot mostly using CMOS / CCD cameras that are not that heavy + filter wheel so vignetting on that sensor (close to APS C) should not be a problem. Would it allow for better coma correctors in 3"?

Thanx

B

 

[rl]

I'm running a very similar rig; a secondhand  OO 12" AG12 with a 3" Wynne corrector and FLI Atlas focuser, which is theoretically capable of a 60mm diameter corrected circle at prime focus.  It will cope with bigger cameras than I'm ever likely to be able to afford. But the cameras I currently use have an APSC -size sensor which would be quite happy with a 2" coma corrector and fittings. They'e also lighter which is a consideration, not requiring extra support rings on the focuser.

The matching filter wheel that came with it takes 2" square filters which is better than a 2" system will do but still would vignette a 60mm circle. I use the big celestron OAG which again vignettes. You can get bigger ones at a price...

3" sounds very good but there is not a lot on the market for spacers, adapters, reducers etc. A lot of stuff has to be custom made which is slow and expensive. You need a friend with a lathe. 

Just collimating the scope requires a 3" to 2" reducer; one is available off the shelf from TS at 93 euros.....

If I were buying new again I would not get the 3" option but settle for the best quality 2" setup I could get. 

One reason slightly off topic to go for the AG series or TS equivalent is the collomation stability; the spider is machined from solid aluminium plate.

RL

[Bobinius]

13 minutes ago, rl said:

I'm running a very similar rig; a secondhand  OO 12" AG12 with a 3" Wynne corrector and FLI Atlas focuser, which is theoretically capable of a 60mm diameter corrected circle at prime focus.  It will cope with bigger cameras than I'm ever likely to be able to afford. But the cameras I currently use have an APSC -size sensor which would be quite happy with a 2" coma corrector and fittings. They'e also lighter which is a consideration, not requiring extra support rings on the focuser.

The matching filter wheel that came with it takes 2" square filters which is better than a 2" system will do but still would vignette a 60mm circle. I use the big celestron OAG which again vignettes. You can get bigger ones at a price...

3" sounds very good but there is not a lot on the market for spacers, adapters, reducers etc. A lot of stuff has to be custom made which is slow and expensive. You need a friend with a lathe. 

Just collimating the scope requires a 3" to 2" reducer; one is available off the shelf from TS at 93 euros.....

If I were buying new again I would not get the 3" option but settle for the best quality 2" setup I could get. 

One reason slightly off topic to go for the AG series or TS equivalent is the collomation stability; the spider is machined from solid aluminium plate.

RL

Thanx RL. It was my feeling too. I think it depends on your camera. I have a full frame Canon, but I plan to shoot in narrow band and CMOS/CCD camera. If I go for the Newtonian, then I'll choose the Feather touch focuser. Are you pleased with the Wynne corrector (I guess is the one buit in from OO)? TS are advocating that there my be less lighting with the Wynne system.

[rl]

I'm not an expert in correctors but the big 3" Wynne works excellently as far as I can tell but I don't have a full-frame camera. Personally I'm not a perfectionist and don't lose sleep over marginally un-round stars right in the corners but mine covers the field virtually perfectly (always a dangerous word)

Having said that I 've had equally good results in 2" format with a skywatcher aplanatic coma corrector, and the ES 4-element jobbie on an APSC sensor. Both admittedly in a slightly slower f/4.5 Newtonian. 

A lot of issues with these scopes arise either from miscollimation or not having the camera square-on to the optical axis. F/4 is very unforgiving in more ways than one..the depth of the focal plane is tiny. I've been lucky in not needing a tilt adjuster (or maybe I'm just not critical enough?)

One other thing; I was told an EQ6 would be ok for an AG12.....NO WAY! It might just about cope with the naked OTA but add in the rings, Wynne, Atlas focuser, filter wheel camera, finder  and I was up to nearly 30kg.  You are talking about only a 10" but I suspect an EQ8 may be on the cards if you go the full nine yards in 3" format. 

My EQ6 is just fine with my 8" f/4.5 and 2" kit....

[Bobinius]

1 hour ago, rl said:

I'm not an expert in correctors but the big 3" Wynne works excellently as far as I can tell but I don't have a full-frame camera. Personally I'm not a perfectionist and don't lose sleep over marginally un-round stars right in the corners but mine covers the field virtually perfectly (always a dangerous word)

Having said that I 've had equally good results in 2" format with a skywatcher aplanatic coma corrector, and the ES 4-element jobbie on an APSC sensor. Both admittedly in a slightly slower f/4.5 Newtonian. 

A lot of issues with these scopes arise either from miscollimation or not having the camera square-on to the optical axis. F/4 is very unforgiving in more ways than one..the depth of the focal plane is tiny. I've been lucky in not needing a tilt adjuster (or maybe I'm just not critical enough?)

One other thing; I was told an EQ6 would be ok for an AG12.....NO WAY! It might just about cope with the naked OTA but add in the rings, Wynne, Atlas focuser, filter wheel camera, finder  and I was up to nearly 30kg.  You are talking about only a 10" but I suspect an EQ8 may be on the cards if you go the full nine yards in 3" format. 

My EQ6 is just fine with my 8" f/4.5 and 2" kit....

Thanx for the input. Really valuable. I'm afraid that the weight could quickly get close to the limit (I have an Orion 8" which works ok on the EQ6 but no filter wheel yet and the basic focuser that comes with it). I'm waiting for their answers concerning the weight. Do you have stability problems caused by the wind with that huge tube?

[rl]

Not on the eq8 in mild breezes....both the mount and tripod are incredibly solid. The tube rings are far apart and the dovetail is pretty chunky all of which helps a lot. I can have the mount/ota assenvbled from scratch in about 25 minutes aligned but it's not for the faint-hearted. I hope one day soon for a permanent obs.

RL