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12-27-2011, 09:46 AM   #16
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Pentax K-Mount Lenses Explained: The differences between various Pentax lens series

This is a good link showing the capabilities of each type of pentax mount lens and what capabilities it has.

12-27-2011, 09:48 AM - 1 Like   #17
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Good Morning,

There are two types of lenses, Prime and Zoom:
  • Prime - Prime lenses are a single focus length. 50mm, 100mm, etc. They are somewhat simple, and as such are then able to put the engineering into the optics. They tend to be optically superior. Also, they tend to have larger apertures, and thus "faster" for lower light situations - the f stops have numbers like 1.2, 1.4, 1.7, 2.0, 2.4, 2.8, etc.
  • Zoom - Zoom lenses cover a multiple of focal lengths - like 50 - 200mm. These lenses also tend to be more complex since they need to focus across a range of focal lengths. Also, these lenses tend to be slower with f stops in the 3.5, 4.0, 4.5, 5.6. Also, zoom range is important. This is the ratio between the lower and the upper range - for instance 50 - 200mm is a zoom ratio of 4x (200/50=4). The rule of thumb is 4x is normal. Anything beyond this rang tends to needs to compromise on something within the design. There are exceptions like the Sigma BigMa 50-500mm - however you pay for this as its $1500. The other item is that zoom lenses tend not to be fast - as have wider apertures (low f stops). This is because the lenses tend to become VERY costly and VERY large in order to gather the light and thus becomes VERY VERY Heavy - in weight and LARGE in size.
Lenses also fall into two other types of categories:
  • Rectilinear - These are most of the types of lenses you will see. The optical engineering goes into keeping straight lines straight - they work very hard at minimizing distortion.
  • Distorted lenses - These lenses essentially are fisheye lenses. They pull a greater view in, but are less concerned with correcting the distortion.
Lenses can also be categorized across their focal lengths - as you have noted (and theses focal length ranges vary from person to person)
  • Ultra Wide Angle - 0mm to 15mm
  • Wide Angle - 15mm to 35mm
  • Normal - 35 to 50mm
  • Short telephoto - 50mm to 85mm
  • Telephoto - 85mm - 200mm
  • Long Telephoto - 200mm +
Lenses for the K5 essentially come in two mounts that you will be interested in:
  • K Mount - this is the standard mount
  • M42 Mount - this is a screw in mount that Pentax used prior to 1975. You need an adapter (M42 to K mount). Only use the genuine Pentax mount so that you can ensure that the M42 lens will be able to focus to infinity. - It runs about $25 from Pentax.
These lenses are made by Pentax, Sigma, Tameron, and use to be made by Tokina (you can still find Tokina lenses in the K mount in the used market). However for Sigma, Tameron, and Tokina and there are others, you need to make sure that they have the Pentax K mount.
12-27-2011, 09:51 AM   #18
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very helpful thanks again!
12-27-2011, 10:19 AM   #19
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Lots of good info above, and I see that my CHEAP MACRO article has been cited a couple times. Macro options have been dealt with, so I'll talk about wide-angle options. The good news: some exist. The not-so-good news: they mostly ain't cheap.

The basic questions here are: 1) How wide is wide? 2) What you gonna do with it? and 3) How much you wanna spend?

1) How wide is wide? On our APS-C-sensor dSLRs, the 'normal' focal length (the diagonal of the sensor) is 28-30mm, depending on the exact sensor size. Roughly 16-25mm are 'wide' and shorter than 16mm is 'ultrawide'. Ultrawides with edge-stretching distortion are called Rectilinear; those with edge-curving distortion are Fisheyes.

Pentax makes a wizard fisheye zoom, the DA10-17, the lens that brought me to Pentax, priced under US$500 new. But it's specialized. Sigma makes 8-16mm and 10-20mm rectilinear zooms, priced above US$500, but there are QC issues. The Pentax DA12-24 is great but pricier. I chose the Tamron 10-24 (under US$500) for my rectilinear ultrawide. Other choices in the neighborhood are Pentax 14mm and 15mm primes, and the bargain slightly-fishy Zenitar 16/2.8 for around US$200.

For not-so-wide, there are the popular kit-zoom replacements at 16-45 and 16-50 (Pentax) and 17-50 (Tamron, Sigma), the excellent DA21/3.2 Ltd prime, and various AF and MF primes around 20-24mm. If you're looking to shoot distortion-free 'scapes, use a 28mm or 31mm lens. If a little edge distortion is OK with you, a good lens in the 20-24mm range is fine.

2) What you gonna do with it? Landscapes don't move around much except in 'quake zones, so fast AF lenses aren't needed. I prefer shooting land-sky-sea-town 'scapes with manual primes: 16-21-24-28mm, and my 21 ain't fast. If you're shooting people and other creatures moving around, or in lower light, then a faster lens is good. I use old manual-focus f/2 primes at 24-28-35mm, and the Zenitar 16/2.8 when I have time to compose images that exploit its slight fishiness.

3) How much you wanna spend? I've mentioned some price points above. Except with ultrawides, fairly low-cost manual primes are abundant. I'll argue that AF is less important with wide glass because their DOF is so thick. My M42-screwmount Tokina-made 21/3.8 (well under US$100) when stopped-down to f/11 and prefocused to 2m, has DOF from 1m to infinity -- it becomes a super-duper P&S lens. If your budget extends up to US$500, then the Tamron 17-50/2.8 is probably the best deal around. Pretty wide, pretty fast, very good optics.

Hope I haven't wandered too much. Cheers!

12-29-2011, 02:31 AM   #20
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QuoteOriginally posted by moral decay Quote
i am looking to get a macro or wide angle lens for my k-5... both of them are close to $600... anyone know any other good alternatives? this seems ridiculously high
$600 is fairly inexpensive/normal for a macro lens. Yes, you can get one for less - especially used lenses, but what do you expect a macro lens to cost? The Zeiss 100 mm macro lens for instance is worth $1600, people still search for a copy of the Leica apo macro elmarit, the Voitgländer 125 macro sells for $1000+ used. Check out Sigma, Tamron, Vivitar, et al. for low cost macro lenses. A macro adjustment dioper lens may do the trick for less as would a reversing ring.
Macro lenses are typically some of the best lens designs - even older lenses - look out for older Pentax macro lenses on ebay. Often they show little use and the lack of AF does not matter in for macro photography. I would prefer a used Pentax 100 macro in decent condition over a new third party lens assuming the price is right. The design of the Pentax 100 macro has not really changed over the last couple AF versions... check ebay for A, FA, DA, DFA copys of this lens.
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