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Widefield Astrophotography

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RikM

RikM

Posted
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Ah, sure :)

Images of constellations, and parts of the Milky Way is what I'm thinking of.

From replies earlier, it seemed that if the camera was mounted on a driven mount, DSOs could be a possibility (I guess this is wrong?). So, the plan I had in mind was to start by getting images of constellations & Milky Way, and then if I wished, purchase a motorized mount to take the next step towards DSOs.

You have the right idea there. From a static tripod you will be able to get constellation shots. The shorter the lens you use, the longer you will be able to expose for before stars start showing trails. 20-30sec with the 18mm end of an 18-55mm Canon kit lens should be fine. With a 50mm prime lens you get better results using a driven mount. To frame most of the brighter DSO's you will want something around 300mm or longer I expect but worry about that later. Lots of people use light weight driven EQ mounts for mounting a DSLR and lens.

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JamesF

JamesF

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I was thinking much the same as Rik. You may well be better off using the kit 18-55mm lens. Once you start wanting to get tighter shots of individual DSOs I reckon the EQ3-2 Synscan would be sufficient for just a camera and the lighter lenses, but to be honest at that point the glass is likely to be costing you at least as much as anything else.

James

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JamesF

JamesF

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There you have me. I don't even have a normal camera tripod myself :) I do have a Kood BH-05BQ ball head though, which was cheap as chips and has turned out to be very handy for waggling the camera around at all sorts of angles to get the framing right. I'll have to let someone else recommend a tripod.

James

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jimjam11

jimjam11

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These are my first attempts at m31 using a 500d and kit lens. One shot at 18mm, the other at 55mm. I am going to try 100mm when I next get a chance with even shorter exposure times and see what happens!

You can also make a barn door mount as a basic tracking mount. I made one but it overloads my tripod so I need to rethink my design...

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Ags

Ags

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I have also used the 18-55 zoom and it has two drawbacks compared to the 50 f1.8. Firstly it is less sharp and has color fringing, and you can see this clearly away from the center of the image, but more importantly it is photographically slow. You can expose at more than twice the speed with the 50 f1.8, and this makes a big difference if you are not tracking the sky - you might only get a 10 second exposure with the 18-55 (at 50mm), but the same 10 second exposure with the 50 f1.8 will gather 20-40 seconds of light relatively speaking (depending on how wide you open it). This won't make a big difference with stars (although you will get more) but it will make a huge difference when capturing a comet, the milky way or aurorae - or any other extended object.

Of course the 18-55 zooms out, and the nifty fifty can't do that.

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JamesF

JamesF

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IMHO the ability to use the kit lens at 18mm is of value if you're interested in imaging constellations. I've not properly tried my 50mm f/1.8 for wide field yet, but having the kit lens wide open allows you to image extended areas of sky such as this:

cygnus-display-1-1024x681.png

Cygnus is in there, just. They're both useful lenses. For me it would be a tough call to chose between them despite the unarguable failings of the kit lens in terms of quality.

Just for illustration and perhaps to help you think about the future btw, here's a recent image of M31 & friends I took using the Canon 200mm f/2.8L lens (not exactly cheap) on my EQ3-2 using 240 second exposures:

andromeda-small1.png

Bear in mind that (although you can't make all of it out in this image) that M31 is something like six times as wide as the full moon and one of the bigger DSOs. If you want to get larger images of smaller DSOs than this then you're probably looking at expensive lenses or telescopes and that makes mount choice important.

James

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JamesF

JamesF

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Thank you. It's not perfect and it does show up some of the faults of the kit lens (the stars at the corners are stretched, for instance), but for only my second ever attempt at a wide field shot I was very pleased with it. I shall be attempting to improve on it next summer though :)

James

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jgs001

jgs001

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A dSLR, any sort will work, on a camera tripod can be used for widefield (although you'll want a sturdy tripod)... take a look at.

http://stargazerslou...era-and-tripod/

a lot will depend where you're aiming, as to how long the subs can be, but 20 to 30 seconds should be doable.

Even unmodded, it's possible to pick up the Ha emissions, although you'll have to work hard to drag the detail out.

If you can track, and an EQ1 with motor drive can be used, you can certainly capture more details... If you can track well and consistently for 5 minutes, you'll be laughing (not sure an EQ1 can quite achieve this, but I'd think an eq3-2 will. The HEQ5 and Astrotrac can do 5 minute subs with focal lengths of 50mm or shorter without issues or guiding.)

The programmable timer is a real boon, but you'll need at least a remote shutter release, or have to be very careful using the shutter button and self timer. Star trails are even easier..

Apart from the examples in that thread, I can dig out examples using an SLR on an EQ1, HEQ5 and Astrotrac.

Here's my latest with my 50mm on my Astrotrac

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RikM

RikM

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This was taken with a Tamron zoom @ 300mm and Canon 1000D. 3 min unguided subs on an EQ3-2 using a programmable remote. Okay so it's out of focus, but the stars are generally roundish.

med_gallery_18573_493_1338790435_9798.jpg

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pvaz

pvaz

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I found this formula in a photography site a while back. It works very well to calculate the maximum exposure time you can get away for any particular focal length, without tracking:

Exp. Time in seconds = 600 / Focal Length (this is for full frame format)

Adapted for APC-S Cameras (the ones in the price range specified):

Exp. Time in seconds = (600 / 1.6) / Focal Length = 375 / Focal Length

In practice, an APC-S camera with a regular canon kit lens at 18mm, can go up to 20s before you get star trails.

The 50mm f/1.8 will add a lot of light gathering ability but will be limited to 7,5s.

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pvaz

pvaz

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This shot is a single exposure, taken at 16mm on an APC-S camera. I used 30s exposure, that was before I knew of that formula, so you can notice a bit of start trails. The aperture was set to f/2.8 and ISO was up to 12800, which causes all that noise. The shot was taken at 900m altitude in a very dark spot (no artificial lights for about 10km) and I done a lot of adjustments in Lightroom.

The 2nd shot was near the sea with roughly the same settings but lower ISO.

post-17317-133877684691_thumb.jpg

post-17317-13387768462_thumb.jpg

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peroni

peroni

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I think most of what I was going to say has been said already. I'll add my ten pence worth so you have another person's similar view.

I don't own a telescope or telescope mount. My interest is in astrophotography and I've been trying a few things out over the last couple of years. My entry level equipment is...

Canon 1000D DSLR bought with the 18-55mm kit lense in mid 2011. (about £400)

I had a tripod already that I used for my binocular viewing sessions. It was a cheapie from Jessops for about £35.

Later on I bought a fixed focal length 50mm f1.8 lens (£50)

I can confirm exposure times posted by others and the 600/aperture rule seems to work.

I get up to 30 second exposures on my 18mm f3.5 lens

I get 10-12 second exposures on my 50mm f1.8 lens

Example below is a 25 frame stacked shot using the 50mm lens at ISO1600 with 10 sec exposure.

post-15911-0-42454900-1349119903_thumb.j

Not as good as other peoples but you get an idea of a novice shot now. :smiley:

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JamesF

JamesF

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I found this formula in a photography site a while back. It works very well to calculate the maximum exposure time you can get away for any particular focal length, without tracking:

Exp. Time in seconds = 600 / Focal Length (this is for full frame format)

Adapted for APC-S Cameras (the ones in the price range specified):

Exp. Time in seconds = (600 / 1.6) / Focal Length = 375 / Focal Length

Why should the camera with the crop sensor have a different time compared with a full-frame camera? The pixels are the same size, aren't they? You surely just get to see a smaller section of the image with a crop sensor.

Or is the reduced time for EF-S lenses and similar?

I feel sure I must be missing something here, but I can't see what it is.

James

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Ags

Ags

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The pixels are smaller on a crop camera. I think this is less true for a 12MP camera like the 1100D, but even there trailing is becoming apparent at 10 seconds with 50mm.

For example, an 18MP full frame camera obviously has much bigger pixels than an 18MP crop camera. To put it differently, the image is magnified 60% on the crop camera, so trailing is more obvious.

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RikM

RikM

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The pixels are smaller on a crop camera. I think this is less true for a 12MP camera like the 1100D, but even there trailing is becoming apparent at 10 seconds with 50mm.

For example, an 18MP full frame camera obviously has much bigger pixels than an 18MP crop camera. To put it differently, the image is magnified 60% on the crop camera, so trailing is more obvious.

I don't think that can be it.

Canon 350D and 5D-II both have 6.4µm pixels. The 60% crop factor is just down to the physical dimensions of the APS-C chip.

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Ags

Ags

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I don't think that can be it.

Canon 350D and 5D-II both have 6.4µm pixels. The 60% crop factor is just down to the physical dimensions of the APS-C chip.

Yes, but the pixels are distributed over a different area - it doesn't matter about the phyiscal size of the individual pixels, only their spacing. Think of it in terms of a star point moving over the surface of the chip - let's say it moves 1mm on a crop camera sensor. To traverse the same number of pixels, the star dot would have to move 1.6mm on the full frame sensor.

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