thanks guys for your suggestions..
BTW i find pentax has this option. refer to the link below. so i thought of D90 has too..
http://a.img-dpreview.com/news/0801/pentax/pentax_k20dk10d.jpg
sometimes i find this option is useful for taking multiple exposure or taking same object/landscape in different situations and overlap if needed (HDR?). For zoom lenses such as 18-105 or 55-300, i just take pic as long as the coverage is just right for the frame. Next time if i want to take same pic same angle, setting focal length is head ache to me...
well... actually even if you had this feature how would you know exactly where to stand like the previous time? you might get the right focal length but the actual distance to the subject might differ, no?