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03-22-2009, 04:33 PM   #1
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17-70 constant 2.8 zoom... Why doesnt it exist?

I was looking around at the available aperture / focal range combination and one thing that made me wonder is that a 17-70 2.8 constant zoom does not exist in any mount from any lens maker. Is this a technical impossibility or is there just no demand for it? I guess the best compromise would be would be a 24-70/2.8 or a 17-70/2.8-4.5. I realize that sometimes I do miss the wide end... Maybe I'll sell my excellent Tammy copy for the 17-70....

Someday Or maybe by then I'd have a K-M with the DA 15 mounted

03-22-2009, 05:43 PM   #2
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Lens designs are pretty much a "look up in design DB and tweak" thing...yes, there is a database of all lens designs and software that helps you design w/ this data.
If it were possible to build this and bring it to market in a usable way (cost vs. weight), the big two would have done this already...

The Sigma 17-70 seems to be the best compromise for this range...
03-22-2009, 06:05 PM   #3
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The thing is the 17-70 design started somewhere, just like (I assume) the design for the 50mm changes until we have the 1.2-2 max aperture range that we have today. Before the advent of DSLRS I assume that the 16-50 design doesn't exist since they were too wide for general use. This means they do add new aperture / focal range combination to the DB every now and then. Maybe one day we will really get a 17-70/2.8, once they can figure it out
03-22-2009, 06:08 PM   #4
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a f2.8 17-70 would kill a couple of lens sales. A 18-105mm F2.8 would annihilate several ranges.

I myself would like an 18-135 range F2.8 for everyday lens but i am guessing manufacturers either do so under license or reverse engineer what is already available rather then make a model that would piss off the original manufacturers.

03-22-2009, 06:14 PM   #5
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That zoom is going to cost Pentax even more to produce while da* 16-50 has a bad reputation already. It is hard to imagine 17-70 f2.8 would be like.

I doubt there will be any more lenses to be announced in the next few years to come. Only the lenses that are supposed to be released last year might be released in the economy down time ...
03-22-2009, 06:43 PM   #6
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QuoteOriginally posted by Reportage Quote
A 18-105mm F2.8 would annihilate several ranges.
And weigh 10 lbs and be huge

You can't pull ranges out of thin air and say "I want it to be 2.8" :-)
03-22-2009, 07:07 PM   #7
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I think a reason is that the users who want fast zooms are often users who are not willing to sacrifice much image quality. It is generally accepted that once you get over ~3x zoom ratio, you have to start making more serious compromises. The 17-70 is said to be not-so-good above 50mm.
Also, the 16-50 is already quite a beast, a 17-70 would be even larger. It's all about what compromises in size, weight, speed, image quality and perhaps most importantly price photographers are willing to make.
03-22-2009, 07:21 PM   #8
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QuoteOriginally posted by EricT Quote
The 17-70 is said
...by some guy on amazon.com who probably doesn't realize that at longer focal lengths you need faster shutter or a more stable set-up to get a sharp shot...

QuoteQuote:
to be not-so-good above 50mm.
photozone's center MTF results at 40 and 70 were pretty close. Note that their copy "showed a slight centering defect at 70mm - a perfect sample may even be slightly better at this setting."


Last edited by asdf; 03-22-2009 at 09:10 PM.
03-22-2009, 08:45 PM   #9
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QuoteOriginally posted by kenyee Quote
And weigh 10 lbs and be huge
Agreed. I think of the Nikon 24-70 constant f/2.8, more so than Pentax's 16-50, as the closest thing to what the OP seeks, and proves kenyee's point. It does weigh 900 g (2 lbs, if not 10), cost USD 1700 or thereabouts, and sport a huge 77 mm ring such that every filter is a pretty serious additional tax atop the $1700. Extend the low end of the range on this thing down to 17 mm (still holding to f/2.8) and it would have to get into absolutely silly cost and weight territory (if this isn't already there).
--Dave
03-23-2009, 08:49 PM   #10
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QuoteOriginally posted by EricT Quote
It is generally accepted that once you get over ~3x zoom ratio, you have to start making more serious compromises...It's all about what compromises in size, weight, speed, image quality and perhaps most importantly price photographers are willing to make.
EricT puts it well. A 17-70mm is not technically impossible, but is basically not practical. Notice how most F2.8 constant lenses have ~3x zoom ratios, (a16-50mm is ~3.1x, a 28-75mm is ~2.7x, a 50-135mm is 2.7x, a 70-200mm is ~2.9, etc) while the 17-70mm lens has a ratio of ~4.1x. To keep it at F2.8 over this ratio would drive up the complexity of the design, and a theoretical 17-70mm F2.8 would most likely be pretty big and heavy, due to the need for large front element and a lot of glass. This increase in glass and materials, would then in turn drive up the cost. So while I also would also love a 17-70mm F2.8, (the sigma 17-70mm F2.8-4.5 is my most used lens), I'm resigned to the fact that it isn't going to happen.
03-24-2009, 01:11 AM   #11
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QuoteOriginally posted by pop4 Quote
EricT puts it well. A 17-70mm is not technically impossible, but is basically not practical. Notice how most F2.8 constant lenses have ~3x zoom ratios, (a16-50mm is ~3.1x, a 28-75mm is ~2.7x, a 50-135mm is 2.7x, a 70-200mm is ~2.9, etc) while the 17-70mm lens has a ratio of ~4.1x. To keep it at F2.8 over this ratio would drive up the complexity of the design, and a theoretical 17-70mm F2.8 would most likely be pretty big and heavy, due to the need for large front element and a lot of glass. This increase in glass and materials, would then in turn drive up the cost. So while I also would also love a 17-70mm F2.8, (the sigma 17-70mm F2.8-4.5 is my most used lens), I'm resigned to the fact that it isn't going to happen.
All things being equal, it should be easier to do such a design for a cropped sensor than full frame. Perhaps Four Thirds would be the place to look for anybody dreaming of such wide ranges at larger apertures.

/Jens
03-24-2009, 03:37 AM   #12
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Tamron has/had a 28-105 f/2.8 zoom.
03-24-2009, 03:50 AM   #13
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QuoteOriginally posted by pederd Quote
Tamron has/had a 28-105 f/2.8 zoom.
I just looked it up. Looks interesting although the reviews are mixed =) Some love it but most noted lack of contrast (but not sharpness). Although the size is reported to be quite big, looks like it's still manageable. I hope it's only a matter of time before they crack the 17-70/2.8 formula. I won't get my hopes up for the first version to be any good, I guess. Until that day comes I'll use my 28-75.

I was actually thinking whether it's possible to reverse the aperture... say 17-70/4.5-2.8? If it's possible we can get best of both worlds since usually the longer focal lengths need faster shutter speed. But i digress since this is probably just pipe dream =)

Last edited by Andi Lo; 03-24-2009 at 03:56 AM.
03-24-2009, 04:04 AM   #14
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I have DA 17-70mm f/4 and FA 35mm f/2 and love that combo. These two lenses costs about $800? A good 17-70mm f/2.8 would cost alot more and probably have worse IQ.

The only thing I think is stupid about DA 17-70mm and lenses like it, is that it's not buildt like DA*50-135mm. I'm not thinking about weathersealing! I want zoom's in the normal range to have inner zoom. The same lens size at 17mm and 70mm, like the DA* 50-135 have.

Does anyone know if Hoya/Pentax wants to receive idea's from their customers?
03-24-2009, 06:22 AM   #15
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QuoteOriginally posted by NorthPentax Quote
I want zoom's in the normal range to have inner zoom. The same lens size at 17mm and 70mm, like the DA* 50-135 have.
Does anyone know if Hoya/Pentax wants to receive idea's from their customers?
I want to make gold out of glass too. Why can't I get these steel companies to do that for me?
Hopefully someone will figure one out, but the issue is probably still physics...
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