Sensor issue or Lens issue?

[GunisG]

Hi Guys,

 

I've been a beginner in astrophotography, I've just taken a few photos and my photos regardless of the lens have a green highlight across the image and somewhat a round circle on the left side and bottom side of the image; is this due to low light shooting?

Im using the A7 iii and the 24mm 1.4 GM, in my backyard in London with a bortle 10 sky.

 

If someone could give me help I'd greatly appreciate it.

 

Thank you,

 

Swiss

[PeterCPC]

Could be either. Have you tried taking flats to see if they remove them?

Peter

[alan potts]

A very good question I don't have an answer to, I have cleaned all my system and still have them, personally I feel they hang in the air.

Alan

[wimvb]

Looks like dust to me. If you take flats, they should be at the same position. Look for dust on the inside of your lens. 

[GunisG]

Hi Guys,

 

I've checked both my lens and my sensor; it has dust around the same corners of the issue, it could be that.

 

And also how do I take flats? Or what does it mean generally speaking?

 

Thank you so much in advance,

 

Swiss

[GunisG]

Hi Guys,

 

Here's an example of noticed on all my astrophotography photos:

 

A green halo/highlight:

 

 

[pete_l]

There is a green circle that goes all the way round the image (or my eyes are playing up ) It intersects with the "blob" you have highlighted.

I reckon the circle is a reflection, although the blobb looks like a grease smudge or some such. The question is: where? Generally the larger these things look, the further away from the sensor they are.

[GunisG]

Yeah you're right, but the question is; is it the illumination of the dust speckles or some sort of vignetting.

 

Because if I take normal photos indoor or outdoors none of the issues arise, its just when I take astrophotography shots?

Perhaps its the heavy light pollution since I am in London?

[happy-kat]

Hi

1- I would make a lens shiled. I made mine from flocking a flower pot and it's held on the lens with a rubber band. 

2- a rocket blower is a good way to blow off dust bunnies on either lens or sensor. Do not use those air cans they are anything but air.

3-: once you have done 3 you could then take flats. Same lens same focus same ISO same aperture same orientation set camera to AV mode point at white screen such a monitor on notepad with a few sheets of paper over. Take 30 images. Put lens cap on change nothing take 30 images that is dark flats. Change to M only change shutter to fastest possible, take 50 that's bias files.

Bias files can be taken after your lights on the night of shooting.

If your dust bunnies move you'll need new flats.

4- Note if you can set camera to using back button focus I find this very useful for generally shooting and astro as very unlikely to accidently change focus if you didn't mean to.

[sharkmelley]

As others have said, the dark patches are caused by dust.

The concentric coloured rings are most likely caused by Sony's crude lens vignetting ("shading") correction.  There are lots of threads about this e.g. https://www.dpreview.com/forums/post/62199570

It helps to switch off lens corrections but even so, you can't totally get rid of it because there are remaining "corrections" that cannot be switched off.  

Mark

Edited September 14, 2019 by sharkmelley

[sharkmelley]

For diagnostic purposes, I've boosted the saturation in your image:

Notice that the rings are much more like polygons than circles.  Those polygons are a sure sign this is caused by the lens correction issue on Sony cameras.

Mark

 

 

Edited September 14, 2019 by sharkmelley