images are getting redder

[SkyExplorer]

Hi all,

Wondering if anyone can help....

I noticed last night when taking 120s subs with my 450d that the background progressively got redder (more orange) as the camera produced more subs. After 25 subs the background was noticeably different to the first sub. I think I had 10 seconds between subs.

I'm thinking this could be because the camera is not cooling down enough between subs and slowly getting hotter.

Is this a reasonable assumption to make?

Thanks

[brianb]

Possibly the atmosphere was getting damper, or there was a very thin layer of high cloud gradually thickening, so scattering more of the "red" light pollution into the sky background. But I think your theory holds water. You could try that out without wasting clear sky time by shooting a series of exposures with the lens cap on ... if the background progressively reddens, it's got to be somthing internal to the camera, and just about all that makes sense is progressive heating (which will plateau as you describe) or a voltage drop as the batteries discharge (which will continue to grow, possibly accellerating, as time goes on).

[SkyExplorer]

Could be voltage drop as the battery was on it's last legs last night (forgot to charge it after the last imaging session )

There were also clouds rolling in from the west so again could be that I guess. But it was progressive over 25 subs and not sudden, so maybe not clouds

How long do people leave between subs when using a dslr ?

Is say 10% of the sub a good target to aim for?

[ollypenrice]

Don't know about cooldown but one of my regular DSLR experts cools his camera. He now has a pukka cooler but used to use physio ice packs kept in rotation in our freezer! They are bendy and can be persuaded to stay in close proximity to the camera. Last year his cooler actually froze his camera to death - or into suspended animation, since it came back to life in the morning. Sighs of relief all round.

Try the physio packs...

Olly

[dph1nm]

Progressively going lower in altitude will produce this effect. Was the target setting?

I would definitely put my bet on the atmosphere.

NigelM

[SkyExplorer]

I was imaging NGC7000 so it was almost right over me whilst I was imaging it.

[lukebl]

How long do people leave between subs when using a dslr ?

I have about 9 seconds between subs, and they don't get any redder over time. If anything, my images get less red as the sky gets darker through the night. I'd go along with the theory that it's light pollution brought on by increasing high cloud, mist or humidity. It's amazing how even the slightest increase in humidity will result in the reddish cast of the images.

A Light pollution filter makes a massive difference, even the basic SW one which I use. Do you use one?

[dlp]

Humidity makes a huge difference to how much orange I get in my images from the darned street lamps.

David

[themos]

My bet is either increased Light Pollution from increasing humidity or possibly dew forming on the lens.

[Beyond_Vision]

There is no point in having a delay between shots other than to let the camera write to card etc. The amount it would cool down by in 10s or even 30s would be minimal compared to the exposure time. It's better to let the camera equalise in temperature and let the dark subraction take care of the noise. There is precious little time to do imaging so no point wasting time during the imaging run.

Regards

Kevin

[SkyExplorer]

But the odd thing is when I slewed to M31 and took a 3 min sub it was dark again.

Thanks Kevin, will reduce the gap between subs then.

To stop dew forming do I just need a heater around the lens element of the 80ED?

A Light pollution filter makes a massive difference, even the basic SW one which I use. Do you use one?

Yep I have the SW one, are there better ones then?

[themos]

A dew shield is the first line of defence.