Which is the minimum aperture on my Nikon DX AFs 55-200mm 1:4.5 6g ED lens
When I look physically at the size of the aperture it look a lot smaller than 4.5 and when I put the camera on auto with & very bright light it goes down to f 11 and when I put the camera on A it goes down to f22? So finally what is the minimum aperture?
My camera is Nikon D50
When you're in aperture priority wind the aperture setting down (increasing number) until the number doesn't change. That's the minimum aperture.
Looking at the specs it's f22 at 55mm and f32 at 200mm.
The Maximum aperture is f4 at 55mm, dropping to f5.6 at 200mm - pretty much an average for a lens in this category(the aperture changes gradually as you zoom, but your TTL meter takes this into account).
Unlike older MF lenses, while the iris diaphragm (which controls aperture) is in the lens, there's no aperture ring on the lens, and the body controls take their place.
Minimum aperture is subject to the same changes as maximum, beginning at f22, and stopping down to f32 - again, pretty much average.
In M or A modes, you can control the aperture manually, but it takes skill and practise to get the best out of this.
Did you not get a data sheet when yon bought that lens?
As Andrew says, the minimum aperture varies between f22 and f32, depending on the focal length setting. Variations of that sort are normal with zoom lenses.
The fact that your lens has a maximum aperture of f4.5 has no relevance to its minimum aperture. And "F4.5" will look different on different lenses, depending on their focal lengths. The appearance of the lens aperture is not a reliable guide to its scientifically determined aperture.
You camera has a setting in which you can control the aperture, (A for Aperture) and in that setting you can set any aperture you want.
Camera is irreverent. The answer to your question is solely based on the specific lens that you're talking about. In the case of the 50-200 f/4-5.6, the minium (smallest) aperture is f/22. The maximum (largest) aperture varies from f/4 (wide angle position) to f/5.6 (telephoto position).
So depending upon the zoom position, the maximum aperture of your lens will be f/4 to f/5.6 or somewhere in between.
Most lenses have a minimum aperture of f/22 but some go to as low as f/32.
Take note that the larger the f/number, the smaller the aperture size (or hole) and that aperture size is a lens property, not the camera (although you control aperture size through the camera).
Settings do change now and then and there are different combinations of settings that can come up with a correctly exposed shot so it is perfectly normal for the camera's Auto settings to differ from settings in other modes. If in Auto mode aperture is at f/11, and in A mode it's f/22 then either the shutter speed in A mode is longer than in Auto mode or ISO in A mode is higher than in Auto mode. A mode is Aperture priority so it's up to you to select the aperture size. The camera will match the correct shutter speed to it automatically. For ISO however, you would have to do that manually.
Physical comparisons of different lenses is a Total Waste Of Time.
Compare their Specifications instead.