Evoguide 50ED Field Flattener

[happy-kat]

The Evoguide 50ED has had a short use now on the Virtuoso mount with the Canon 1100d.

Whilst the sky was clear there was a lot of low mist, live in a hollow, and even though I was on Mars with a Lord Y mask the central spike didn't really show even on taking an image (I will add a picture later as it is on my phone).

Lovely crisp stars in the middle but terrible corner fall off though it starts quite close to the middle, certainly well in from the normal expected image rotation area cropped from what I use. So a field flattener would be good to add, but here lies the problem.....back focus distance. General testing has shown that the back focus really is only around 60mm.

Canon 1100d 44mm, T ring 10mm, T mount 3mm, focus travel for infinity 4mm.

If i mix the T ring straight to the T2 thread on the ED50 I gain like 3mm!

What I have not been able to find out is how much back focus do straight through field flatteners actually take up.

30 second image attached.

Edited October 13, 2018 by happy-kat
Added Lord Y mask image on Mars

[Stub Mandrel]

I doubt it was expected to be used with cameras bigger than a guidescope chip.

You won't be able to fit the OVL in as it adds 2" top the train.

[happy-kat]

OK thank you. It does look that way it is not suited to being treated as a large lens/small refractor for occasional images with my DSLR. I was expecting some distortion but not the amount there is, perhaps I should have tried to calculate the amount up front first. Even using 300% lens correction in StarTools is not enough to pull the shapes out.

Edited October 14, 2018 by happy-kat

[RolandKol]

Nice topic... I always wanted to try attaching it to my Canon 1300D...

Most of the websites have description line like this: "It can also be used as a finderscope, small lens for your camera or just as a small richfield telescope for travelling!"

Does not look like it can be "small lens for your camera" at all  

Unless it's a small chip size one ... like ZWO 224 or similar.

 

[happy-kat]

And from testing it can only be used with a diagonal if the diagonal has an unusually short light path sub 60mm.

[cuivenion]

 

[happy-kat]

I had forgotten I had made this earlier thread, so this is the link to using the 50ED with my FF

https://stargazerslounge.com/topic/384531-50ed-preparation/?do=findComment&comment=4155926

 

Edited October 18, 2021 by happy-kat