Zoom Lens For D3100

[kailewjay]

I've just upgraded from my Panasonic Bridge camera to a D3100 with a stock 18-55 lens.

I mainly shoot amateur rugby league so I'm looking to buy a zoom lens.

Budget's not massive but I'm not sure whether to go for a 50-200 or 70-300, am I correct in thinking that the D3100 has a magnification factor of 1.5 so these sizes will increase?

Thanks in advance.

[jet_kit]

Yes, sort of.

In the old days of film (yes, I'm that old) the 'Standard' lens on a 35mm Camera was 55mm (although most manufacturers settled for 50mm). This gave the perspective most like you would view the scene with the naked eye. If you fitted a Wide Angle lens (say 24mm) everything would appear further away and the distance between objects would appear greater. i.e. Something 10M away might look as if it was 20M, and something 20M away might appear 40M. The opposite effect is achieved with a long (Telephoto) lens where everything looks closer and more compressed.

The mathematics are simple. If 50mm is 'standard' then 100mm will make you subject appear half as close (twice the size). These simple sums tend to stick in the minds of us oldies and we still think of a 300mm as a 6x magnifier. However, there is a crop factor to consider because DX digital sensors are proportionally smaller than the 24mm x 36mm format of 35mm and you need to add a 1.5 multiplier (1.6 with Canon). So, the 300mm is the equivalent of a 450mm lens on a 35mm camera. In other words a 9x magnifier.

The tendency with Bridge cameras is they provide a zoom with 'equivalent 35mm' markings. Also their sensors are smaller still, so the effect is even greater. This is why you can get a "200mm" on a Bridge that is half the size of one on a DSLR. First of all, it's 'equivalent' focal length, so it's a 4x magnifier while the real 200mm on a DSLR will be a 6x.

Bridge manufacturers would be more honest if they just used magnifying indicators instead of the equivalents that they do use.

[MattUK]

The Tamron 70-300 is probably your best bet, unless you want to pay more for a faster 200mm lens? What is your budget?

[OldBoy]

Originally Posted by kailewjay

Budget's not massive but I'm not sure whether to go for a 50-200 or 70-300, am I correct in thinking that the D3100 has a magnification factor of 1.5 so these sizes will increase?

Thanks in advance.

No. A 70-300mm lens on a full frame will give the same reach as on a crop camera, only 300mm. What does change is the field of view, as a full frame will cover a bigger area than a crop frame. So that means the FOV of a crop camera using a 300mm lens will look the same as a 450mm lens on a full frame, but the distance to the subject will remain the same at 300mm.

[MattUK]

Originally Posted by OldBoy

No. A 70-300mm lens on a full frame will give the same reach as on a crop camera, only 300mm. What does change is the field of view, as a full frame will cover a bigger area than a crop frame. So that means the FOV of a crop camera using a 300mm lens will look the same as a 450mm lens on a full frame, but the distance to the subject will remain the same at 300mm.

Which effectively means "yes"

[kailewjay]

Budget is about £300

[MattUK]

A man of few words eh.

Here you go: http://www.amazon.co.uk/gp/product/B...DS7ADG7TNG8KZ6

[thefonz78]

I would personally spend another 40 and go for the Nikon 70-300mm

[MattUK]

The Tamron has proven better in tests than the equivalent Nikon

[thefonz78]

I own neither so can't speak personally. Dxomark rate nikon better, Matt who favours the Tamron?. The Tamron will also have a slower auto focus it doesn't have the new peizo motor.