How much integration time?

[Herzy]

The clear nights are rare here. I mean really rare... Like one every two months. 

I really want to get a beautiful image of a nebula of some kind, and I'm willing to pull an all-nighter of imaging. However, I'm in a very light polluted sky so would spending one of my very rare nights imaging something so faint yield bad results? For reference, I can't see any of the Little Dipper except Polaris. 

I really want to capture the North America nebula or the crescent nebula.

[Brent]

I'm by no means an expert and someone else will be along soon, but I would say give it a go, it's the only way you'll find out for sure.

Results will partly depend on your equipment of course, but you WILL get something. As an idea, I can only see at most 3 stars in Ursa Minor including Polaris on most clear nights. I also get maybe only one or two clear nights a month which I can actually use, so I feel your pain on that one!

By the way, both targets you mention are rich in Hydrogen Alpha so you'd need a modded DSLR or a CCD camera to be able to get something really worthwhile on them.

Without an LP filter you possibly won't be able to go far past two minute exposures but there's still plenty to go at with that.

I made the move into imaging about 2 months after getting my smallish 'scope because the horrendous light pollution was stopping me seeing much at all. Imaging kept me in the hobby basically! (but then emptied my wallet )

[matt-c]

I'm not sure what gear your using but the only way I've been able to overcome light pollution is moving to narrowband. 

If you can't go narrowband try and get a decent light pollution filter and stack as many as you can.  Learning to process will help alot and plug-ins like gradient xterminator will make life easier. 

Main thing is just to have a try and enjoy it.....easier said than done 

[jimao22]

Check this out - http://www.gibastrosoc.org/sections/astrophotography/optimum-exposures-calculator

 

[wimvb]

I agree with the above: to image the NA nebula, you need a camera that is sensitive to Ha (650 nm), and from a light polluted site, this is best done with narrow band imaging.

Depending on the IR -cut filter in your Nikon, it may still pick up some Ha, you'll just have to give it a try. A decent light pollution filter will make it possible for you to take longer exposures.

Personally, with my unmodified Pentax, I haven't had much luck imaging the NA nebula, but have had some success with the California nebula (NGC 1499). This nebula seems much brighter and therefore easier. Other possible targets would be the Heart and Soul nebulae in Cassiopeia. Whichever you capture, it will take a lot of processing to bring out the nebula.

Good luck.

[Herzy]

 

28 minutes ago, wimvb said:

I agree with the above: to image the NA nebula, you need a camera that is sensitive to Ha (650 nm), and from a light polluted site, this is best done with narrow band imaging.

Depending on the IR -cut filter in your Nikon, it may still pick up some Ha, you'll just have to give it a try. A decent light pollution filter will make it possible for you to take longer exposures.

Personally, with my unmodified Pentax, I haven't had much luck imaging the NA nebula, but have had some success with the California nebula (NGC 1499). This nebula seems much brighter and therefore easier. Other possible targets would be the Heart and Soul nebulae in Cassiopeia. Whichever you capture, it will take a lot of processing to bring out the nebula.

Good luck.

Here is a bit more reference. The only two nebulas I've ever tried to image are M42 and the Flame/Horse Nebula. The flame nebula was barely visible in a single frame (1m ISO 1600), and the horse nebula was not visible. The flame nebula has a magnitude of 1.9. 

It scares me to think that the Flame Nebula, with a magnitude of 1.9, is barely visible, and the Heart Nebula has a magnitude of 18.3. If I spent the whole night imaging the Flame Nebula I could get some good results... but with the Heart Nebula? I don't know. :/ The California Nebula has a magnitude of 7, which is not  THAT bad.

Would you mind posting your picture of the California Nebula and giving me the details? Also, what are your skies like? Sorry for flooding the questions, I just get very aggravated with astrophotography when I spend 8 hours imaging and get awful results.

Edit:

I guess magnitude of 7 isn't all that bad because M101 has a magnitude of 7.9 and I could get quite a bit of detail in that with only 2 hours of integration time.

[wimvb]

The California Nebula images are in my album (see my profile, notify me if you have trouble viewing them).

The widefield which includes M45 is 12 x 300 secs (unguided) at ISO 1600, 35mm f/4.5

The image with just the nebula and Atik (the star, not the camera ) is 25 x 180 secs (unguided) at ISO 1600, 135 mm f/3.5

The hardware is in my signature. No filters were used during capturing.

Here's a single frame (converted to jpeg using RawTherapee) from the latter. The nebula is barely visible to the right of the center.

As for my locations, I haven't rated them, but this will give you an indication:

My darkest site: Milky way clearly visible, Andromeda galaxy just visible

My backyard: approximately 4 stars of Ursa Minor visible. Light pollution from the suburbs, a street light and neighbours lights.

Then I also have a site which is inbetween, where these images were taken. This site is somewhat better than my backyard, the milky way is barely visible, with some light pollution from Stockholm to the south.

All my images were stacked and processed in PixInsight using bias frames, but no flats. I did take dark frames at the time, but I have reprocessed the images without them and used cosmetic correction instead. (see my post here, which shows an extreme crop of the California Nebula, taken from the wide field image:)

 

[Herzy]

Interesting. Your single frames have way more stars then my single frames, but if I just get twice the integration time I could probably get similar results. Do you know of any other relatively bright nebulas that I could go for? Preferably ones that are up at like 10:00pm.

[wxsatuser]

A decent LP filter will really help.

Do we need a modded camera, if you pick the right camera, no.

Canon 6D and 7D MK2 see the red perfectly fine, others may do as well.

7 x 30 secs from an unmodded Canon 6D.

Flaming Star 28 x 120secs from a unmodded Canon 7D mk2

[Herzy]

1 minute ago, wxsatuser said:

A decent LP filter will really help.

Do we need a modded camera, if you pick the right camera, no.

Canon 6D and 7D MK2 see the red perfectly fine, others may do as well.

7 x 30 secs from an unmodded Canon 6D.

Flaming Star 28 x 120secs from a Canon 7D mk2

Your skies must be fantastic. I couldn't dream of that in only 7 x 30s exposures.

[wxsatuser]

Just now, Herzy said:

Your skies must be fantastic. I couldn't dream of that in only 7 x 30s exposures.

Unfortunately my skies are pretty bad so I use Astronomik CLS clip filters.

The Flaming Star subs were taken when it was to the West of here and I have a school
and leisure centre floodlights to deal with.

[The Admiral]

5 hours ago, Herzy said:

Your skies must be fantastic. I couldn't dream of that in only 7 x 30s exposures.

But if you recall seeing this image in the "No EQ Challenge" Herzy, it was taken using a 50mm lens, and presumably with quite a big aperture, which is a far cry from what you are working with. With such a short focal length those photons are concentrated onto the pixels.

Ian

[ollypenrice]

I think the first thing I'd say is that astrophotos need time. That's just how it is.  I have a first class dark site and, even here, I never expect to take an image in a single night unless it's with our dual scope/camera rig (which means one night equals two nights.)

The second is to agree with Matt. If you are working in heavy light pollution then monochrome and narrowband is the only way to take excellent pictures. Narrowband works brilliantly in LP.

As for exposure time, I honestly believe that the only way to find out is to experiement because specific equipment and local conditions control the outcome.

Olly

[wxsatuser]

Samir Kharusi basically worked out that a typical urban light poluted site would need 16x more exposure than a dark site.

[wimvb]

15 hours ago, Herzy said:

 

Here is a bit more reference. The only two nebulas I've ever tried to image are M42 and the Flame/Horse Nebula. The flame nebula was barely visible in a single frame (1m ISO 1600), and the horse nebula was not visible. The flame nebula has a magnitude of 1.9. 

It scares me to think that the Flame Nebula, with a magnitude of 1.9, is barely visible, and the Heart Nebula has a magnitude of 18.3. If I spent the whole night imaging the Flame Nebula I could get some good results... but with the Heart Nebula? I don't know. :/ The California Nebula has a magnitude of 7, which is not  THAT bad.

Would you mind posting your picture of the California Nebula and giving me the details? Also, what are your skies like? Sorry for flooding the questions, I just get very aggravated with astrophotography when I spend 8 hours imaging and get awful results.

Edit:

I guess magnitude of 7 isn't all that bad because M101 has a magnitude of 7.9 and I could get quite a bit of detail in that with only 2 hours of integration time.

Be carefull when comparing magnitudes. Because nebulae are large/extended objects, they can have a low value magnitude, such as a bright star, but still appear very dim in an eyepiece or on a sensor.

https://en.wikipedia.org/wiki/Surface_brightness

The second thing that makes magnitude unreliable in this case is that it doesn't say anything about colour. An object may be bright in Ha (red), but still not register on the sensor if the sensor just doesn't pick up on that wavelength.

In the end it's all down to testing your equipment and conditions. But it seems to me that whichever way you go, a light pollution filter would be a good investment.

 

Good luck