These Takahashi Ultra Wide/Flat Field 1.25” eyepieces use proprietary eight and ten lens optical systems to give you a very wide 90° apparent field of view that is remarkably flat from edge to edge. Their aplanatic (spherical aberration-free) design eliminates coma and spherical aberration, while still providing a relatively long eye relief and exceptional sharpness.
Their flat field design makes them particularly adept at wringing the last bit of performance from truly flat field telescopes. Telescopes with inherently curved fields (standard Schmidt-Cassegrains, doublet and triplet refractors without field flatteners, etc.) will not benefit from the flat field performance of these superb eyepieces. Their 90° field will simply reveal the shortcomings and aberrations of scopes with curved fields that narrower field eyepieces can hide.
These Takahashi eyepieces are not inexpensive, but neither are the telescopes they are designed for. If you have an expensive and superb flat field scope, these equally superb Ultra Wide/Flat Field eyepieces will show it off to its best advantage and will totally justify their cost and your scope’s cost.