If you are going to shoot flowers or static nature, the Nikkor micro 60mm. If you are going to shoot live nature, insects or anything like this, then buy the 105 Nikkor micro, because you will not invade their fear circle.
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Could be a good option, you will get a 400 f/5,6 , I would use it as a 400 f8 for better resolution in spite of speed. But put a good Teleconverter in the lens, with a 2x TC you will have a little quality lack. The better TC you get the less quality you loose. Anyway, you can improve your...
Modulate the strobe light (flash) and mix with natural ilumination. Use natural ilumination as long as you can, is the best. I try to avoid flash, I only use flash in the last moment. Get fast lenses, the 50mm f/1.8 you are waiting is a good beginning.
For wildlife photography the 80-200mm isn´t long enough. You need at least 400 or 500mm at the long end. The 80-400VR could be a good option, for less price you have the Sigma 135-400mm or the Sigma 170-500, which is a good recomendation for wildlife. You will need a good tripod, IR shooter, a...
My wife has a Nikon D50, which I use often, and it is a good camera, Nikon feel, and images are very sharp and contrast, less noise than my first Nikon D100 and you can use almost all the current Nikon lenses.
I have tested the Nikon D40 and I prefer the Nikon D50 feel an performance...
Well, a real macro has a 1:1 ratio, as said before. If you want to shoot flowers or not moving subjects, pick the Nikon 60mm f/2.8, really nice bokeh and very sharp images, but if you want shooting insects you need a little longer as Nikkor 105 f/2.8. Both has CRC, proximity correction, and you...
My personal lens recomendation for sports in your, sorry, in any Nikon DSLR is the Nikkor 70-200VR f/2.8. As said before, use a monopod too and raise the ISO to 800 or 1600 for indoor sports.
I have cleaned my cameras sensors (from my first D100) sometimes twice a month and I never had a problem with this. It is difficult to scratch the glass filter protecting the sensor, unless you use a screwdriver with diamond tip. Normally it is as hard as a good UV filter.