Am I right in thinking these are related to vibration in some way? any ideas on how to prevent this in future stacks. I have just ordered several sorbothane feet to see if that helps.
What are these dots?
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stormcrowuk
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What are these dots?
I've noticed that after stacking in zerene I have these dot trails. there are several of them (4-5) in each image and they are different in each different stack of images.
Am I right in thinking these are related to vibration in some way? any ideas on how to prevent this in future stacks. I have just ordered several sorbothane feet to see if that helps.
Am I right in thinking these are related to vibration in some way? any ideas on how to prevent this in future stacks. I have just ordered several sorbothane feet to see if that helps.
Hello Dale,
They look like "hot pixels" to me (although mine are red), and the trail is made as you stack. Do you have a pixel remap mode on your camera? Alternative you can retouch over them from one single image.
-Johan
They look like "hot pixels" to me (although mine are red), and the trail is made as you stack. Do you have a pixel remap mode on your camera? Alternative you can retouch over them from one single image.
-Johan
My extreme-macro.co.uk site, a learning site. Your comments and input there would be gratefully appreciated.
Yup. Hot pixels. And dust on your sensor will leave the same trail pattern. I clean this up in post using the close tool. If the dust trails get too bad then I clean the sensor.
Hot pixels can be avoided if you shorten your exposure time...that is one reason why I shoot with a Canon 430EX II speedlite versus a constant light source.
Hot pixels can be avoided if you shorten your exposure time...that is one reason why I shoot with a Canon 430EX II speedlite versus a constant light source.
I'm in Canada! Isn't that weird?
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rjlittlefield
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Not really "vibration", but rather systematic motion.
What happens is that the original images each have a single dot that occurs at a fixed pixel position in every image. Due to motion in the setup, the image of the subject moves across the frame as the stack is shot. When the stack is processed, frames are realigned so that the subject stays lined up, but then the dots move around. Each dot looks like detail to be preserved, so what you end up with in the end is a collection of dots that shows the original single dot in every different position that it had with respect to the image of the subject. Typically there is a lot of correlation between those positions from one frame to the next, so the collection ends up looking like some sort of line, which we usually call a "trail".
The shape of the trail suggests what sort of motion caused this effect. In your case, the series of loops is typical of a systematic wiggling motion that often occurs with screw drive mechanisms as the screw goes around and around.
Dots like you have here, that occupy a single pixel position and are brighter than their surroundings, are caused by "hot" or "warm" pixel positions that accumulate extra charge from electrical leakage. The problem is worse with long exposures (which gives more time for stray charge to accumulate), so one effective approach is to add light and shorten your exposure time. They are also worse with higher temperatures (which causes faster leakage), so they'll be worse when shooting with live view turned on. Shooting with flash, as suggested by abpho, is powerful medicine for warm pixels because it allows a short shutter-open time and also allows turning off live view while still giving sharp images.
If you have Photoshop, try using the Healing Brush. It was designed to handle problems like scratches and dust, but it works equally well here.
--Rik
What happens is that the original images each have a single dot that occurs at a fixed pixel position in every image. Due to motion in the setup, the image of the subject moves across the frame as the stack is shot. When the stack is processed, frames are realigned so that the subject stays lined up, but then the dots move around. Each dot looks like detail to be preserved, so what you end up with in the end is a collection of dots that shows the original single dot in every different position that it had with respect to the image of the subject. Typically there is a lot of correlation between those positions from one frame to the next, so the collection ends up looking like some sort of line, which we usually call a "trail".
The shape of the trail suggests what sort of motion caused this effect. In your case, the series of loops is typical of a systematic wiggling motion that often occurs with screw drive mechanisms as the screw goes around and around.
Dots like you have here, that occupy a single pixel position and are brighter than their surroundings, are caused by "hot" or "warm" pixel positions that accumulate extra charge from electrical leakage. The problem is worse with long exposures (which gives more time for stray charge to accumulate), so one effective approach is to add light and shorten your exposure time. They are also worse with higher temperatures (which causes faster leakage), so they'll be worse when shooting with live view turned on. Shooting with flash, as suggested by abpho, is powerful medicine for warm pixels because it allows a short shutter-open time and also allows turning off live view while still giving sharp images.
If you have Photoshop, try using the Healing Brush. It was designed to handle problems like scratches and dust, but it works equally well here.
--Rik
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stormcrowuk
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Thanks for the info everyone, very informative I just wanted to check what it was and if there was anything I can do to my setup to prevent it. I suppose the odd hot pixel is easy to miss in photographs its only when you stack them that they become more obvious. I've no problem removing them in photoshop I was more curious as to what was causing them.
Thanks
Thanks