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PhotonCollector
13-02-2006, 01:04 PM
Hello everyone,

Here's a recent image I did of the Tarantula Nebula.

Image Details:
Telescope: 12-inch f/5 GSO reflector telescope, hand guided.
Camera: Canon EOS 300D (not modified).
Exposures: 3 x 8min. exposures @ ISO200
Total Exposure time: 24 minutes.
Filter/equipment: Used Baader Multi-purpose Coma Corrector.
Ambient Temperature: >20C hot summer weather

You can see a higher resolution version here http://www.skylab.com.au/pmsa/Tarantula%20Nebula.html

Clear Skies
Paul Mayo

h0ughy
13-02-2006, 01:11 PM
Very Nice, be nice to see a modded shot and add that to the mix, might have to work on that one!

Robby
13-02-2006, 01:34 PM
Very intriging! Love the whisps of red...... Stunning!

PhotonCollector
13-02-2006, 01:38 PM
Yeah, objects like this really make it obvious that there is a lack of Ha. I'm intending on modding my camera real soon.

Paul

Robby
13-02-2006, 01:59 PM
See this thread for a shot of the Tarantula that I took with Houghy's modified 300D a couple of weeks back... http://www.iceinspace.com.au/forum/showthread.php?t=7308
You can see how more sensitive it is to Red, but something in me still likes the asthetics of the un-mod'ed images! In particular this one...
Cheers

PhotonCollector
13-02-2006, 02:17 PM
Geeday Robby,

Oh yes I see what you mean. The image with the modified camera shows the Tarantula to be a red and red only! (apart from some blue). While the unmodifed camera shows hues of green AND red. Your right I think I like my image better too!

So why does the modified camera only seem to see red ? where are the green hues ?

cheers
Paul Mayo

Robby
13-02-2006, 02:51 PM
Red is the dominant colour in most Nebula, so it pretty much overpowers most other colours. The advantage being more detail, for less exposure time. You can boost the other channels in Pshop if you so desire, but in this case I left the colour balance as imaged.

Robby
13-02-2006, 02:59 PM
I have boosted a little of the Green & Blue in my Tarantula shot. Perhaps this is more to your liking!
Ahh the ethics of astrophotography! Should we try and show accurately what is there is just make pretty picture!.. Me like pretty pictures :D
Cheers

Robby
13-02-2006, 03:02 PM
Hi Paul,
What did you do post processing to make the filaments look so soft? Is that done with one of those noise removal programs?
Cheers

ving
13-02-2006, 03:38 PM
astrophotography is more of an art than just taking pic hey :)

lovely spiders people :)

atalas
13-02-2006, 03:44 PM
Nice shot Paul !

PhotonCollector
13-02-2006, 05:44 PM
Hi Robby,

Soft filaments maybe from using ISO200 ?

Paul

rogerg
13-02-2006, 05:59 PM
Paul,

That's quite a nice image of the 2070. Your image has different colours to what I have seen in the past, most being very red/pink vs your very blue wihch is interesting. I expect simply because of processing and the particular DSLR/telescope combination?

I really like the softness of the colours - not over processed and not too "contrasty".

It's interesting you use ISO 200 for it on the DSLR - as I am soon to be an owner of a 350D can you tell me - with a DSLR is there a difference in image quality between 1600 ASA and 200 ASA? Does the 200ASA speed produce a smoother (less noise) image?

Roger.

PhotonCollector
13-02-2006, 06:16 PM
Hi Roger,

gee I forgot to mention that I used a mask technique with this image so that the core of the nebula was not over exposed.

Yes that's right, the ISO200 produces a smoother and less noisy image, but of course at a reduced sensitivity.

With my 12-inch equatorial telescope I can afford lower sensitity in return for smoother images.

For matter of interest the image isn't dark subtracted either! but yes I did use the freeware version of Noiseware on the image to reduce noise. I process all my images with Photoshop = manual stacking/averaging/image alignment/etc).

Paul

Robby
13-02-2006, 06:35 PM
That's what I was getting at Paul... I thought it looked like Noiseware softness. I have yet to have much success with Noiseware, as it always seems to soften the lines too much... But you seem to have found a reasonably nice balance here.

Robby
13-02-2006, 06:39 PM
Hi Roger,
There are many thoughts re. ISO settings, but it does seem the best signal to noise ratio is achieved at ISO200... I am still stuck in ISO800 dark ages as I now have such a comprehensive Dark & Flat field library it seems like such hard work to move lower, & have to redo all these! :sad:
Cheers

tornado33
13-02-2006, 10:00 PM
Thats a very nice Tarantula, the different colours grading from pink to blue look great Paul. I will have to see about re imaging that at lower ISO too, seems that lower ISO allows the greater dynamic range, coupled with masking to get the outer detail while not washing out the bright bits. (and 12 inches of aperature dont go astray either ) :)

tornado33
13-02-2006, 10:03 PM
BTW, Robby, with your tarantula shot, seeing it was with the modded camera, were you using an IR cut filter to stop excess IR light coming in?
Scott

Robby
14-02-2006, 06:44 AM
Yep I used an IR-cut filter. It's a very red bugger!

FOOTPRINT
14-02-2006, 10:03 AM
Hi All,
An interesting discussion as regards the colour of ngc2070, I downloaded an offical Pix. taken on Film (should be about right colours) and am attaching it, with my picture taken with the modded Canon (no filters) and and ED80, my guiding was very poor that night, had a problem at this low Dec. (fixed next night, got 47 Tuc. again but the weather dident let me redo ngc2070) but will give some idea of what you get with a modded Canon, no colour correction was made, but it could be adjusted to suit the processor.

regards.....Jim

Robby
14-02-2006, 10:20 AM
"Correct" colour is very assumptious. Just becaus it is film, doesnt' mean the colours are correct... Every film has a different colour balance, and in many respects are even more variable than digital..
Eddie T had some good comments re. colour in a thread about a year ago.
He reckons he can calibrate for "correct" colour based on some reference stars. http://www.iceinspace.com.au/forum/showthread.php?p=27413 Post #31.
I'm sure you have all seem his award winning 2070 pic http://astroshed.com/ which is colour calibrated...
IMHO there is no such thinkg as "absolutely correct" colour in Astrophotography. Pretty pics are the go here as far as I'm concerened... So as long as we enjoy what we image and get a couple of "wow's" from friends and family I'm happy!
Cheers

Itchy
14-02-2006, 07:21 PM
Hi Robby,

I absolutely agree with you about colour. Indeed, I have heard it said that colour film shots are biased to the red. We are so used to seeing red film shots that we tend to expect the same from digital. Of course, an modded camera certainly picks up the Ha a lot better. NGC2070 is a very interesting object for colour. Here are two shots that i have done with an unmodded 300D. The first one is straight prime focus. No matter what I did I could not get any red in the nebula. 12 months latter, I shot 2070 again, same scope and camera, but with a Baader UHC-S Filter (and a lot of careful processing).

Cheers

PhotonCollector
15-02-2006, 02:48 PM
Hi Robby and Itchy,

yeah I didn't want to say previously..... but since you have said it for me.

I certainly do and always have believed we have been "conditioned" over the past several decades (the film era) to expect to see nebula as red (or a hue thereof).

I don't really agree that all emission nebulae are just glowing in H-alpha (red) I think some glow in H-beta as well. H-beta is in the green part of the spectrum ! Don't get me wrong I'm sure lots of nebulae are just emitting Ha.

After Robbys posts on this thread I rechecked my images of the Tarantula to see if I could make it all red - but that would have meant removing all the photons collected in the green channel - which didnt make sense to me. I mean to say - if the camera collected strong photons in the green region of the spectrum then according to the data this nebula (2070) is glowing in green as well as red.

I guess this could be checked by seeing if the Tarantula is known to glow in Hb as well as Ha.

On this issue - you may note the amount of green I managed to get in a previous image of the Helix nebula at this location http://www.skylab.com.au/pmsa/Helix%20Nebula.html

I can say with certainty that the same camera on my 8-inch f/6 reflector basically did not reveal any green in the Helix (I'm using the 12-inch f/5 now) even with longer exposures.

Great talking to you guys

Paul Mayo