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Note: This lens also seems to be sold under the Phoenix,Vivitar and Sirius
brand names.
Build
About the same length as a standard 28-80 zoom lens, but a bit narrower this
metal shelled lens is constructed quite well considering its price. It's weight
of 0.49kg is not too intrusive, although it does require 72mm filters to fit its
protuding filter ring.
I've had the lens for a couple of years, during which it's gone through a
couple of periods of heavy use - without any wear or tear being visible as
yet.
Optical
Any 11 group 14 element design sold as cheaply as this lens is will entail
compromises. Bearing that in mind performance is reasonable, although flare and
image falloff can be a problem. It's claimed that the maximum aperture is F4-4.5,
but I'm unconvinced as the viewfinder image seems a lot duller than with other
lenses I own with equivalent maximum apertures. Fortunately focusing with such
wide angles doesn't really need to be all that exact and art.
Stopping down to F8 or F11 will produce the best results - using it wide open
is a recipe for soft, dark corners in the resultant image.
Handling
A straightforward two-touch zoom, with reasonably wide focus and zoom rings,
and a well weighted aperture ring, this lens has good handling characteristics,
only being let down by the rather murky viewfinder image. No depth of field or
infra-red index are marked however (a common zoom lens problem), which is a
little annoying, especially as a lenses of this focal length do lend themselves
to use of hyper-focal distances.
Compatibility
Mostly the Centon has been used on a Pentax P30T body, loaded with Fuji Velvia
(which is not exactly noted for exposure latitude), where it has provided correct
exposures under a wide range of circumstances. Coupled with a Pentax Z1p,
shooting Fuji Provia slide and Fuji Reala print film has also provided acceptable
results, without necessitating the use of exposure bracketing so far.
Price
I paid 99 poumds Sterling (160 USD) in 1996 for this lens (from Jessops in the
UK). As there are no close competitors currently in the market I feel this is
good value. In the US I've seen the lens in it's Vivitar incarnation for as
little as 139.95 USD.
Conclusion
I bought this as a introduction to use wide angles - to see if I liked the
results and to find out whether I would be justified in spending more on a better
quality replacement. For that purpose it has been an excellent choice, and some
of my favourite images to date have been taken with this lens. At the present
time I am only waiting for the Tokina ATX-Pro wide angle to hit the market (in
Pentax fit) before purchasing a replacement (as the only Pentax manufacturered
wide angle zoom is a unique, but less useful, fish-eye design), but I expect the
Centon to go on providing service, coupled to my P30T, for some time to come.
copyright 1998 Steve Graham
The picture at the top is of the Forth Road Bridge, near Edinburgh in
Scotland. It was a grab shot using a Pentax P30T, Centon 18-28mm F4-4.5 wide open
onto Fuji Velvia. The vignetting on the full slide has to be seen to be believed,
which is why the image is cropped into a panoramic format.
While focusing is less critical for a wide angle lens like this, I usually use one of two tools to focus: the focus indicator in the viewfinder or the distance scale on the lens barrel.
A minor shortcoming of this lens is that the aperture is not indicated in the viewfinder if the the aperture ring is turned away from "A". However, the camera can still detect what the aperture setting is, since I can see it varying the shutter speed appropriately. This is true for both my PZ-70 and Z5n. This may be true for all KA lenses on autofocus bodies. This is my only KA lens.
I've a Vivitar 17 - 28 in Pentax mount and think it has a real good price/quality ratio. However, as you may expect with a so wide - angle lens, any filter causes vignetting at under about 21 mm., and you can't sometimes judge it and adjust accordingly while taking a picture (dim viewfinder, not 100% of area visible). Since I often use a polarizer, I determined exactly (on a ground glass) the extent of vignetting and simply engraved a mark in the focusing ring that lets me know exactly when the filter will start to show up.
