Ha imaging how long subs do you need?

[blinky]

This is 6 X 13min subs - The longest subs I have used yet. Very pleased as there is no star trailing evident. I am however surprised at how faint the Pinwheel galaxy is, I know i had an Ha filter in (To block out the moonlight) but it's a 13Min sub! The scope was a ZS66 with one of those little focal reducers in as well.

[blinky]

Oh and does anybody have any idea what the blob at the top left might be?

[Ben Ritchie]

I'm not too surprised.

An H-alpha filter is most effective for emission-line nebulae, e.g. M42. With galaxies, you're seeing light from their star-forming regions (e.g. the equivalents of M42 within M101) plus a small fraction of the starlight from the galaxy, but galaxies are predominantly broadband targets - i.e. you're collecting the combined starlight from billions of individual stars - so a H-alpha filter serves to drop a large fraction of the signal.

[blinky]

TBH I am wondering if I want to keep this camera and Ha filter. I dont think my scopes have a long enough focal length to go for the small planerty neb's like the cats eye etc

What targets are around at the moment that would suit either the ED80 or ZS66 and Ha?

[Ben Ritchie]

Don't give up - you just need to pick emission-line targets like diffuse nebulae, which are both large (suit the 80ED/ZS66) and well-suited to H-alpha imaging. I know some people who do nothing but narrowband imaging and they seem to keep busy.

Part of the problem is that the classic Messier list is not particularly well suited to narrowband imaging - of course there are some nebulae, but the majority are open/globular clusters or galaxies. A good list of H-alpha targets is the Sharpless list, e.g.

http://galaxymap.org/cgi-bin/sharpless.py?s=1

[Whippy]

tbh Craig if I was planning on imaging Ha on galaxies, it'd be in conjunction with LRGB data and even then, it's be on objects like M82 and M33 where the Ha would make a real difference to the image.

Emission and planetary nebulae are your choice targets for Ha and there's not a lot of them about at the moment . If you get out early enough you could get some time in on the Rosette but we're heading into galaxy season, unless you want to stay up late and wait for Cygnus to rise out of the east, it's slim pickings for a while I reckon.

btw, not sure what the blob is, dust ***** maybe?

Tony..

[Doc]

Maybe NGC 5474 at 10.8 mag.

[blinky]

Don't give up - you just need to pick emission-line targets like diffuse nebulae, which are both large (suit the 80ED/ZS66) and well-suited to H-alpha imaging. I know some people who do nothing but narrowband imaging and they seem to keep busy.

Part of the problem is that the classic Messier list is not particularly well suited to narrowband imaging - of course there are some nebulae, but the majority are open/globular clusters or galaxies. A good list of H-alpha targets is the Sharpless list, e.g.

http://galaxymap.org/cgi-bin/sharpless.py?s=1

That site looks good but how do I locate these objects in starry night?

[Psychobilly]

Craig.

Wait a few months for Cygnus and you'll have a field day... my fav area of the sky and I cant wait to get back at it again with the modded 1000D...

have you thought of IC1396?

Billy...

[blinky]

Craig.

Wait a few months for Cygnus and you'll have a field day... my fav area of the sky and I cant wait to get back at it again with the modded 1000D...

have you thought of IC1396?

Billy...

Nope but I will add it to my target list!

[RobH]

Hello Craig.

As others have said, this is mainly galaxy season until the summer stuff arrives, when you have all sorts of targets perfectly suited to the ZS66 and Ha. The Veil nebula complex, North America nebula and loads more.

There is a lot to be said for grabbing some Ha with some galaxies, especially the more face-on they are, as the star forming regions are more easily seen and Ha data will often work well in these cases when you add it to the red channel.

I generally add it as another layer over the red, and set the blend mode to 'LIGHTEN'. This has the effect of highlighting the areas strong in Ha, while not making the stars smaller, which can result in green/blue rings around the stars.

If you grab some LRGB data of M101, the Ha you have there will add nicely to it.

Cheers

Rob

[brendant]

Craig as Doc correctly identified the blob at the top left hand corner is NGC 5474.

Brendan

[MartinB]

Craig, hang onto that Ha data just like Rob says. A bit of Ha nicely enhances an LRGB 101. How about the Leo triplet, M81 and 82. The Makarian Chain. Enough to be going on with?

[Tim]

Isnt the Rosette Neb pretty rich in Ha too?

Its always the way though, clear nights are nearly always moon nights.

[blinky]

The thing with the rosette and makarians chain etc is the wide FoV that I dont get with this cam but do get with the DSLR. I am not sure if I could get all of the rosette in the same frame!

[MartinB]

Sorry Craig, what camera are you using?

[GordonH]

Hi

Regarding imaging of galaxies people are correct that they are not best suited to narrowband imaging unless you use Ha in conjunction with traditional LRGB, however it doesn't hurt to experiment as you may be rather surprised by the results, Check out the thread that I did on the Owl nebula and M108 entitled " The Owl and the pussycat", this was done using the HST palette and the Owl nebula came out very well, but so did M108 which is a galaxy. Regarding exposure times and how many, you should always aim at a minimum of 10 minutes for the sub frames (longer is better but this depends on the weather) and get as many subs as possible for each channel, using the zenithstar 66 with a reducer brings it down to about f5 which is the same as my Takahashi BRC-250 and I used 10 minute subs for my Owl nebula and M108 image

Below is the image of the Owl and M108 to help make my point

Best wishes

Gordon

[Whippy]

The thing with the rosette and makarians chain etc is the wide FoV that I dont get with this cam but do get with the DSLR. I am not sure if I could get all of the rosette in the same frame!

True, but you can always do a mosaic. The image I'm probably most proud of is my 3 pane mosaic of the California Nebula (in Ha funnily enough) done with the Atik and ZS66. Personally, I think you'd be mad to lose the mono camera and Ha filter. I know my imaging opportunites would be much more limited without one.

Wait until it gets warmer for the summer constellations, and you'll laugh as you watch the Moon crossing the sky while you're imaging some nebula.

Tony..

[blinky]

I suppose it makes sense to keep it. I was aware that galaxies are not best suited to Ha but wanted to try it as everybody keeps saying you can image as normal with Ha when the moon is around.

I will keep it till I at least get to try it on some nice Ha Nebula, the camera BTW is an Orion Starshoot II.