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03-01-2010, 07:05 AM   #1
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Pentax LX as night camera

I'm curious as to whether anyone here has any experience using the LX as a camera at night for taking long exposures off a tripod. The way I see it, with its low-light sensitive metering and shutter-speeds up to 125secs in automatic mode, it seems perfect for that kind of thing.

The concern I have with the Pentax SLRs I have (K2, KX, Me Super and SuperProgram) is the need to use the bulb mode and possibly an external light meter too. Assuming the light meter would do me any good. The LX's meter seems to easily trump external meters going down to a preposterous EV -6.5.

Is my thinking here correct?

Cheers,
Tassilo

03-01-2010, 04:22 PM   #2
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There are light meters that exceed -6.5 EV. But don't be surprised if they cost more than an LX camera.
The LX meters through the lens during the actual exposure, so it is likely to be more accurate as well.

The original Olympus OM-2 has a similar specification but reportedly can make autoexposures several times that length.
Interestingly the later "improved" OM-2n has an absolute limit of 2 minutes for autoexposures.

I wonder if the LX exceeds the stated specification in actual use, and if the actual maximum changed over its 20-year production history?

With exposures of this length reciprocity failure becomes a real issue. I'm not certain how one copes.
I wonder if the exposure compensation dial behaves normally at the low extreme of the range?

FWIW I have seen wonderful night photos made with OM-2 and LX cameras.

Chris

Last edited by ChrisPlatt; 03-01-2010 at 04:37 PM.
03-01-2010, 05:13 PM   #3
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Is t -6.5 the real figure? That's impressive for near any meter, at least as usually reckoned, never mind a built-in one.
03-01-2010, 05:15 PM   #4
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Thus spake ChrisPlatt:

> The original Olympus OM-2 has a similar specification but reportedly can make
> autoexposures several times that length. Interestingly the later "improved" OM-2n
> has an absolute limit of 2 minutes for autoexposures.

I am wondering about this myself. I found online a claim that someone's longest exposure was 15 minutes.

The laws of reciprocity are also bothering me and they look to be a real show-stopper. I just looked it up in the fact sheet for Ilford's Delta 100: A measured exposure of 30 seconds does in fact require an actual exposure of 150 seconds, or so they claim. That's more than two stops off! Other Ilfords are in the same range. So even if an EC of 2x works, this would not be enough for even longer exposures. T-MAX 100 only appears to require +1 stop of light but I'd be very unhappy to part with my beloved Ilford film.

Meanwhile, I just stepped out onto my roof here and tried my Seconic light meter. It's hopelessly inadequate, of course, and reads nothing. I am hearing good things about the Gossen Luna meters, and used specimens are cheap. So there's maybe a fallback.

Cheers,
Tassilo

03-01-2010, 05:16 PM   #5
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QuoteOriginally posted by ChrisPlatt Quote
With exposures of this length reciprocity failure becomes a real issue. I'm not certain how one copes.
Chris
My rule of thumb was always: double the exposure every time you feel bored with a long exposure or impressed by a short one.

It's like push-processing: past a certain point, you're basically coping with diminishing returns.

Last edited by Ratmagiclady; 03-01-2010 at 05:25 PM.
03-01-2010, 05:33 PM   #6
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The LX is the perfect night-time camera. It works on auto at any light level. I've tried up to 45 minutes.
These images are shot with the LX on Auto:



03-01-2010, 05:44 PM   #7
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LX and reciprocity failures

So I've dug around a little and I found some encouraging evidence that the LX somehow compensates for it, namely here and here. It isn't strong evidence and there seems to be a bit of hand-waving too because no camera should be able to handle this correctly without knowing the exact type of film used.

Maybe the LX has a few unexpected tricks up its sleeve. It is afterall popular for astra-photography.

Cheers,
Tassilo
03-01-2010, 05:47 PM   #8
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QuoteOriginally posted by Pål Jensen Quote
The LX is the perfect night-time camera. It works on auto at any light level. I've tried up to 45 minutes.
These images are shot with the LX on Auto:
Wow, this is excellent! I'm getting excited already as you presented a pair of compelling reasons to get an LX purely for that one purpose.

Cheers,
Tassilo

03-01-2010, 06:09 PM   #9
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wow! What lens were you using on these?

QuoteOriginally posted by Pål Jensen Quote
The LX is the perfect night-time camera. It works on auto at any light level. I've tried up to 45 minutes.
These images are shot with the LX on Auto:



03-01-2010, 06:11 PM   #10
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QuoteOriginally posted by Blue Quote
wow! What lens were you using on these?
The first one is shot with 31 Limited (it might be the A 24/2.8 but I don't think so)
The second one is the 77 Limited.
03-01-2010, 09:15 PM   #11
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Terrific shots. I'm looking forward to trying it now.
03-01-2010, 09:25 PM   #12
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QuoteOriginally posted by Pål Jensen Quote
The first one is shot with 31 Limited (it might be the A 24/2.8 but I don't think so)
The second one is the 77 Limited.
They are excellent shots regardless and I like that 1st one the best.
03-02-2010, 11:43 AM   #13
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The main drawback with using the LX at night is you can't admire its unearthly beauty.
03-02-2010, 03:43 PM   #14
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Nah, because of reciprocity failure, automatic exposure and metering has limited value for exposures beyond the realm of a few seconds-- at least this is true with most films. The 2 stop +/- compensation dial on the LX doesn't buy you much for exposures that run into many minutes or hours because reciprocity failure tends to be logarithmic, not linear. (e.g. an reciprocity-failure compensated 2 stops up from 30 seconds could run to something like 30 minutes or more, not merely 120 seconds).

One thing I do find the LX to yet be truly exceptional at is precise 1/3 stop bracketing in the several second range, in lighting that may be changing while the shutter is open, which few other cameras can do (the Olympus OM-2 and it's successors are all that come to mind).

If you haven't got a good read on what your particular emulsion does in a given night photography circumstance, extensive bracketing is highly recommended. Fuji transparency emulsions like Astia 100F and Kodak Portra VC for neg films have excellent reciprocity characteristics, incidentally. But they still require compensation for reciprocity failure.

Likely the prime reason for the LX's one-time popularity in astrophotography was that on manual- timed bulb exposures running to an hour or more, batteries are unnecessary. Digital doesn't suffer reciprocity failure and because of this it was a huge sea change in astro-photography. This happened a number of years before DSLRs became mainstream. Resultingly, few serious astromers are using film, except possibly for star trails.
03-02-2010, 04:05 PM   #15
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The 125s limit of the LX is only valid at ISO100 f/1.4. Any other combination will yield other max. exposure times. I used the LX a lot for nighttime shots and it proofed to be very capable. I use mainly slide films.

For reciprocity failure, there are several approaches to either ignore it or work with it.

1. I actually find reciprocity failure helpful for nighttime shots, as it "automatically" preserves the nighttime mood, which would be ruined by an exposure according to any light meter reading!

2. modern colour film, especially negs have a very high reciprocity coefficient of 0.96 or better. The best film was Kodak Pro Gold 400 in that regards, but even its lowly successors are not too bad. Only old emulsions, like Tri-X (especially so!) exhibit worse behaviour. So, any exposures under 1 minute are more or less carefree. And I often used exposures of 2–3 minutes without compensating for reciproicity failure, even with less than optimal slide film, simply because this preserves the dark night mood.

3. in most suburban and urban environments, your exposure time will be limited by general light pollution. Even if I shoot straight into the night sky near the zenith (which would be the darkest part) I cannot expose longer than 30s at f/6 at ISO800 without getting some detail burned out. And I live in a small town with the next big city 30km to the South. This will be different away from populated areas, though.

Ben
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