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FORUMS Photo Sharing & Visual Enjoyment Astronomy & Celestial 
Thread started 23 Nov 2008 (Sunday) 03:23
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The Mighty Orion.... with a problem

 
bowtie`
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Nov 23, 2008 03:23 |  #1

Anyone else using a 5D body for shots? Ever have this problem? I originally meant to use ISO 100 in this one but a bout of shivering must have overcome myself and I ended up shooting this at ISO125. Are the intensity variations of the brightest stars due to the algorithim in the chip boosting the 100 upto 125? Or is there an atmospheric transparency variation that only effects bright stars? I am really confused on this as the faint stars do not show any of the *pulses*.

Shot with a Canon 5D, ISO 125, TV 1999sec. (33+minutes), AV 8.0, Lens 24-70mm @ 43mm, no filters, single exposure, noise reduction on


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siddr20
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Nov 23, 2008 04:50 |  #2

Im not sure what you are trying to capture, but with a 33min exposure you are bound to get star trails. Is this what you are after?

I have shot a picture of orion with iso 160 and found no problems..

Sorry im a little confused as to what you are trying to ask..


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Nighthound
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Nov 23, 2008 06:01 |  #3

Nice shot bowtie.

I have used my 5D, 20D and 300D. Firstly, the brightness of any given star is measured in terms of its magnitude allocation. Explained a little more in depth here:
http://www.stargazing.​net/David/constel/magn​itude.html (external link)

The camera sensor is detecting and recording the variation in star magnitude* in your shot. The pulsing that you refer to is caused by both atmospheric distortion("bending" the light) and distortion that occurs during its long journey before reaching our atmosphere. As star light travels such huge distances it falls under the influence of all it passes through or by, being "bent" by gravitational effects from other stars, galaxies, etc.

* Star magnitude is determined physically by several things including a star's mass and temperature and it's color is influenced also by temperature as well as material make up of the star and the stage at which the star is in its life span.

Increasing your camera ISO only increases the light gathering speed(sensitivity) in the sensor. Those dim stars are still pulsing just not as obviously to our night-challenged vision. The long exposures we take are recording pulses on all stars but it's taking the sum of those pulses which on very poor seeing nights can create some odd looking stars(and lack of clarity on the object being imaged-all light is effected) when using a tracking mount to avoid the movement seen in your shot.

There are many dimmer magnitude stars visible in your shot however some are neutralized by the light pollution bleeding into the lower left of the frame. So to sum it up, the dimmer star pulses are being recorded equally with the bright star pulses. Their lack of brightness just means you'll have to gather more of their light(i.e. more exposure time and/or higher ISO) in order to make them brighter and more pronounced.

Sorry for the rambling.


Steve
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strgazr27
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Nov 23, 2008 06:34 |  #4

There is a definite electronic issue or pattern in the shot. It is way too perfect to be atmospheric. That is if your asking about the dark bands in all the star images.

CS's


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bowtie`
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Nov 23, 2008 06:44 |  #5

strgazr27 wrote in post #6742789 (external link)
There is a definite electronic issue or pattern in the shot. It is way too perfect to be atmospheric. That is if your asking about the dark bands in all the star images.

CS's

Good, I am not the only one that see's it. Thanks for the confirmation strgazr. I was trying for star trails in the shot. What had me baffled is that the brighter stars have pulses or banding while the faint stars do not. It only happened on this shot. Not later ones. I did cold-soak the camera an hour before the image was taken. Maybe it was not long enough. Lord knows I hate the cold weather, maybe the camera was picking up my bad vibes.




  
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bowtie`
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Nov 23, 2008 07:04 |  #6

Nighthound wrote in post #6742729 (external link)
Nice shot bowtie.

The camera sensor is detecting and recording the variation in star magnitude* in your shot. The pulsing that you refer to is caused by both atmospheric distortion("bending" the light) and distortion that occurs during its long journey before reaching our atmosphere. As star light travels such huge distances it falls under the influence of all it passes through or by, being "bent" by gravitational effects from other stars, galaxies, etc.

...

Increasing your camera ISO only increases the light gathering speed(sensitivity) in the sensor. Those dim stars are still pulsing just not as obviously to our night-challenged vision. The long exposures we take are recording pulses on all stars but it's taking the sum of those pulses which on very poor seeing nights can create some odd looking stars(and lack of clarity on the object being imaged-all light is effected) when using a tracking mount to avoid the movement seen in your shot.

...

Sorry for the rambling.

Thanks for the reply. Please always ramble with me. I always find it informative. You have gotten me thinking with this. I did know that all stars are variable. I just did not think that at these small focal lengths that it could be visible. So in a sense it could be a product of the stellar variation and it's interaction with atmospheric variation. I have seen gravity waves in the atmosphere around low pressure center in pictures of clouds. I did not know that high pressure regions could produce gravity waves also. High pressure was in the Ohio River valley and West Virginia when I took this shot. So it could have been an interaction with the atmosphere and the brighter stars were of sufficient magnitude to illuminate the gravity waves while the dim stars are not?




  
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40Dude6aedyk
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Nov 23, 2008 08:13 |  #7

Looks more like an anti-aliasing issue with your software. What does the RAW image show?


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Nighthound
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Nov 23, 2008 11:12 |  #8

Ok, that settles it. I should not post so early in the morning.

For some reason the star trail irregularity didn't even register with me, I misinterpreted your question(slap in forehead). Now that I am on the same page and awake, it does look like a technical issue in the image writing or processing. Don't think I've sen this before in star trails.


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bowtie`
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Nov 23, 2008 20:48 |  #9

40Dude6aedyk wrote in post #6743008 (external link)
Looks more like an anti-aliasing issue with your software. What does the RAW image show?

Thanks 40Dude. Here is a crop straight from DPP of the RAW. I would guess about a 250% crop. This is the end of Betelguese and the faint ones from the*head*. ANd yes I jiggled the camera closing the shutter.


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The Mighty Orion.... with a problem
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