"Digital" lenses


Link Posted 12/03/2007 - 15:53
Please bear with me on this small ride: We've all been told that APS-C format digital SLR cameras have a smaller sensor than classic 35mm film frames. We've all also been told that this would mean a crop factor on the classic lenses and, consequently, lenses built specifically for APS-C sensors would be smaller and lighter.

So, I was expecting smaller and lighter optics, or faster glass with the same size and weight. I was expecting Pentax to come out with slightly faster primes, like a 30mm F/1.4, a 55mm F/1.2 or a 70mm F/1.4. But instead, we get a 21mm F/3.2, a 35mm F/2.8 (Ok then, it's a Macro lens, but still), and a 70mm F/2.4. Ok, they are small and light, but they are slower than the classic versions.

And zooms: my 18-55mm kit lens is F/3.5-5.6, the 16-45 is F/4 and they are hardly a lot smaller and lighter than their sisters 28-80mm and 28-70mm. The 16-50 F/2.8 seems to be comparable to the F/2.8 Pentax or Tokina sister zooms.

Where is the gain from the smaller sensor? Am I missing something obvious?


Link Posted 12/03/2007 - 16:26
The missing link is that a 16-45mm f4 lens would be unthinkable in 35mm. Ultra-wide to standard....it would be complex, huge and very, very expensive. Even an 18-55mm would be almost as tall an order to produce.
Have you ever seen one with full frame coverage?

Now I know that the coverage is probably similar to a 28-80mm lens, but a 28-80mm lens for APS-C would indeed be small and compact. As are the DA prime lenses on offer.

We never get something for nothing.
Best regards, John


Link Posted 13/03/2007 - 12:05

It makes sense if you think about really wide angle, like wider than we normally had in

35mm. Like less than 28mm. Even so, we do have a few ultra-wide 35mm zooms on the


But my expectations where in the prime area; a 30mm is not that hard to design small,

and I really would like a small, fast 30mm normal for digital. Just look at the Sigma

30mm 1.4: what a beast for a prime! Dimensions: Diameter 75.5mm X Length 59mm; or 2.97

inches x 2.3 inches; Weight: 430g/15.2 oz.

A 50mm is probably the simplest design of all, so it shouldn't be difficult to produce

an APS-C version the same size and weight of my 50mm 1.4, but faster. Or a 70mm. The 77

Limited is bigger and heavier, but it's also a stop faster than the DA70 and has an

aperture ring.

You can see something in the tele designs; the FAJ 75-300mm is F/4.5-5.8 and 385g. If

you compare it to the the DA 50-200mm, for example, it is F/4-5.6 and 260g. And quite a

bit smaller.

So, what might be the problem to build ultra-fast glass in these focal distances that

overlap 35mm and APS-C? Maybe Pentax just chose to build even slower, much smaller

glass. But I can't see a better offer elsewhere, not even on the

Canon/Nikon/Minolta/Sony/Sigma/Tokina arenas...

Or maybe there is really no need for a 31mm F/1.2, or a 55mm F/0.9...


Link Posted 13/03/2007 - 15:13
Up until the release of the K10D, Pentax have been playing the small and light card pretty heavily. Each successive *ist model was the smallest lightest DSLR on the market at its release and the Pancake lenses are designed to compliment those bodys.

Now with the K10D moving into the semi-pro market the roadmap is showing more fast * lenses. I'm sure given time there will be fast short primes too.


Link Posted 13/03/2007 - 17:59
...and Pentax are a relatively small company, I'll bet their engineers are working flat out on the lenses in the current roadmap, so it might take a couple of years to get around to the new primes (maybe released at the same time as the K1D )
Tim the Ammonyte
K10D & sundry toys


Link Posted 13/03/2007 - 18:29
Well, Pentax may be a small company but what about the big makers?...their prime ranges for DSLR's are even less impressive than pentax.

You do get the feeling that the current makers are not really trying when it comes to serious lenses for APS-C.....

I think there may be two possible reasons;...firstly, makers actually have been expecting sensors to go 'full-size' so have not been willing to spend time money on what they think is going to be obsolete quite soon....secondly, it may just be that we are passing thru a period where still camera makers are simply becoming more trivialised and, as with the cameras themselves, they are unwilling to be adventurous and just want to stick to what everyone else can make and sell,...namely, zooms.

Only Oly/Panny/Leica seem to be interested in the more serious prime lenses,..but then they MUST make the 'four-thirds' system work because there will be no 'Full-frame' for them.


Link Posted 14/03/2007 - 11:22
the DA* 16-50 2.8* is lighter than the FA* 28-70 2.8 (and a wider focal range, being equivalent to 24-75)

The DA 18-55 is a LOT smaller and lighter than the FA 28-80 (and a fair bit smaller than the FAJ 28-90)

Primes are a problem - wide primes have to be retrofocus because of the mirror box. To make a retrofocus design requires more elements. If it is going to be fast they have to be big. So it is hard (possibly impossile) to make a small, fast retrofocus lens. Pentax have sacrificed speed for size. Pitty they could not have got the 21mm down to the magic f2.8 though..

Personally I don't see much of a future in these 'limited' lenses, especialy if the 'enthusiast' market goes for the K10D. Then again shove some of the extra software and the 10MP chip into the K100D (and maybe the front wheel) and you have a very desirable small lightweight camera screaming out for those limited lenses...
Tony Milner
Super A, ME Super, MZ6, K5II, Ricoh GR & lenses from 8-500mm
www.amilner.org www.flickr.com/photos/tonymilner
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