What is this on my star trail photo's?

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edthedrummer

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Edward
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Hello everybody :)

I popped over to sandringham forest tonight, the tree's provide what i percieve to be excellent coverage from the surrounding towns light pollution (I may be wrong...)

So here are a couple of photo's from the evening, they aren't anything amazing, just two I picked out to highlight the problem i keep getting.

I would like to know, what the red/purple flare is at the top left of both photographs, its present in a few others from this evening.

These photo's have much different exposure times, both have different aperture settings, but both share an ISO of 800.


DSC_1044 by Edward Ashton, on Flickr


DSC_1045 by Edward Ashton, on Flickr

Thanks,
Ed.
 
It looks suspiciously like some light spill or maybe even some light leak it seems to be linked to the legth of the exposure, as is significatly worse on the much longer exposure, were there any light sources near your when you shot this?
 
The only bright lights were tucked behind many tree's, located behind us, you couldn't see them through the tree's, but could see the feint glow over the top. We shot away from these.

However, I don't cover the eyepiece? Could this be the cause?
 
edthedrummer said:
The only bright lights were tucked behind many tree's, located behind us, you couldn't see them through the tree's, but could see the feint glow over the top. We shot away from these.

However, I don't cover the eyepiece? Could this be the cause?
Click to expand...

Yeah I suspect that is exactly what it is, some light leak through the viewfinder, you would be amazing even the smallest of light source can have a big effect on a long exposure ;) even if you cannot see them with the naked eye, if the camera is constantly seeing it it will show up in a big way
 
MWHCVT said:
Yeah I suspect that is exactly what it is, some light leak through the viewfinder, you would be amazing even the smallest of light source can have a big effect on a long exposure ;) even if you cannot see them with the naked eye, if the camera is constantly seeing it it will show up in a big way
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Okay, well I am willing to go with this! So what do you use to cover the eyepiece? Can you buy a Nikon eyepiece cover? Or is it a case of taping a bit of black card over the top of it?

Ed
 
edthedrummer said:
Okay, well I am willing to go with this! So what do you use to cover the eyepiece? Can you buy a Nikon eyepiece cover? Or is it a case of taping a bit of black card over the top of it?

Ed
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Both will work just fine :) Insulation tape.
 
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It's amp glow (sensor overheating) - nothing you can do about it apart from use shorter exposures or a different camera. It's not light leak through the viewfinder.
 
jpw said:
It's amp glow (sensor overheating) - nothing you can do about it apart from use shorter exposures or a different camera. It's not light leak through the viewfinder.
Click to expand...

You know what its been that long since I've seen a case of it I never even considered it but yes I suspect this is the issue
 
'm a bit late to the party, but would have to agree that it looks like light ingress of some kind.
 
MWHCVT said:
You know what its been that long since I've seen a case of it I never even considered it but yes I suspect this is the issue
Click to expand...

But its visible on the corner of the first image, thats an exposure time of 53 seconds? Not that long in the grand scheme of things? Although It makes sense because its worse the longer you expose for...

I'm a bit dissapointed if this is the case, somewhat disheartened.
 
Right there is going to be a very easy test to see if it was light leak or if it's a sensor issue, that is cover the viewfinder and stick the lens cap on and do a 5 minute exposure at ISO800 and see what the resulting image, hopefully it will show nothing but a few dead pixels, if however there is still this fringing in the corner then it would say it's a sensor issue if however all is well then it suggest it was a light leak issue (y)
 
MWHCVT said:
Right there is going to be a very easy test to see if it was light leak or if it's a sensor issue, that is cover the viewfinder and stick the lens cap on and do a 5 minute exposure at ISO800 and see what the resulting image, hopefully it will show nothing but a few dead pixels, if however there is still this fringing in the corner then it would say it's a sensor issue if however all is well then it suggest it was a light leak issue (y)
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Confirmed as a sensor issue then.

Still getting feint glow in the same corner on a 30 second exposure, and it is still present on a 15 second exposure.

I guess this means that there is to be no adventure into star trails for me? Seeing as i can't even stack the images?
 
Jimi-the-fish said:
Canon provide an eyepiece cover on the camera strap. Do Nikon not do the same thing?

J
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I had no idea that's what that was!!!
 
Long exposure noise reduction should take a blank shot after your normal shot and subtract the amp glow if your D70 has that feature. It will double your shot time though....

Nick
 
If it's dark... what light is leaking into the viewfinder? Unless he's using a torch behind the camera I find light leakage through the viewfinder unlikely. Not to this extent anyway. He's in a forest, with the eyepiece pointing at the ground. There shouldn't be enough light leaking in to do that. Think about it, if such low levels of light can do this, then it would be evident pretty much all the time... unless, he's using a torch behind the camera to see other stuff thinking that it won't effect his exposure because the camera is skywards.


Also... trees will not shield you from light pollution. Light pollution is in the sky. it doesn't mean local light near you. In light polluted areas the whole sky is polluted, hence the other name for light pollution "Sky Glow".


I know a lot of Nikon cameras have an infra-red shutter timing LED that shines through register holes in the shutter blades. I wonder if it's anything to do with that, coupled with a slight fault with the IR filter? If not that, I'm in the amp glow camp.
 
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Jimi-the-fish said:
Canon provide an eyepiece cover on the camera strap. Do Nikon not do the same thing?

J
Click to expand...

Both my D3100 and D7000 were supplied with one.
 
jpw said:
It's amp glow (sensor overheating) - nothing you can do about it apart from use shorter exposures or a different camera. It's not light leak through the viewfinder.
Click to expand...

Agreed
Could well be the sensor getting very warm on long exposures and nearly always appears in a corner of the frame. Let your camera acclimatise if it's very cold outside, leave the batteries indoors in your pocket till you start shooting to keep them warm.

Do shorter exposures then stack them.

And yes cover the viewfinder, light can only get in if there is light in the vicinity.

Use a red light too see camera settings etc, but you probably know that.

Try this http://www.startrails.de/html/software.html


The list goes on...:LOL:
 
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Nikon Man said:
Agreed
Could well be the sensor getting very warm on long exposures and nearly always appears in a corner of the frame. Let your camera acclimatise if it's very cold outside, leave the batteries indoors in your pocket till you start shooting to keep them warm.

Do shorter exposures then stack them.

And yes cover the viewfinder, light can only get in if there is light in the vicinity.

Use a red light too see camera settings etc, but you probably know that.

Try this http://www.startrails.de/html/software.html


The list goes on...:LOL:
Click to expand...

Yep i am willing to accept that its amp glow. But I wasn't really doing any rediculously long exposures? 2 to 3 minutes each, but only 4 or 5 shots over half an hour period?

It still suffers from amp glow after 15 second exposures, so i don't stand much chance at all even if i took short exposures and stacked them.
 
Glad it's been diagnosed. My original DSLR was a D80 and suffered terribly from amp glow. There's little you can do about stopping it; certainly the Long Exposure Noise Reduction is not worth anything in this fight.

However, the glow always happens in the same positions (worst being top left, then top right, then just right of centre) and varies in intensity only as a result of ambient temperature and exposure duration.

So, if you're able to mount your camera hanging upside down from your tripod you can either compose your shot so the lower 1/3 is in silhouette and get rid of the glow in PS with an easy clone; or conceal the glow in the first place by lightpainting your foreground.
 
edthedrummer said:
Yep i am willing to accept that its amp glow. But I wasn't really doing any rediculously long exposures? 2 to 3 minutes each, but only 4 or 5 shots over half an hour period?

It still suffers from amp glow after 15 second exposures, so i don't stand much chance at all even if i took short exposures and stacked them.
Click to expand...

Some camera's suffer while others don't luck of the draw. Cmos sensors tend to do better than ccd types.

I use a Starlight Xpress astro camera for my telescope. the sensor is cooled by a Peltier device to try and eliminate electrical issues with the sensor chip

It might be spurious light getting in where the lens is mounted, just drop a tea towel over the camera body will eliminate stray light and condensation.

I use a Pentax k5 for shooting the night sky (widefield) and can easily take 2 min exposures at a dark site and zero amp glow.:D

Most irregularities can be eliminated with software as a last resort.

Don't give up I did this with film camera , we used to hypersensitise the film to make it more sensitive start an exposure the watch the clouds roll in. :LOL:

Problem with astro shooting is your trying to learn many new techniques at the same time and can get frustrating but rewards astounding, as images can be taken that are unseen to human eye.
 
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double post
 
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