55mm-XXXmm lens distance away?

[CircaM]

I don't know much about focal lengths but a camera I was looking to buy has a 55mm-XXXmm instead of the 18-55mm.

How far away would I have to be from my subject if I kept that lense at 55mm as opposed to 18mm?


Thanks.

 

[Deleted1929]

That depends on the subject size, how much of the frame you want it to occupy and what focal length and camera you use.

 

[nelsonal]

Your field of view is tied to the same ratio as your focal length. So 55/18 is roughly 3x so you would need to be about three times further from your subject to achive the same framing (of your subject).

However unless everything in the frame is at the same distance, Everything else in the frame would be framed differently since your distance away from the other objects did not change by the same ratio. As an example. Let us imagine you were 6 feet from a person with an 18mm lens. To frame the person in the same way you would need to back up 12 feet with a 55mm lens. If there's a tree 6 feet behind the person, you're twice as far from the tree, so less of the tree will show (if there's a hill a mile or so behind them both, considerably less of it will show since the relative distance to it hardly changed).

 

[iancrowe]

CircaM wrote:

I don't know much about focal lengths but a camera I was looking to buy has a 55mm-XXXmm instead of the 18-55mm.

How far away would I have to be from my subject if I kept that lense at 55mm as opposed to 18mm?

Thanks.

Try this Canon Lens Simulator. Jut drag the slider across the bottom to see what effect different focal lengths has on the image.

Ian

 

[Chris R-UK]

CircaM wrote:

I don't know much about focal lengths but a camera I was looking to buy has a 55mm-XXXmm instead of the 18-55mm.

How far away would I have to be from my subject if I kept that lense at 55mm as opposed to 18mm?

Thanks.

You will be talking about an APS-C camera which has a 1.5-1.6x crop factor. You need to multiply the focal length by 1.5 to get the full frame equivalent focal length which is what is quoted for compact cameras.


An 18-55mm lens on a camera with an APS-C sized sensor is equivalent to about 28-85mm full frame (FF). It is a general purpose lens that goes from medium wide angle to short telephoto. If you are photographing a group of people at 8-10 ft you will be able to get 3-5 people in the frame at 18mm but probably only one. head and shoulders, at 55mm.

A 55-200 or 55-250mm lens would normally be used for more distant subjects like wildlife or sports.


You are likely to shoot far more of your photos at 18-55mm than at 55-200mm. If you only get one lens you definitely need the 18-55.

I would check that the offer doesn't include both the 18-55mm and 55-200 (or 55-250). It would be extremely unusual to offer a camera without a general purpose lens like the 18-55mm.

 

[CircaM]

sjgcit wrote:

That depends on the subject size, how much of the frame you want it to occupy and what focal length and camera you use.

 

[trekkeruss]

The 18-55mm lens is the standard kit lens for every manufacturer making DSLR's because 18-55mm is the range that is the most versatile for general photography. It would suck not to have any focal length under 55mm.

 

[nelsonal]

nelsonal wrote:

Your field of view is tied to the same ratio as your focal length. So 55/18 is roughly 3x so you would need to be about three times further from your subject to achive the same framing (of your subject).

However unless everything in the frame is at the same distance, Everything else in the frame would be framed differently since your distance away from the other objects did not change by the same ratio. As an example. Let us imagine you were 6 feet from a person with an 18mm lens. To frame the person in the same way you would need to back up 12 feet with a 55mm lens. If there's a tree 6 feet behind the person, you're twice as far from the tree, so less of the tree will show (if there's a hill a mile or so behind them both, considerably less of it will show since the relative distance to it hardly changed).

I read that but I don't know if I fully understand, maybe if I include an example it might help.

Would the lens be good for everyday shots of dogs and kids playing in a small backyard?

How far would I have to be from a subject if I wanted to do a shoulder up shot with the 55mm?

It might be a little tight depending on how big your yard is, how much you're willing to move, and how much space you want around the kids/dog. 19 feet away would give you an 8 foot framing (in the landscape orientation). There's a calculator here, that you can use to calculate subject size and disatance for a lens (though you have to back out the subject size for a given focal length):

http://www.cambridgeincolour.com/tutorials/camera-lenses.htm

It's about 1/4th of the way down the page, just below the eagle picture example. I believe that Pentax uses sensors with a 1.5x crop factor.

For a head and shoulders shot (I'm giving 2 feet for the subject size which will be a looser framing) you would be about 5 ft from the subject with a 55mm lens. That's probably far enough not to worry about any perpsective distortion (if you do a tight headshot at 55mm there would likely be some distortion). Perspective distortion usually helps or doesn't hurt children's faces but tends to be less flattering on adult faces (though it varies with face shape, it's harder on narrower faces and flatters more the broader the face appears).