SLR lenses VS compact lenses!

[mikaelwardhana]

Hi guys...

Has any of you ever think why compact camera lenses seem to be ...errr...better spec-ed?

Im looking at the CANON S2 IS specification now. This camera has 36-432mm equiv. (12x zoom) with a very big aperture of F2.7-3.5.

My question is...how can this be

I know that the lens quality of a compact camera can never be as good as an SLR lens but why I have never seen any 12x zoom lens for an SLR with a big aperture of 2.8 with Image Stabilizer ??

Is it possible to manufacture a lens with a spec of...let's say ... 18-200 f2.8 IS?

[JohnC]

It is quite easy to be. The lens on the Canon S2 is a 6mm to 72mm zoom. It is a variable aperture. At 6mm it is f/2.7, at 72mm it is f/3.5. If it was a constant 2.7 it would have to be much larger, heavier, and more expensive. 2.7 isn't all that big an aperture for such a short lens.

The S2 can probably not stop down past F/8 due to the short focal length, so the range of full f/stops is 2.7 (3.5), 4, 5.6, and 8. And also because of the short focal lengths it will be practically impossible to do any selective focusing, too much depth of field. This might also cover any small focusing inconsistencies.

And the lens only has to project an image circle to cover a tiny sensor (about 4mm x 5.5mm) instead of 24x46mm. And the lens is built specific to the body, no worry about a mirror being in the way, so it can be as close to the sensor as it needs to be.

My guess is that someone could manufacture an 18-200 2.8 constant aperture zoom lens. But I don't know if anyone would want to deal with the size, weight, and cost.

John

[mikaelwardhana]

thank you John C for your explanation...

Yes...it would be very very nice though if there's a 18-200 f2.8 IS lens.

Even if it weigh 2kg, with a filter thread of 87mm, with a cost of over $3000, I think it still would be nice to have it around.

One and for all lens that is! imagine how light your bag would be to have this one and only lens.

[JohnC]

I don't know if it would be much lighter. Right now I typically carry a 16-35 2.8 and a 70-200 2.8. Sometimes add a 300/4. Or I might switch out the 16-35 for a 24-70. That distributes the weight between the camera and the bag. I think I would prefer that over having all the weight in one lens always on the camera.

I have not tried the 28-300, though. Maybe my mind could be changed.

John

[sean_buerger]

Hello,

it was mentioned, that the lens quality of compact cameras can never be as good as that of a (D)SLR.

Why is that so? Actually compact cameras with their smaller size image sensors might be helping in designing a suitable lens for it. The smaller the image sensor, the shorter the actual lens focal length (at the same 35mm equivalent). The lens needs to be able to deliver just enough resolution for the used image sensor.

I use a somewhat high end digital compact (where the lens can hardly be described compact ). I find that the lens is very well suited for the camera. It does have less problems than comparable zoom lenses on my DSLR.

Just my opinion. Sean.

[JohnL]

Sigma makes an 18-200 but it's not f/2.8. It's 3.5 at the wide end, slower for tele. I think it's a DC lens, which means it only covers the 1.6x or 1.5x crop factor formats.