8

I've just started doing a bit of astrophotography and finally after the third night of trying I found my target, the Whirlpool galaxy. I'm pleased I've managed to capture it but I'm looking into how I can further the image, and the detail captured. This is the image I've captured:

Whirlpool Galaxy

The setup for this is:

Camera: Sony A77ii (APS-C)

Lens: Sigma 18 - 300mm f/3.5 - f/6.3

Light Frames: 103 exposures at 300mm f/6.3 ISO 3200 and exposed for 1 minute each. The camera was placed on a Move Shoot Move star tracker on a tripod

Dark Frames: 30

Bias Frames: 31

This was then stacked using DeepSkyStacker and processed slightly in Lightroom.

My question is would stacking another say 100 exposures on top of this bring out much more detail/reduce more noise? I realise my setup isn't exactly ideal for this sort of astrophotography but I'm interested to see if there's a way I can improve the image quality further, or if this is the sort of limit I can reach with what I currently have.

  • 4
    Congrats, I'd be delighted to get this result. And "finally after the third night" doesn't sound like too long. Astrophotography can be frustrating, complex and expensive. – Eric Duminil Mar 27 at 22:11
5

Stacking more images reduces noise to signal ratio, but don't add resolution or details.

In order to enhance resolution, my advice is to use a prime lense, instead of a zoom one. Even if it has less focal length.

In my personal experience, I get more details with a 80mm prime than with a 55-250mm at 200mm

| improve this answer | |
  • 2
    Good advice, especially if the smallest visible details are larger than a pixel. I completely forgot he was using a zoom. And wide open, no less. Stopping down to the sweet spot (likely f/11-ish) might also helip a lot. – Zeiss Ikon Mar 27 at 16:06
  • 1
    And, looking back at the question, that's a super-zoom, with more than 15:1 zoom ratio. Those have dozens of elements. A cheap 500 mm Tamron with the right adapter might do better, both in terms of resolution and image size. – Zeiss Ikon Mar 27 at 18:20
  • Interesting, I never thought of that. It certainly isn’t the highest quality lens out there, and the vignette for night shots is quite noticeable. The only other lenses I have at the moment are a Sony 16-50mm f/2.8 or a Tokina 11-16mm f/2.8. 50mm probably isn’t anywhere close enough to capturing objects like this – Serberuss Mar 27 at 18:48
  • 1
    A 50mm probably will not be enough for what you want. I mean, the best equipment for this is a refractor telescope for astrophotography. But speaking about regular lenses that you can use for any kind of fotography, a 100mm will be usefull for a lot of deep sky objects, and maybe for that galaxy. – vsis Mar 27 at 18:57
  • I agree, even on APS-C, a 50 mm won't be long enough to get a useful image size. The 11-16 might be good for "rich field", like Milky Way and Veil Nebula (Orion Nebula is a dense spot in the Veil, which covers the whole constellation of Orion and then some). – Zeiss Ikon Mar 27 at 19:14
4

Yes, but No.

Your question is will it produce more detail, and yes stacking more images will reduce noise which will let you see more detail. And at least as important, you are taking calibration frames. But this is all post processing.

Post processing will get you from to

Or from

But, it will never get you from to (Each first image is an unprocessed raw image. The latter are processed including stacking and calibration. The last image is from astrobin and is not mine.)

For that you will need a longer focal length. Image taking a photograph of the Eiffel tower from a mile away and expecting to stack a couple and crop it until you have a postcard perfect 8x10.

You either need to get a focal length appropriate for your target, or get a target appropriate for your focal length.

M31 is a great place to start with a 300mm if you want a galaxy. M42 is not only colorful but bright and as also a great target with 3oo and a DSLR.

Also, I can't tell for sure looking only at post processing, but your stars look big and I wonder if you are a little out of focus. Find focus is extremely hard with a DSLR - and harder to keep. Your stars a a little football shaped and your exposure might be a little longer than your tracking allows.

| improve this answer | |
  • Thanks for the comment. Yeah my mount isn't really best suited to the sort of photography like this as it's more designed for wide field landscape astrophotography. So I've definitely pushed its limits here. How do you find appropriate subjects for various focal lengths? Do you care more about the magnitude of an object or just the object size? – Serberuss Apr 13 at 14:49
  • 1
    I use an app to determine framing. I use SkySafari on android but there are lots of others - including lots of free options like Stellarium and Cartes du Ciel, and even web pages like telescopius.com - all of which can show you how big the object is going to be in your frame if you enter the focal length of your lens and the size of your camera sensor. The magnitude of the object will effect the length of time and/or the the number of images you will stack - the brighter it is, the shorter the exposure(s). (Really bright things like planets are actually often best imaged with video loops.) – RadOD Apr 15 at 4:10
4

In my limited experience (back when Astrostack was the hot item, and using video captured at 640x480 with a webcam -- call it 1998 or so), stacking more frames will decrease the appearance of noise by averaging it away, but won't increase detail beyond about double the actual pixel resolution of the image (you only get that much because the image wanders a little over the pixel field, and the stacking software does sub-pixel alignment).

What you need in the above image to see more detail in the galaxy is probably higher magnification. If you can add a tele-converter to that lens without degrading the image quality, you may see some improvement, but otherwise, you'll just have to either invest in a telescope and polar tracking mount of some kind, or get a longer lens for your current setup. A high quality lens longer than 300 mm is likely to cost as much or more than a small refractor, so it's probably a toss-up -- ideally, you'd have the ability to test the telescope before buying, as some will have the resolution you need, and some won't.

As noted in another answer, the lens you're using is also part of the problem. Zoom lenses aren't the preferred kind for astrophotography; a super-zoom like your 18-300 probably has more than twenty elements, and every interface subtracts a little resolution and adds a little flare (reducing contrast, even with subjects like this).

It's likely that an inexpensive long prime such as a Tamron 500 mm with the right adapter to fit your camera would do at least as well. You'd get a larger image, have only (at most) five or six elements in the lens, and likely have better total light gathering (though partly offset by the higher magnification). You don't need the lens to support autofocus (you'll be at infinity at all times) or even auto aperture (you'll set it and forget it anyway). Lenses in that class can sometimes be had for less than the adapter to fit your camera's mount.

| improve this answer | |
  • Yeah I did wonder if that would be the case. There is still a bit of noise in the image but it's the greater detail I'm really after. Would you say with my current setup it's probably worth going for an object that has better a better magnitude (lower number I believe)? – Serberuss Mar 27 at 13:37
  • 1
    Based on the image above, I'm not sure luminosity is the problem. You've got a well recorded image. The problem is that 11x7 arcminutes takes up so little of your sensor. There are larger nebulae (with lower surface brightness), and of course M31 is much larger on the sky -- possibly larger than your field of view. – Zeiss Ikon Mar 27 at 14:23
  • I appreciate the advice. Looks like I’ll need to look into either a prime telephoto or a telescope, as I guess my 18-300 nor 16-50 is really going to cut it – Serberuss Mar 27 at 18:56
  • 1
    Also just wanted to ask - are you recommending to reduce the exposure length just to counter star trailing? – Serberuss Mar 27 at 19:27
  • @ZeissIkon It appears from the OP that a tracking mount is already being used. Without a tracking mount, one minute exposures at 300mm on an APS-C camera would make the sample image impossible. With a 3° AoV on the short side, the stars would move about 1/12 of the width of the short side in one minute. – Michael C Mar 28 at 4:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.