if you by "details" want to say "mega pixel" i can say lumia has 6.7mpx, iphone4 has 5mpx, so you must have a more detailed image.
If you see your image with less than 6.7mpx i think you're taking the photo synched on skydrive! By default Windows Phone sync photos "on the fly" resizing them and uploading them via 3G. To fix this you can go on:
Settings -> Backup -> Photo -> Select the maximum photo quality. Phone will upload them ONLY when connected via Wi-fi to save battery and 3G data.
Rest assured, your phone can shoot great photos, a lot better than iPhone4 (and iphone 5 IMHO) even in normal light condition :)
edit: i'm adding a photo just taken with my lumia 720 and a zoom in that photo, enough detail? :P (i just take it with Nokia Pro Camera, so only 5mpx photo!)

