Orion Nebula

[kimo]

Hi,
I have No experience on Astrophotography.

Early morning I tried Photography on Orion M42. I am having problem with light pollution. multi-storey car-park cause too much light pollution.

I like to know which exposure time is the limit for me?
Here I posted some images. single exp raw image 1 min , 1.5min, 2min. I posted combined 24 mins processed image, its don't looks great to me, lots of noise.



1- min exp



1.5 min exp


2 min exp


26 min. 7 X 2min, 8 X 1.5 min.

Thanks for Advice.

[shirox]

Hi Kimo,

I'm guessing the process of capturing your mount is not auto-guided.
Actually for deep space objects, normal guiding is sometimes not so efficient.
There are a few steps or items required in place to take a satisfactory image.
Even for short exposures, the results are rewarding.

for example,

this is a single raw exposure of 1 mins auto guided



even for 15 secs on this image below, you can see the amount of details when its autoguided


Join us for imaging sessions sometimes there are a few imaging group around singastro and i'm sure everyone of us will be more than glad to share how to do it.

*P.S. I'm no expert too. barely crawling in astrophotography.

[kimo]

thanks . what types of camera have you used DSLR or CCD? any LPR on it?

[shirox]

i was using a 500D with a CLS filter. took this in punggai

[kimo]

Thanks Bro, Yes, in singapore is not possible to take such clear pic in 1 min exp.

[shirox]

thats why haha. you'll notice why most of us goes to malaysia

[rcj]

Hi Kimo,

Good attempts on going into bracketing of exposures to harness how much signal one can extract per given conditions of site and setup!
Basically, the best raw sub-exposure is one of moderate ISO (200-800) and at an exposure duration that will not saturate the histogram (see from your camera's histogram display). What this means is there should not be a spike at the right end of the histogram (spike means, stars or signal has reached saturation clipping point, and the dynamic range is compromised). The "ideal" exposure is when you histogram is like a bell-curve with the peak emphasis more towards the left end and making sure the ends of the curve tapers down to a "nice" zero at either ends. I cannot give you a quantitative number now based on the images that you have posted, more details need to be known before ascertaining the "correct" exposure - but it looks to me the 1min subs are ok...the stars are not bleeding white, and the background sky colour (light pollutive) is not overwhelming, but again, this is from eyeballing which is never as good as determining from the raw histogram itself. As Elton has mentioned, the data is a lot cleaner when you execute the procedures under darker skies. Data is also very much easily processed, lesser to stack for a certain desired result, etc. What did you use for stacking? Try to neutralize the background, the 26 stacked result is a bit on the red side. You can use Levels in photoshop for this. But do not overdo the neutralization and ending up making the background jet black. A good number (out of 255), would be to attain readout numbers of 20 counts per channel for a start, maybe a bit bluish (25 counts) for blue channel for a dark blue background, or whatever that is pleasing to you. Have fun most of all!

[kimo]

Hi RCJ,
Thank you very much for your constructive advice. I tried few ISO up to 800 but 200 is acceptable and can’t go beyond that due to pollution. I am not using Autoguider as it requires more advance setupand canculation to maintain good guiding. May be LPR filter will extend the exposure limit. I used Deep sky Stacker. Thanks again.

Histogram of raw image.

1 min exp
1.5 min Exp
2min Exp

[rcj]

Kimo,

looks to me somewhere between 1 - 1.5min is optimal for your setup and location at that time. ISO 200 will be great. What camera are you using, is the DAC 14 or 12 bit? You can try IDAS LPS P2 filtration, although may be a bit expensive, but it does not skew or alter spectral response much, and easier to colour balance.

[kimo]

I was having some problem with focusing after the camera was modded. Focus no
longer works with view finder. I made a measurement scale on to the telescope focuser
to achieve near focus. Two pictures were toughed little bit with Photoshop. No filter was used.

I used GP2 mount which I modified to attach Auto guider. It was used for long exposure star tracking.