How far is 100mm ??

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Steve Ray - 19 Jul 2007 13:11 GMT

Guys

If I have 2 DSLRs with the same linear or no additional zoom (for example
the EOS350 has a built in zoom of x1.4)

So, using 2 EOS350Ds......

1 of these cameras has a 200mm lens at full zoom and the other has a 300mm
lens at full zoom focused on the same image and positioned next to each
other (using the same exposure settings). Lets say that the zoom lens(es)
are made by the same manufacturer as well (just incase it makes ANY
difference at all)

How far would I have to walk forward to get the same image in the view
finder with the 200mm lens as with the 300mm lens

Please don't tell me 100mm or 1m ;-)

Thanks in advance

Steve

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Trev - 19 Jul 2007 13:43 GMT

> Guys
>
[quoted text clipped - 17 lines]
>
> Steve

There is a difference in angle of view 200 aprox 9 Deg 300 x 1.4 = 420 and
around 7 deg that's not a lot but how far you walk is dependent the distance
of the point of focus say 300 lens focused at 1 meter using the 200 just
lean forward.

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A.Lee - 19 Jul 2007 17:38 GMT

> So, using 2 EOS350Ds......
> 1 of these cameras has a 200mm lens at full zoom and the other has a 300mm
[quoted text clipped - 5 lines]
> How far would I have to walk forward to get the same image in the view
> finder with the 200mm lens as with the 300mm lens

Get your calculator out, and follow the formulaes on this page:
http://en.wikipedia.org/wiki/Angle_of_view

On a digital body(apart from the few full frame bodies), the effective
focal length will be longer than the 'nominal' size stamped on the lens.
Alan.

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Michael J Davis - 19 Jul 2007 18:19 GMT

Steve Ray <nochance@all.com> observed

>Guys
>
[quoted text clipped - 13 lines]
>
>Please don't tell me 100mm or 1m ;-)

By 'forward' you mean same framing, with the camera in your hand?

The answer is one third or the distance.

Mike

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Adrian Boliston - 19 Jul 2007 20:26 GMT

> Guys
>
[quoted text clipped - 11 lines]
> How far would I have to walk forward to get the same image in the view
> finder with the 200mm lens as with the 300mm lens

Just to be a bit pedantic, remember that the minute you move closer you will
change the *perspective* so you will never get the "same" image when you
move closer.

cheers adrian www.boliston.co.uk

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Tony Polson - 19 Jul 2007 20:26 GMT

>Guys
>
[quoted text clipped - 13 lines]
>
>Please don't tell me 100mm or 1m ;-)

It is in exact proportion to the ratio between the focal lengths.

For example, taking pictures of the same object, if the 200mm lens
fills the frame with the object at a distance of 20 metres, the 300mm
lens will fill the frame at a distance of 30 metres.

If the 200mm lens fills the frame at a distance of 10 metres, the
300mm lens will fill the frame at a distance of 15 metres.

You have a ratio between the focal lengths of 300/200, which is equal
to 1.50. So for any object that fills the frame at a certain distance
with the 200mm lens, the distance at which the same object will fill
the frame with the 300mm lens will be 1.50 times further, or in other
words, 50% further.

However, the pictures will probably look different, because the
relationship between multiple objects will change as you change to a
different positioning to take the shot.

>Thanks in advance

I much prefer to be thanked afterwards. It is far more sincere.

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