Greg, a few thoughts....
Your requirements for close-up medical work and your son's requirements for sports are quite different. The sigma 70-200 f/2.8 you mention does have macro capability but it's big (1.7 kg, 184 mm long) and expensive (over 600 in the UK, a lot more than your camera plus standard lens). Patients might find it slightly offputting to have their teeth photographed close up with a lens the size of a small drainpipe. and this is much more lens than a beginner needs to learn sports photography (unless you are a particularly indulgent father of course!). Also - more to the point - it is not yet available with the in-lens focussing motor that the Nikon D40x needs so it won't autofocus on your camera. This is one of the main drawbacks of the D40/D40x - the lens selection is more limited than it is for other cameras..
A much better bet would be to get your son a Sigma 55-200 f/4-f/5.6 zoom (about 145 in the UK for the version with the in-lens motor, specifically for the D40/D40x); or the Nikon equivalent (55-200) which has built-in vibration rediction (about 200)..
Then for your medical work get a smaller macro - possibly a NIkon 60mm f/2.8D Micro or the Sigma 17-70 f/2.8 - f/4.5 (which is available with the necessary lens motor for the D40/D40x and would make an excellent general-purpose lens). I'm no expert on macro photograhy so there may well be better options out there. But a combination like this will cost a lot less than the massive Sigma 70-200 which won't autofocus on your camera anyway..
The Canon lens won't fit your Nikon, the mounts are different..
Hope this helps.Best wishes.
... how big do you need to make your medical pictures? If you want publication-quality 10x8s for publication in a journal then you'll want a good macro lens. But if you only need (say) 4 x 6 pictures, or will be looking at them on a computer monitor, your standard 18-55 may do the job..
Its closest focussing distance is 28cm, and at a focal length of 55mm that will allow you to get pretty close (e.g. fill the frame with an open mouth, bit not close-up on one tooth). WIth a 10MP camera, even if the subject of the photo is small and fills only the central fifth of the frame, you could crop the picture down to 2MP in photoshop. that is still more than enough resolution for sharp postcard-sized pictures, or to view on a PC monitor (which usually have about 1MP resolution). Worth a try before you spend some more money..
Lenses that will fit your D40x are listed here (scroll down to "AF-S"):http://www.nikonusa.com/template.php?cat=1&grp=5and here:http://www.sigmaphoto.com/news/news.asp?nID=3356.
There is a review of the Sigma here:http://www.photozone.de/8Reviews/lenses/sigma_70200_28_nikon/index.htm.
And a review of the Micro-Nikkor AF-S 105mm here:http://www.photozone.de/8Reviews/lenses/nikkor_105_28vr/index.htm.
Canon lenses will only fit Canon cameras..
A one lens solution to your problem is not possible. The minimum focus distance for that Sigma is 1 meter and the lens is an intimidating brute that really needs to be on a tripod..
The only f/2.8 alternatives to the Sigma 70-200 that will work on the D40 are the Nikon 70-200 VR which is an excellent lens but VERY expensive and the shorter range Sigma 50-150 (both also reviewed on Photozone). The cheaper Nikon AF 80-200 f/2.8 (about the same price as the Sigma 70-200 will not work on the D40x). There are cheaper alternatives like the 55-200 Nikon which are not such good low light lenses being f5.6 at the long end and thus will have trouble stopping action. Nikon do not make any f/4 constant zoom lenses. They make f/2.8. That makes the gap from more ordinary telephoto zooms quite a big one..
I suggest for your son the Sigma 70-200 plus a monopod to steady it and for you the Micro-Nikkor..
Despite Mike's comments above the Sigma definitely WILL fit the Nikon as the lsit indicates (and to avoid any doubt will autofocus with it).
You may be able to get a cheaper solution for YOUR needs using extension tubes. This is not an area where I have any expertise and, given your lack of (photographic!) experties I do not feel it would give you a satisfactory solution..
Sounds like you can offset the Micro-Nikkor against yout taxes so I would go for that. The Sigma 17-70 will close focus but is not a real macro lens so it will not magnify in the way you want. It is a good lens but not one that will really benefit you..
The perfect solution for you would be the Micro-Nikkor and a ring flash..
The NIkon 60mm f/2.8D Micro will NOT autifocus on the D40X.
I started typing this shortly after your post but then got distracted by other things. I have edited it to take acount of later posts..
*Nikon* D Eighty + Fifty - Other equipment in Profile.
Despite Mike's comments above the Sigma definitely WILL fit the Nikonas the lsit indicates (and to avoid any doubt will autofocus with it).
Yup - the list I was looking at was out of date.Mike..
Mike & Chris- thank you both so much for your responses, I'm sure you have no idea how totally helpful you both have been ! You've cleared up my misconceptions and misunderstandings, cemented my understanding and I now have a much clearer idea of where I am headed on this..
At this stage I like the sounds of the Micro-Nikkor plus the Sigma 70-200 (but if this doesn't sound silly am tossing up whether the shorter range but possibly easier to handle -much lighter- Sigma 50-150 might do for now).
Thanks again !..
Sure your a newbie, but you would be welcomed in the Nikon Lens Forumhttp://forums.dpreview.com/forums/forum.asp?forum=1030Warm regards,DOF..
A further thought. I did not want to clutter the earlier post with it..
You can buy a telephoto convertor. Nikon makes them and so do Kenko, Tamron, Sigma and others..
A 1.4x convertor will:a) add about 1cm to the length of the lensb) change the 50-150 to a 70-210mm zoomc) reduce the aperture by one stop (f/4).
In theory any tele convertor should work but I have heard suggestions that Sigmas can be a bit fussy. Her is a link to the relevant page on their UK site:.
There would be some degrading of quality but not much..
(To add to your knowledge one can get 1.7x and 2x convertors. They would respectively turn the lerns into a f5.6 and an f/8. I would not recommend either)..
It would NOT make sense to to buy the 50-150 if you know that 70-200 is what your son needs. The 50-150 is a good indoor lens (but I manage without one. I now cover 24-200mm with two f/2.8 lenses on two cameras going from shots of a complete stage to closeups. That may give you the idea that the 70-200 is what is required)..
The Sigma 70-200 regularly appears on Ebay in the UK - new and used. It might be worth taking a look. You could import one at a big saving. Also there are several reputable sellers of used equipment in the US. I do not have them bookmarked however..
If you are looking for a used lens you might also keep your eye out for a Sigma AF 100-300mm f/4 EX HSM APO. That costs slightly more than the 70-200 but you might find one used at a good price. That lens really must be on a monopod or tripod. I have only seen a review of this lens on a Canon mount but it gets a very good review:.
But I stick with the Sigma 70-200 f/2.8 as my primary recommendation. However the Sigma 50-150mm is a lot more portable than the 70-200. If YOU are going to make use of the cam for leisure purposes it would make a nice compliment to the 18-55. (Personally I would have recommended you to get the 18-135 when buying the D40x but that is not where we are at and the 18-55mm is an excellent low cost lens).
Hope that helps and does not confuse to much!.
*Nikon* D Eighty + Fifty - Other equipment in Profile.
Thanks again Chris. I've looked into your further excellent recommendations, and the 70-200 does after some thought indeed seem to be the way to go, your advice is absolutely impeccable as always and much appreciated..
Anyway I've ordered the 2 lenses that you recommended and am now looking into ringflashes. I now realise (as I now know after reading the reviews on the link you gave me) that the 18-55 was probably not the best choice but I did not realise that I had the option of any other lense at the time,( and realistically wouldn't have known better at the time anyway !!). Still ,one lives and learns..