Evoguide FieldFlattener hack for mirrorless cameras

[thomasv]

The SW field flattener for Evoguide 50ED is not suitable for DSLR or mirrorless cameras, as it's backfocus is 17.5mm. My mirrorless camera (Fuji X-T1) has a flange to sensor distance of 17.7mm and the T2 to camera adapter ring that I have on order is 8.3mm thick, so the original flattener tube is too long by 8.5mm. I've noticed however that the extension tube that comes with the evoguide is approx. the correct length. Unfortunately, the internal diameter of the extension tube is slightly (by about 0.3mm) smaller than the diameter of the lenses, nothing that cannot be solved by a couple of hours of sanding.

Next step will be to 3D print a couple of rings that hold the lens assembly from each side. Conveniently these rings can be fixed in place by the two sets of  3 grub screws, one set in the extension tube another in the scope itself, allowing for an easy way of adjusting the exact position of the lenses.  

Showing the length difference between the flattener and the extension tube below, and the lenses now inside the extension tube. Will report back on progress and performance, unfortunately the T2 to fuji adapter is going to be 2 weeks wait.

 

[vineyard]

That's a brave hack - hope it works - could be genius.  Don't know enough about optics but am wondering whether the flattener lenses need to be a certain distance apart from each other and whether that would be within the length of the extension tube?  Good luck!

[thomasv]

Yes, it consists of two lenses held at a distance by a spacer ring. Sorry my first picture is not very sharp, the middle bit between the lenses is the spacer ring. I've moved all three parts over to the extension tube, so hopefully will be OK. 

[vineyard]

Fingers crossed it works - it'll be a great hack if so, b/c then that should mean OAGs or filter drawers could possibly also be put in if someone wanted to?