Curve_in Loc: Virginia

My first outing with a SkyGuide pro was both thrilling and disappointing!

Polar alignment was speedy, but from my backyard, all the nebula were in the trees. I used a Pluto trigger for a timing the shots, but, I set up for just one shot versus 100. After the hour of shooting (while I was inside the house), I was happy that Capella was still in the frame. I included the basic raw conversion and the zealous crop. Light clouds tonight so I'll need to wait for a re-shoot.

Nikon D750
1600 iso
25 seconds
Sigma 120-400 (the camera reported 320mm but I thought it was at 400mm)
f/5.6

Sadly, one single image

Any pointers are greatly appreciated.

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Ballard Loc: Grass Valley, California

You got some good star colors. The focus might be a hair off. I would recommend hooking up a laptop to the camera and using live view and magnify the image of bright but not too bright a star to tweak the focus. (I will sometime crank up the iso while focusing using live view if needed to see a few stars, then set it back down for the actual exposures).

alberio Loc: Casa Grande AZ

I like the colors also, but as Ballard said the focus is just on the edge. I fight getting camera lenses perfectly focused more than anything. Capella does look nice.

Curve_in Loc: Virginia

I used a Bahtinov mask and I thought the spikes were even. I'll have to more critical the next outing. I used Capella for the focus, but it seems you are saying that star may be too bright.



I thought that since Capella looked good, the rest would have been in focus too. I have much to learn!

alberio Loc: Casa Grande AZ

So do I.

JimH123 Loc: Morgan Hill, CA

Definitely, better focus needed. But I want to also point out that using long exposure times on just stars can lead to problems such a blooming or saturating. The spikes on Capella are due to the aperture blades on the lens. Wide open removes them, but often has poorer focus.

I looked through some of my images and found Capella. I oriented it to match your image and worked on matching the magnification.

Some differences:

I used a 135mm f2 Samyang lens at ISO 1600 for just 2 sec. You were at 320mm at f5.6 using ISO 1600 for 25 sec. I used an Olympus EM5ii which has been modified for full spectrum IR vs your full frame. The 135mm x 2 = 270mm equivalent, so we are close. I magnified just a bit to make them close to equal.

Image 1 is a side-by-side comparison. Mine is on the left. Yours on the right. I did stretching to show the stars. You did longer exposure. Since my aperture was wide open at f2, there were no spikes. I also lost my color due to the fact I used a camera catching some IR and as such, the color was not the real colors. So when I used Photoshop, I used a filter RC-Astro/XGradientTerminator to fix the background, and I made no effort to preserve the star colors.

Image 2 is a side-by-side with them both magnified. I suppose my Capella is fatter since I am magnifying more - maybe? But with the shorter exposure, the other stars showed better focus.

Conclusion here is to not use longer exposure than you need. For galaxies and nebula, long exposures are very necessary. They are extended objects and absolutely need longer light gathering times. Stars are point sources of light and don't need long exposures unless you are trying to see 23rd magnitude stars.

Something else you can see here is that we took these images at much different points in time. Many stars are variable stars and change brightness over some time period. I see stars I compare on the two images that are a lot different in brightness between the two. I suspect that these are probably variable stars at different places in their brightness cycle.

Anyway, welcome aboard the astrophotography experience.

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Added a third image. Also, of Capella on the prev night. This time a Rokinon 24mm f1.4 lens and this is a 15 sec image at ISO 1600 using the same camera. I didn't do much stretching since the exposure time was longer. There are a few clouds passing through. With the much shorter focal length, it is not possible to expand to see stars as clearly as above.

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JimH123 Loc: Morgan Hill, CA

I also do not use a Bahtinov mask with camera lenses. Instead I use the dimmest star I can see and very carefully adjust focus for the brightest point while will indicate perfect focus. You can't determine the brightest point using a bright star. Only the dimmest you can see in live mode.

I do use a Bahtinov mask with a telescope and astro camera since it is slower to download results to a laptop where I can see them.

Using a camera provides instant results. Using a dedicated astro camera is slower downloads and it is difficult to judge the effect until some number of seconds later.