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03-19-2013, 04:01 AM   #1
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Choosing Prime lenses

I've had a Pentax k-m DSLR for about 9 months now, with a kit Pentax SMC 18-55mm f3.5-5.6 DA lens and a Pentax SMC 80-200mm f4.7-5.6 FA. The former seems to produce fairly solid results and is a good "general purpose" lins, but I've found the results of the latter rather disappointing (and checking the lens reviews I find I'm nopt the only one!), and I'm thinking about getting some primes.

I'm not a complete novice (had a Ricoh film SLR back in the 90s), but I was using Fuji bridge cameras during my first digital days until last year. I'm not against using older manual focus lenses, what I'm after is clarity/sharpness and utility. I've found the lens reviews very helpful, but the real question here is utility - which lenses do people find they use most? I use my camaera for a LOT of different things - photographing small objects (macro), general family shots, wildlife, airshows etc, so I don't really have a "niche" as such. There's such a bewildering array of lenses avilable (including legacy lenses), which is great, but I need to be able to "chunk it down" somewhat!

I can't afford hundreds and hundreds of pounds to spend on lenses, so which 2-4 lens sizes would you recommend I focus on? Also, can you suggest what lens would be better for me than the 80-200 zoom?

03-19-2013, 04:57 AM   #2
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It's difficult as you seem to have a very wide genre to photograph, with me is much easier 15mm, 50mm, 85mm and 135mm probably cover 95% of what I do.

Have a look back at your recent images and see what focal lengths you been using the most on those zooms. Start there with nearest prime to match your most used focal length and go forward from there.

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03-19-2013, 05:14 AM   #3
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Good point - thanks for the tip!
03-19-2013, 05:21 AM   #4
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Yep, have a look at which leghts you take your shots mostly, and choose accordingly. And for your 80-200 zoom, I find it very weird. I read the reviews, and if you would compare them with the reviews of the F80-200, you wonder what Pentax did with the FA version. I have the F version, and have no problems with sharpness of it. So if you can find one cheap, give it a try. Looking at the reviews, it should outperform the FA version. (or go for the 100-300, apparently even better)

03-19-2013, 05:26 AM   #5
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Some good general starting ideas from Karrowdown, but let me try to expand upon those ideas a bit further - tactfully if I may.

Be cautious as to which 50 one gets. The OP mentioned an interest in macro. Even though one of my favorite Pentax lenses happens to be the DFA 50mm f2.8 macro; I would not in fact suggest it for most people, because it is also one of the lenses that has an extraordinary long focus throw; frequently taking about two second to lock onto a subject.

Two 50's I would suggest based upon price alone... The Sigma f2.8 macro is much faster focusing, but still considerably faster is the Sigma f1.4 (the fastest focusing at that focal - but one has to make due without the macro option).

The entry level Pentax DA 50 is somewhat resistant to the elements, but the construction of the lens leaves a bit to be desired; nowhere near as good as the Pentax FA50.

Two other options for entry level use... Would the 40xs work with the KM?? Some claim it's the same optics as the 43, but with a very limited filter size. Then there's also the Pentax 35mm, but also noting - one can quite easily tell it's a plastic constructed lens as well.
03-19-2013, 05:33 AM   #6
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OK, some more detail - macro work I'm talking about either static subjects where focussing time is really not an issue, or perhaps insects etc, where I'm happy to take my chances! Still, looking at the wide ramge of choice on 50mm lenses out there a faster one would certainly be an advantage (both in terms of wider aperture and focus speed).

Most of my shots fall into the family portrait/landscape variety, though obviously at airshows this is different and I'm looking for a decent lens that can capture good in-air shots of aircraft, and can also do the same for wildlife. Would a shorter tele with a converter/doubler be a good option?
03-19-2013, 05:54 AM   #7
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I'd take a look at the photographs that you have taken with your current zooms lenses and use something like ExposurePlot to look at the focal lengths via the Exif data. An analysis of your photos can lead you to seeing clusters within your current focal lengths that would guide you toward what Prime lenses would best suit your actual photography.
03-19-2013, 05:56 AM   #8
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QuoteOriginally posted by alexmann Quote
Would a shorter tele with a converter/doubler be a good option?
No.

If you are comfortable with a 50mm Macro I would suggest the Sigma A 50/2.8. It's manual focus, but it has the A contacts, and it is 1:1, unlike the Pentax A50/2.8.

Sigma 50mm F2.8 Macro Lens Reviews - Sigma Lenses - Pentax Lens Review Database

Flickr: Search bmcgann1's photostream

For a telephoto zoom there are some good ones that are at the cheap end of the scale...

The SMC Pentax-F 70-210 (Not the Takumar or Pentax-F)

The FA 100-300 4.7-5.8 (Not the 4.5-5.6)

The FA 80-320

The DA L 55-300 is better than the 100-300 or 80-320 but it does cost about twice as much...

03-19-2013, 06:27 AM   #9
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If you want fast apertures and auto focus, be prepared to spend.

If you're trying to save money, an older manual focus macro prime would be a good option. The A 50mm f/2.8 or A 100mm f/4.0 might suit you nicely if you can source them.

The DA 35mm f/2.4 "plastic fantastic" gets rave reviews and would make an excellent cheap autofocus normal lens.

For your airshows, I would look at the Sigma EX DG 70-200 f/2.8 Macro HSM II. Fast, long enough, very quick AF. Cheaper than the newer version but still an excellent performer. I absolutely love mine. The Tamron is apparently also good (and cheaper), but has slower and noisier screw-drive AF.

On the wide side, shell out for the DA 15mm f/4.0 limited or DA 21mm f/3.2 limited. Both are compact gems of the highest order, but have their quirks. A zoom in the 16/17-50 f/2.8 range (Pentax DA*, Sigma EX DC or Tamron) would be another realistic option.
03-19-2013, 08:24 AM   #10
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QuoteOriginally posted by Sandy Hancock Quote
If you're trying to save money, an older manual focus macro prime would be a good option. The A 50mm f/2.8 or A 100mm f/4.0 might suit you nicely if you can source them.
It is out there, somewhere.... I got really lucky and found one on the cheap at a local camera shop (that I don't visit anymore, arrogant bastards...), intending to sell it. Damn LBA - I don't really use it, even though it's very sharp, but I can't bring myself to sell it for what would probably be 100% profit.

THat's one thing I'd add to this discussion, even if it's slightly off topic... beware LBA when you start heading down this path...
03-19-2013, 08:30 AM   #11
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QuoteOriginally posted by Macario Quote
Yep, have a look at which leghts you take your shots mostly, and choose accordingly.
Agreed. Find what focal lengths you have the most affinity for. Once you've done that you can start to consider specific lenses.
03-19-2013, 08:45 AM   #12
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OK so downloaded the program and analysed my past shots;



This represents some of my non-DLSR "history", as I thought it might be more representative. Here are a couple of other analyses - one from a trip to Moscow last year and one just on a cycle ride today;




03-19-2013, 08:55 AM   #13
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The bridge camera focal lengths give a different angle of view than they would if mounted on your DSLR (which of couse they wouldn''t be).

Judging from what you've posted, it looks like 40mm and 50mm lenses would suit you. There's a couple of 40's available and, if you take older glass into consideration, a gazillion 50's.

Both 40's are comparable, quality wise -- or so I've heard.

And I don't think there's such a thing as a bad 50--you'd probably be safe in buying the first reasonably priced one you come across. I just bought a M501.7 (for $30.) which really impresses me IQ-wise. Before I got it, the K 55 1.8 was my go-to lens in that range.

So, you might want to consult this site's lens reviews to see what's available.

Last edited by johnyates; 03-19-2013 at 09:06 AM.
03-19-2013, 08:57 AM   #14
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Yeah the tool uses a "35mm equivalent" as a default - I didn't change it for anything, just ran them all through the same settings...does it make a difference?
03-19-2013, 09:02 AM   #15
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Well, yes. The field of view for any given focal length depends on the sensor size.

So a 50mm 35mm-equivalent on a DSLR would be roughly 35mm.

The crop factor on a DSLR is 1.5.

The 27mm 35mm focal length equivalent field of view on a DSLR would be 18mm.

Last edited by johnyates; 03-19-2013 at 09:06 AM. Reason: precison
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