DSLR wide-field, not getting great results: Help!

[pipnina]

I have had a couple of attempts at DSLR wide-field AP but tonights is the first time I've gotten results that weren't entirely hideous. So I'm going to ask for help now

Here's the image I took (jpeg @ 95% quality) http://i.imgur.com/qyJ9woR.jpg (The orange bit in the bottom-left is my neighbour's house getting in the way!)

And this is the uncompressed stack w/16-bits per channel (143MB) https://dl.dropboxusercontent.com/u/264557087/First%20stack.TIF

My main question regards the odd effect at the edges of the image: Why do the stars seperate and blur out so much? Is there anything I can do to get rid of this effect?

My second question regards exposure time: This used 70 exposures at 8 seconds each (can't take higher because of star-trailing). DSS has an option that just continuously adds the data instead of averaging it (Entropy-weighted average/HDR?) , would that let me get brighter images or is the averaging the best way to do things?

I don't really know what I'm doing, please help me!

        ~pipnina

[Kropster]

Looks like lens aberrations on the stars towards the edge.

This might improve if you close the aperture a couple of stops.

Stars are a severe test of lenses and will show up distortins that you wouldn't notice in normal daytime photography subjects.

[jambouk]

The artefact affecting the stars at the edges is just one (or possibly more than one) of the numerous artefacts which commonly occur when passing light through glass, or reflecting off mirrors, and then trying to project a curved image onto a flat sensor. I want to say it's mostly due to the field not being flat, but i'm honestly not sure but will be interested to hear if someone else comes alonf with an explanation.

I think i have read that if you reduce the "pupil" size of the lens (use a higher f/ value, so if these were at f/4.5, try f/5 or f/5.6), see if that helps. Obviously that will reduce the amount of light hitting the sensor so to compensate you'd need to increase the exposure duration, but you donmt want to do this as you get trailing. ISO? This isn't a fix as you increase the noise too and your inages will just get noiser and grainy, but worth experimenting with that also depending on the camera in question and what these inages were shot at. Number of subs? I tink this will be the key; doubling the number of subs for each increase in the f/ value will hopefully keep you on track to at least keep this amount of light capture. So i recon you just need more data. Or go to a darker site and play with the ISO and see if that does help without too much "cost".

Do you have any form of tracking mount? If so you could track and capture longer exposures.

It's a lovely start though. I do love Orion even though it's an obvious constellation to fall in love with.

James

[pipnina]

The artefact affecting the stars at the edges is just one (or possibly more than one) of the numerous artefacts which commonly occur when passing light through glass, or reflecting off mirrors, and then trying to project a curved image onto a flat sensor. I want to say it's mostly due to the field not being flat, but i'm honestly not sure but will be interested to hear if someone else comes alonf with an explanation.

I think i have read that if you reduce the "pupil" size of the lens (use a higher f/ value, so if these were at f/4.5, try f/5 or f/5.6), see if that helps. Obviously that will reduce the amount of light hitting the sensor so to compensate you'd need to increase the exposure duration, but you donmt want to do this as you get trailing. ISO? This isn't a fix as you increase the noise too and your inages will just get noiser and grainy, but worth experimenting with that also depending on the camera in question and what these inages were shot at. Number of subs? I tink this will be the key; doubling the number of subs for each increase in the f/ value will hopefully keep you on track to at least keep this amount of light capture. So i recon you just need more data. Or go to a darker site and play with the ISO and see if that does help without too much "cost".

Do you have any form of tracking mount? If so you could track and capture longer exposures.

It's a lovely start though. I do love Orion even though it's an obvious constellation to fall in love with.

James

I don't have a tracking mount (I have an EQ that i mount my scope on, but it's not motorised )

I was using 1600 ISO, 8 second exposures, lowest f the lens supported at 55mm (5.6). 70 subs. (9 mins of exposure)

This was under some very poor LP, much from the city, additional from the moon.

Maybe I should try again at a dark site?

[jambouk]

What canera is it?

iSO 1600 is probably as high as you should go, but always worth experimenting; one mans grainyness is anothers acceptible image.

Dark site will help.

Moon light mever helps.

Light pollution never helps.

Personally i don't find light pollution filters help with this sort of imaging as they block out too much of all wavelengths of light.

Have you tried star trails?

https://m.facebook.com/photo.php?fbid=10153682376830968&id=505420967&set=o.130033853814216&source=46&ref=bookmark

And

https://dl-web.dropbox.com/get/Public/Star%20trails.pdf?_subject_uid=1673286&w=AAAqBHXwbbcRBpK82LO2Pfdg83GmZUHhXG2hQ0-4U8UnqQ/

James

[jambouk]

"Lens aberration" - i told you someone clever would know which artefact it is. Good to see the same potential solution of stopping down one or two has been suggested.

As with many things in all areas of astrophotography I've encountered, there are a few "rules" but on the whole there is also a lot of trial and error and finding out what works best with your specific combination of kit, in your hands, and from your location (and depending on the phase of the moon, season and atmospheric conditions)....

But it's great to see such an impressive start.

Are you a member of a local astronomy group, or ohotography group? Itms always good to meet up with local people who share a unique interest.

James

[pipnina]

"Lens aberration" - i told you someone clever would know which artefact it is. Good to see the same potential solution of stopping down one or two has been suggested.

As with many things in all areas of astrophotography I've encountered, there are a few "rules" but on the whole there is also a lot of trial and error and finding out what works best with your specific combination of kit, in your hands, and from your location (and depending on the phase of the moon, season and atmospheric conditions)....

But it's great to see such an impressive start.

Are you a member of a local astronomy group, or ohotography group? Itms always good to meet up with local people who share a unique interest.

James

Half the reason I'm taking this image is because the Plymouth Astronomical Society (Which I visited this month for the first time) stated their next meeting would be about AP, and that they'd be taking people's images and saying what we did right and wrong. I intended to use it as an icebreaker, mostly. (Last time, me and my dad said nothing, we're fairly introverted people!)

Of course, the weather has not been kind recently (cloud, rain, rain, rain, rain, cloud, mist, cloud, rain), so I took the opportunity tonight to do what I could.

My last attempts were worse, actually, my old camera had issues and it lost focus after the first image resulting in me making a star trail image whether I liked it or not once I stacked the images. (DSS read the stuck pixels as stars because the real stars were way out of focus.)

I'll see if I can find the funds for a motor for my mount. But it's burried under a lot of things I need and having to buy a new camera took a large chunk out of my budget.

I should probably find a job... XD

[jambouk]

Get plenty of advise off here and from the astronomical society. Do they have a loan scope / mount? Worth asking.

There are some good books on atrophotograohy with a dslr out there, not cheap. Alao some good online resources, if you don't find any say and i'll look at the weekend.

James

[pipnina]

Get plenty of advise off here and from the astronomical society. Do they have a loan scope / mount? Worth asking.

There are some good books on atrophotograohy with a dslr out there, not cheap. Alao some good online resources, if you don't find any say and i'll look at the weekend.

James

They do have a loan scope, it's a SCT and I think it's about 8". It's alt/az though (as far as I can tell)  so it wouldn't be great for imaging. I could take some planet shots with it, though. (You get those great shots of Jupiter scattered around the forum through stacks as well, right?)

[wxsatuser]

Looks like the camera moved during the exposure.

Did you use the self timer or a remote trigger, if not you need to.

Hard to tell what abberations your lens has, no doubt it will have some coma.

[JamesF]

Get plenty of advise off here and from the astronomical society. Do they have a loan scope / mount? Worth asking.

There are some good books on atrophotograohy with a dslr out there, not cheap. Alao some good online resources, if you don't find any say and i'll look at the weekend.

James

There's a guide to wide field imaging with a DSLR and tripod as a sticky in one of the imaging sections here too, if I recall correctly.  Could be worth a read through, though it looks like you're going about things the right way anyhow.

As has already been said, stars, particularly those near the edge of the frame, are a serious test for camera lenses and many (even high end ones) are not perfect to the edge.  If it's a zoom lens I'd probably use the shortest focal length and stop it down anything up to two stops down from wide open.  You might have to experiment a bit there.  Generally with my cheaper lenses I expect to have to crop a bit off the edges to get rid of the worst of the deformed stars even so.

You may find that if you stop the lens down you start to get diffraction spikes on brighter stars.  You might be happy with that.  Personally I dislike them, but they're a bit of a marmite thing.  An alternative method of stopping down if you don't like them is to get a circle-cutter (kind of like a pair of compasses, but with a knife blade at the end) and cut an aperture stop of the right size from card or thin plastic.  This can be fitted to the front of the lens.

James

[JamesF]

Looks like the camera moved during the exposure.

Did you use the self timer or a remote trigger, if not you need to.

I did wonder if that might be the case myself.  Eight seconds seems a very short time for getting trailing so perhaps some of it is caused by something else.

James

[pipnina]

Hehe, I am in fact pressing the button to start each exposure. Oh and my tripod is wobbly and on top of a wooden outdoor table. I'd imagine that might account for some of my issues regarding exposure time.

My setup is hardly ideal. But it's a great deal better than with my old olympus... http://i.imgur.com/foETTFE.png (Same settings (ISO, aperture, zoom (near enough) exposure, both with RAW and with the "Auto balance" feature from paint.net applied to it.) Left is my old Olympus e-410, right is my Nikon D3200. One big difference.

[JamesF]

Definitely worth giving it a go on the timer if you can then, or ideally with a remote shutter release.  They're pretty cheap for Canon cameras from ebay, but I have no idea about Nikon.

Common tips for improving the stability of tripods are to keep the legs as short as you can get away with and to hang a bit of weight off the tripod head.

There's also no reason you couldn't put the camera on your telescope tripod instead.  Sometimes you have to get a bit inventive with the fittings, but it's quite possible.  If you have the scope I think you have then there's a camera fitting on top of the scope rings, but rather than use that directly (though it's probably worth a try) it might be more effective to fit a dovetail (or any sufficiently stiff piece of metal strip you can get drilled out to fit) across the top of both rings, then fit a ball-head to that and mount the camera there.

James

[jambouk]

Ah, well worked out team about the trailing and 8 second exposures...

You can get a remote for your canera for under £10 off ebay:

http://m.ebay.co.uk/itm/221331284688?nav=SEARCH

Many of these can be set up to do it all auto atically for you, so you can go and have a cup of tea and warm up.

You mught start to notice the front of the lens misting up, so need to think about addressing that.if you are at home i've found using a fan to just blow air across the lens keeps it mist free, but again usual precautions about having mains leads outside in the dark where there is mousture!!!!

I wondered if the apparent movement artedact in the stacked inage was DSS trying to keep all the stars aligned but doing something odd with the neighbours house and makinf a smeary inage of it.

With regards rhe loan scope, yes, you could do some planetary inaging. Does your dalr have a video mode. Search the planetary inaging forum for Nikon and see what other people have achieved. Dslr cideo imaging of planets isn't as good as a webcam, as the camera compresses the data and you lose some, but people do get some impressive shots. You'd need to research how to connect the dalr to the scope too, and would probably need some for of nikon-to-t2 ring and maybe a nose piece...

James

[wxsatuser]

The faint stars show the movement the bright ones hide it a bit.

When I first started AP it was the same way, my images were just like that when pressing the shutter release manually.

Your on the right path just improve each time you image and in no time you will get some nice images.,