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04-23-2009, 08:34 PM   #1
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Need advice on a 14mm FF versus 18mm APS-C lens

I want to buy a wide angle lens and I got a nice opportunity to get a Tamron SP AF 14mm F/2.8 Aspherical [IF], but this lens is for full frame 35mm that also works in APS-C sensors.
Taking the crop factor into consideration, this 14mm will have a FOV of an equivalent 21mm in the APS-C sensor (hoping my reasoning is correct!). Is there a reason I should get this 14mm since I already have the 18mm from the kit lens? Or should I buy a wide angle lens specifically for APS-C sensors to get more FOV?
Thanks for any suggestions.

Andre

04-23-2009, 08:40 PM   #2
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14mm is 14 mm is 14mm, 18mm is 18mm is 18mm. The crop factor or FOV doesn't matter. When they label a lens with a certain focal length, it's not specific to that APS-C or 35mm only, otherwise your kit lens would be labeled 28-70mm instead of 18-55mm.

If you use a 14mm lens on APS-C, it's considerably wider (4mm) than the 18mm of the kit lens. The 18mm end of the kit is less than spectacular anyway (I usually put it to 20-23mm instead). So if the 14mm is a reasonably good lens, it should be considerable improvement to your kit lens.

If you put the 14mm on a film body, the FOV would be much much wider than the 18mm in APS-C. IIRC the 18mm end of the kit cannot be used on film body without vignetting.

Personally I don't use the wide end (18mm) too much, so I can't really justify a 14mm prime... a 35mm prime would probaly be much more useful for aps-c, but this is just my personal preference / use.

Last edited by Andi Lo; 04-23-2009 at 08:53 PM.
04-23-2009, 09:15 PM   #3
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What Andi says is correct, but I'll just put a differenct spin on it. It doesn't matter is the lens was made for film or digital. Crop factors apply to *all* lenses. But they are only relevant if you are trying to compare the FOV of a lens on APS-C to the FOV on film. If you're not using a film camera, there is no point in doing the calculation. A 14mm lens is wider than an 18mm, period. The 14mm lens on APS-C will look similar to a 21mm on film, true - which is relevant only if you actually use a film camera and know what the FOV of a 21mm lens looks like. If so, then you'd also want to realize that 18mm on APS-C will look similar to 24mm on film. Again, no matter how you slice it, a 14mm lens is wider than 18mm lens.
04-24-2009, 02:33 AM   #4
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All the above are absolutely right. Also note that the further below 20mm you go, whether full-frame (FF) like your MZ and ME, or half-frame (HF) like your K20D, each 2mm makes a BIG difference in the image. It's not like going from 50mm to 52mm to 55mm, where the field of view (FOV) doesn't really change much. I use the DA 10-17 and DA 18-55 (occasionally) and stepping from 10 to 12 to 15 to 17 results in much more noticable changes than going from 18 to 20 to 22 to 24, etc. That 14mm lens' FOV should be about 90 degrees; your kit lens at 18mm has an FOV of 76 degrees. Big difference!

04-24-2009, 08:27 AM   #5
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Thanks for the answers. Well I don't really justify a 14mm but it will be a very interesting and fun lens to have. How about the Tamron 14mm F2.8? I can get it for less than $400. I'm going to take my camera an take a couple of shots to compare with the 18-55 (that's my wider lens).
I thought I had the crop factor concept understood but maybe not...we all learn something everyday.
If the lens still there I'll post some shots over here.
04-24-2009, 09:50 AM   #6
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One thing nobody mentioned before is that the image circle of the APS-C lens is too small to be used on full frame 35mm. cameras. You can always use a lens designed for a large image circle on a camera designed with a smaller image circle, but the reverse doesn't work, unless you really like strong vignetting.
04-24-2009, 10:04 AM   #7
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You might want to read this review/test of the Tamron (I assume it's the same one). My take, newer designed-for-digital lenses are probably better if you're never going to use it on film. I haven't shopped around but $400 is probably not a terrible price for a lens that likely cost big $ when new. For digital, I'd personally rather have a DA12-24/4, DA14/2.8, or DA15/4 but those will all likely probably cost a little bit more. Even in the (unlikely) event that Pentax has a full-frame D-SLR, there will likely be better ultra-ultra-wide choices available than that Tamron.

One other note about focal length--the focal length on the 10-17 fisheye zoom is not equivalent to 10-17 on a rectillinear lens; the 17mm fisheye has similar angle of view as the 12mm end on the DA12-24.
04-24-2009, 09:30 PM   #8
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Thanks for all the comments and info. Now I will be able to make a more informed desicion. Probably I will same the money for later or end up buyin a wide zoom. Thanks!

04-24-2009, 09:56 PM   #9
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I don't have the DA 12-24 but everyone's singing praises on it and the images that I've seen are gorgeous =) You might want to save up on that or the sigma 10-20 if you want to go ultrawide.

If you want prime, for quality and speed go with DA 14, for size go for DA 15.
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