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( 4 / 5 )
Product no.: 43761

Field Flattener 2''

$ 259.00 incl. VAT, plus shipping costs
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in stock
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Express shipment possible for delivery tomorrow, 17.04.2024!
  • Suitable for telescopes from f/4 to f/8
  • M48 thread for complete illumination at 2"
  • 109mm backfocus for accessories between flattener and camera

Product description

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

Our expert comment:

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: www.astroshop.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: www.astroshop.eu/other-astro-photo-accessories/omegon-off-axis-guider/p,33139

(Bernd Gährken)



Connection (to the telescope)
Connector (at camera end)
Appropriate for...
Refractors f/4 to f/8
Connector (other end)


Flatteners, Correctors, Reducers
Type of build

Recommended accessories

Telescope accessories (1)

Omegon M48/T2 adapter – short version

$ 14.90*

*All prices include VAT plus shipping costs.

Omegon Field Flattener 2''
The galaxies M81 and M82 in Ursa Major - photographed with a PhotoScope and Omegon field flattener

Omegon Field Flattener 2''
M8 Lagoon Nebula, taken with an Omegon Photography Scope and Omegon 2'' field flattener.

Omegon Field Flattener 2''
M57 Ring Nebula - taken with Omegon 104/650 ED triplet plus Omegon field flattener

Omegon Field Flattener 2''
Omegon 104/650 ED triplet telecope without Omegon field-flattener

Omegon Field Flattener 2''
Omegon 104/650 ED triplet with Omegon field-flattener

Customer reviews

Larger threads options? 48mm is too small for larger camera sensors

Review by S. S. on 27.02.2023 08:55:27

( 4 / 5 )

Do you have a version of this flattener with a much larger telescope side thread (say m68 or larger) and m54 on the imaging side? My Stellarvue SVX130T and SVX180T have 92mm female thread coming out of the Moonlite Nitecrawler WR35 focuser. On the imaging train I use M68 or M54. My camera is a full frame ZWO ASI6200, but I am thinking of upgrading to the monstrous ASI461MM medium format camera with 44 x 33 mm sensor size. That's 55mm diagonally.

Response on this review by our expert Ulrich Zehndbauer

on 27.02.2023 11:39:57

Dear Customer,
We have informed our advisors concerning your inquiry. They will get in contact with you soon.
Best regards and clear skies!
Team Astroshop

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