Night Sky and D70

[trekin]

Has anyone taken shots of the night sky and had purple fringing on the photo

Gary

[Killakoala]

This is normal and due to CCD heating in the left-top part of the CCD. There is very little you can do except choose 'long exposure correction' or it's equivalent in the menu.

[sirhc55]

Welcome Gary to the forum. Can you give us some details of the EXIF data from an infected pic?

The normal reason behind this is long exposures and heat being generated by the sensor

[trekin]

Hi sirhc55
this is some of the data of the image

shutter 173.7
aperture f22
focal 18mm
iso 400

Gary

[Yi-P]

The 3 mins exposure sure created a heat build up noise on the CCD sensor (mostly on the top left borders)

What you can do is put a cap on the lens, manual focus (so it takes the shot) and run it through 3 minutes again, this will create a pitch dark image with just the purple noise.

Then apply dark frame subtraction on the final image using the dark frame as a reference. Google for 'dark frame subtraction' for more details on this technique.

[firsty]

I think you have closed down your aperture to much, you well get a better clearer starting point at about f11 also drop you ISO back to 200 then adjust the exposure time from there
bringing your aperture to f11 or even f8 will cut time needed to expose a lot
and drop your heat build up correspondingly

[pippin88]

The 3 mins exposure sure created a heat build up noise on the CCD sensor (mostly on the top left borders)

What you can do is put a cap on the lens, manual focus (so it takes the shot) and run it through 3 minutes again, this will create a pitch dark image with just the purple noise.

Then apply dark frame subtraction on the final image using the dark frame as a reference. Google for 'dark frame subtraction' for more details on this technique.

The D70 has an auto option for this. Called long exposure noise reduction.

[trekin]

Hi pippin88

Just tried the long exp NR on setting and it worked like a treat

Thankyou everyone for your advice

Gary

[radar]

Hi Gary,

welcome to the forums, glad to seen another Newcastle resident. Is that Australia or UK?

NR will certainly do the trick but also take note of Keith's suggestion or opening up your lens. Unless there is a specific reason you want f22, f11 would be much better as it will take the lens back to a much "sweeter" spot.

If you do want an exposure that long, it may be worth looking at a Neutral Density filter.

Cheers,

André

[trekin]

Hi Radar

thankyou for the welcome
yes I am in Newy (mayfield)
I have to get my D70 out and practise so I can get used to the controlls

Gary