Please don't laugh ...

[mph999]

... but could someone explain what the numbers refer to ...

nikkor 18-200 F/3.5-5.6 VR


ok, 18-200 is the focal length, and I presume that F/3.5 is the lowest f number at 18mm and 5.6 is the lowest f number at 200mm ???

Thanks,

Martin

[coldrain]

No need to explain you anything.... and thats no fun, now we can not laugh at you! :D

[BonjiB]

... but could someone explain what the numbers refer to ...

nikkor 18-200 F/3.5-5.6 VR


ok, 18-200 is the focal length, and I presume that F/3.5 is the lowest f number at 18mm and 5.6 is the lowest f number at 200mm ???

Thanks,

Martin
Nice response rain. :P lol

You don't need any explaining. You got it all right. 18-200 is your lowest-highest mm rating on the lens and the f/3.5-5.6 is in fact the lowest f stop at those respective mm ratings. Nikkor indiciates that it's Nikon glass and the VR means vibration reduction. That's an image stabilized lens. Hope that helps.

[Rhys]

... but could someone explain what the numbers refer to ...

nikkor 18-200 F/3.5-5.6 VR


ok, 18-200 is the focal length, and I presume that F/3.5 is the lowest f number at 18mm and 5.6 is the lowest f number at 200mm ???

Thanks,

Martin

Yes. You have it right. However, on a lens such as this, it's possible to set the lens on f3.5 throughout the range from 18-200 but the light will drop off rendering the transmitted light to f5.6 by 200mm. It's quite technical and I'll do my best to explain so don't feel stupid if you don't understant totally.

The aperture has the effect of reducing the amount of light that passes through the lens. That is the only aim of the aperture. It has an interesting and useful effect in terms of depth of field but that's not part of this explanation but is something you need to read about later.

So... Lens apertures each let in half the light of the preceding aperture and twice the light the following aperture lets in. The range commonly goes:
1.4-1.8-2.8-3.5-4-5.6-8-11-16-22-32. It is possible to get apertures as wide as f1.0 and Canon did make a 50mm lens that fast. Generally though, 1.8 or 1.4 is the maximum seen.

There are f-stops at the open end that can be strange such as f2.0, f2.5 etc - these are nonstandard f-stops that have been squeezed in by the manufacturer to make their lens appear faster but realistically let in very little extra light.

Now, the effect of a zoom lens is commonly to reduce the amount of light passing through the lens the further the lens is zoomed. SOmebody else can explain that but my understanding is that it's due to light rays spreading outside the sensor/film area.

So... take a lens and zoom out and in most instances the image darkens thus giving an aperture of f3.5 an effective aperture of f5.6 at maximum zoom. Sometimes, camera manufacturers include this in their internal display, updating the displayed f-stop as you zoom to reflect the amount of light striking the sensor.

VR stands for Vibration Reduction. This is a handy thing that allows you to hand hold the lens at lower shutter speeds than you otherwise would. If only all lenses were VR.

[aparmley]

I would assume though that with this lens somewhere around 25mm wide open will be 4.0, then maybe around 45mm wide open will be 4.5 and then around 70mm 5.0 and somewhere around 100mm wide open will be 5.6 - those are guess with the focal lenghts but I'd assume thats how it will work - its not like you are going to be able to shoot at 185mm wide open at 3.5

[mph999]

Thanks for the detailed responces, I'm pleased to see I was on the right lines, though I didn't know about the VR feature, doesn't appear to be mentioned in the manual, unless I missed it.

Once again, many thanks.

Martin

[AlexMonro]

Yes, Zoom lens with a focal length of 18 to 200mm, maximum aperture f/3.5 at 18mm, f/5.6 at 200mm, with Vibration Reduction (Nikon's optical image stabalisation system).

Yes. You have it right. However, on a lens such as this, it's possible to set the lens on f3.5 throughout the range from 18-200 but the light will drop off rendering the transmitted light to f5.6 by 200mm. It's quite technical and I'll do my best to explain so don't feel stupid if you don't understant totally.

The aperture has the effect of reducing the amount of light that passes through the lens. That is the only aim of the aperture. It has an interesting and useful effect in terms of depth of field but that's not part of this explanation but is something you need to read about later.

So... Lens apertures each let in half the light of the preceding aperture and twice the light the following aperture lets in. The range commonly goes:
1.4-1.8-2.8-3.5-4-5.6-8-11-16-22-32. It is possible to get apertures as wide as f1.0 and Canon did make a 50mm lens that fast. Generally though, 1.8 or 1.4 is the maximum seen.

There are f-stops at the open end that can be strange such as f2.0, f2.5 etc - these are nonstandard f-stops that have been squeezed in by the manufacturer to make their lens appear faster but realistically let in very little extra light.

Now, the effect of a zoom lens is commonly to reduce the amount of light passing through the lens the further the lens is zoomed. SOmebody else can explain that but my understanding is that it's due to light rays spreading outside the sensor/film area.

So... take a lens and zoom out and in most instances the image darkens thus giving an aperture of f3.5 an effective aperture of f5.6 at maximum zoom. Sometimes, camera manufacturers include this in their internal display, updating the displayed f-stop as you zoom to reflect the amount of light striking the sensor.

VR stands for Vibration Reduction. This is a handy thing that allows you to hand hold the lens at lower shutter speeds than you otherwise would. If only all lenses were VR.

Sorry, Rhys, I think you might be slightly confused about some of the complex issues here - it took me a while to begin to get my head round it!:o

F-stop numbers are the ratio of of the entry pupil diameter of the lens to the focal length. Because the amount of light admitted is dependent on the area, the standard f-stops are related by a factor of the square root of 2 (approx 1.4). This means that changing the aperture by 1 f-stop changes the amount of light reaching the sensor by a factor of 2. So the standard f-stops are f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32. The strange ones are things like f/1.8 or f/3.5, which are usually maximum apertures imposed by the physical design of the lens.

The reason that you often have a smaller maximum aperture when a zoom lens is set to full zoom is that since the f-stop is dependent on the focal length, it is often difficult to arrange to increase the entry pupil as the focal length increases.

Other issues related to aperture include diffraction, which can be a problem with the short actual focal length lenses used with the small sensors on compact cameras. At small apertures (high f-numbers) at wide angle settings, the actual physical dimensions of the diaphragm opening are so small that the optical phenomenom of diffraction occurs, which basically causes light rays to spread when they pass through a small hole. This can lead to blurry images with f-stops of f/8 or smaller at wide angle with compact cameras.

For a detailed explaination of lens focal lengths and apertures, look here:

http://www.cambridgeincolour.com/tutorials/camera-lenses.htm