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Forum: Troubleshooting and Beginner Help 01-02-2019, 05:57 PM  
HELP with next lens purchase!
Posted By mikesbike
Replies: 58
Views: 1,933
And this depends on what focal lengths you need to have available, and how fast the lens? There is no perfect lens for all needs. The Pentax DFA 24-70mm f/2.8 will give you some wide angle at its shortest setting with APS-C use. It is made for FF use, where it would provide a much wider angle. Of course no problem using it on APS-C bodies where you'd get less wide angle. But with its hood on, it weighs around 2 lbs and is 4.3 inches long without the hood, has a front circumference of 82mm for any filter you might use, and has around $1,000+ price tag. I'm sure a good multi-coated circular polarizing filter of 82mm will be quite costly also. Distortion is very high at 24mm as is wide open vignetting (darkening of image corners), which is to be expected of such a lens.

But do you really need to have f/2.8 speed? The beauty of APS-C is moderate size. The DA18-135mm is only 3 inches long without hood, just a 62mm filter size, weighs under 1lb. with hood, and is priced well under $500. Wide open between 18-70mm, already a much greater zoom range than the DFA lens, it will be at f/3.5-4.5, or about one stop slower than the DFA lens. This means it will need to have the ISO doubled in lower lighting to get the same shutter speed, which will increase noise. For example, If the DFA lens wide open can use ISO 1600 to get the needed shutter speed, the DA 18-135mm lens, wide open from 18-70mm will need ISO 3200 to get the same shutter speed. Your kit lens, however, and many other shorter zoom lenses, will already be at f/5.6 wide open at 55mm, which will require ISO 6400, where noise increase with the K-5 will definitely be significant.

The DA 18-135mm, however, exhibits somewhat lower vignetting and distortion at its widest angle, which is a lot wider than the DFA lens, and at 24mm, which is the DFA's widest, this DA lens comes in at very low distortion and vignetting. What many of us do is get the zoom lens that best suits our needs. It might not be the fastest available, unless that is what we need. If not the fastest, for low light and other fast-aperture needs, we obtain one or more fast primes, which are faster than most fast zoom lenses. Like the FA 35mm f/2, a FF based lens, or the cheaper DA 35mm f/2.4 prime lens. For moderate telephoto there is, of course, the superb FA 77mm f/1.8 Limited.

If requiring a shorter pro-style zoom lens of f/2.8 aperture for APS-C, there are alternative lenses like the very nice Sigma 17-50mm f/2.8 EX DC. It is 3.6 inches long without hood, and weighs just 1.24 lb. with a common filter size of 77mm. No weather sealing, but otherwise a well-built lens with fine performance. I have one for low light and fast action shooting when needed. Its price at B&H has been running at $369. Sometimes a fast prime lens will not cover situations where one needs to constantly change the focal length, so a fast zoom lens is the only answer.
Forum: Troubleshooting and Beginner Help 01-01-2019, 02:33 PM  
HELP with next lens purchase!
Posted By mikesbike
Replies: 58
Views: 1,933
The 24-?mm is going to be more versatile, for use with both FF and APS-C. On the latter, 24mm still provides moderate wide angle, where 28mm would provide none. Any f/2.8 zoom lens will be on the large and heavy side. I have 3 shorter f/2.8 zoom lenses, my very long-time Tokina ATX 28-70mm f2.6-2.8 pro II, my long-time FF Sigma 24-60mm EX DG, and this past year, the for APS-C Sigma 17-50mm EX DC. The Tokina lens is seldom used due to the WA lack. I get fine results from both Sigmas, and choose which depending on whether I will need wide angle with a little more reach, or much wider angle with less reach. How often do I use these lenses? Basically when I need the f/2.8 speed they offer.

Otherwise, why carry the added weight? If I need only a moderate FL zoom range for all around people shots and scenics, it is largely my DA 20-40mm Limited, due to its lightweight compactness, along with very sharp image quality. But for all-around versatility, like going from a squirrel to a cow, for instance, and mixing in some people shots, it is hard to beat the DA 18-135mm lens, especially for the price. Its image quality is much better than generally thought. I suggest the OP visit the neighboring thread, "Which K-70 package?" to see some sample photos by Des on p. 2 which really tell a story of versatility and quality. Even its Bokeh is quite decent. Both its range and its quality, let alone its fast, accurate AF, is better by far than the kit lens.

Of course, the FA 77mm LTD can deliver outstanding bokeh and great refined image quality, along with its fast aperture (I've long had this lens too), but a prime lens will not suffice for the various needs the OP has in mind. This is why we have cameras that can allow changing lenses.
Forum: Troubleshooting and Beginner Help 12-31-2018, 10:24 PM  
HELP with next lens purchase!
Posted By mikesbike
Replies: 58
Views: 1,933
I also agree about the FA 35mm f/2. One of the best primes for Pentax. A bit more money than the DA 35mm f/2.4, but still not all that expensive, and you get a better built lens, faster aperture, and comes with a dedicated hood.
Forum: Troubleshooting and Beginner Help 12-31-2018, 07:15 PM  
HELP with next lens purchase!
Posted By mikesbike
Replies: 58
Views: 1,933
I agree regarding the DA 20-40mm Limited. However, one of the few deficits of the K-5 (I still have mine) is a sometimes shortcoming of speed and accuracy of its AF. But this is not noticeable, as I have found, when using my DA 18-135mm DC WR lens. In fact, this lens has one of the very fastest and most accurate AF of all lenses for Pentax, even on the K-5! It can also produce fine image quality in addition to its versatility. Very well built, yet compact.

For the types of uses you indicate, it would be a top candidate. You can zoom in for a candid, or zoom again for a group shot or to include the surrounding scenery. It is very good for portraits. When used at a virtual ideal FL of 70mm, it can still maintain f/4.5 aperture, and at that FL can produce a well-blurred background, with very good bokeh- which is unexpected for such a lens. I wouldn't be without mine, especially on the K-5. Not a true macro, but it can also produce very impressive closeups.

Since you already have a good, fast 50mm, in addition to the DA 18-135mm, you might also consider the DA 35mm f/2.4 as a normal, very sharp prime. The DA 12-24mmm for an excellent wide angle, or as someone else suggested, the DA 15mm f/4 Limited as a compact alternative.
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