In brief:
- Screwed, not plugged (both 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 (and more) – the optimum working distance for different focal lengths is indicated on the housing
- Thread on telescope side M54x0.75
- Thread on camera side M48x0.75 (clear aperture 45 mm)
- No change in focal length
- Ohara glass from Japan with partner glass
The Lacerta Field Flattener (LFF) fulfils several tasks:
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 achieved by setting the correct working distance between the flattener and the camera sensor. Standard lens designs 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 produce round stars across the entire image field.
Due to different optical designs (ED doublet, triplet, fluorite APO, etc.), the working distance may differ slightly from the values specified on the flattener housing. Apochromats, which have more off-axis coma than astigmatism in their optical design, cannot be completely corrected (e.g. some Kunming apochromats with lanthanum glass).
Tested with: Skywatcher EvoLux 62 ED, Lacerta ED 72/432 (and similar), Skywatcher ED 80/600, Sharpstar 107/700, Takahashi TSA 120.
