Esprit 80 - what is the correct field flattener to sensor distance?

55mm and I have both the Esprit 80 & 100 and it is well documented that the is the correct distance, I was 5mm out and got odd stars, and until I fixed the distance then the beauty of this scope could not be revealed.

I have had to switch to a Moravian camera, OAG and FW just so that I can achieve that distance as ATIK can cannot accommodate that short a back focus.

No problem on my RC as I don't use a flattener but with the Esprits you really need to achieve this distance.

HTH

According to the manual it is 61mm.

well, the SL131204 manual I got with the scope states it is 61mm !!!

Now that's interesting. I wonder if since the OTA was originally released the engineering has changed and so the optical focal length from the flattener has also changed? At this point it probably makes sense to call Skywatcher and ask.

Right Gentlemen, The SW Field Flattener has a screw on adapter that is 11mm in width, if you use this then from the front of the screw in adapter to the CCD is 55mm for the Esprit, if you want to try and gain additional back focus then as the manual says and I quote Page 9 of 13: -

"Note: Inside the box the 11mm ring spacer is assembled with the field flattener body. When assembled, the two parts may look as if there were only one piece. When taking pictures with a CCD camera it can be useful to remove the 11mm spacer ring to gain 11mm additional back focus distance"

So unless you have made up a special adapter or configuration you will have to use this 11mm spacer and therefore the back focus distance is 55mm

QED.

Hope that helps.

Hi NeedsMoreCoffee. I just spoke to the guys at Sky-Watcher. I purchased an Esprit 100 today and wanted to verify the spacing for my DSLR and CCD cameras. They told me that the manuals at their website are correct for the OTA's they are currently shipping. Here is the link for the Esprit 80 (http://skywatcherusa.com/downloads/manuals/S11400_Esprit80EDT.pdf). The relevant information is on p.8. I'm guessing that since you are asking about spacing that you are not the first owner of the scope and so did not receive a manual. So, there are at least two possible spacings. For new scopes it is 66mm. For older scopes, it is 61mm, as noted by Boutros (here is a link to the older manual, https://www.manualslib.com/products/Sky-Watcher-Esprit-100-Ed-Super-Apo-3386196.html). In both cases Sky-Watcher shipped a spacer (step down from 66mm threads of the flattener to 48mm threads of the DSLR T-ring) already assembled with the flattener. For the 66mm version the spacer is 11mm. For the 61mm version the spacer is 6mm. So, to find out what scope you have check the spacer on the flattener. If it is 11mm the optimal spacing from the flattener to the sensor is 66mm. If it is 6mm the optimal spacing is 61mm.
Good luck, NeedsMoreCoffee. Looking forward to your images.