Zwo asi 178 mc with William optics gran Turismo 71

[woldsman]

I’d like to do some lunar imaging pairing the zwo asi 178 mc with a William Optics Gran Turismo  71.  First night of experimentation failed to result in an image on screen. I tried with and without a televue x2.5 powermate and a zwo atmospheric disturbance corrector. 
 

Probably I need to add spaces to the image train. Does anyone know what distance I need to achieve focus?
 

 

 

[newbie alert]

With my 80 I think I either used a diagonal or a 2 inch extension adapter, or maybe both... 

[CraigT82]

Yes you will need a fair bit of extension as fracs are mostly designed to be used with a diagonal, so when shooting straight through you’ll need a good length extension tube. Have a look at this pic from Mike Nash @WestCoastCannuck and see how much extension he needs on his APM140.

To get a rough idea how far back the sensor needs to be you could measure 419mm back from the last lens of the objective (though you’ll have to guess where the last objective is in the tube - unless you want to insert a felt tipped dowel rod with 419mm marked on it into the scope and down to the lens, do so at your own risk!)
 

[Skipper Billy]

I used a 178 with a 71 mm scope (different brand) and had to add about 100mm (from memory) of spacers to achieve focus.

I don't own it any more so I cant measure it.

 

[woldsman]

3 hours ago, Skipper Billy said:

I used a 178 with a 71 mm scope (different brand) and had to add about 100mm (from memory) of spacers to achieve focus.

I don't own it any more so I cant measure it.

 

Thanks for the reply and for the very helpful pictures.

[woldsman]

On 05/02/2023 at 10:16, Skipper Billy said:

 

Just to round this discussion off,  the reason why 100mm of spacing is needed is because refractors are designed to reach focus with a star diagonal. Typically diagonals have a light path of around 100mm. 

A flattener would provide some distance to which spacers are added to reach the correct back spacing. With a small sensor and a planetary camera imaging the centre of the FOV, however, flatteners are not

required. Thanks to FLO for their advice on this. 

On 05/02/2023 at 10:16, Skipper Billy said:

 

 

I used a 178 with a 71 mm scope (different brand) and had to add about 100mm (from memory) of spacers to achieve focus.

I don't own it any more so I cant measure it.

 

 

Edited February 6, 2023 by woldsman

[900SL]

William Optics do an extension for the m63 focuser thread 

https://williamoptics.com/m63-male-to-m48-male-photo-adapter