DSO Photography from a suburban setting.

[JimStan]

I have been an active amateur astronomer for years, but astro-photography is a new venture for me.

I am trying to capture fainter objects with a Nikon DSLR and an 8 inch F:10 scope from a fairly dark suburban setting. Running at ISO 1000, I am able to take 45 second subs, but when I try stretching the exposures to around one minute or more, the individual exposures just start to take on an orange glow, and a stack 10 or more has a distinct orange cast.

I hear of people taking five to ten minute subs, but I cannot imagine that this is going to be possible without taking the equipment out to some setting a long ways away from town.

Is there any answer to this problem, or am I stuck with taking pictures of the brighter star clusters, planets and the moon ? Something as dim as M101 is almost lost in the skyglow and no amount of processing can separate the arms from the background light level . Help !

[JohnnyD333]

Hi Jim,

Taking photos at a high ISO over long periods is going to fill up with light and noise. You need to subtract the light and noise using processing software. When using DSS for stacking, you can use the curves and RGB settings to pull out the detail in your image and darken the background. I dont know how dark your skies are, but unless they are extremely light polluted you should be able to get some detail.

Your scope is also at F10, which is a little slow for imaging. You will have to use much longer subs than a scope at F5 to pull out details. However, there are talented people on this site who get DSOs with webcams so this should not deter you.

Dont worry if your images are bright. Take some darks, get several subs of M101, and stack them in DSS. Play around with the colors and curves in the final image and you will be surprised what you can get from such a bright orange image. Good luck and let us know how you do during your next session.

[Sparrow]

Hi Jimstan - for astro imaging in an urban area, you need a light pollution filter - I too imagine in an urban setting and would not really be able to do so without an LP filter.

Regards

John

[jgs001]

I image from a suburban setting, lp could be worse but LP filters do the trick nicely. I use either the cheap sw LP filter which works, or a CLS clip filter (for my canon, I don't think they make them for nikon, but a 2" filter would work just as well). it all depends on what focal ratio I'm imaging with. Slower focal ratios I use the SW, faster the CLS. I've got an RC at f/9 and I'm using 10 minute subs on that with the SW filter.

[todd8137]

get a lpf filter or as said move the sliders in dss,or with your photo sofware remove the color cast,but its best to use the 2" sky watcher filter they cheap and do the job ,just make sure you do not clean the sw lpf to much the coatings are not the best

[JimStan]

I appreciate all the answers. Regarding the LP filter, I do have a 1.25" filter for my standard eyepieces, and a friend of mine ( who is working with me on astro-photos ) has a 2 " one. But our problem is when we try to put a Nikon camera directly on the back of a SCT telescope, using the camera "T" mount to Nikon bayonet at the prime focus.

We have worked with several different OTAs , the 8 " Meade, a 127 mm Mak style , and a 500mm Nikon F:4 telephoto lens.

None of these OTA/camera combinations ( you Brits call them "kits" I believe ) will allow either a 1.25 or a 2 inch LPF to go between the camera body and the OTA. That is the problem.

I cannot understand why some filter manufacturer has not come up with a size that will fit in a "T" mount barrel and take care of the light pollution situation. I bet if I could do that, I would be rich!

I am amazed at how universal our light pollution and sky conditions are. Here in Maryland, we go for weeks at a time with cloudy skies. Right now, we are seeing the effects of yet another hurricane and Thunderstorms from the Midwest bearing down on us, and when the skies finally do clear up, we will probably be under a FULL MOON !

Very frustrating.

Thanks for your suggestions. Feel free to comment further as you wish.

Jim S.

[JB80]

There are some Nikon fit filters here if it helps.

Hutech Astronomical Products - Filter Accessories

[JimStan]

Fantastic answer ! Now, can you tell me, is LPS-P2 a light pollution filter? Or need I ask the manufacturer that question?

Jim

[JB80]

Ummm, I think so. The LPS stands for Light Pollution Suppression. Hutech Astronomical Products - Light Pollution Suppression Filters

But they have two different ones listed, best to ask what the differences are if in doubt.

[Digz]

oooh good link Pibbles, Ive been after a clip in style filter for my D200 for a while

[JohnnyD333]

Jim, can you post one of your subs, Im just curious how bad the LP is.

[JimStan]

Here is a single sub of the Whirlpool Galaxy, taken with a friend's Nikon camera, using his Meade 8" F10 telescope. Ignore the dirty sensor, etc. for the time being. We were just trying to see if his setup was tracking and capable of taking DSOs. You can see the light pollution, as it is vignetted, and doesn't appear to have any "hot spots" around the edges, like I would suspect Amp Noise to appear. I believe the exposure was around 1 minute at ISO 800. We captured some of the spiral structure, but it is almost the same contrast as the orange glow! The Galaxy is at bottom center! BTW, you could NOT see any color in the sky with the naked eye.

[JohnnyD333]

Hey Jim,

It looks like you know the issues you are facing. There is quite a bit of vignetting, but you can fix that by using flats. Light Pollution is bad as mentioned, but you can pull data out of these photos with darks, noise reduction, and processing. The big one to me is the amount of data in the photo. At the F Ratio you are using and the short subs, the photos simply dont have enough data to work with. Even though many people are putting in hours and hours of data in photos, you can start off slow with 15 to 20 minutes worth of exposures. I played around with the sub you posted, there isnt much to work with but you do have M51 in your sights. I posted a 5 minute sub of mine to show how bright they come out. After some processing, you get the result I posted last. Keep taking more subs and read the tutorials and guides on processing. It takes time but you have made progress and it only gets better from here. Keep posting and good luck