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12-26-2009, 02:01 PM   #1
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Advice on lens for low-light outdoor photo

I have a K-7 and I do some outdoor photographs. During the early sunrise, late sunset and at dusk, the light levels are low requiring to use a dedicated lens with high aperture. In addition, I often take some moving objets (waves, bores, waters) that require a shutter speed of 1/10th s or faster, and the subject is typically about 10-50 m away from the camera.

1- In these conditions (low light and shutter speed 1/10th s or faster), what lens would you recommend?

I noted the following lenses (www.photozpone.de provides some useful comments.):
Pentax Lens 40mm f/2.8 DA ()US$509)
Pentax SMCP-FA 43mm f/1.9 (US$578)
Pentax SMC-FA 50mm f/1.4 (US$369)
Pentax D-FA 50 f/2.8 Macro (US$428)
Pentax Lens 55mm f/1.4 DA* SDM (US$633)

The ratio quality/price is an issue, since I use a Pentax K-7 and the lens would be used only 10-20% of the time.

2- What lense(s) would you recommend among the above ?

3- Further what is your personal experience with outdoor photography in low light and with some motion? Is the auto-focus useful or is it best to focus manually?

Thank you for the advice

12-26-2009, 02:23 PM   #2
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G'day mate.
A prime lens is fine, given their speed, but with such a broad range of distances you're working from you may benefit from a fast zoom like the Tamron 28-75 f/2.8 or Pentax DA* 16-50 f/2.8 - this way the lens would be on the camera a little more than 10% of the time.

Nevertheless from the above list, the FA 50/1.4 keeps coming back as a value for money lens. You'll find its performance at f/2 just brilliant, but for landscapes, the DoF would just be too thin. Focus manually at just before the infinity mark and use a tripod rather than a fast lens in these situations, but that's up to you.
12-26-2009, 02:26 PM   #3
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When you get into really low-light conditions, like dusk and darker, f/2.8 just isn't fast enough to use the less-noisy ISO speeds with. Also, the only reason to use a macro lens instead of another is because of the up-close shots you can get with it, and when you get very close to your subject, you lose even more light. So the 50/2.8 and 40/2.8 are out right off the bat.

Since price is an issue, I would also take the 55/1.4 out of the equation. Not only is it very expensive, but there are cheaper, perfectly acceptable alternatives to that focal length and aperture combination.

This leaves the 43/1.9 and the 50/1.4. They would both get my recommendation. I would personally endorse the 43/1.9. Although it's slower (aperture-wise) and considerably more expensive than the 50/1.4, the wider FOV will probably be more comfortable on your K7, and the image quality is much better at the same apertures. It's also a bit more compact which is a bonus.

But there are alternatives. Some lenses that spring to mind immediately are the Sigma 20/24/28mm f/1.8 series of lenses. 28mm on an APS-C sensor is a very comfortable focal length for outdoor shots, and f/1.8 is extremely fast for the given focal lengths. They are also quite cheap, generally around $350-450 depending on which model you choose. However, they are very large, especially compared to something like the 43/1.9 limited.

In very low-light, like moonlight, even the fastest AF lens I've ever used (f/1.4) could not keep up with subjects all the time. It's just a limitation of current technology. I don't know if you'll be shooting in conditions this dark, though. If you keep it to around sunset and early dusk, the AF should still work very well in any of the aforementioned AF lenses.

Best of luck!
12-26-2009, 03:40 PM   #4
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Ash, Wallyb,

Many thanks for your valuable inputs. I genuinely appreciate.

In practice, I sometimes work at late sunset or early sunrise: there is enough light to see where I put my feet, and to see the incoming waves and tidal bores. The object (wave, bore) is however coming at a speed of 0.5 to 2 m/s, and passing in front of me (20-50m) and then continue past. The tripod is out of question.

The Pentax 43 f1.9 and 50 f1.4 lenses seem the best options: I will have to experiment.

Thank you again for your input.

12-26-2009, 05:00 PM   #5
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hcc, you may want to consider the FA35/2. I believe that it the more ideal lens for those kind of shots and use.
12-26-2009, 08:44 PM   #6
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Good Evening (I think its tomorrow down under), My interest in photography is very similar to yours, except I do not have an ocean near by. I have several thoughts. First if your working in the water, I would probably go with weather resistant (or sealed) lenses to complement the K7. That would also include the limited lenses.

However, the primary problem is light - or lack of light. I usually use wide angle lenses - the 12-24 and more recently the FA31Ltd. The 12-24 at f4 is slow. The most you can do is mount it on a tripod and pay the penalty in terms of shutter speed. My exposures have been on the order of seconds to 10s of seconds, rather than 1/10s. At 10 to 50 meters you have distance working for you in terms of depth of field, - however (and I'll just use the 31) with f5.6 at 10 meters, you have infinite focus (from about 5 meters and beyond). But f5.6 is not terribly fast, especially in low light. Going to f1.8 at 10 meters, you have a DOF of 8.5 meters, which is may or may not be sufficiently wide for what your shooting.

You listed a set of lenses from 40mm to 55mm. I would think that you will need to go wider, in order to get a reasonable DOF at faster apertures. The problem being the FA31Ltd at f1.8 is the fastest wide angle lens Pentax has. Sigma has a 20mm f1.8 in a Pentax mount, and at a distance of 10 meters you would get a DOF of 85 meters at f1.8 which would probably be sufficient (but may lack the resolution you desire). I would think that would be the aperture and DOF you may be needing, however 20mm might be too wide. Any narrower in the focal length, you start loosing DOF at the larger apertures.

I use this online DOF calculator located at...

Online Depth of Field Calculator

... one nice feature it has is the ability to create DOF field tables (over on teh left hand side margin, or at....

Depth of Field Table

This way you can figure out what DOF at what set of distances you are interested in, and then find the corresponding apertures that provide that across what focal lengths. The tables are also printable.

You have a difficult problem. Do you have a minimum focal length that you have found to be usable? I think that would be a good starting point, since that will frame the lens speed issue, along with what is an acceptable DOF based on experience.

The other thing is that aperture is not the only game in town. By increasing the ISO speed coupled with the larger apertures (f1.8) you can pull your shutter speed down. The Pentax KX does offer better ISO at higher levels, but the body is not sealed. It is all a trade off....

hope that helps...

Last edited by interested_observer; 12-26-2009 at 08:50 PM.
12-26-2009, 09:03 PM   #7
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Sigma 30mm f1.4?
12-28-2009, 06:25 AM   #8
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Check out the Voigtlander Nokton 58mm f1.4 SLII. It's MF only, but since you will be shooting at a distance between 10-50m, you will have the lens focused mostly at infinity or near infinity. IMHO, the Voigt has equal or even better IQ and is sharper at most apertures than the FA50/1.4 or even the DA*55/1.4. It is also built like a tank, making it great for outdoors and rugged hikes.

And oh, it costs $379 brand new...

12-29-2009, 05:48 PM   #9
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Thank you everyone for your input and advice. Your experience and expertise is most valuable and your advice is much appreciated.

At the end, I choosed between the Voigtlander Nokton 58mm f1.4 and the Pentax FA 50 mm f1.4. Both received good to excellent reviews from Welcome to Photozone!
Pentax SMC-FA 50mm f/1.4 - Review / Lab Test Report (Pentax FA 50 mm f1.4)
Voigtlander Nokton 58mm f/1.4 SL II - Review / Test Report (Voigtlander Nokton 58mm f1.4)

Both lenses were about the same price at Digital cameras, all other cameras and everything photographic from Adorama Camera, and I just purchased the Voigtlander Nokton that Vinceloc and photozone.de recommended strongly. I will post in due time some examples of the K-7 with Voigtlander Nokton 58mm f1.4.

Last edited by hcc; 12-29-2009 at 05:50 PM. Reason: typos
12-29-2009, 10:25 PM   #10
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QuoteOriginally posted by hcc Quote
Thank you everyone for your input and advice. Your experience and expertise is most valuable and your advice is much appreciated.

At the end, I choosed between the Voigtlander Nokton 58mm f1.4 and the Pentax FA 50 mm f1.4. Both received good to excellent reviews from Welcome to Photozone!
Pentax SMC-FA 50mm f/1.4 - Review / Lab Test Report (Pentax FA 50 mm f1.4)
Voigtlander Nokton 58mm f/1.4 SL II - Review / Test Report (Voigtlander Nokton 58mm f1.4)

Both lenses were about the same price at Digital cameras, all other cameras and everything photographic from Adorama Camera, and I just purchased the Voigtlander Nokton that Vinceloc and photozone.de recommended strongly. I will post in due time some examples of the K-7 with Voigtlander Nokton 58mm f1.4.
that is a great choice as well. enjoy your new lens.
12-30-2009, 05:28 PM   #11
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Great choice. I wish Voigtlander offered more primes for Pentax... with autofocus.
12-30-2009, 05:58 PM   #12
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Sigma 50 f/1.4 (which I own) is probably the sharpest lens (at f/1.4) out there. I like the smeared bokeh, although at (f/1.4) the circles of confusion look a little onion-like--this improves by f/2.0.

Sigma AF 50mm f/1.4 EX DG HSM (Canon) - Review / Test Report

Last edited by asdf; 12-30-2009 at 06:05 PM.
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