Stargazing What is the best way to reduce overexposure in DSLR astrophotos?

[QuantumPion]

Hi, I've been trying to take some deep sky images with my DSLR. However, my pictures tend to get washed out and overexposed after more than just a couple seconds. Is there something I can do to fix this, or is this just an issue with ambient city light? I'm already using a lens hood, and viewfinder cap, and it's a moonless night. I am using a 50mm f1.8 lens.

image hosting api

 

[Chronos]

Have you tried adjusting the ISO setting? Having it set too high is a common cause of poor contrast.

 

[russ_watters]

What is "a few seconds"? But yes, that looks like a symptom of skyglow. Using the "levels" function in photoshop, you can clip the low end. It is a standard technique.

 

[davenn]

However, my pictures tend to get washed out and overexposed after more than just a couple seconds. Is there something I can do to fix this, or is this just an issue with ambient city light?

What is "a few seconds"? But yes, that looks like a symptom of skyglow. Using the "levels" function in photoshop, you can clip the low end. It is a standard technique.

very easily fixed in PS or lightroom ... lightroom has a nice feature called de-haze that darkens the backgrounds very well
let me see if I can find an example from my own collection

Dave

 

[davenn]

OK here's a real fast comparison and edit of a pic of mine in lightroom The object is the LMC ( Large Magellanic Cloud).

first pic is the jpg out of the camera
second pic is the RAW file edited and a jpg conversion done
you can see the huge difference in colour, and detail

Note I used the term "RAW File" ... I don't know what camera you are using, hopefully it has a RAW imaging mode
if you are not using it, USE IT ! I cannot stress this enough. Editing jpg files is very self defeating because of the huge
amount of image compression done to generate the file ... lots of data is lost.Dave

 

[QuantumPion]

I don't have photoshop but I guess that is the only way around it! I'm using a Canon T5i. ISO was 800 or 1600 I believe. Exposure was 2 seconds for first picture and 3 seconds for second IIRC.

 

[davenn]

I don't have photoshop but I guess that is the only way around it! I'm using a Canon T5i. ISO was 800 or 1600 I believe. Exposure was 2 seconds for first picture and 3 seconds for second IIRC.

OK what about lightroom ?
These days you can get a photoshop and lightroom package for around US$10 - 12 / month subscription really good value
I had to look up a T5i ( that model naming style is mainly only used in the USA) ... ahhh, the EOS 700D ... It's one of the 3 Canon cameras I have
Also have the 5D MKIII and the 6D.
The 700D I did surgery on and removed a couple of the filters to make it a better astro camera ... more sensitive at the red end of the spectrum

you didn't respond to my comments on the use of RAW files ??
I hope my pic's helped you to show you how to overcome city light skyglow ?

Dave

 

[QuantumPion]

Yes thanks for the help. Next time I will get RAW's instead of JPEG's so that if I eventually get photoshop or lightroom I can mess around with them. Are there any free/open source tools that can do the required editing? Also, would image stacking multiple ~2 second exposure shots be worthwhile to try?

 

[davenn]

Are there any free/open source tools that can do the required editing?

there is GIMP -- free, I don't know if it has all the features that LR and PS have, but, from what I understand, it has many of them
I don't know if it is easier or harder to use

Also, would image stacking multiple ~2 second exposure shots be worthwhile to try?

yes, that is always good ... it won't stop the sky glow, but will give more detail on the starfield

I have to assume you were shooting those images from a suburban area ... being that the trees were also well lit
find a spot out of your town/city where the ambient light and the sky glow level is low

for image stacking a commonly used and free program is DSS ( Deep Sky Stacker) use DSS only for the stacking
the processing is still done in your other fav editing program. DSS can do processing, but isn't as good as say LR or PSDave