Backfocus Help Needed

[hughgilhespie]

Hi,

I really do need some help with this. I originally posted this message in the Equipment - Scopes / Whole Setups section but I didn't get any replies so I am posting again here in the hope of some knowledgeable people who can check / correct my sums before I part with the dosh!  Apologies in advance if this breaks the SGL rules but I don't know what else to do.

I want to have an all-screwed connection between the Featherlight focusser on my Tak106 and my ZWO EFW. At the same time I am trying to use as many standard parts as possible and keep the costs down too - well try to at least. I have the f/3.6 reducer as well so the parts should cover fitting that and - following my eagerly awaited lottery win - I would also like to get the f/8 extender.

I have done some sums for the three configuration as best I can and I wonder would people have a look at my figures and check they are realistic before I start to buy the bits I need. The biggest expense will be a 6 mm PreciseParts adapter, M72 x 1 male to M42 x 0.75 male (T-thread I believe). The other parts are standard Tak adapters so they only cost one arm and a leg each.

My sums here:

Current Adapter Train (f/5)                       Exit Diam. mm           Length, mm

(Target Distance 178 mm metal back)

(10) Coupling TKP36001                                ?                            4

(8) Coupling TKP30003                                M72 x 1                11

(70) Ocular adapter TKP27110                     n/a                        50.8

(35) CA-35 TKA31201                                  M52 x 0.75          50.8                     

M52 x 0.75 male – T-thread                         42                          6.4

T-thread female – T-thread female              42                          10.9

T-thread male Filter wheel adapter                                            2

ZWO Filter wheel                                                                        20

ZWO Camera flange to sensor                                                  6.5

Total                                                                                          162.4 mm

Focus travel from minimum                                                        15.6

Sensor Distance                                                                                          178.0 mm

               Exit

New Adapter Train (f/5)                              Exit Diam. mm           Length, mm

(Target Distance 178 mm metal back)

(10) Coupling TKP36001                                ?                            4.0

(8) Coupling TKP30003                                  M72 x 1                11.0

TKA23250, 2 off                                              M72 x 1                104

PreciseParts M72F – T thread M                 T-thread (m)             6

T-thread male Filter wheel adapter                                               2

ZWO Filter wheel                                                                          20

ZWO Camera flange to sensor                                                  6.5

Total                                                                                           153.5 mm

Focus travel from minimum                                                         24.5

Sensor Distance                                                                                          178.0 mm

 

New Adapter Train (f/3.6)                           Exit Diam. mm           Length, mm

(Target Distance 72.2 mm metal back)

(10) Coupling TKP36001                                ?                            4.0

(8) Coupling TKP30003                                  M72 x 1                11.0

PreciseParts M72F – T thread M                   T-thread (m)          6

T-thread male Filter wheel adapter                                              2

ZWO Filter wheel                                                                         20

ZWO Camera flange to sensor                                                    6.5

Total                                                                                            49.5 mm

Focus travel                                                                                   22.7

Sensor Distance                                                                                          72.2 mm

 

New Adapter Train (f/8)                              Exit Diam. mm           Length, mm

(Target Distance 117.5 mm)

(10) Coupling TKP36001                                ?                            4.0

(8) Coupling TKP30003                                  M72 x 1                11.0

TKA23250                                                       M72 x 1                52

PreciseParts M72F – T thread M                    T-thread (m)          6

T-thread male Filter wheel adapter                                               2

ZWO Filter wheel                                                                          20

ZWO Camera flange to sensor                                                     6.5

Total                                                                                             101.5 mm

Focus travel                                                                                   16

Sensor Distance                                                                                          117.5mm

 

Thanks for looking.

Regards, Hugh

 

[oobydooby]

Crikey! Need strong spectacles to read that lot!