Magnification

[billybob99]

Hi
I was wondering which is dangerous what length of lens I would need to have the same view as from my 8x40 binoculars would it be 320mm as in 8x40 or is that to simple
Thanks

 

[trapper501]

Binoculars are rated as the magnification factor and the diameter of the outer lens, so 8x40 is 8x magnification by 40mm lens.

the diameter of the lens is important because it gives you an indication of how much light you will get in.

I'm sure someone can do that more technically!

 

[Carl V]

The first number is the magnification with the second number being the diameter of the lenses. The higher the second figure, the more light they'll let in.

 

[trapper501]

How about this..

http://www.the-digital-picture.com/Canon-Lenses/Canon-Lens-Magnification-Value.aspx

it says divide focal length by 50, so for 8 times you need a 400mm but the view finder has an effect too.

Read the article because it isn't as simple as that.

 

[billybob99]

Thanks guys I think your right with 400 but does the fact that my camera has a crop sensor come into it? If so then it would 250 ie 250x1.6= 420
argh I've confused myself.....

 

[Carl V]

I think that would make sense. A 250mm lens with a 1.6 sensor would be equivalent to a 400mm. Sadly, I'm not a digital camera expert.

 

[trapper501]

Thanks guys I think your right with 400 but does the fact that my camera has a crop sensor come into it? If so then it would 250 ie 250x1.6= 420
argh I've confused myself.....

As I said, read the article.

The crop sensor doesn't alter the focal length of the lens but alters what actually ends up on the sensor. To turn that into a picture you have to enlarge it which gives you the the view you would get in the middle of a longer lens.

The divide by 50 thing gives you an approximation of the comparable binocular view to that in the view finder. (not exact because of the viewfinder eyepiece.)

 

[billybob99]

I did read it but got all confused when I got to the viewfinder bit, I think 22 years in the motor industry have addled my brain

 

[trapper501]

I did read it but got all confused when I got to the viewfinder bit, I think 22 years in the motor industry have addled my brain

I think all it is saying is that the viewfinder is another lens you are looking through

 

[joxby]

Gawd, is this a parallel universe..

You wait for 10 thousand threads, and then 2 come along at the same time..

 

[HoppyUK]

Making a direct comparison is difficult but it has always been reckoned that a 50mm lens on a film SLR is equal to 1x magnification, therefore 8x = 400mm. Since you have a crop camera, divide by 1.6 or 1.5x so the 250mm estimate is about there.

It's not just a question of focal length but also a question of magnification so format does come into it.

That's the way it has traditionally been done, but while a pair of 8x binoculars is quite good for wildlife and birds, a 250mm lens even on a crop camera will be much too short. For birding, it's almost impossible to have too much focal length.