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Why Do SLR Lenses Not Have More Powerful Zoom Capability?

by tonyny77 / September 25, 2006 7:20 AM PDT

I'm really ignorant about optics. With that said, I'm wondering why the lenses for SLR cameras (both film and digital) seem to not have the same zoom capability you can easily find in many video cameras and less costly digital still cameras.

If I had to guess, I'd say it may be because the lenses would be prohibitively large for the amount of light the SLR lenses ''pull in'' or because of the size of the film-plane image they yield.

Am I close? I hope there's an optics-savvy forum reader who can answer.



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Your on the right track.
by snapshot2 Forum moderator / September 25, 2006 9:09 AM PDT

DSLR cameras are based on the 35mm film size.

The lower cost DSLR camera have a smaller image sensor than 35mm but compared to the non DSLR cameras it is very big.

A larger target inside the camera means a larger diameter lens. And that means a lot more weight.

You can get lenses that are comparable to a 10X optical zoom. Most will come with a tripod mount on the lens to support the weight.

But that does not keep some people from using long zooms on DSLR cameras.

Check this link:


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Most point & shoots do not have the zoom power that you
by Kiddpeat / September 25, 2006 12:07 PM PDT

think they do.

For starters, they are giving you a zoom ratio rather than a true measure of magnification. They tend to have very wide angle specs are the low end, and a mediocre spec at maximum zoom. However, a mediocre number, lets say 100mm, divided by a very wide angle, lets say 10mm, yields an impressive 10x as a zoom ratio.

The magic is done with a very small sensor. The small sensor can only record a small part of what the lense is seeing. For the lense on a 35mm camera to see only that small section would take an extremely powerful lense. That means the sensor has a conversion factor which boosts the 35mm equivalent of the camera. Is the sensor actually recording the same information as the 35mm camera would? Of course not! It doesn't have anywhere near the surface area as the 35mm frame. Thus, what it sees is comparatively low in resolution and very noisy. Is the small camera ahead in the end? Probably not.

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Thanks, Folks
by tonyny77 / September 27, 2006 12:29 AM PDT

I just wanted to convey my appreciation to SnapShot (Joe), a CNet moderator, and to Kiddpeat for two great and well-written replies.

We sometimes see just problems and solutions posted in the forums. There's nothing wrong with that, but sometimes I just like to know why things work like they do.

Thanks again, folks, and have a good one.


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I should add one more thought.
by Kiddpeat / September 27, 2006 2:10 AM PDT
In reply to: Thanks, Folks

The quality of the lense has much to do with the image that the sensor 'sees'. Things like sharpness, lack of distortion, clarity, etc. come into play. My guess is that the lenses on a DSLR far exceed the quality of the point & shoot cameras.

Indeed, many (most?) of the DSLR lenses cost more than the entire point & shoot camera. The reason is the quality of the image they deliver.

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