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Lens conversion from SLR to DSLR

k p , Mar 24, 2005; 04:39 a.m.

What does a 18-200mm zoom lens become on a DSLR??? Do i multiply it by 1.6, = 28.8-320 ???

Responses

Jeff Medkeff , Mar 24, 2005; 04:52 a.m.

It becomes nothing different than what it is - it remains an 18-200mm zoom. The FOV of such a lens when used with an APS-C sized sensor will be roughly equivalent to a 29-320mm zoom, but other optical characteristics of the lens do not scale by the same factor.

k p , Mar 24, 2005; 05:26 a.m.

What i dont understand is that if i put a traditional 50mm lens on a DSLR...when i take a picture will the output be 50mm or more?

Also i have seen various manufacturers make lenses specifically for digital, i'm assuming that in this case the numbers do not change

Alton Earle , Mar 24, 2005; 06:27 a.m.

The way that I think of it is that from a DOF viewpoint, it is an 18-200mm. However, from a "how much stuff is in the frame" viewpoint, 28-320 is about right.

Skip Douglas , Mar 24, 2005; 06:50 a.m.

KP, there are many threads in this forum covering this topic. However, I'll make it simple here.

The difference between a 35mm film camera and the digital SLR's you refer to is the size of the sensor as opposed to a full-frame 35mm film size. The digital sensor is smaller. It's just like taking a 35mm slide (or negative) and cutting off 1/4" or so all the way around. What's left, if magnified to the original size - as in making a print - looks like you used a longer lens.

Digital lenses are designed to project an image that is not able to fill the 35mm frame, but other than that there is no difference in how the focal length affects the image.

The "normal" lens for a classic 35mm camera is generally considered to be 50mm. The "normal" lens for a typical digital camera with a sensor sized so that the "multiplier" is 1.6 would be about 31mm. Any lens with a focal length longer than "normal" is considered telephoto and any lens with a focal length shorter than "normal" is considered wide angle. To figure out how much telephoto or wide angle, do the math based on the "normal" focal length. Forget the multiplier.

This math is precisely the same as for other film (or sensor) formats. Medium format cameras have "normal" lenses in the range of 80mm to 100mm. Larger format cameras (4X5, etc.) use even longer lenses as "normal".

Rob Bernhard , Mar 24, 2005; 09:18 a.m.

http://www.photo.net/learn/optics/dofdigital/

There's already a ton of info on photo.net if you'd just search before posting.

Jon Austin , Mar 24, 2005; 12:13 p.m.

Giampi . , Mar 24, 2005; 12:28 p.m.

Super-simple explanation:

Get two piece of 8.5x11 paper (like copu paper, etc...)

Draw a circly on both of them having 5 cm diameter (arbitrary amount)

Now, cut 1.5 off the EDGE of one of the papers (again, arbitrary amount).

The circle will now appear bigger in the smaller paper but, it's actually the same size as it was, 5cm.

Michael Lopez , Mar 24, 2005; 06:03 p.m.

Some "digital" lenses can cover both 35mm film as well as smaller digital image sensors. As a practical matter, there does not seem to be any practical quality difference between regular and "digital" lenses designed for FILM cameras, in terms of their image quality on digital cameras. You don't need to pay extra for a "digital" lens.

On the other hand, a digital lens designed to be used ONLY on digital cameras produces lousy results on film.

If you spend $8000 or so on a full-frame digital camera, whose image sensor is the same size as a film image (multiplication factor of 1x), then you need a very high quality, film-compatible lens to produce good images even on the tiny pixels at the edge of the big sensor. With a Canon full-frame DSLR, you'd want the quality of an expensive "L" lens.

Brad Finch , May 17, 2006; 03:50 p.m.

Michael Lopez , mar 24, 2005; 06:03 p.m.

"On the other hand, a digital lens designed to be used ONLY on digital cameras produces lousy results on film."

I keep hearing this, but can't find any posts that actually SHOW this result. Sure, there's a crop-factor. That shouldn't mean that the results are unusable. Just blow it up beyond the under-coverage. A good fine grain B&W film should handle this. Any reason why this wouldn't work for the occasional ULTRA-wide shot, say 12mm on film?

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