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09-18-2017, 01:58 PM   #1
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Pentax K-50 on bulb setting - is it possible to set aperature?

I would like to photo thunderstorms at night, when internal and/or cloud-ground lightning lights up the clouds. I was trying to use "bulb" for this - just open the shutter, wait until 3-4 flashes occur in my area of interest, then close the shutter. That has been only partly effective. But I am also getting some ground lights strongly registering with a long exposure, so I would like to try with a smaller aperture.
I'm also having problems getting focus right - finally tried manual focus set to infinity, but only partly successful.

09-18-2017, 02:01 PM   #2
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Sure, go into Manual mode and set ISO100 and f11, as an example.

For focus, go into Live View, maximum zoom, find and make a star go as small as possible.

09-18-2017, 02:07 PM   #3
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How long is long?

Are you using the 2s timer so the mirror is up when you start the exposure? Is your tripod heavy enough to keep things stable? Shake reduction is off (turns off automatically in the 2s mode I believe)?

A graduated ND filter with the dark part set over the city lights might work as an idea.

Assuming your lens doesn't have an infinity stop? I usually look down in the focus range window on my 50-135 to set it at infinity manually and it seems to work for me.
09-18-2017, 03:25 PM   #4
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QuoteOriginally posted by rpair2017 Quote
I would like to photo thunderstorms at night, when internal and/or cloud-ground lightning lights up the clouds. I was trying to use "bulb" for this - just open the shutter, wait until 3-4 flashes occur in my area of interest, then close the shutter. That has been only partly effective. But I am also getting some ground lights strongly registering with a long exposure, so I would like to try with a smaller aperture.
I'm also having problems getting focus right - finally tried manual focus set to infinity, but only partly successful.
In order to get a correct exposure with other lighting around, you would need to calculate (or meter) the correct exposure and set the shutter speed accordingly. Just opening the shutter for an arbitrary amount of time will not work. In this case the 'keep it open until something happens' is causing over exposure. Better would be to set a correct exposure with the longest shutter possible, then keep shooting multiple frames until something happens within one of them.

As for focus, what do you mean by only partly successful? Can you post an example image to show what was unsuccessful when doing this?

09-18-2017, 04:42 PM   #5
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QuoteOriginally posted by victormeldrew Quote
In order to get a correct exposure with other lighting around, you would need to calculate (or meter) the correct exposure and set the shutter speed accordingly. Just opening the shutter for an arbitrary amount of time will not work. In this case the 'keep it open until something happens' is causing over exposure. Better would be to set a correct exposure with the longest shutter possible, then keep shooting multiple frames until something happens within one of them.
You can leave it open a long time, Victor, like doing fireworks. This is 1.3 seconds, but you can do 30 seconds ... some will happily cover the lens until something happens, then cover after the burst, uncover for the next, and so on.

09-18-2017, 11:59 PM   #6
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QuoteOriginally posted by clackers Quote
You can leave it open a long time, Victor, like doing fireworks. This is 1.3 seconds, but you can do 30 seconds ... some will happily cover the lens until something happens, then cover after the burst, uncover for the next, and so on.
This would definitely work with fireworks, when you know when to expect the action. But not so much with lightning when you might be waiting a long (and variable amount of) time, and there are other light sources in the frame.
09-19-2017, 08:18 PM   #7
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QuoteOriginally posted by victormeldrew Quote
This would definitely work with fireworks, when you know when to expect the action. But not so much with lightning when you might be waiting a long (and variable amount of) time, and there are other light sources in the frame.
?

It's especially relevant to lightning.

You don't know when the strike is going to happen, you have to have the shutter open beforehand.

So a successful strategy is to keep the shutter open a long time, repeatedly - long exposures with the intervalometer setting. Composite the good ones as necessary to be more impressive.

As photographers, we can't be afraid of other light sources in the frame.

Below are mixed light source exposures of 5 seconds, 20 seconds .. and get ready for it ... 117 seconds.







Last edited by clackers; 09-19-2017 at 08:52 PM.
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