What's causing this

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axle01
Posts: 46
Joined: Thu Mar 12, 2015 4:08 am

What's causing this

Post by axle01 »

I have used 3 different cameras, a Nikon D300 a Sony A7s and a brand new Sony A7Rii also different lens combinations with Nikon 10x objectives on a Raynox 250 and on a Nikon 200mm lens also a Zhongyi 20mm Super Macro lens, different lightning, ring light, 3 Lume Cubes and i always get these black lines.
What am i doing wrong.
Image

Alan

rjlittlefield
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Post by rjlittlefield »

Those are dust trails. Each one corresponds to a single dark dot that appears at a fixed position in each source frame. As you change focus while shooting the stack, the subject changes size and perhaps moves across the frame, while the dark dots stay in one place. But then the stacking software adjusts the scale and offset of each image so as to align the subject, keeping the subject the same size and place across the whole stack. As a result, the dots appear to move.

To the stacking software, each dot looks like detail to be preserved, so in the final output you see each dot in every position it ever had after alignment of the subject. The sort of "zoomburst" pattern that we see here is one typical appearance.

The best cure for this problem is to clean your sensor and keep it that way. It is possible to remove the spots or trails in post-processing, but inevitably some data really has been lost and there's no way to get it back. On the bright side, the trails seen here are mostly appearing in out-of-focus regions, where they can be quickly and easily retouched from the single frames at the front and back of the stack.

--Rik

axle01
Posts: 46
Joined: Thu Mar 12, 2015 4:08 am

Post by axle01 »

Appreciate that Rik I can understand the Nikon D300 and the Sony A7s being dusty but the A7Rii is brand new,,,,maybe Chinese dust on the sensor, I'll clean them and have another go.

Alan

JH
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Post by JH »

Hi
When photographing with very small effektive aperture even almost invissible dust is a problem. Unfortunattely it therefore is
1 almost impossible to get the sensor totaly clean
2 highly possible to end up with new/more dust after cleaning.

So be carefull - If you use an airblower make sure it has a filter. Every one I used witout filter left new dots on the sensor.

If you after cleaning still have some dust You can take care of the spots in Adobe light room before stacking.
I use an out of focus picture of gray card to do
1 white balance
2 dust removal
3 retouch hot single pixels

Then I copy this to the rest of the pictures before stacking.
Best Regards
Jörgen Hellberg
Jörgen Hellberg, my webbsite www.hellberg.photo

axle01
Posts: 46
Joined: Thu Mar 12, 2015 4:08 am

Post by axle01 »

Thanks for that JH

Alan

axle01
Posts: 46
Joined: Thu Mar 12, 2015 4:08 am

Post by axle01 »

Blew out the Sony A7Rii sensor and think it's ok now
Image
Al

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