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03-05-2013, 07:00 PM   #1
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Pentax LX for star trails.

Afternoon all.

This weekend (weather dependant) I'm intending of having a go at some star trail photography, I've been meaning to try it for a while but never had the gear (ie: a cable release)

Anyway, it turns out that I have a Pentax LX temporarily in my possession (my father purchased it the other day from the internet and had me pick it up from the seller) as a result, I've got an LX to play with for a couple of weeks.

I figured I'd use the LX to have a go at the trails because it has MLU (which my cameras don't) and I can remove the prism and look down into the waist level screen rather than have to bend down awkwardly (yep, lazy)



Anyway, finally to the point.


I know the LX ligth meter is quite good in darkness, is it good enough to allow me to use Automatic shutter speed for star trails? Or will I still need to measure manually and do it manually?

Also, what would be a recommended Aperture setting for star trails? I'm guessing wide open since there's minimal light? (I'll either use my 28F2.8 or a 50F1.7)


Thanks in advance.

03-05-2013, 07:24 PM   #2
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QuoteOriginally posted by hks_kansei Quote
Also, what would be a recommended Aperture setting for star trails?
My rule of thumb is 1 hour @ F3.5 with Kodak Plus-x/Arista Prem 100
Negatives tend to be a little thin, one of these days I will try 1 1/2 or 2 hour exposures.


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03-05-2013, 08:19 PM   #3
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If you have the time, try Treker's recommendation, and also try letting the LX do its thing. As an LX owner I'd like to hear how things work out. Because of reprecocity failure you might want to derate the ASA, er ISO by about ... 50%. Just a guess.
03-05-2013, 11:10 PM   #4
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Here's an idea. Try a few shots without film (or with film if you dont mind wasting) to see what it will do:
1) Put it on auto wide open and see what time it takes to do a shot. Then stop down, do another shot. Stop down again and do another shot. See if the f-stop/time relation is linear (it should be).
2) Then calculate what f-stop you need for the exposure time you need.
3) Then decide what speed film you need to use for a correct exposure.

Happy playing!

03-06-2013, 09:33 AM   #5
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QuoteOriginally posted by Chuckie Quote
Here's an idea. Try a few shots without film (or with film if you dont mind wasting) to see what it will do:
1) Put it on auto wide open and see what time it takes to do a shot. Then stop down, do another shot. Stop down again and do another shot. See if the f-stop/time relation is linear (it should be).
2) Then calculate what f-stop you need for the exposure time you need.
3) Then decide what speed film you need to use for a correct exposure.

Happy playing!
I'd suggest using film. Since the LX will be reading the majority of the exposure off what it expects to be film the black pressure plate may well fool it into calling for a far longer exposure than needed.
03-06-2013, 01:35 PM   #6
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^Is that actually true?

Because of the camera obscura effect there should be a focused image on the back plate, certainly reflecting any light precipitated onto the black metal. Would not off-the-plate metering work as well?
03-06-2013, 02:30 PM   #7
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QuoteOriginally posted by asaru Quote
^Is that actually true?

Because of the camera obscura effect there should be a focused image on the back plate, certainly reflecting any light precipitated onto the black metal. Would not off-the-plate metering work as well?
I think what they mean is that the black pressure plate is likely to have a different level of reflectivity than film.

Especially since the plate is glossy, and it's the matte side of the film that faces the lens.
03-07-2013, 07:59 AM   #8
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QuoteOriginally posted by Treker Quote
My rule of thumb is 1 hour @ F3.5 with Kodak Plus-x/Arista Prem 100
Negatives tend to be a little thin, one of these days I will try 1 1/2 or 2 hour exposures.


Pentax MZ 30
Very interesting, gonna have to try it with my LX. It's -12C outside + windchill right now, so I'll wait until summer though.

03-07-2013, 01:40 PM   #9
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about 1-1/2 hours in mountain air or a clear/dark night seems right....
I didi this years ago with HP4 and one with TMZ
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