Canon 350D

[ikw101]

As a complete novice to DSLR I'm trying to work out what set up would give me a similar image size to the x8 or x10 magnification I'm used to with binoculars.

At the moment I'm thinking of buying a Canon 350D with a 70-300mm canon IS lens. Based upon 50mm being roughly equivalent to x1 am I being naive in assuming that 300mm = x6 and with the 350D's multiplier of 1.6 I'd end up with something around x9.6 magnification?

Before I part with any hard earned cash I'd appreciate confirmation I've not lost the plot.

Many thanks

Ian

[Malcolm Stewart]

I've pondered this many times, and I think you normally need more apparent magnification on the camera side to compare with binoculars. I don't understand why, buy that's the impression I get.
I use a 30D behind my EF300 f2.8L and a 2x Canon extender. That camera/lens combo definitely has noticeably more magnification than my 7x35 bins.
Some zooms work better than others when used with an extender, and for birding it's definitely worth checking this aspect. Affordable Canon bodies only AF with lenses of f5.6 or wider aperture, and the Canon extender doesn't lie about the effective aperture (unless you tape the pins).

[ikw101]

Thanks for your quick reply on this one Malcolm. Good to see I'm not alone. What really complicates things is the APS-C size sensor that apparently enables an effective angle of view that is 1.6x the normal EF lens focal length. So in effect does a 300mm lens fitted on a 350d (or any other camera with the same sensor size) become equivalent to a 480mm lens?

[Malcolm Stewart]

Thanks for your quick reply on this one Malcolm. Good to see I'm not alone. What really complicates things is the APS-C size sensor that apparently enables an effective angle of view that is 1.6x the normal EF lens focal length. So in effect does a 300mm lens fitted on a 350d (or any other camera with the same sensor size) become equivalent to a 480mm lens?

Yes, very definitely; so my 30D, 300mm & a 2x combo has an apparent focal length on full frame of around 960mm; very similar to my astro telescope! (I use a Manfrotto #393 gimbal head on a Benbo MkI tripod for stability. Hand-holding long lenses is something I know little about.)

When shooting birds on water, I've found that I get better results using the Spot meter feature, but I've still had problems when my aiming point has moved from a dark to a light area on the bird.

[macshark]

Note that there is a big difference between a camera (DSLR) and binoculars. Binoculars form a "virtual" image by refracting the incoming image. The image is effectively formed on your retina. A DSLR forms an actual image on the viewfinder, so the effective magnification you see on the viewfinder of a DSLR is typically less than binoculars.

However, when you take the shot, the mirror flips up and the image is now formed on the sensor. Even though this is a relatively small image (about 24mmx16mm for a 1.6x crop DSLR), it is very high resolution, and can be used to generate a much larger photo on a display or on print. A high quality image from a 8MP or 10MP camera can easily be "blown up" to fit on the largest computer display (e.g. a 24" or a 30" display) and still looks very sharp at normal viewing distance. Or with the right software, it can be used to generate a poster size print.

So don't be surprised when you mount a 400mm lens on your DSLR and don't obvserve nearly as much magnification as binoculars.

A 1.6 crop camera does not change the focal length of the lens. The focal length is a property of the lens and it will be the same regardless of which camera the lens is mounted on. The viewfinder magnification is also not really affected by the crop factor, though this can change from camera to camera. For example, EOS 20D/30D viewfinder magnification is different from 350D/400D though the difference is not much. The sensor size affect how much of the image is "captured" when you take the picture. This is more like the size of the negative. In many cases, 1.6 crop sensors have higher pixel density than full frame sensors, and therefore, if a very high quality lens is used, it is possible to capture more detail at the same distance for telephoto applications. Also, if two images captured by a crop sensor DSLR and full-frame sensor DSLR at the same distance from the subject are blown up to the same size (e.g. 4x6), the picture from the crop sensor DSLR will appear to have higher magnification, though the objects in the image generated by the lens would have been the same actual size in both cases. This is why most people think that DSLRs with crop sensors increase the focal length of a lens. What actually happens is that a crop sensor reduces the field of view.

[ikw101]

Blimey! I've got a lot to learn. A brilliant explanation Macshark. Many thanks.

Ian

[gmax]

Thank you mac ... simple and straightforward ;)