Diffraction spikes and noise reduction in photoshop

[StargeezerTim]

Hi there,

First problem. Sometimes the diffraction spikes are just long lines with no star attached. Curves and processing makes it worse. There is one on the attached image. Does anyone know what could cause this and is there any way of preventing/dealing with it?

Secondly, When I try the noise reduction in Photoshop CC, the whole image just turns a completely different colour.. Blue in this case. Even with all the controls set to zero, it still does it. Is this normal and does anyone know of a way around this?

Thanks in anticipation. Tim.

p.s. this is a very heavy crop... so lacks pixels I suppose...and the red channel is boosted a lot. Don't know if that would affect the noise reduction ...

 

[kalasinman]

Diffraction spikes are formed by bright point sources, I suspect this is a satellite, meteor, etc. Your spikes look normal. The best forms of noise reduction are more data and dithering at least 12-15 pixels every shot. If you have 30 or so subs, kappa-sigma clipping on your lights will remove outliers like meteors, gamma rays, etc.

[Astroboffin]

First of all that long line is not a diffraction spike, but a satellite crossing the image during exposure.

The blueish halo you have round your stars looks like it might be due to star bloating, are you using an IR filter in your imaging train anywhere, as you should be.

And as for noise then cropping the image will make it show up more and upping the red channel will also, you are using an EOS camera so will suffer with a certain amount of noise, try lower ISO and or maybe shorter exposures.

DSLR cameras suffer with a bit of noise at the best times of the year, but trying to image with one in the summer with warm nights, is really asking for trouble in the noise front.

Hope that helps a little

Regards

AB

[StargeezerTim]

First of all that long line is not a diffraction spike, but a satellite crossing the image during exposure.

The blueish halo you have round your stars looks like it might be due to star bloating, are you using an IR filter in your imaging train anywhere, as you should be.

And as for noise then cropping the image will make it show up more and upping the red channel will also, you are using an EOS camera so will suffer with a certain amount of noise, try lower ISO and or maybe shorter exposures.

DSLR cameras suffer with a bit of noise at the best times of the year, but trying to image with one in the summer with warm nights, is really asking for trouble in the noise front.

Hope that helps a little

Regards

AB

Diffraction spikes are formed by bright point sources, I suspect this is a satellite, meteor, etc. Your spikes look normal. The best forms of noise reduction are more data and dithering at least 12-15 pixels every shot. If you have 30 or so subs, kappa-sigma clipping on your lights will remove outliers like meteors, gamma rays, etc.

Thanks...but I'm not sure its a satellite. Here is the source image for the crop. The lines are all orientated the same way and there was no sign of any satellites on any of the subs. I've had the same thing on other images as well. 

[kalasinman]

The other unmentioned possibility is an internal reflection. Try with a clear train. No filter, reducer, Barlow, etc.

[Astroboffin]

This is the line we are talking about I assume, I still think it may be a satellite, as there is not star on the line to cause a diffraction spike, if not then as Kalasinman has said an internal reflection.

AB

[Astroboffin]

The other thing that could be causing it, is a bad column of pixels on the camera, especially if other images show this, but it will be in exactly the same point on all images, if this were the case.

AB

[Scott]

I'm with you Tim, you'd have to be very lucky to get a satellite perfectly parrallel with the spikes. If you look closer, theres another at 90 deg to the one marked. I think its a reflection of 56Cyg. as for the noise.....always gonna be more data

edit: Nice Pelican by the way

[glowingturnip]

actually, I reckon that is a diffraction spike, from Deneb a couple of frames or so off to the top.

I've got exactly the same thing going on here in my Pelican image:

See what looks like a light spill in the bottom left, but it's in the same place relative to the stars in each dithered sub (so isn't a light spill), it's parallel to  the other diffraction strikes and it lines up with Deneb off to the left.

(i wasn't planning to release this image yet, it's had no processing at all apart from the initial stack, so you'll all have to pretend to be surprised when I do publish the final one)

If anyone has any processing tips to help with that rogue spike i'd be keen to hear too.

[StargeezerTim]

actually, I reckon that is a diffraction spike, from Deneb a couple of frames or so off to the top.

I've got exactly the same thing going on here in my Pelican image:

Capture.PNG

See what looks like a light spill in the bottom left, but it's in the same place relative to the stars in each dithered sub (so isn't a light spill), it's parallel to  the other diffraction strikes and it lines up with Deneb off to the left.

(i wasn't planning to release this image yet, it's had no processing at all apart from the initial stack, so you'll all have to pretend to be surprised when I do publish the final one)

If anyone has any processing tips to help with that rogue spike i'd be keen to hear too.

Case solved!   Look forward to seeing your image Stuart. No idea how to deal with it apart from moving Deneb....