The apparent field of view and the usable eye relief to stay the same as the focal length changes.

Smooth zoom action with click-stops at 3, 4, 5, 6,7 and 8mm for quick changes to precise preset magnifications.

Parfocal across the entire zoom range (minor tweaking may be necessary, however).

SV171 Super-wide Angle 1.25" 8mm-24mm zoom eyepiece allows you to change magnification power without swapping out eyepieces. Designed with FMC Fully multi-coated glasses for excellent image. Sharp optimal performance with low chromatic aberration.Comfortable long eye relief design; Exceptionally long 18mm-19.5mm eye relief range allows eyeglass wearers to enjoy the entire field of view without needing to remove their glasses. Sleek black barrel with safety undercut to reduce the possibility of the eyepiece slipping out of the focuser or diagonal. Standard 1.25" fitting diameter compatible with any astronomical telescope of 1.25" focuser;The bottom M28.5 x 0.6 thread can also be used with standard 1.25" Filter.

Svbony SV191 super-wide-angle 1.25'' zoom eyepiece 7.2-21.6mm, allow you to change magnification power without swapping out eyepieces.

Svbony super-wide-angle 1.25'' zoom eyepiece 10-30mm, allows you to change magnification power without swapping out eyepieces.

Zoom Eyepiece eliminates the need to change eyepieces so you can spend more time viewing the night sky instead of fumbling in the dark when you want higher or lower magnifications.