The Omegon field flattener - Provides perfect image flatness for your astronomy photos
Many refractors and reflector telescopes suffer from field curvature. A curved image field means that stars at the edge of the field of view no longer appear as pin-sharp points but as out of focus discs. But now the new Omegon field flattener will conjure astronomy photos with pin-sharp stars right out to the outer edge of the image field.
Bringing the problem under control
Field curvature is a common optical defect that is not noticeable with visual observing or photography using small chips. If, however, you use a large chip or a full-frame camera, then this defect becomes glaringly obvious. Of course you could always crop your images to remove the blurred outer region; but using a field flattener it is much more elegant solution for using your expensive camera with its large format chip.
Flat field over the entire field of view
The field flattener gives you an absolutely flat image over the entire photographic field of view. Also, the focal length remains the same when using the flattener.
Suitable for telescopes from f4 to f8
You can use the Omegon field flattener with any refractor with a focal ratio between f4 and f8.
M48 thread for better aperture illumination
The Omegon field flattener has an M48 thread on both sides - giving you complete aperture illumination. A T2 thread plus M42 would limit the incoming light beam and so not provide sufficient aperture illumination for telescopes with 2" focusers. But using only the M48 thread, you make use of the entire light entering the telescope.
Use additional accessories - 109mm of back focus
This field flattener has a very generous 109mm of back focus. This means that you need a spacing of 109mm between the lens plane and the camera chip. This is an advantage, as it means you can use other accessories in between - such as a filter wheel, a flip-mirror or an off-axis guider. Using the correct Omegon extension rings will let you set the optimum spacing - whether you use accessories in between or not. Please also note the adapter recommendations in our Expert's Advice.
The advantages in a nutshell:
- field flattener for refractors
- suitable for telescopes from f4 to f8
- M48 thread for complete aperture illumination at 2"
- room for accessories between - 109mm of back focus
- excellent multi-coating on lenses
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