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So tonight I had a go at trying to take pictures of the night sky. All the pictures turned out black, I am well aware that aperture and shutter speed and everything has a part in it all. So I googled and all I got was, wide aperture, shutter speed of 15-25 and ISO of 6400 or more, so I tried, still black. So I want all out with shutter speed 25, 2.8 in aperture and ISO 25600, still black… Does anyone know what the problem might be?

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    \$\begingroup\$ Not enough light. Did you try flash? \$\endgroup\$ Commented Aug 24, 2022 at 6:36
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    \$\begingroup\$ @ClicketyRicket, flash for night sky? \$\endgroup\$ Commented Aug 24, 2022 at 6:54
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    \$\begingroup\$ Did you remove the lens cap? \$\endgroup\$ Commented Aug 24, 2022 at 7:55
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    \$\begingroup\$ Do you mean shutter speed 1/25 or a full 25 seconds? I'm assuming you have a tripod for this too. \$\endgroup\$
    – Tetsujin
    Commented Aug 24, 2022 at 8:07
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    \$\begingroup\$ You may have been completely out of focus. Find the brightest star in the sky/Venus, and set your focus manually. \$\endgroup\$ Commented Aug 24, 2022 at 10:04

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Digging my archives, shooting at Jupiter:

  • One shot with about 100 stars visible (but Jupiter over-exposed): 3200ISO, 1s, f/5.6 (EV3)
  • One shot with a handful of visible stars (but Jupiter less overexposed): 3200ISO, 1/8s, f/5.6 (EV0)

Since I was shooting with a 400mm lens, f/5.6 is as open as I could, and the field of view is about 5 moon diameters.

So night skies are EV0 or under.

If you are shooting with a standard lens (50mm equivalent) and you aren't in an area with very little light pollution and very clear skies, it is possible that 1) there aren't than many visible stars (do you see the Milky Way?), and 2) their contrast is too low (especially if focus isn't optimal).

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Does anyone know what the problem might be?

Focus

If your lens is not focused almost precisely at infinity, the dim light from stars and other astronomical phenomena will be out of focus. The more defocused a point source of light is, the more spread out the light from that point source is projected onto the sensor (or film). Eventually you spread the light out enough that you can't distinguish it from the noise floor.

Unless you're pointed at the Moon, the night sky does not usually provide enough of the kind of contrast needed for cameras to autofocus. Try using magnified Live View to bring one of the brightest starts into focus manually, then refine using a medium bright star. You won't be able to se anything on the camera's LCD until even the brightest stars are almost in focus.

Noise Reduction

Some cameras are known as "star eaters" because the analog noise reduction applied between the sensor and the ADC (analog-to-digital convertor) identify small points sources of light as noise. They then eliminate the "noise" before the information is digitized. Sony α7 series cameras are notorious for this, some models more than others. If you expose brighter and focus properly, eventually some of the brighter point sources of light will survive the application of NR.

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  • \$\begingroup\$ You can usually turn off the NR manually. \$\endgroup\$
    – drewk
    Commented Sep 7, 2022 at 12:29
  • \$\begingroup\$ @drewk You can't turn off the analog NR done before digital-to-analog conversion, which is where this issue occurs. It's not user accessible. \$\endgroup\$
    – Michael C
    Commented Sep 11, 2022 at 6:48
  • \$\begingroup\$ In both Nikon z7 and z9 have Long Exposure Noise Reduction and High ISO Noise Reduction as a user accessible item. \$\endgroup\$
    – drewk
    Commented Sep 11, 2022 at 13:11
  • \$\begingroup\$ @drewk Yes, they do. But that setting doesn't affect the analog NR that is done before ADC. Those are different steps in the imaging pipeline. \$\endgroup\$
    – Michael C
    Commented Sep 12, 2022 at 4:16

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