# astronomy camera



## den9 (Sep 6, 2008)

hi i was using my D50 for taking pictures of the stars, then my cousin used his D80. he told me that the D50 had a better sensor for shots of the sky, but i didnt understand why. 

for 20 min exposures his pictures were coming out green, and mine were working fine.

he also told me that for long exposures the sensor could get hot. is that true? 

if he ever sends me the pictures i could show u the green ones.


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## Garbz (Sep 6, 2008)

The colour shift can be due to heating and noise reduction. Sensors tend to get purple when they get hot, something older nikons are very susceptible to. The Noise reduction often turns this green afterwards because the already warm sensor is used again for a NR image. The NR image is then more purple than the original.

Sensors of all kinds heat up significantly. In many cameras you can literally damage the sensor by taking a long enough exposure, although I haven't heard this affecting a current generation camera. Only the 350D, and I know my D200 gets DAMN HOT after 30 minutes.

If you're interested in some astrophotography I suggest either shell out the many thousands for a dedicated sensor which is peltier cooled to maintain a noise free long exposure, or spend about $30 on ebay and go buy a roll of film  The other option that's digital is to do image stacking. Searching for stacking on this forum should bring up quite a few threads.


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## den9 (Sep 6, 2008)

how come my D50 wasnt getting hot like the D80?


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## den9 (Sep 7, 2008)

bump?


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## den9 (Sep 10, 2008)

any1?


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## Bifurcator (Sep 11, 2008)

The weather?


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## den9 (Sep 12, 2008)

we were shooting both cameras at the same time, it was probaly 65 degrees out


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## Garbz (Sep 14, 2008)

No reason to keep bumping threads in this subforum. Try that when it's off page one.

Different sensor, different voltage, but most critically a different body. How do you know the sensor wasn't heating up, did you pull the lens off and touch it with your ear?


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## potownrob (Sep 14, 2008)

Garbz said:


> How do you know the sensor wasn't heating up, did you pull the lens off and touch it with your ear?


:lmao:  :lmao:


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## Bifurcator (Sep 15, 2008)

Hehehe good one Garbz! :thumbup:


There are 100's of variables that can contribute to sensor heat.


Direct sunlight on on a black body,
Angle to the Sun,
Proximity to a busy memory card,
Speed and thermal properties of the memory card,
Shot interval,
Exposure length,
Proximity to a warm battery,
Live View Sensor focusing,
Proximity to any warm internal components (in my case AntiShake almost over-heats it),
How you hold the camera (hands/cloths as thermal insulator),
Camera Body material thermal dissipation characteristics,
Your breath (humidity has an affect),
Component age,
etc.

Granted each separately may not be all that significant but it is additive.


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## den9 (Sep 25, 2008)

well therese were taken back to back, same temp, it was about 60 degrees out, and they were both long exposure shots, say 20 minutes

first shot is with a D50, the greenish shots are with a D80


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## Garbz (Sep 26, 2008)

Yep the pink is a clear sign of the sensor heating up. The green I will assume is the noise reduction trying to eliminate the pink.

You should maybe consider an image stacking technique, the reset the sensor gets are every frame causes the pink noise to disappear (sensor still heats up though)





http://www.tawbaware.com/imgstack.htm


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## den9 (Sep 27, 2008)

i wonder why the D50 wasnt going green, i think the green looks pretty cool but obviously not desirable everytime.

should i be concerned about the sensor heating up?


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## Garbz (Sep 27, 2008)

Yes, but I can't give you a quantitative number of when to be concerned. I have seen a Canon 350D break by overheating the sensor during a 50min exposure. Repair was not cheap.


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## den9 (Sep 27, 2008)

how do people do 4+ hour exposures? im guessing film?


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## Garbz (Sep 28, 2008)

Or dedicated astro photography cameras. These often have a peltier cooled sensor and a heatsink on the back. Or they stack with gaps in the images. Like a 30second exposure then a 20 second gap x100 doesn't cause nearly as much heat as the alternative 80minute exposure. Providing the resolution is low enough you don't notice disjointed stars. Obviously this has it's limitations though. 

But given that a film camera is available for $50 and a roll of film $10...


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