How do I find the focal length of my zoom distance?

Diosworld · Jan 2, 2016

Helllo, I am using a Canon Powershot SX530 camera . Google says focal length is 24-1200mm.Google

(Digital Zoom Disabled) As I zoom in, to increase the focal length, I get the following indicators onscreen: 5 cm, 10 cm, 30 cm, 70 cm, 1.0 m , 1.3 m, 1.5 m, 2.0 m, 1.5 m, and finally 1.3 m.

Is there any way I can tell how these distances correlate to exact focal lengths? I want to do an experiment on how focal length affects my face, like this one:

http://i.kinja-img.com/gawker-media...l_progressive,q_80,w_800/18kxy5bbtul32jpg.jpg

Is there any way to find out the exact zoom distance focal length? And is there a method to find the correct distance to stand away from the camera at a specific focal length?

Thanks in advance!

petrochemist · Jan 2, 2016

I don't really see how the exact focal length will help you, as its the display on screen that will be available while shooting.

Are you sure you've copied the on screen display right? The focal lengths at both extremes 50mm (5cm) & 2000mm (2m) are both longer than I'd expect as full frame equivalents (worse still if true focal lengths not including sensor crop). It also doesn't make sense for them to go up to 2m then back down again. Googles listed focal length range looks to be about what I'd expect a super zoom to manage as full frame equivalent.

When viewing your images on a computer, you should be able to read the EXIF which will normally list both real & equivalent focal lengths. In all my cameras the data here is more precise than available on a zoom lens itself. I guess not all picture editors can display EXIF information. I normally use 'FastStone' (free) which displays the basics, an alternative that displays much more EXIF info but not the image is 'Picture Information Editor' (also free though registering gives extra features). Do be aware that some editors can strip EXIF info when saving - I gather Photoshops 'save for web' option does this...

One other point: Despite often being quoted as the source of perspective distortion it's NOT affected by focal length. The factor is the camera position (usually the focal length is selected to fill the frame from a position) being closer to a subject will increase perspective as often seen with wide angle shots. If all the photos are taken from the same distance and cropped to give the same field of view the perspective distortion will be the same (though there may be a shortage of pixels on the wide angle end).

Focal lengths around 70 to 100mm are often quoted as being ideal for portraits as they can fill the view (with head & shoulders) at a distance that gives pleasant perspective. Wider lenses can still do great portraits but they have to be used from a distance typically showing full body & shots with the environment.

480sparky · Jan 2, 2016

I think you're confusing focal length with focus distance. Focal length is a measurement of the optics of the lens. Focus distance is how far the lens is focused at.

KmH · Jan 2, 2016

The focal lengths reported for your camera are equivalent focal lengths not the actual focal lengths.
The equivalence is to a camera that has a full size 35 mm sensor (36 mm x 24 mm).
The sensor in your camera is a tiny 1/2.3" sensor (6.17 mm x 4.55 mm) and has approximately a 4x crop factor.
Consequently, the actual focal length range of your camera's lens is closer to 6 mm to 300 mm (24 mm - 1200 mm / 4x crop factor)

The images you link to show how focal length can effect a person's facial features with subject scale in the image frame constant.
Lens focal length has less effect as focal length increases.
Crop factor does not change how focal length effects a person's facial features in that your 6 mm focal length delivers the same distortion a 6 mm lens would deliver on a full size 35 mm sensor camera.
What would be different is that your camera delivers a small field of view so you would have to be 4x further from the person to have the person's face at the same scale in the image frame as the frame of a full size 35 mm sensor.