The flattener is a lens that evens out the field, as this is slightly curved by the primary optics. This curvature causes stars that are imaged at the edge of the field of view to be less sharp. The flattener, also called a field flattener, corrects this effect. Astrophotographers can then enjoy images where the stars remain sharp right out to the edge of the exposure. The flattener is installed between the telescope and the camera.
A lens has a concave curved image shell - the strength of the curvature depends mainly on the focal length.
The shorter the focal length, the stronger the image shell is curved and the harder the flattener has to work to make it flat.
This is done by setting the correct working distance from the flattener to the camera sensor.
In addition, lens objectives (all refractors) with a standard design only produce a round star image in the centre of the image; the further away from the centre, the more distorted the stars become ("off-axis astigmatism").
Both problems must be corrected by the flattener in order to obtain round stars even in the corners of the image.
The Lacerta Universal Field Flattener is suitable for many ED and triplet refractors thanks to the included adaptors. It can also be used for photography with "rich field" telescopes, i.e. short focal length (achromatic) refractors, e.g. 102/500, 102/600, 120/600, 150/750.
Main features of the Lacerta Universal Field Flattener:
- Screwed, not plugged (both on the telescope and camera side) - no risk of tilting
- Optimised for f/4.5-f/12 apochromats with standard optical design, from 300 mm focal length
- Also suitable for full-frame sensors
- Working distance between 55 and 76 mm (the optimum working distance for different focal lengths is indicated on the housing)
- Thread on telescope side M54x0.75 (compatible with Takahashi, Lacerta) and M56x1 (Skywatcher ED-Apos and refractors)
- Thread on camera side M57x0.75 (clear aperture 49 mm) and M48x0.75 (clear aperture 45 mm)
- No change in focal length
- Ohara glass from Japan with partner glass
