Our weather has not cooperated till last night for awhile, this gave me time to test the 4mm on a few double stars and Jupiter and Mars when they came up.
I used my Russian TAL-75R - (75mm lens, 600mm focal length, f/8 telescope) which gives me a power of 150x and 300x with my 2x barlow. On Polaris and Epsilon Bootes, The stars showed the Airy Disk, and I could split both stars as the 62 degree field was better than a cheaper small filed 4mm I have. Jupiter showed the main belts and the polar shadings with a few features at moments of steady seeing . Mars was a gibbous disk and the polar cap and a faint marking were noted. The wide field gives a bit more time for me see the object as they drift though it's field. I could not see any problems with this eyepiece, I also own a 26mm one of same brand and have no complaints as to their crafmanship and quality, I am please with it and hope our weather allows me do more observing of the planets and other objects with the eyepiece. i can say very happy with the 4mm eyepiece,,