I just purchased a William-Optics Fluorostar 91 telescope and Flat 68 iii field flattener, and have a question about connecting a ZWO ASI 533 MC Pro camera. The W-O web site for the Flat 68 iii shows the back focus for the FLT91 as 75 mm, but also indicates the adjustment distance for a DSLR or mirrorless camera as 5 mm. Because of the large discrepancy between these two numbers, I’m a little confused about what to adjust the Flat 68 iii to, as well as what spacers to use between the Flat 68iii and the ASI 533 camera.
Is the distance from the rear glass plane of the Flat 68 iii to the camera sensor supposed to be 75 mm as suggested by the web page? Or do I set the Flat 68 iii adjustment to 5 mm and then use spacers to achieve the usual distance of 55 mm between the flat and camera sensor?
That is, since the ASI 533 sensor is located 6.5 mm back from the camera connection point, it seems that I have two choices:
1. Set the Flat 68 iii to 5 mm, and then add 48.5 mm of spacers to achieve a total of 55 mm, or
2. Set the Flat 68 iii to 5 mm, and then add 68.5 mm of spacer to achieve a total of 75 mm?
Which if these two is correct, or if I’ve completely misunderstood, what should the total distance be?
Is the distance from the rear glass plane of the Flat 68 iii to the camera sensor supposed to be 75 mm as suggested by the web page? Or do I set the Flat 68 iii adjustment to 5 mm and then use spacers to achieve the usual distance of 55 mm between the flat and camera sensor?
That is, since the ASI 533 sensor is located 6.5 mm back from the camera connection point, it seems that I have two choices:
1. Set the Flat 68 iii to 5 mm, and then add 48.5 mm of spacers to achieve a total of 55 mm, or
2. Set the Flat 68 iii to 5 mm, and then add 68.5 mm of spacer to achieve a total of 75 mm?
Which if these two is correct, or if I’ve completely misunderstood, what should the total distance be?
