Dear Duncan, Thank you very much for the objective. I have already sent it back to you, so you should receive it today. Although I haven't been able to find out what causes the problem, at least I am now sure that it is the objective. Your objective doesn't show the effect, or at least it is not very marked. In fact you can see a very dim halo, but not as marked as with ours. Funny enough, appart from that halo, our objective seems to produce a better image than yours! As I said, I am still not sure about the cause. Moreover, I still don't know whether the immersion oil can get into the objective or not! Olympus (UK) told me that that shouldn't happen unless a rubber seal is broken (eventually due to excessive pressure while focusing). The other important question is whether it is really affecting our images (I mean, when these are real specimens, not just point sources) which, at the end of the day, it's what matters. I think I'll try to contact P. Shaw who's got a lot of experience with point sources. The other possibility is to stain microtubules (that's quite straightforward to me) an compare two orthogonal images to see if there's any directional distortion. The big problem is... our system is not working: the scancard is dead and our grant is finished so we can't afford the new one... Let's hope that some of the applications succeed and we can get it back to work! Besides, I am very grateful and surprised for the copy of the Light microscopy book that you sent me. I am quite happy that you found it of some use and I must say that the Bio-Rad logo looks very nice indeed! If I had known in advance I would have surely expanded some sections (at least the confocal one) As you probably imagine, it started as "can't say no to Dave Rickwood..." ;-) Anyway, I would appreciate any comments that you may have about the book. Thank you very much for your help. Regards Carlos