The field flattener fits all modern ED refractors
Please note the following:
- The shorter the focal length, the longer the spacing that must be used to compensate for field curvature.
- The longer the focal length, the shorter this spacing must be due to the lower field curvature.
The telescope's focal length is important for determining the correct spacing:
- focal length <450mm: 128mm
- focal length 450-490mm: 123mm
- focal length 500-550mm: 118mm
- focal length 560-590mm: 116mm
- focal length 600-690mm: 113mm
- focal length 700-800mm: 111mm
- focal lengths above 800mm: 108mm
Delivery includes an extender combination for spacings of up to 53mm. You will need the flange focal distance of your camera and the thickness of its T2 ring to calculate the correct additional extender length for your telescope.
Your telescope has a 480mm focal length and needs a chip spacing of 123mm behind the flattener. You are using an EOS DSLR with a flange focal distance of 44mm and a T2 ring that is 9mm thick. In this case, the chip distance= 53mm (extender provided) + 44mm + 9mm = 106mmmm Hence the spacing still needs to be increased by 17mm.
Extenders to compensate for the residual difference can be found here: omegon.eu/telescope-accessories/adaptors/15_37
It is OK if the extender is not correct to the millimetre, as a residual deviation of +/-4mm is still acceptable.
The back focus of more than 10cm allows the use of an off-axis guider. A well matched and inexpensive version can be found at: omegon.eu/other-astro-photo-accessories/omegon-off-axis-guider/p,33139