How hard...

[dweezil]

<p>And no...Can it be to build a lens that is not like the super zooms but more like the D70 kit lens (18-70) but with a 3,5 or 4 flat aperture over the whole range?<br>

The way I look at it it would be a great lens and it would not have the drawbacks of some of the current lenses;</p>

<ul>

<li>Limited range that forces you to carry at least 2 lenses with you.</li>

<li>slow aperture if you go the 'super zoom' way and not a constant aperture.</li>

<li>lighter weight than the 2.8 zoom</li>

</ul>

<p>and now we go into whishfull thinking mode:<br>

If we could have this for around say $500 new, I know I'd be buying<br>

or am I only dreaming and is this too hard to create?</p>

 

[Matt Laur]

<p>It's not too hard to make one. It just makes the lens bigger, heavier, more optically, complex to design and build, and thus more explensive. Which is exactly why Nikon's 17-55/2.8 is big, heavy, and expensive. One that's a bit slower at f/3.5 would be a bit smaller, a bit lighter, and a bit less expensive. But it wouldn't be $500, either. Unless it was built like Tamron's 17-50/2.8 - which costs around $425, but doesn't have a built-in AF motor, and won't hold up like its Nikon counterpart.</p>

[kari v]

<p>There's something magically wrong with constant f4 I guess.<br>

(Pentax has nice 16-45/4 but that lacks in range.)</p>

<p>More interesting is why Nikon doesn't have 70-200/4 VR. ;)</p>

[waltflanagan]

<p>Both Nikon and Canon have expensive constant f2.8 zooms and they also have slower consumer level zooms that are f5.6 at the long end. The difference is that Canon makes quite a few constant f4 zooms. Nikon made some older constant f4 manual focus zooms but hasn't updated them with AF. Whether Nikon ever makes/updates these lenses is anybody's guess.</p>

[lex_jenkins]

<p>Years ago, before auto-exposure modes and sophisticated TTL flash were common, a constant aperture moderately slow zoom made sense. It eased the process of using flash, which had to be manually calculated or used auto thyristor settings with limited adjustments.</p>

<p>But since virtually all auto exposure cameras made during the past 20 years can automatically compensate for variable aperture zooms in available light and flash exposures, there's no specific need for a non-variable aperture zoom in the lower and middle market tier. (Desire by photographers, sure, but absolute need? Nope.)</p>

<p>I suspect that lens engineers realize they can offer lenses with fewer optical compromises when they have the freedom to deviate from a fixed maximum aperture. Years ago a similar decision was made for some manual focus "zooms" which were actually varifocals, not true zooms, because the lenses had to be refocused when the focal length was changed. But this design choice enabled better optical performance while remaining within budget.</p>

<p>But, sure, I'd bet a pair of f/4 midrange and moderate tele zooms would be readily embraced by Nikonistas as a reasonable compromise in cost and size. The 12-24/4 Nikkor and Tokina equivalent were very popular, so it's reasonable to anticipate that a 24-70/4 and 70-200/4 zoom would also be successful, even if the optical performance turned out not to be inherently superior to variable aperture zooms. If nothing else it would remove the stigma some photographers feel about variable aperture zooms.</p>

[StuartMoxham]

<p>Nikon did offer the 75-150 3.5 E constant aperture some years ago. It is a manual focus lens very small and light and is great on a small film body like the FM2. It also works very well on my D1h also.</p>

[kuryan_thomas]

<p>I sometimes think Nikon sees more value in supporting sports, people, and nature photography than landscapes. So they make lots of f/2.8 and larger lenses, plus big telephotos for nature and sports, but very few light f/4 lenses for landscapes. They seem to prefer variable aperture consumer grade zooms to f/4 professional zooms.</p>

<p>Don't get me started about the 70-200 range - Canon has 4 zoom lenses with exactly this range, so you can choose between all combinations of f/2.8 and f/4 with VR (they call it IS) or non-VR.</p>

[glenn_c1]

<p>The direct problem with constant aperture lenses is that they actually have a <em>broadly variable</em> aperture - the actual effective aperture of the lens is much larger at the long end than at the short end. To make an example of the 17-55 f/2.8, its effective aperture is 5mm at the wide end and almost 20mm at the long end.</p>

<p>By allowing the lens to have a slower aperture at the long end, the same hypothetical 17-55mm, if it were say an f/3.5-5.6 lens as many of the consumer zooms are, the actual effective aperture would go from 4.9mm to 9.8mm - less than half the max size. For a given optical formula, that means you are using a much smaller piece of glass surface area to transmit the image. This results in several benefits:<br /> - Spherical aberration is less. This requires less correction, so in fact the lens can be of simpler design; or,<br /> - The lens can be built with a wider zoom range while remaining within the allowable range of optical quality<br /> - The lens can be smaller and lighter, as we usually see<br /> - The lens is less sensitive to imperfections in alignment and production variations, allowing lower cost<br /> - Most importantly the physically smaller elements are MUCH less expensive to manufacture.<br /> Or, of course, any combination of the above. Note that you do not necessarily have to give up sharpness. The slower lens can be every bit as sharp and still have less cost, weight and a wider zoom range.</p>

<p>Or, another way to look at it. Take the following three lens characteristics:<br /> - Speed<br /> - Size and price (assume these go together at a given quality level)<br /> - Zoom range<br>

- Quality</p>

<p>Those four qualities are always traded off against one another in lens design. To get more of one you need to give up some combination of the other three.</p>

<p>So there now tend to be fast, expensive, pro zooms that are heavy and generally very good; slower, variable-aperture, less expensive consumer zooms with wider ranges that are also often very good; and 3rd party lenses that mix and match the various elements in a variety of ways.</p>

[tommyinca]

<p>2 cents worth: The economic are, if you want to pay $500 each, they, the lens maker, want you to buy two. If you need one only, they want at least a grand and more from you. If you pay $1000, they have to give you some weight and size, else you won't be happy. They can't also give you everything you need or else the guy next to you who jusy bought four will be become uphappy.</p>