Good cheap macro lens?
I liked the Nikkor Micro 40mm, as it is cheap and true macro. But I read since you have to be so close to the subject for 1:1 magnification, you get bad lighting and it is therefore bad for "serious macro photography". One of my friends online has superb pictures of bees and spiders that fill the frame with perfect quality, and he uses a Nikon 50mm v 1.8, with extension tubes. Is that a good choice? Is it better than the 40mm? What are other good options compatible with a D5100 body?
Get a vintage 50mm, 28mm, and a vintage 35mm lens (they're all around $50). And get reverse rings for each of those (I find mine for around $5 each). You can get something like a 2:1 with a reversed 50mm, and around 5:1 or 6:1 with a 28mm. And if you want to go further, just get some cheapy extension tubes or a cheap bellows for the nikon mount.
That's in my opinion the best you can do for macro without spending many thousands of dollars on a dedicated macro lens, which can be limiting compared to reversing lenses. Hope this helps.
There are a few of things to consider
* The difference between a 40 mm and 50 mm lens is not that great.
* The 40 mm macro lens is a special flat field lens (as are all macro lenses) and can be specifically set to calibrated 1:1, 1:2, 1:3 and 1:4 image to subject ratios.
* Before the advent of dSLR's, photographers around the world used the Nikkor 55 mm f/3.5 macro lens with never a problem with "bad lighting". They just had to make sure that they did not cast a shadow on their subject caused by them, the camera or the lens.
* If you look at the angle of view of the 40 mm (38°50') that is is only slightly narrower than the Nikkor AF-S 60 mm f/2.8 when it is used on a full frame camera (39°40') and the old 55 mm f/3.5 had a much wider angle of view than both of those (42°50')
All this to say that you do NOT have to worry about bad lighting unless YOU create it.
If you want to shoot true macro, the AF-S 40 mm f/2.8 is the best choice
I may be out of line here but this is what you may be needing aside from a macro lens or tube setup.
What you need is a light source, either a ring flash, or light
Serious macro photographers use additional lighting like off camera speedlights or a ring flash. The reason is not just because you are close to the subject (and on camera flash would leave a shadow from the lens barrel), but because in order to get a decent depth of field with macro, you need to stop down the lens a fair bit and this lets in less light.
The Sigma 50mm f2.8 macro and 105mm macro are both good - they have different working distances.
Extension tubes/reversing rings are good cheaper ways of getting macro images, but again you will find often that your depth of field is incredibly shallow - so you may have to focus stack if you want a subject in focus from front to back.