Mauna Kea (Hawaii) Astrophotography advice?

Started 2 months ago | Discussions thread
Astrophotographer 10 Veteran Member • Posts: 9,589
Re: Mauna Kea (Hawaii) Astrophotography advice?
7

First of all - lucky ******.

I have done a lot of nightscapes with both Fuji, Sony and Nikon cameras.

The XT2 is a very good astro camera with its low noise and no amp glow.

Lenses:

1. Samyang 12mm F2 is good and its cheap. Fuji 14mm F2.8 is excellent and you can lock the focus ring once focused. I am currently using a Samyang 12mm F2 and Irix 15mm F2

full frame lens (Canon mount). It will also work on an XT2 with a Canon EF adapter.

Other lenses that work are the 16-55 F2.8 at 16mm F2.8 (works well). I am not aware of any of the other Fuji lenses and the 10-24 at F4 is getting a bit slow but it may be fine with longer exposures and a tracker. Samyang lenses are commonly used for astro although my experience with them is their quality control is so poor that its unlikely you will get a good lens first off.

2. You can do up to 30 seconds untracked and suffer some minor star trailing and its fast and easy and you just need a tripod. That's the entry point. Single images 30 seconds ISO 3200/6400 F2.8 or faster and RAW, daylight white balance, LENR off, High ISO NR off, manual focus using magnified view at ISO6400 and F2.8. Pick a very bright star, magnify the view of it to max then focus. The star will get smaller and tighter as you approach eact focus. Go past it and back a few times and you can see where its tightest. That's exact focus. Infinity markings mean nothing neither does the distance scale, AF does not work in the dark.

3. A basic image is simply something like the Samyang 12mm F2 (wide open you get a bit of CA - blue fringe around bright stars, F2.8 its clean, I use F2 as the fringing cleans up easily in LR). F2 or F2.8, 30 seconds ISO 3200 and boost in post. Or even ISO1600 and boost in post. The camera is somewhat ISO invariant but per a Lonelyspeck.com review it seems ISO3200 is the sweet spot of least noise to brightness of the image.

You do a single image and process it later.

4. Framing. The Milky Way is really the secondary subject. Really good nightscapes always have an interesting landscape to look at as the primary subject. A mountain range, a windmill, a lake with reflections etc. In your case the Observatory domes are an obvious primary subject and the Milky Way above it would look super.

In Australia at the moment the Milky Way is just past straight above you horizon to horizon just after dark. You can download an app called Stellarium for your smartphone and you can predict where the Milky Way will be at that location and a time after dark. That would be helpful to know in advance. I suspect you want to be imaging it straight after dark as the MW will set around midnight in Australia. Hawaii is a lot further north so it may set much earlier so set up before dark and be ready to go.

5. Mosaics. A panorama is a common choice. That is where you take lots of images overlapping about 1/3rd to half the image and stitch in a mosaic stitching program after post processing.

6. The above pretty much applies to any style of nightscape you do but there are basically 3 or 4 types of approaches to nightscapes. The above is the simplest. You could do a bit shorter at 20 seconds to reduce star trailing but at 12mm the trailing is minimal unless you look at it 1;1.

The biggest gain comes from using a tracker. I use a Vixen Polarie. It costs about US$299, is about the same size and weight as the XT2 and is easy to use.

There is Astrotrac,iOptron makes a few types. Once setup and aligned they can enable you to do upp to 15minutes 14mm F2.8 (I've actually done that). I have also used the 50-140 to image the Large Magellanic Cloud (a companion galaxy to the Milky Way that is visible in the southern hemisphere). Round stars, 5 minute exposures, at 140mm.

If you have a tracker now you can do 30 seconds at ISO3200 and get perfectly round stars.

I go 6 x 30 seconds for each panel of a mosaic tracked for the stars and when I do the landscape part I turn the tracker off so its static. So it would typically 3 or 4 images across and 2 up (one angling the camera down about 20 degrees and 1 up looking up so its catching a small amount of horizon to help with stitching. Use the camera in portrait mode in all of these methods and use an L angle to help get more angling ability on the tracker.

If you use a tracker you could also simply shoot 90 seconds ISO3200 F2/F2.8 shots and stitch them. Landscape component is untracked.

You could do 6 x 30 seconds and align and stack them (more complicated) and untracked long exposure for the landscape. If the moon is up and more than a 1/3rd moon ( we are moving towards a full moon at the moment with the full moon due around 6 Oct. With a full moon you won't catch too much MW and you will need to do shorter exposures but of course you will pick up the environment very easily.

Once the moon is full the next days afterwards the moon rises later and later. So if you go there say 2 or 3 days after the full moon it will be pitch dark for the first 1.5-2 hours before the moon rises and that's plenty of time to do the nightscape.

So there you have it. How you align and stack is another post. How you align the tracker with the Earth's rotation is another post (it has to be aligned to get round stars).

Your choices are:

1. 12mm F2 F2.8 ISO3200, manually focused using magnified view, LENR off NR off I use Velvia but that's me.

2. Single shortish exposures say 15 seconds ISO3200 will get a reasonable image with minimal star trailing. But to get enough exposure 30 seconds is usually needed so suffer a bit of star trailing in order to get a brighter exposure. Tripod only no tracker.

3. Do the same as #2 above but take 6 - 10 exposures and align and stack in post. It gets rid of noise really effectively to take multiple shots and stack.

4. Use a tracker. Now you can do any of the above but without any star trailing and expose for up to 15 minutes and get round stars.

I think the sweet spot is 6 x 30 seconds ISO 3200 RAW tracked and a mosaic of 2 x 4 ie 2 up and 4 across and use a 12mm or a 14mm lens.

The 16 1.4 may work if stopped down or if you overlap heavily. It has bad coma in the corners.

Longer focal lengths let in more light for the same F ratio but give a narrow view and will require more panels to make up the mosaic and is more advanced and I would not start with that. Don't go above 16mm and even 16mm is too long really.

I am happy to go into more detail on any aspect of this.

Greg.

 Astrophotographer 10's gear list:Astrophotographer 10's gear list
Sony Alpha a7R II Fujifilm X-T2 Sony FE 55mm F1.8 Fujifilm XF 50-140mm F2.8 Fujifilm 16-55mm F2.8R LM WR +7 more
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