I'm an eye surgeon and take photos for patients with squint (crossed eyes) showing the eyes only. I also need to take photos of lid lesions which may be only 3-10mm I already have the 18-105mm lens. What is the best macro lens for me and my Nikon D90?
Well a few considerations...
You need something very sharp for what you do, so putting extension tubes on a zoom lens isn't going to give you your best results there. Zoom lenses, especially with a fairly wide range like 18-105mm are quite a bit softer than a macro or even a normal prime lens. You want either a normal sharp prime lens and extension tubes or a dedicated macro lens for sharpness sake.
A dedicated macro lens is going to look more professional and be less hassle, which are both important when working in a professional capacity like a surgeon.
You're going to be indoors, under artificial light (which is almost always 'dim' compared to outdoors, even when its considered bright inside) - so you'll want:
- A good working distance so that you don't block your light source with your lens and body.
- A large aperture so that you can focus in low light and stop down a little to get it ultra sharp but still not be 'slow'.
There's two lenses that generally meet this criteria, depending on your budget.
- Sigma 105mm f/2.8 around $500 US.
- Nikon 105mm f/2.8G ED-IF AF-S VR Micro-Nikkor Lens around $1000 US.
The Sigma is the budget friendly option, but the Nikon is definitely the sharper and better lens. The Nikon brings faster, quieter autofocus and a stabilization (VR) to help you handhold in lower light.
(The Tamron 90mm Macro is another popular telephoto macro lens, but its price about equivalent to the Sigma and the Sigma has slightly more reach).
I own the Nikon 105mm f/2.8G ED-IF AF-S VR Micro-Nikkor Lens and use it on a D7000. It is a great macro lens, all-though a little pricy, with a long Nikon history. It is really sharp and will provide a good working distance for your squint shoots. To capture the lesions in detail you will have to get really close (e.g. 1:1 reproduction). I think this lens will serve you pretty well.
However, the VR (Vibration Reduction, Image Stabilization) is a nice ad-on if you need to shoot handheld or use the lens as a short telephoto (maybe squint shoots), but it will not replace a sturdy tripod for serious macro photography, which a 3-10mm subject (lesions) is IMHO.
Since I have the eyes of a sparrow hawk ;-) and never was at an eye surgeon/specialist, I therefore do not really know how you work and how you might use the lens. But you might also want to think about using sturdy tripod with a proper tripod head and fixing the patients head or provide a comfortable backup so the patients head will not shake. I guess as an eye-surgeon you should already be aware of the latter.
An alternative would be to buy extension tubes for your lenses. You can get great results without having to buy dedicated macro lenses.
This lens allows a reasonable working distance (about 5.5 inches) and is reasonably priced at about $500. However, it cannot be fully utilized on FX-format (full-frame) camera bodies.
You might check B&H or Adorama for a new or used 55mm Micro Nikkor. They're usually available for less than $400 new or under $200 used. It's a manual focus lens, which should work fine for your use, and is tack sharp.
Here's some good info: http://www.kenrockwell.com/nikon/55f28ais.htm