Luminous Landscape Forum

Equipment & Techniques => Digital Cameras & Shooting Techniques => Topic started by: Steve Kerman on November 04, 2004, 04:42:49 pm

Title: Purple Dot
Post by: Steve Kerman on November 04, 2004, 04:42:49 pm

I could tell you, but then I'd have to kill you.

Rest assured, "the truth is out there..."

Title: Purple Dot
Post by: Rainer SLP on November 05, 2004, 05:41:05 pm

Hi Kaelaria,

Is it always on the same place ? Is it always purple ?

Never heard of the term Hot Spot.

On the chips you can have dead pixels or Hot Pixels. Dead pixels are very seldom and could be a reason that you can get on Warranty a new chip for your camera.

What is normal up to a certain degree are Hot Pixels but they normally come in colors Red, Green or Blue, never in Purple. I have never seen purple hot spots in my astrophotos.

The Hot pixels show normally up when you do long exposures but the photo you showed is no reason yet for Hot pixels.

If you make Astrophotography then you can see a show of Hot pixels   on your images.

Are you shure that your sensor is absolutely clean and by no means has a dust particle of transparent material ? That could make that color aberration and turn that spot purple.

Just a thought

Title: Purple Dot
Post by: kaelaria on November 06, 2004, 10:51:35 am

Yes it's always in the same spot, yes it's always purple and that exact shape.  That pic and others like it were a 1-3 sec exposure.  Nothing shows up on lighter or faster pics.  I don't *see* anything on the sensor or glass, but I can't clean it - no tools yet.

If it was a pixel - wouldn't it actually be one pixel?  This is several and fades around it's center.  I'm kind of thinking debris, but not sure why I only see it in longer dark exposures.

Title: Purple Dot
Post by: kaelaria on November 06, 2004, 12:03:54 pm

I bought it over the net.  None of my other lenses have arrived yet.

Title: Purple Dot
Post by: kaelaria on November 03, 2004, 04:33:26 pm

When I take shots at night longer than a couple seconds with my DR, just off center there is a small purple blob that appears.  I don't see it on any shorter exposures, but it is on multiple dark, long shots.  What is it?
(http://www.sbtontheweb.com/images/purpledot.jpg)

Title: Purple Dot
Post by: jliechty on November 04, 2004, 08:05:34 pm

That's called a "hot spot." These happen only on long exposures, as you've found, and are just a more extreme form of noise (since the longer exposure, the greater the noise, and beyond a certain point the noise is so great that it makes specks like what you're seeing).

Title: Purple Dot
Post by: jliechty on November 05, 2004, 07:17:56 pm

If both a red and a blue pixel are affected, could it not be purple? And I'm sorry, I thought "hot spot" and "hot pixel" would be relatively interchangeable. Actually the latter term didn't come to mind when I was writing my post, so I just picked "hot spot" since it was the closest term available. Sorry it offended.

Title: Purple Dot
Post by: Rainer SLP on November 06, 2004, 12:02:18 pm

Hi,

I would suggest that you take the camera to the shop where you bought it and show them the image.

If it is still in Warranty they surely will clean it for you.

Have you the same with other lenses ?

Title: Purple Dot
Post by: Rainer SLP on November 06, 2004, 01:19:24 pm

Well then wait after you get the other lenses and try it out again. It could be also something in the lens.

If you change the lens and the spot is again there, then you have something on the sensor and if not you have something in the lens.