Lagoon and Trifid in Sagittarius - Wide Field - 1st attempt

[Gina]

Got some breaks in the clouds last and I was able to get a small amount of imaging done. I ran the wide-field setup beside the scope and made double use of the imaging time. I mainly concentrated on the Sagittarius area. Here is the wide-field result, taken with my Super Takumar 55mm f1.8 lens stopped down to f4. Exposure was 30 secs at ISO 3200. 49 lights, no darks or flats yet. Stacked in DSS and post-processed in PS. Cropped slightly to remove trees and cloud at the bottom and vignetting at the top and scaled to 1024px wide. I need to sort out the focus but I had so little time last night with limited gaps in the cloud. It clouded over entirely by 1am and at that point I gave up. I also had to dump a considerable number of lights where belts of cloud cropped up.

[ultranova]

Hi Gina, that is a nice shot, looks like your having a bit of trouble with the focus, had the same problem with my canon 1.8 lens, it was so prone to moving(focus) because it was quite loose in the end i had to put a elastic band around it to hold it, after i finaly got it good, even using the live focus, still had the same problem, looks like its good untill you zoom in using playback, hate to think how much time i wasted lol.

its a shame ,you have the makings of a great shot.

Paul

[nmoushon]

Looking good so far. Does need work on the focus though. Just a suggestion but I would pull the camera up a stop to like 2.8 and drop the ISO to at least 1600. Would help a lot with noise and star color. Though now I'm thinking you prob did those setting because of the short time in between cloud covers.

[nightskystargazer]

Hi Gina,

Very nice 1st attempt at Lagoon & Trifid .

CS,KLU,

.

Tom

[themos]

Keep at it! f/4 should eventually produce some decent results with that lens. There's plenty of nebula signal there. To beat CA, you might want to focus separately for the red and the green-blues and combine only the focused bayer channels. I tried this method a couple of summers ago but SGL's search facility is not helping at the moment.

[Tom OD]

Hi Gina,

Good start Gina. It might be the processing but there are bright star cores. Maybe it was in focus for some of the frames, giving you bright point cores, and then the temp changed, or the lens shifted a bit to go out of focus.

[Gina]

Hi Gina, that is a nice shot, looks like your having a bit of trouble with the focus, had the same problem with my canon 1.8 lens, it was so prone to moving(focus) because it was quite loose in the end i had to put a elastic band around it to hold it, after i finaly got it good, even using the live focus, still had the same problem, looks like its good untill you zoom in using playback, hate to think how much time i wasted lol.

its a shame ,you have the makings of a great shot.

Paul

Thank you The lens shows no loose ness but something seems not right.

[Gina]

Looking good so far. Does need work on the focus though. Just a suggestion but I would pull the camera up a stop to like 2.8 and drop the ISO to at least 1600. Would help a lot with noise and star color. Though now I'm thinking you prob did those setting because of the short time in between cloud covers.

Thank you Yes, the focus definitely needs looking at - must make a Y mask and try that. I suspect focussing needs to be extremely precise. Might be worth adding remote focussing with reduction gearing. I need to have a closer look at my lenses. Yes, I had to keep the time low so as not to lose too many frames to cloud. It was a bit long as it was but without cooling on this camera I couldn't go to a higher ISO. This was very much a compromise. I look forward to a properly clear night

[Gina]

Hi Gina,

Very nice 1st attempt at Lagoon & Trifid .

CS,KLU,

.

Tom

Thank you Tom

[Gina]

Keep at it! f/4 should eventually produce some decent results with that lens. There's plenty of nebula signal there. To beat CA, you might want to focus separately for the red and the green-blues and combine only the focused bayer channels. I tried this method a couple of summers ago but SGL's search facility is not helping at the moment.

Thank you - that's a very interesting point

[Gina]

Hi Gina,

Good start Gina. It might be the processing but there are bright star cores. Maybe it was in focus for some of the frames, giving you bright point cores, and then the temp changed, or the lens shifted a bit to go out of focus.

Thank you Tom I think I'll go through the subs and see if I can see any variations - there may be more to reject with advantage.

[Gina]

I've now been through the lights again and pruned out the poorest ones and a couple of rejects I missed earlier leaving 36 which is still a reasonable number. I've also examined the individual frames zoomed in and the stars are a light green disc with a bright central point in the source data - so it isn't the processing and it isn't that some frames are better focused than others. I wonder what's going on here.

I've now stacked the 36 lights and processed the resulting TIFF file in PS. I've again rotated it to the right way up (roughly) and cropped off the trees and low cloud from the bottom. Then resized and uploaded. I'm planning to get some flats this morning and darks tonight. I think flats will make quite a difference. I've also included a sample sub in JPEG form, just rotated and resized but otherwise totally untouched.

[themos]

Hello Gina, I've found a link to what I wrote 2 summers ago:

http://stargazerslounge.com/topic/77819-dealing-with-chromatic-aberration-in-dslr-lenses/

[Kbramley]

Nice, especially in challenging conditions, I do believe you also got M16 and M17 in the top left too

[Gina]

Hello Gina, I've found a link to what I wrote 2 summers ago:

http://stargazerslou...in-dslr-lenses/

Ah yes, thank you That does seem to be the problem. When you said before that you got red fringes I though it was different because I'm getting green fringes/discs. I guess this is the GG & B pixels - with 2G to one B making it look more green than blue. So... I'm focused for R and out of focus for GGB pixels.

One thing I could do is put my Ha clip filter in and focus that on a bright star then run a session on that. Then take it out (maybe replace with CLS-CCD filter) and refocus for a session for G & B. I could then use Ha for the R channel and add to the separated G & B. I could also use the Ha as a luminance and add it in.

BTW - I've been taking flats this morning and noticed I had the aperture set to f2.8 not 4 and yet I was sure I turned the stop ring by 2 clicks. Wait a minute... does it have clicks at 1.8, 2, 2.8, 4, 5.6 etc. I'm thinking I guess the CA will be less at f4 than f2.8.

[Gina]

Nice, especially in challenging conditions, I do believe you also got M16 and M17 in the top left too

Thank you Yes, I noticed what I thought might be other nebulae

[Gina]

Took darks, flats and bias frames today and ran DSS on that plus the lights. Processed in PS, rotated, cropped and resized. Here's the result. Can't see much improvement myself...

[JamesF]

Thank you Yes, I noticed what I thought might be other nebulae

I'm pretty sure they're M16 and M17, too.

James

[Gina]

Yes, think they must be

Now I know what the focussing problem is I think I'll concentrate on Ha for wide-field - no CA then. I'll probably have cooling on that camera by the time we get another clear night so can up the exposure. Clearly without an APO lens I can't take full colour in one session so I'll go for Ha, G, B with the G & B combined in the second session. I don't think there would be any benefit in doing a red only session.

I've been trying to separate out the red channel of this image in PS - I tried setting the green and blue levels very high but it didn't work. Looks like I shall have to do it another way. I note that there is software to do this very thing.

[themos]

You'll still have to fight field curvature, some people say that focusing on a star halfway to the edge works better than focusing on a star in the middle, you "split the difference".

[Gina]

You'll still have to fight field curvature, some people say that focusing on a star halfway to the edge works better than focusing on a star in the middle, you "split the difference".

Ah yes, good point - thank you

[Gina]

I've had another play with this in PS - I think it's a bit better. Well the weather won't let me re-take it!

[Gina]

Apart from M8 and M20 there's M16 and M17 and also M24 in this image. There are also a couple of small star clusters - I can make out what I think is M23. I think if i can get more imaging time on this area I can drag quite a lot more out of it