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So i got a new telephone a couple months ago, i got a Explore Scientific Ed80 (480mm, f/6) to pair up with my Canon T4i, and with this i got a Orion Field Flattener. I saw that i needed to have 55mm of backfocus, but when i had around 55 of backfocus, i couldn’t even focus on the subject. I had to use extenders to even get my camera to focus. So from the edge of the field flattener to my camera sensor was around 93.5mm. Am i doing something wrong? I feel like the edges look horrible compared to other peoples images with the same ff. Does this ff just not work with my scope? if so would greatly appreciate it if someone told me what ff would work for it. I just want to get back out imaging again.

Image i got with the ff:



Edited by ryanh
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27 minutes ago, ryanh said:

Am i doing something wrong?



To achieve the magic 55mm of backfocus, the field flattener (FF) must be attached directly to the t-ring. The extenders need to be on the telescope side of the FF.


* I've no idea why ES make their tubes so short.

** If you're in the market for a different FF anyway, for corner to corner, even over full-frame, this one is the best we've found so far.

Edited by alacant
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My simplistic way of looking at things is that you have 44mm within the dslr and the T ring gives you an additional 11mm giving you your 55mm backfocus between dslr sensor and the next piece of glass. So your field flattener bolts immediately after the T ring. As alacant says, if you need to add spacers to getfocus, they gobetween FF and telescope. All the best. 

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I've always put extenders after the reducer/flattener lens, no matter which telescope setup I've used as that's how it's drawn on technical drawings. Your DSLR should only need the T ring to attach to the back of the reducer as typically they have 44mm within the camera itself and 10/11mm on the t ring. The larger your camera sensor the more stringent you need to be on your spacing. If you use a reducer in future, spacing becomes even more critical. It's easier to crop the image.

Edited by Elp
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