Piggyback scope on dob

[BS269]

Has anyone ever fitted a 2nd scope as a piggy back on a larger dobsonian? I was given these 2 accessories for my 12” flextube by the person I bought it off, and he said they can be used to mount a 2nd scope.. only I’ve no idea what else I need. Could anyone direct me in what I’d need, and if even piggybacking a small scope on a dob is possible?

cheers

Ben

[Paul73]

I’ve got a light weight 70mm travel scope on my 16” Dob as a super finder. Although it rarely gets used as the Telrad/low power eyepiece generally does the job and the Dob gives better views on the vast majority of targets.
However, I could see you running into major balance problems as your main tube is fixed in relation to the pivot / alt bearings.
Paul 

[fifeskies]

Those "hoops" fit onto the tube then you need finder rings (perhaps along with a bar)

 

the rings or bar will screw onto the hoops

You may need a weight on the other side of the tube from the finder to keep the balance right

Finder rings that adjust can help align both finder and main scope, and also make the exact "hoop" positioning less critical if there are nor predrilled holes for them.

[BS269]

2 hours ago, Paul73 said:

I’ve got a light weight 70mm travel scope on my 16” Dob as a super finder. Although it rarely gets used as the Telrad/low power eyepiece generally does the job and the Dob gives better views on the vast majority of targets.
However, I could see you running into major balance problems as your main tube is fixed in relation to the pivot / alt bearings.
Paul 

I was thinking of it so it could provide the lesser magnification views that the dob can’t get, But I did figure balancing issues would be a problem. I don’t know if magnetic counterweights would work? 

I also don’t really know if it’s worth it due to the significant reduction in aperture compared to the dob. Do you think it’s just worth sticking to the higher mag but better detail that the dob offers? 

[BS269]

2 hours ago, fifeskies said:

Those "hoops" fit onto the tube then you need finder rings (perhaps along with a bar)

 

the rings or bar will screw onto the hoops

You may need a weight on the other side of the tube from the finder to keep the balance right

Finder rings that adjust can help align both finder and main scope, and also make the exact "hoop" positioning less critical if there are nor predrilled holes for them.

Interesting, thank you! Seems like a bit of a waste to not but them to use, but they were free so it’s not the end of the world if it didn’t work. Could they be used for something else perhaps? 

[fifeskies]

Do you need any cupboard handles   😜

 

 

A big finder is unusual on a dob because of the balance issues , often a Telrad is a better option , though less accurate

 

A possible use for these is to put a losmandy plate onto your dob so it can be used with an EQ or Alt Az mount , the curve should match the OTA radius

(a bit unworkable with a 12 in flextube though , would need a plate on the inside at the very least , and full tube rings are better)

Edited November 17, 2020 by fifeskies

[Paul73]

2 hours ago, BS269 said:

I was thinking of it so it could provide the lesser magnification views that the dob can’t get, But I did figure balancing issues would be a problem. I don’t know if magnetic counterweights would work? 

I also don’t really know if it’s worth it due to the significant reduction in aperture compared to the dob. Do you think it’s just worth sticking to the higher mag but better detail that the dob offers? 

With the right eyepieces the 12” Dob gives some nice wide(ish) views. There aren’t many targets that you can’t fit in one fov.
Paul

[BS269]

19 hours ago, fifeskies said:

Do you need any cupboard handles   😜

 

 

A big finder is unusual on a dob because of the balance issues , often a Telrad is a better option , though less accurate

 

A possible use for these is to put a losmandy plate onto your dob so it can be used with an EQ or Alt Az mount , the curve should match the OTA radius

(a bit unworkable with a 12 in flextube though , would need a plate on the inside at the very least , and full tube rings are better)

I think tube rings would be the only way an EQ mount would hold it, and even then I’m not convinced. It’s a big [removed word] as well so would need a £££ mount which I won’t have for a while sadly. 

Shame. I might see if a little camera piggyback mount would work. Might allow for slightly longer exposures than untracked, before the rotation of the sky affects it too much?

[BS269]

16 hours ago, Paul73 said:

With the right eyepieces the 12” Dob gives some nice wide(ish) views. There aren’t many targets that you can’t fit in one fov.
Paul

I recently got an APM 100° 20mm as my first wide field EP. Not had the chance to use it yet but hopefully it will be a big improvement over the small FOV of the baader zoom at 24mm (this gives 0.80° FOV, the APM gives me 1.33° with 12.5x more magnification 😁).

hopefully it proves to me that I don’t need another scope on there!