12" f5 and 10" f6 Interchangeability

[ariefm71]

I have just acquired a nice (I think) 10" f6 Lightholder mirror from a CN classifieds. I'm looking for a quick way to mount this mirror on a structure, it seems like I can actually use a readily-available 12" f/5 dob structure for this 10" mirror. I'm thinking to either get the 12" Lightbridge structure or the Geoptik Nadirus kit ( https://www.teleskop-express.de/shop/product_info.php/language/en/info/p7550_Geoptik-Nadirus-12-inch-Truss-Dobosnian-Telescope-KIT.html )

Attached is the output of the Newt for Web calculations I ran. Notice that the same tube can be used for either mirrors without any sacrifices in performance (I have to modify the mirror cell and take care of the balancing).

Is this correct or am I missing something here?

Cheers,
Arief

[mental4astro]

Arief,

The biggest issue will be the difference in ballast between the two mirrors meaning the centre of gravity of the 10" OTA will be much higher than what the 12" structure is designed for. The dob will be significantly top heavy.

You will need to add weight to the mirror box in order to re-establish the COG and correct balance geometry.

Trying to get around this with friction mechanisms for a quasi balance will create a dog of a dob as the action will be so tight so to make it impossible to attain quality of action necessary for a scope, along with a horrendous amount of backlash.

Alex.

[GrahamL]

Hi Arief



As your thinking you just have to match the weight differance between the two mirrors (weight down low ) and the structures will likely work fine . F5/F6 is still 1500.


Best secondary size I'm not sure .


You could easily make a scope to fit for not a lot they arn't to hard to do .

[ariefm71]

Thanks Alex. Yes, definitely will need a counterweight system to compensate the COG difference.

Graham, yes the default 2.75" secondary will be replaced with a 2.14" one for a 12mm 100% illuminated field and 21% CO. I'm not sure I have the skills and time needed to build them myself though :|