Which lens today ?

Canon Bob

Canon Bob

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Bob
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This may be obvious to some but maybe not to everybody........

Going on a shoot and need to know what focal length is required?

How far away will you be from your subject....Distance
How wide is your subject (frame).................Width
What size is my sensor...............................Sensor

The focal length required will be obtained by using the following equation;

(Distance / Width) x sensor size = required focal length

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Example 1.....you're going to shoot motor sport. You expect to be 45 metres from the track and want to get close-ups of the cars.....a 5 metre frame width (car + a little bit of background)...and you're using a Canon crop body.

Your required lens would be....(45 / 5) x 22.5mm = 202.5mm

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Example 2.....you're out to catch a bluetit. You expect to be 4 metres from the birdie and want a 15cm frame width.

Your required focal length would be...(4 / 0.15) x 22.5 = 600mm

(if you expect to be 20 metres from the bird...I suggest that you stay home and work on a money making scheme to fund your 3000mm lens requirement!)

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If you're using a full frame camera then substitute 35.8mm in place of the 22.5mm in the above equations.

I hope that helps someone out there make the right choice.

Bob
 
This sort of thing appears at 03.00am in New Zealand with jet lag!
 
Great guide. Thanks very much. Now I just need to remortgage for my 3000mm lens.
 
Just to check that I have this right:

The 1.6 crop of canons is worked out by 35.8/1.6 = 22.5 rounded to the nearest .5

So Nikon's 1.5 crop should be 24?

Cheers

Panzer
 
Panzerbjorn said:
Just to check that I have this right:

The 1.6 crop of canons is worked out by 35.8/1.6 = 22.5 rounded to the nearest .5

So Nikon's 1.5 crop should be 24?

Cheers

Panzer
Click to expand...

Yep, that's correct.
Bob
 
Thanks CB. That's actually very useful to me.
 
Canon Bob said:
Example 2.....you're out to catch a bluetit. You expect to be 4 metres from the birdie and want a 15cm frame width.
Your required focal length would be...(4 / 0.15) x 22.5 = 600mm

(if you expect to be 20 metres from the bird...I suggest that you stay home and work on a money making scheme to fund your 3000mm lens requirement!)
Click to expand...

birdy961 said:
Cheers Bob
Very Helpfull, where do you get these 3000mm lenses then!:LOL:
Click to expand...

I was saving up to have have one custom made and then realised what it would cost. I have now invested the money in a plan to genetically engineer a 2 metre tall 85kg bluetit...it was the cheaper option.:nuts:
 
Nice one Bob.
 
Thanks Bob, very interesting information.

Hmm :thinking:. I have the bits for making my scope have a focal length of 3000mm. It'll never work though unless the bluetit was stuffed and glued to the branch.
 
Canon Bob said:
I was saving up to have have one custom made and then realised what it would cost. I have now invested the money in a plan to genetically engineer a 2 metre tall 85kg bluetit...it was the cheaper option.:nuts:
Click to expand...
When you put in the spec for that bluetit, could you request a slow take off and fly mode as well so I have a chance of getting one :LOL:
 
susie said:
When you put in the spec for that bluetit, could you request a slow take off and fly mode as well so I have a chance of getting one :LOL:
Click to expand...

I strongly suspect that an 85kg Bluetit will be slow take-off.

(Interesting resurrection of a 13 month old thread)

Bob
 
Nice info, but I don't understand it.



Being English I only understand feet and inches :LOL:
 
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