Sigma DC lenses

Doug Kerr · Oct 27, 2003

I note with interest the announcement of Sigma's new line of "DC" (digtial camera?) lenses, intended for cameras with APS-C size sensors (such as the 300D). As does the Canon EF-S lens, they take advantage of the fact that the image circle to cover an APS-C size sensor can of course be smaller than to cover a full 35 mm frame.

However, I imagine that (in their Canon forms) these have a conventional EF mount (not a EF-S). The special design properties allowed by the EF-S mount (short back focus) provide extra economy with short focal length lenses (beyond just that afforded by the smaller image circle), but I would expect that substantial economies of design can be achieved without that. (It just means that a more severe "retrofocus" design is needed than if the lens guts are allowed to hang out the back, as with the EF-S lens.) As a result, these lenses will doubtless be of interest to 10D, D60, and D30 owners as well.

It will be interesting to see whether any critters like this show up in the Canoin line in time.

Best regards,

Doug Kerr

Adam-T · Oct 27, 2003

Doug Kerr said:
I note with interest the announcement of Sigma's new line of "DC"
(digtial camera?) lenses, intended for cameras with APS-C size
sensors (such as the 300D).

Unfortunately they are NOT EX series lenses, more like the budget DLs and they're poor performers (the 28-80s, 100-300s etc) - I woud't expect miracles, shame they didn't do EX series ones

Doug Kerr said:
It will be interesting to see whether any critters like this show
up in the Canoin line in time.

I sincerely hope not, the whole thing about the EOS lens lineup is lack of confusion, the only non fully compatible one being the EF-S for the 300D and it can't be bought on it's own . Canon need to concentrate on other areas first such as updating lenses well past their sell-by date such as the 75-300IS (needs Ring USM and better IS, a few optical tweaks to get rid of CA would be good too) , the 100-400L (needs better IS and 500mm), the 28-135IS (better IS and widening to 24mm), Heck, a 400mm F5.6L with IS would go down a bomb too and there is no longer a 100-300L Lens, an F4 one like the Sigma but with IS would be great!.

--
Please ignore the Typos, I'm the world's worst Typist

-- Canon EF35-80 F4-5.6 Owners Club Member #3580 -- ;-)

Doug Kerr · Oct 27, 2003

The announcement of teh Sigma DC lenses and my comments in the post above are sure to bring to the fore thoughts about the EF-S lens and its whys and wherefores. Let me revisit the drill.

The Canon EF-S lens design gives economies of weight, cost, and maybe size from two quite separate matters.

1. Image circle

The image circle of the lens if the area over which it can properly project an image onto the fiolm or sensor. For a lens of any given foacl length and ,maximum aperture, the larger the image circle must be, the greater is the potential cost, sixe, and weight of the lens.

Thus a lens designed only for the APS-C sensor, rather than one that will work as well for a full-frame 35 mm camera, can be less csotly, smaller, and lighter. The EF-S lens is designed only for the APS-C sensor size.

2. Back focus

A we decrese teh focal length of a lens, and hold to "classical" design, the smaller becomes the back focus - the siatance from the rear surface of the last element to the film/sensor plane.

As single-lens reflex cameras came into existience, this posed a problem, since for lenses of fairly small focal length, theback focus was so small that the rear of the lens needed to extend into the camera to the point that it would interfere with the reflex mirror.

The solution was the "retrofucus" design principle, which leads to a lens in which the rear principal plane was in fact outside the lens body, to its rear, thus increasing the back focus for any given focal length. Almost all "wide angle" lenses for SLR cameras have for many years been of the "retrofocus" design. It of course brings penalties in lens complexity, weight, and cost.

If we can allow the lens guts to protrude into the mirror box of the camera by a little bit more, we can reduce the degree of "retrofocus" needed and thus mitigate these cost and weight penalties. Doing so is feasible if the sensor size is smaller, as it allows for a smaller mirror, which can be more readily kept out of the way of rearward-extending lens guts.

The 18-55 mm EF-S lens, with a relatively short minimum focal length, is allowed to project a bit further back than do regular EF lenses, taking advantage of that improvement.

It may be that design for a smaller image circle and design for a shorter back focus are somehow coupled, so that is is especially advantageous to do both in the same lens.

Best regards,

Doug

DRG · Oct 27, 2003

Doug Kerr said:
The announcement of teh Sigma DC lenses and my comments in the post
above are sure to bring to the fore thoughts about the EF-S lens
and its whys and wherefores. Let me revisit the drill.

I happen to endorse the concept of and hope for the increased availability of lenses that take advantage of the engineering tradeoffs possible with a reduced sensor size. Given the outstanding balance of resolution and noise already present in APS-C sensors with their existing pixel areas, it makes sense for manufacturers to turn their attentions to other bottlenecks such as weight and bulk and to include lens design as part of the overall optimization. The 4/3 standard shows that at least three manufacturers are thinking this way (Kodak, Olympus and Fuji, AFAIK). Unless one is striving for even better light sensitivity or greatly improved resolution, the only remaining reasons for larger sensor size are wider field of view with existing lenses and shallower DOF at a given field of view and aperture. The DOF difference is not that compelling compared with APS-C sensors, however, and the wide angle issue can be solved with new lenses, taking advantage of the smaller sensor in the ways that Doug mentions.

It would be interesting to consider the total "legacy" population of lenses out their from the film SLR market compared to the expected number of digital SLRs that might be out there in the next few years. I'd hate to see the 35mm full frame stick around just to preserve value in existing glass collections if this means giving up more optimal designs for future lenses that may eventually sell in great numbers.

Anyone have any marketing data on this? Just how many lenses are out there and what are manufacturers projecting for future sales?

David

Doug Kerr · Oct 27, 2003

David,

I agree completely.

Best regards,

Doug

Phil Wheeler · Oct 27, 2003

Doug Kerr said:
I note with interest the announcement of Sigma's new line of "DC"
(digtial camera?) lenses, intended for cameras with APS-C size
sensors (such as the 300D). As does the Canon EF-S lens, they take
advantage of the fact that the image circle to cover an APS-C size
sensor can of course be smaller than to cover a full 35 mm frame.

However, I imagine that (in their Canon forms) these have a
conventional EF mount (not a EF-S). The special design properties
allowed by the EF-S mount (short back focus) provide extra economy
with short focal length lenses (beyond just that afforded by the
smaller image circle), but I would expect that substantial
economies of design can be achieved without that. (It just means
that a more severe "retrofocus" design is needed than if the lens
guts are allowed to hang out the back, as with the EF-S lens.) As a
result, these lenses will doubtless be of interest to 10D, D60, and
D30 owners as well.

It will be interesting to see whether any critters like this show
up in the Canoin line in time.

Best regards,

Doug Kerr

T3 · Oct 27, 2003

Neither of these DC lenses is very interesting to Canon users. The Sigma 18-55 DC isn't very interesting to 300D users because they are already using the Canon 18-55 EF-S. And other Canon users (of the 10D, 1D, 1Ds) are quite happy using the higher-quality full-frame 17-40/4L. As for the Sigma 55-200 DC, why not just get the Canon 55-200 EF? That lens is also full frame. Maybe your next camera will be a 1.3x or 1.0x camera. In either case, the DC lenses will be no good.

And as someone mentioned earlier, these DC lenses aren't Sigma EX lenses.

Doug Kerr said:
I note with interest the announcement of Sigma's new line of "DC"
(digtial camera?) lenses, intended for cameras with APS-C size
sensors (such as the 300D). As does the Canon EF-S lens, they take
advantage of the fact that the image circle to cover an APS-C size
sensor can of course be smaller than to cover a full 35 mm frame.

However, I imagine that (in their Canon forms) these have a
conventional EF mount (not a EF-S). The special design properties
allowed by the EF-S mount (short back focus) provide extra economy
with short focal length lenses (beyond just that afforded by the
smaller image circle), but I would expect that substantial
economies of design can be achieved without that. (It just means
that a more severe "retrofocus" design is needed than if the lens
guts are allowed to hang out the back, as with the EF-S lens.) As a
result, these lenses will doubtless be of interest to 10D, D60, and
D30 owners as well.

It will be interesting to see whether any critters like this show
up in the Canoin line in time.

Best regards,

Doug Kerr

Donald Cooper · Oct 27, 2003

Phil,

I'm not sure you'd want one. As your comment indicates, you understand that "full frame" is just an arbitrary size brought over from 35 mm. Maybe for digital that size doesn't make sense. As technology develops, we get more and cleaner pixls into a given size.

So perhaps you won't want that large a sensor -- it may be a bad idea.

Phil Wheeler said:
Doug Kerr said:

I note with interest the announcement of Sigma's new line of "DC"
(digtial camera?) lenses, intended for cameras with APS-C size
sensors (such as the 300D). As does the Canon EF-S lens, they take
advantage of the fact that the image circle to cover an APS-C size
sensor can of course be smaller than to cover a full 35 mm frame.

However, I imagine that (in their Canon forms) these have a
conventional EF mount (not a EF-S). The special design properties
allowed by the EF-S mount (short back focus) provide extra economy
with short focal length lenses (beyond just that afforded by the
smaller image circle), but I would expect that substantial
economies of design can be achieved without that. (It just means
that a more severe "retrofocus" design is needed than if the lens
guts are allowed to hang out the back, as with the EF-S lens.) As a
result, these lenses will doubtless be of interest to 10D, D60, and
D30 owners as well.

It will be interesting to see whether any critters like this show
up in the Canoin line in time.

Best regards,

Doug Kerr

Click to expand...

danizoe · Oct 27, 2003

T3 said:
Neither of these DC lenses is very interesting to Canon users. The
Sigma 18-55 DC isn't very interesting to 300D users because they
are already using the Canon 18-55 EF-S. And other Canon users (of
the 10D, 1D, 1Ds) are quite happy using the higher-quality
full-frame 17-40/4L. As for the Sigma 55-200 DC, why not just get
the Canon 55-200 EF? That lens is also full frame. Maybe your
next camera will be a 1.3x or 1.0x camera. In either case, the DC
lenses will be no good.

Remember the sigma barrel is not plastic (compare to Canon 18-55 EF-S)!

T3 · Oct 27, 2003

danizoe said:
Remember the sigma barrel is not plastic (compare to Canon 18-55
EF-S)!

Do you mean the lens mount? Who cares. I've never heard of a plastic lens mount ever breaking or failing. On the small, compact, lightweight 18-55 lens, it's not a big issue. I've used plastic lens mounts on metal camera rings, and metal lens mounts on plastic camera rings, with never any problems. I guess if it gave you more piece of mind, you could go for the Sigma 18-55 DC for its metal lens mount. And at least you could also use it on a 10D. But otherwise, I'm not terribly concerned with plastic lens mounts on lighter amateur lenses. They are sufficiently strong and durable enough for the task.

Doug Kerr · Oct 27, 2003

Adam-T · Oct 28, 2003

......To use a bottom end non-EX Sigma lens on a 1DS or 14N?? .. they already make an excellent range of EX series lenses which perform very well indeed on the full frame 1DS or 14N so why would you want some DL cheapo putting a spanner in the works?

--
Please ignore the Typos, I'm the world's worst Typist

-- Canon EF35-80 F4-5.6 Owners Club Member #3580 -- ;-)

Adam-T · Oct 28, 2003

and you wouldn't want to clap their 28-210 on your 300D ! - not unless you wanted images for resizing to 1.3 Mp maximum!

--
Please ignore the Typos, I'm the world's worst Typist

-- Canon EF35-80 F4-5.6 Owners Club Member #3580 -- ;-)

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