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Just to show what tracking on the sky will do for star photos, here is Orion taken in twilight this evening, 30mm Sigma, 380sec (sum of 150 + 230sec exposures) @ f/1.8, ISO 250. Its a slight crop to remove the worst of the triangular stars around the edges, particularly the lower part of the frame where they were worst. Its not at perfect focus either, having to estimate infinity because the index marks are in the wrong place is real hassle. Colour balance is a bit weird too, with the dense Milky Way area having a greenish cast to the stars, but since its not evident in other parts of the image its likely to be a lot of work to remove, so I didnt bother. No doubt its partly related to the brightness gradients in the sky during twilight, hard to avoid with a wide angle lens.
M42 (the Orion Nebula) is saturated, as are all the bright stars, and many of them have a majenta colour, which is not their true colour, but an artifact of the camera. The Rosette Nebula is in the lower right hand corner too. Its even recorded the faint red arc of hydrogen emission known as Barnards loop, to the right and below the belt and sword (aka the saucepan) in the middle of the image.

I think I could get quite a nice image of the fainter nebulae in this part of the sky by exposing for maybe 15 or 20 minutes total in multiple exposures and playing with levels and contrast.




Gordon

Gordon,
Lovely stuff and really puts my attempt to shame, could you take us through your workflow a little to explain how you combine the two exposures etc I'd definitely be interested to learn more so I can give it another attempt. Looks like a need a faster lens would a 50mm 1.4/1.8 do the trick ?

Thanks Craig.
Equal length exposures are better, next time I'll take a stack of 30 or 60 sec.
NR on, and auto WB.
Raw images run through NC, I used 80% Vignette control, the light fall-off around the corners with wide open lenses is usually more obvious in astro photos than daylight ones due to the even background of the night sky. Just like photographing a grey card with spots on it really
I then used a very weak D-Lighting adjustment and a 10% unsharp mask.
Saved as a JPG, although I'd use TIFF if it was an important photo.
Then I used MAXIM DL, an astronomical image processing program, but I'm sure you could add them in PS, although I have never tried that. MAXIM has a routine to align the images, which generally works ok, but sometimes I have to manually align them by dragging them around and rotating a bit. Then they are added together as a sum, although when I take a stack of shorter exposures I'll probably split them into 3 or 4 groups, make a median of each group, then add as a sum. With luck that will eliminate some of the random noise in the images caused by imperfect dark frame (NR) subtraction in the camera.
Then into PS for a final bit of colour balance and contrast/brightness adjustment, and maybe a slight sharpen, although I didnt with this one.

Thats about it really

Gordon

woops missed a bit or your question. Yes a 50mm f/1.4 or 1.8 would be good for Orion. However, you would have to use shorter exposures if you cant track the sky. Maybe 10 or 12 sec to avoid obvious trailing

Gordon

Thanks Gordon. Next time I'm away from home I'll try some shorter exposures and try combining them and see how I go. (Now I have another reason to get a 50mm prime ) And a year to practice with the kit lens, hehehe!

Gordon, the sigma lens is not doing the colour of the stars any favours is it..strange colour halos happening I think that is a function of the focus point. It is interestimg that m42 has blown out so much in comp to the rest...The tracking is spot on though and shows the advantage we have of piggybacking to our scopes.. I do like the fact that you have got the loop to show up..Well done

Gordon wrote:Just to show what tracking on the sky will do for star photos, here is Orion taken in twilight this evening, 30mm Sigma, 380sec (sum of 150 + 230sec exposures) @ f/1.8, ISO 250. Its a slight crop to remove the worst of the triangular stars around the edges, particularly the lower part of the frame where they were worst. Its not at perfect focus either, having to estimate infinity because the index marks are in the wrong place is real hassle.

Does the Sigma 30mm focus beyond infinity? That's very unusual for a wide-angle lens, the focus ring should stop dead precisely at infinity.

However, I'm impressed with the tracking accuracy over those pretty exposure times. What kind of rig did you use? Did you piggy-back on a telescope mount?

Cheers
Steffen.

hmm, strange I just got asked for username and pword before I could reply...

I'll try using a UV filter on the 30mm and see if it reduces the halo at all.

Yes this lens seems to go way beyond infinity, its a bit odd, it comes to a stop at the middle of the infinity, which is in the outer feet scale, but there is a ⌐ symbol in the metric scale and the actual infinity focus point is about the thickness of the index mark to the left of the vertical bit of the ⌐.

lets try some ascii art:


.... 3 .... 6 ........ 00
..... ......... .... ___
.... 1 ..... 2 ...|
..... ........... ^ ... ^
.. .. actual inf .. .. rotation stop

ignore the .. ...s I had to use them, as spaces take up almost no space at all in whatever font this is!

Yes its odd to have this on a wide angle, my old Nikkor ED 180 and 300 lenses both allow focus beyond infinity, but infinity is always right on the index mark.

Gordon

yes piggy backed on a telescope, here at Siding Spring in this case, using a less than ideal mounting arrangement that involves balancing on top of a tall Aluminium step ladder to trigger and close the shutter!

Since I'm here until Sunday there arent any other options. I'll do some from home as soon as I get a chance.

Gordon

Gordon

That's an impressive capture. A good reminder of just how amazing the sky would be if it weren't for all our light pollution