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12-20-2009, 02:58 PM   #1
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Pentax 14mm 2.8 OR 21mm 3.2

I would like some input. I am thinking about a new lens for northern lights photography
I currently use a Sigma 20mm 1.8.

I have been looking at a Pentax 14mm 2.8. It looks fast and would give a wide view. However, the added wide view of a 14 mm is not a must - yeah, sometimes the displays are big and it would be nice then.

However, in looking at the 21mm lens - it should be wide enough - especially if I like the views of my Sigma 20mm 1.8.

My question - would the difference between a 2.8 and 3.2 aperature be enough to go with the Pentax 14mm 2.8? I would appreciate some user advice. Note - I like to go with short exposure times 2 seconds to 20 seconds - to capture the definition of the northern lights.

Also, I prefer to use prime lenses for northern lights photography. I have had people out - using wide angle zooms, and they typically do not allow enough light in for some reason.

Thanks for any responses.


Last edited by tgplains; 03-14-2010 at 07:15 PM.
12-20-2009, 03:04 PM   #2
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If short exposures to you are 2-20 secs, then you probably will never need anything faster than f/4.
If 21mm is wide enough for you, go for it. It's a fine little gem, and there will not be any appreciable difference between f/2.8 and 3.2

You'd want to stop down a little anyway to maximise DoF in your landscapes.
12-20-2009, 03:04 PM   #3
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I think the advantage of 21/3.5 clearly is size, even if it is a very unique and capable quality wise.
But if you need the most quality you can get, i'd go for the 14/2.8. Especially with northern lights.
I believe it is a full stop somewhere between 2.8 and 3.5. So the difference may be 15 vs 30 seconds in long exposure times.

In the mean while, i think i must remind that at the wide end, each milimeter have much more significance than at other focal lenghts. This means that 14mm will have strong effect on perspective and considerably wider field of view (92 degreees) than anything 20 and over (~70 degrees).
12-20-2009, 05:57 PM   #4
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From what I have read, 3.2 is only 1/3 stop.

Thus, 10 seconds at 2.8 - would equal 13.33 seconds at 3.2. Not a lot of difference.

Maybe I am talking myself into the 21mm 3.2 lens ...

12-20-2009, 06:28 PM   #5
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If you are happy with the 20, this may already be answered, but way too often I don't find the 21mm to be wide enough. I've use it in my pancake lens array, but I find myself reaching for one of the zooms to get the FOV I need. On the other hand, 14mm might be a little wider than I usually need.
12-20-2009, 08:51 PM   #6
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Da 14 does night time shots wide open well. I think that is probably the only good thing about Da 14 personally.

Still, it is a chunky lens after all.

Da 21 is light and small of course. However, the colour is lacking at times with landscape shots. I prefer Da 21 for street photography really.
12-20-2009, 09:45 PM   #7
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if you already have a 20mm, why would you want another lens in the same focal length?

Get the 14mm. Or look at the 15mm f4 perhaps.

http://www.photozone.de/pentax/463-pentax_15_4?start=1
http://www.photozone.de/pentax/117-pentax-smc-da-14mm-f28-ed-if-review--test-report?start=1
http://www.photozone.de/pentax/120-pentax-smc-da-21mm-f32-al-limited-review-...report?start=1

Interestingly the 21mm seems to be best at f5.6 where as the 14 and 15mm seem best at f8.

The 15mm is better than the 14mm at f4
Tough choice!

Last edited by WerTicus; 12-20-2009 at 09:54 PM.
12-21-2009, 07:48 AM   #8
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QuoteOriginally posted by WerTicus Quote
The 15mm is better than the 14mm at f4
Tough choice!
The first time I saw that, I was amazed. My experience with the Pentax pancakes is that they may not be the ultimate low-lighters, but wide-open is there to be used.

The same has been true of the newer zooms such as the DA 17-70.

12-21-2009, 12:50 PM   #9
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QuoteQuote:
TGplains: My question - would the difference between a 2.8 and 3.2 aperature be enough to go with the Pentax 14mm 2.8? I would appreciate some user advice.
Get the 21mm!
12-21-2009, 01:39 PM   #10
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All this looking at info on these WA lenses has convinced me I will be buying the 15mm soon. I've wanted a pancake version of the 17mm I use constantly on zooms, and it occurs to me from the test results of the 15mm that it would be superb cropped. On my K20d (or future K7), I will still have about a K10d of pixels left.
12-21-2009, 02:58 PM   #11
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The 14/2.8 is a good lens, but if you don't need the wide field of view, I would definitely save money and size and get the 21 (or the 15 as has been mentioned).
12-23-2009, 04:47 PM   #12
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Have them (14 & 21) both.

Given that you have the Sig 20 f1.8 then I would say buy neither.

Why? The 14 mm is a big lens and the fact that you are asking about the 21mm suggests you are also thinking about size.

Therefore why not take a long look at the 15mm as suggested?
That way you get the both of best worlds, compact size and wide. Granted, you dont have f2.8 but for the type of shooting you are talking about you have that covered anyway with the Sigma and as previously said, you will be using long exposures and tripod etc.

I think the 15mm makes a lot of sense.

Cheers
Grant
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