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Standard zoom and mid range Lenses with focal lengths larger than 12mm, but no longer than 60mm, includes standard zooms and portrait primes plus some macro lenses.

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Old 29th March 2018
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Lens size versus distance...

An interesting tutorial by Stewart from TP...

https://www.talkphotography.co.uk/tu...-do-i-need.56/
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Old 29th March 2018
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Re: Lens size versus distance...

Unfortunately it requires a log in.

John
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Re: Lens size versus distance...

I will sort that shortly...........
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Re: Lens size versus distance...

Lens Size versus distance and subject size, by StewartR on Talk Photography...

In my line of business I often get people asking how big a lens (ie what focal length) they'll need for a specfic task. It's actually quite easy to work out if you know - or can estimate - how big the subject is, and how far away it will be. Here's how.

The basic equation is:

Focal Length = 0.75 x Sensor Size x Subject Distance / Subject Size

Here are some examples. In each case I'm using a Canon 350D which has a sensor measuring 22.2 x 14.8mm.


Let's suppose we want to photograph a giraffe, like this.



The big giraffe is about 4m tall, say, and we expect to be able to get within about 30m of it. The sensor dimension which matters here is the 22.2mm because we're shooting the giraffe in portrait orientation - the height of the giraffe aligns with the long dimension of the sensor.

So the focal length we need is 0.75 x 22.2 x 30 / 4 = 125mm.


Or suppose we want to shoot a squirrel, like this:



The squirrel is about 50cm long, say, including its tail, and we expect to be able to get within about 10m of it. Again the sensor dimension that matters is 22.2mm, because the length of the squirrel aligns with the long dimension of the sensor.

So the focal length we need is 0.75 x 22.2 x 10 / 0.5 = 333mm.


And a third example: photographing the moon.



The moon is 3,474 km in diameter and its average distance is about 380,000 km. This time the sensor dimension which matters is 14.8mm because we want to fit the diameter of the moon into the short dimension of the sensor.

So the focal length we need is 0.75 x 14.8 x 380,000 / 3,474 = 1,214mm.


Hope this helps. By the way, the experts amongst you will have spotted that the factor of 0.75 in the equation is an arbitrary one to help give you a decent composition - you don't want your giraffe / squirrel / moon to completely fill the frame, and this factor is there to give your subject bit of room to breathe in the frame.

Addendum.............StewartR has a lens hire business. I have no affiliation with him. The article is of interest, its a subject I have brought up before...........http://e-group.uk.net/forum/showthre...ghlight=metres
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Old 16th September 2018
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Re: Lens size versus distance...

Quote:
Originally Posted by Bikie John View Post
Unfortunately it requires a log in. John
Ditto.
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Old 17th September 2018
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Re: Lens size versus distance...

And a Four Thirds (or micro Four thirds) sensor is 18mm x 13.5mm I think.

Subject size and subject distance have to be in the same units as each other (any unit will do; could be inches if you like) whereas sensor size has to be in millimetres (if you want focal length to be in millimetres).
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Old 18th September 2018
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Re: Lens size versus distance...

Could I suggest changing 'lens size' to 'focal length'? There is actually very little relation between the two!
A 1000mm element is thinner than a 10mm one of the same diameter, even before we get into telephoto/retrofocus designs...


I've tended to work with angular FOV when calculating it with sensor size & focal length, but I have to admit this is a MUCH simpler formula to apply.
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