Took a LTE, what the heck?

[NikonDude]

I took a long term exposure of the starts for about 20 minutes.

It didn't turn out too bad.

But when I zoom in, I see all these little crosses. What the heck is it?

 

[rexbobcat]

Dust on your sensor?

 

[Trever1t]

hot pixles? Did you use NR?

 

[NikonDude]

hot pixles? Did you use NR?

Yes.

 

[chuasam]

Dead Pixels!

 

[NikonDude]

Dead Pixels!

How on earth can it be dead pixels? The whole image is coated with them.

 

[Jaemie]

If you only see them on LTEs, they're hot pixels. You can use a dark frame subtraction program to PP them out of your image. Here's a better description: Dark Frame Subtraction using Adobe Photoshop<br>by Chris Limone | Take Great Pictures

 

[JoshuaSimPhotography]

it is probably dust on your sensor, clean it immediately! It isn't much of a problem as they are microscopic dust pixels not the massive black dots. when you look at the original pic, you can't even see it!

 

[Jaemie]

it is probably dust on your sensor, clean it immediately! It isn't much of a problem as they are microscopic dust pixels not the massive black dots. when you look at the original pic, you can't even see it!

That certainly is not dust on your sensor. Dust on the sensor is easily seen in a daytime sky photo shot at a higher f-stop.

 

[NikonDude]

Is it normal for a camera to have that many hot pixels

 

[Markw]

Well, you have a D60. Which implies it's decently old. So, logic would say that the sensor may degrade over this extended life time. But, I honestly don't know.

I know I had an IR-modified D60, and had no dead pixels. I had zero on my D90, like 3 on my D300s, and zero on my D800 as of now.

Mark

 

[Overread19 7]

Hot pixels are part and parcel of having the sensor running for 20mins. Long exposures generate a lot of heat on the sensor which is why many night shots are done with stacking software so that the photographers can take a series of shorter exposures and then stack the results.
If you need it all in one exposure you've two options:

1) Liquid nitrogen - I'm not joking (totally), but in short a custom setup that keeps the camera cooled so that heat build up is less of a problem

2) Long Exposure Noise reduction - as said above, this hsould help counter the dead pixels by subtracting them and the noise generated from the main frame by taking a second shot (with the aperture blades shut) right after the first (for the exact same duration - so another 20 mins).

 

[Markw]

That brings a question to my mind. Termed "dead" pixels, are they forever gone?

Mark

 

[table1349]

Dead pixels? Yes
Hot pixels? Yes and no. Most times not, but you can end up with a few hot pixels that show up more frequently.

 

[Garbz]

Hot / dead pixels are a function of exposure time and biasing (ISO). Like thermal noise it's a once off experience for the sensor. This is exactly why astro-photographers take lots of short exposures rather than one long one. These are not permanent in the sense that you didn't break your camera. But they are permanent / repeatable in the sense that every exposure taken in a similar timeframe with similar settings / outside temperature will result in the same pixels turning hot.

That is entirely why your spots turned black. Long exposure NR maps out the dead pixels and subtracts them from your picture, the thought being that dark pixels are less distracting than bright ones.