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theironhorse Mar 25, 2011 3:26 PM

noob question regarding focal range..
 
hi,


i have been reading a lot about camera's and photography however one stupid thing that i am unable to understand

is the focal range of a p&s (say 24-400 mm) equal to that of a (24-400mm) on that of a dslr..

if yes please help me get out of this equation.

coz many forums they state about dslr range say 100mm equal to 200mm on a 35mm camera..

please enlighten me..

as this will be a big milestone helping me get my camera..
i am eyeing seriously on hs-20 with range of 720mm..

id they are same i will keep my choice.. if the lower mm range of dslr is eqaul to that of a higher range in p&s i will pick up a d3100 with a 18-55 and 70-200 mm of tamron along with it..

FaithfulPastor Mar 25, 2011 3:52 PM

I have two Canon Cameras.
The XSi is similar to many DSLR's in that the sensor size causes a 100mm lens to "zoom in" as if it were a 160 mm lens. This effect is commonly referred to as "x1.6"

My Canon 5D Mark II is called a "full frame" camera. Because of the sensor being full sized, a 100mm lens will shoot at 100mm.

My guess is that a Point & Shoot does NOT have that 1.6x factor.

Full frame cameras are much more expensive than x1.6 cameras.

That's enough to get you started. If you want to know why or get a more complete explanation, I'd guess some of the really smart guys will chime in soon.

Faithfully yours,
FP

TCav Mar 25, 2011 4:04 PM

The focal length(s) of a lens is (are) a physical property of a lens. But different cameras take advantage of focal lengths in different ways.

When discussing a P&S camera, they are certainly referring to the "35mm equivalent focal length". That is, the angle of view that a 35mm film SLR would have if it were using, for instance, a 24-400mm zoom lens. That would be from 84° to 6.2°.

This is especially important to understand with P&S cameras, because they come with quite a variety of image sensor sizes. But once you've got it, you never need to worry about it again, until you get a new camera.

But dSLRs (and similar canmeras) have removeable lenses, so the issue of the agne of view, and therefore, the "35mm equivalent focal length", changes with each lens you attach to the camera body.

For cameras that have image sensors that are the same size as a 35mm film exposure ('Full Frame') the "35mm equivalent focal length" is the focal length. But other dSLRs have smaller image sensors, so the same focal length lens will have a different "35mm equivalent focal length" on each one. For instance, Nikon, Pentax and Sony all make dSLRs that have image sensors that are 2/3 the size of a 35mm film exposure, and so have a "35mm equivalent focal length" that's 1.5X larger than the actual focal length. Similarly, Sigma's dSLRs have a "35mm equivalent focal length" that's 1.7X larger, Olympus and Panasonic have a "35mm equivalent focal length" that's 2.0X larger , and Canon dSLRs may have "35mm equivalent focal length" that are either 1.3X larger or 1.6X larger.

The vast majority of dSLRs in use, however, use 'Crop Factors' that are either 1.5X or 1.6X, so often people know what others are talking about when discussing those cameras, and just use the real focal length instead of the "35mm equivalent focal length".

rjseeney Mar 26, 2011 1:05 AM

In simplest terms, as long as you are comparing the "equivalent 35mm focal lengths", you will see roughly the same image in the lcd/viewfinder. 35mm was the standard for so long, and most everyone understands it, so that is how the angle of view is described. So if a p&s and DSLR say they have a 400mm equivalent focal length, the angles of view (how much of the frame the subject fills) will be roughly the same. There will be differences in depth of field (how much of the image is in focus) as smaller sensors have greater DOF (that is more is in focus at comparable apertures). In some ways, it is a simple question with a simple answer, however it gets more complicated pretty quickly, and just because a camera has a greater focal range, does not make it better.

peripatetic Mar 26, 2011 7:22 AM

To start with try to convert EVERYTHING to 35mm equivalent focal length, including APS-C DSLR cameras.

So the two options you mention in your first post.

Fuji HS20 has an actual focal length zoom of 4.2-126mm (24-720mm equivalent).

Nikon D3100 + 18-55 actual (27-83mm equivalent) + 70-200 actual (105-300mm equivalent).

So the zoom range of the Fuji is much larger. In good lighting conditions, and where you cannot get close to your subject therefore, the Fuji is a better bet.

Why do you need such an extreme telephoto length?

Ozzie_Traveller Mar 26, 2011 6:59 PM

G'day ironhorse

Understanding focal length "equivalents" is not easy, but once the penny drops as the old saying goes, it will be easy to follow

It comes down to "what angle of coverage does a lens give, and how does this compare with the old 35mm film cameras"

here's a small sketch that might help...
http://i53.tinypic.com/bijn0p.jpg

So, if the maker of a zoom lens for a compact camera found that the lens viewed subjects through angles of 65 degrees in wide-angle mode to 7 degrees in telephoto mode, the maker would state “equivalent to 28 - 300mm” for a 35mm film camera / dSLR 'full-frame' camera sensor.

Hope this helps
Regards, Phil

theironhorse Mar 28, 2011 8:44 AM

hi thanks a ton guys as i was in complete confusion about the focal length for diffrent camera...

i might not need that much telephoto and i also understand that by the end of the day any entry level dslr will be able to surpass any P&S however i like to do landscape, wild life and bird photograpy.. sometimes my fav moon shots as well..

and getting dlsr with a 500mm sigma will be out of my budget and will not be able to carry every where...

thanks again for the guidance... it was very helpful...

theironhorse Mar 28, 2011 8:50 AM

[QUOTE=peripatetic;1212524]To start with try to convert EVERYTHING to 35mm equivalent focal length, including APS-C DSLR cameras.


Fuji HS20 has an actual focal length zoom of 4.2-126mm (24-720mm equivalent).

Nikon D3100 + 18-55 actual (27-83mm equivalent) + 70-200 actual (105-300mm equivalent). QUOTE]


just to bug you again.. as the 35 mm sensor has been taken as standard.
how is that 4.2-126 converts to 24-720mm

and same with nikon.. how do we convert it.. any specific way we can do the conversion. it will be very helpful for me in the future..

TCav Mar 28, 2011 8:00 PM

The "35mm equivalent focal length" for the Nikon DX dSLRs (plus the Pentax and Sony dSLRs excep the A900 and A850) is 1.5X the actual focal length.

There are several different crop factors for P&S cameras, and so are to many to remember, but you can see most of them here: http://en.wikipedia.org/wiki/Image_sensor_format

picsgalore Mar 28, 2011 9:21 PM

TCav, you said: "When discussing a P&S camera, they are certainly referring to the "35mm equivalent focal length". That is, the angle of view that a 35mm film SLR would have if it were using, for instance, a 24-400mm zoom lens. That would be from 84° to 6.2°".

How do you arrive at the 84 to 6.2? I have tough time understanding all this equivalent stuff as you probably can see from this question. Much thanks.


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