William Optics FFIII question

[melsky]

Fellow SGL’ers

I’m about to start imaging with a Canon DSLR on a William Optics Megrez 72 with a FFIII and I have a question about the spacing of the flattener to the chip. I’ve read a lot of recommendations suggesting it should be 56mm. As the flange to sensor distance of a canon camera is 44mm this leaves 12mm for the T-mount, the only info I can find from William Optics themselves is this PDF

http://www.williamoptics.com/accessories/images/FW0.8X_T-RING_950425.pdf

I’ve attached an image of this PDF and please notice it has the words “T-RING” in the title, I’ve highlighted in red what looks like the T-mount in the diagram and calculated that it is 10mm long. The WO diagram indicates that you need 56mm spacing from the back of the T-mount, so, allowing for the Canon 44mm back focus I need to add a 12mm spacer between the T-mount and FFIII, is this correct? I notice several of you are using the same rig, maybe you could confirm this please.

Thanks Mel

[Psychobilly]

I use Canon DSLR's (1000D and 350D) on my Megrez72/FF III combo using Eos T adaptor fitted directly to the FF III...

T mounts for different camera are different thicknesses to give the 55mm FP to mounting flange distance thats required for T mount lenses etc...

Peter...

[david61]

Hello I'm also going to ask for help on this one

i have a W/O 72mm with the 0.8 reducer /flattener viii

with Atik 16HR AND Atik USB FILTER WHEEL

what is the right spacing for this lot

Thank David

[melsky]

I use Canon DSLR's (1000D and 350D) on my Megrez72/FF III combo using Eos T adaptor fitted directly to the FF III...

T mounts for different camera are different thicknesses to give the 55mm FP to mounting flange distance thats required for T mount lenses etc...

Peter...

Thanks for repling Peter, I'm still wondering where the 55mm FP (Film Plane ?) to flange recommendation comes from as the WO PDF clearly shows a recommended 56mm + T-mount = 66mm. I guess if everyone else has experimented and found 55mm total to be correct I'll start with that.

Cheers Mel

[Psychobilly]

the 55mm Focal Plane to flange is defined in the "T mount spec"... remeber the T moutn was initially a system to allow independent lens manufacturers to produce one lens that could be used on cameras form different manufacturers... the "Native" mount to Focal Plane distance varies from manufacturer to manufacturer so the T mounts for each manufacturers lens mount are different thicknesses to achieve this 55mm standard distance...

You need to try your scope... I want to "tune" my setup a bit but theres no easy or cheap way of doing it...especailly as i really should buy CCDInspector2 to analyse the results of the experiments...Currently its possibly a bit overcorrected but its hard to tell once the images have been reduced to 800x60 for web use...

Peter...

[Psychobilly]

Here's a corner screen grab from DSS

Stars are flattened radially in the corners rather than being stretched ...

[melsky]

Hi All

I’ve just checked the link to the William Optics FFIII spacing PDF and they’ve changed it! The original PDF is at the top of this thread and clearly shows the spacing to be 56mm plus T-mount, if you now check the same link below the diagram now shows the spacing to be 56mm including the T-mount, I always thought this was odd but now I’m confident that by adding a 2mm spacer to my 10mm T-mount I’ll have the flattener at the correct 56mm distance.

Sharper Stars here I come

Mel

http://www.williamoptics.com/accessories/images/FW0.8X_T-RING_950425.pdf