Live composite and foreground exposure

[DaPonti]

Hi,

I was recently somewhere without too much light pollution so decided to try light composite for star trails. On one picture I tried to include a sign in the foreground, and since it was quite dark, I had to use my phone flashlight to light it during part of the exposure. From a 25 seconds exposure, I found that about 15 seconds of flashlight was more than enough.

Pictures below are JPEG straight out of the camera, just resized.

The first picture shows a single shot.



Once I was satisfied with the settings I moved to light composite, did the same thing for the base exposure and started shooting. The picture below shows live composite with just 1 shot.



As you can see the foreground is all dark, which is why I stopped as soon as I saw the preview. I tried again a couple of times, but the results were always the same: with a single shot I get light in the foreground, with live exposure it… disappears.

As I mentioned, I was only lighting the sign for about 15 seconds, so I would stop the flashlight before the end of the first exposure. But still… this looks as if I hadn't used the flashlight at all. I didn't want to spend too long experimenting so decided to go with it and merge the foreground later if needed.

But I'm curious to understand why I get such result. I just can't understand how the "base shot" in live composite is different from a normal shot if I use the same settings.

FYI this is what it looks like after many exposures, the foreground is still completely dark and I didn't try to light it during one of the subsequent exposure (not the first short) as I was afraid to ruin it. Maybe it'd have worked?





--
http://www.flickr.com/photos/romainpontida/ | https://500px.com/romainpontida/ | https://www.instagram.com/romainpontida/

 

[Digital Dick]

Don't light the foreground during the preparation click but after the second click to start the exposures light the foreground and watch on the rear screen to see it getting lighter and then stop the lighting when the foreground is as bright as you want it to be.

****

 

[Bassam Guy]

Hi,

I was recently somewhere without too much light pollution so decided to try light composite for star trails. On one picture I tried to include a sign in the foreground, and since it was quite dark, I had to use my phone flashlight to light it during part of the exposure. From a 25 seconds exposure, I found that about 15 seconds of flashlight was more than enough.

Pictures below are JPEG straight out of the camera, just resized.

The first picture shows a single shot.

Once I was satisfied with the settings I moved to light composite, did the same thing for the base exposure and started shooting. The picture below shows live composite with just 1 shot.

As you can see the foreground is all dark, which is why I stopped as soon as I saw the preview. I tried again a couple of times, but the results were always the same: with a single shot I get light in the foreground, with live exposure it… disappears.

As I mentioned, I was only lighting the sign for about 15 seconds, so I would stop the flashlight before the end of the first exposure. But still… this looks as if I hadn't used the flashlight at all. I didn't want to spend too long experimenting so decided to go with it and merge the foreground later if needed.

But I'm curious to understand why I get such result. I just can't understand how the "base shot" in live composite is different from a normal shot if I use the same settings.

FYI this is what it looks like after many exposures, the foreground is still completely dark and I didn't try to light it during one of the subsequent exposure (not the first short) as I was afraid to ruin it. Maybe it'd have worked?

Curious. It seems contrary to the entire point of Live Composite.

In the photo below, all of the light in the lower right corner was from cars in the parking lot. An unwelcome effect but expected nonetheless.



Same lens, same FL, 2.8 v 3.5, 25s v 60s, 400 v 800. Not much different. Judging by the arc of the star trails, my total exposure looks to be several minutes shorter than yours.

Is it possible that you used the light during the "preparing for live composite" step but not during the actual exposure? Doubtful. Have you seen similar results with other LC shots with that camera? ...But that seems like an odd peculiarity - for the sensor not to sense light.

You could try it again and keep the flashlight on until you see its effect on the LCD - or at least try to repeat it in a more controlled and warmer environment.

 

[DaPonti]

Don't light the foreground during the preparation click but after the second click to start the exposures light the foreground and watch on the rear screen to see it getting lighter and then stop the lighting when the foreground is as bright as you want it to be.

****

Thanks, that's pretty clear, but why?

From both you and Bassam Guy's answer I think I should understand that the preparation shot is not actually recorded, is that correct?

I thought the preparation shot was the "base", and then the camera would add light from each subsequent exposure.

 

[EMOslaughter]

No, the first shot is only for exposure values, and is not included in the exposure.

--
Douglas
http://www.flickr.com/photos/douglasfrench/
https://www.instagram.com/mr._french/

 

[Dino Anderson]

Don't light the foreground during the preparation click but after the second click to start the exposures light the foreground and watch on the rear screen to see it getting lighter and then stop the lighting when the foreground is as bright as you want it to be.

****

Thanks, that's pretty clear, but why?

From both you and Bassam Guy's answer I think I should understand that the preparation shot is not actually recorded, is that correct?

I thought the preparation shot was the "base", and then the camera would add light from each subsequent exposure.

The first shot is only used as a dark frame later if I'm not mistaken. In any case, no light is recorded during it.

 

[DaPonti]

Thanks all for your answers. I'll be smarter now!