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Newbie setting up back focus on Skywatcher Evoguide ED50 with T7C astrocam


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Got my Pi4b Stellarmate setup with Evoguide ED50 and T7C astrocam but focusing is an issue each night out. The setup is easily transportable and dismantled frequently so I think the answer is a fixed train setup. Although I contacted the T7C supplier about the focal plane measurement I never got an answer. 

Does anyone know what it is?

Has anyone setup the train and how was it done?

Thanks for any help

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Thanks - It's an idea but sadly the requirements are the kit can be ultra transportable.

My setup needs to be dismantled to pack away small enough to go caravanning (or hiking?) and enjoy better skies than I get here in greater London.

I also wish to learn the principals and apply it to my other scopes if the need arises (Celestron 5se, Skywatcher ED72, 114P, & Heritage 130P

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Yep using that "extra" tube, but the camera, which is a shotgun cartridge in shape, is free to slide in and out of it changing focus until clamped by the thumb screws at the correct distance - 242mm behind the objective lens taking into account the position of the camera sensor in the camera body. It's this forward and backward movement that needs setting to provide a perfect focus at the sensor e.g. 242mm minus the recess depth of the sensor from the forward edge of the camera casing (I think that's correct?).

Problem is I don't know its correct depth or how to accurately repeat this setting for each night's use. It must have a simple solution but I'm not there yet - perhaps I looking to over engineer this?

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I had a play around with my 50ED and a Bresser Microkular camera from my sons microscope a while back.  I had a go in daylight on some distant trees to find out the focal measurement myself.

I found even with the extension tube on the 50ED that the camera needed to be almost hanging right out the back to get focus.   It was possible but I didnt come up with a method of fixing it in place.  It was just musings as I was thinking of an ultra cheap way of utilising the Bresser as a guide camera and didnt take it any further. 

Maybe give it a try in daylight and see if you can find focus that way?  Start of with something like a 25mm eyepiece to get focus and replace with the camera, then you can look towards fixing with spacers or extension tubes.

 

Edited by TerraC
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