Jump to content

Narrowband

First attempt at imaging


Recommended Posts

I finally managed to get out into the back yard and take some shots with my Canon 1100D on my HEQ5 Pro mount (unpowered - I haven't bought a battery yet). Focusing was a real pain because nothing was bright enough to see in Live View, so I had to just take single shots and adjust the focus between each shot, before eventually taking ten 6-second Lights and ten 6-second Darks, of what I believe is Ursa Major. I've attached converted JPEG's (I have RAW's, which look quite a bit better than that JPEG in my opinion) of one of the Lights and one of the Darks.

As you can see, I've got that issue round the edges with he Lights (can't remember what it's called), but I'm not sure why that happened, because I used a lens hood bought from online acting as a dew shield, so in theory that shouldn't have happened seeing as it's supposed to be designed for a lens of that aperture.

Also, I'm struggling to get any kind of result with Deep Sky Stacker. I followed this tutorial:

http://flintstonestargazing.com/2009/06/26/my-quick-deepskystacker-tutorial/

I put the 10 Lights and the 10 Darks into it using the settings in the tutorial, and I ticked the checkboxes for all the files. But I can't see anything in any of the Lights unless I play with the slider bars at the top-right.

Also, I don't understand why the images are displayed as a tall narrow column rather than like the attached JPEG (with is also how the RAW is displayed in the Canon RAW picture viewer software). As you can see the post-DSS image is a very odd shape.

And are the Darks supposed to look like the attached JPEG? I'm a bit concerned about all those pixels.

Also, while I'm using the camera (I will buy a scope eventually, my plan for now is to use the camera, with a powered and polar-aligned mount next, possibly with a 300mm lens, and progress from there), Is there a Bhatinov mask that I could use with it for focussing the camera? Or would I be better off printing and making my own, which I hear is possible?

Thanks for the anticipated help!

post-35725-0-71160100-1406366266_thumb.j

post-35725-0-38396400-1406366343_thumb.j

post-35725-0-10963000-1406369490_thumb.j

Link to comment
Share on other sites

  • Replies 47
  • Created
  • Last Reply

because I used a lens hood...

i wouldn't use this.. it is making the corners rounded in your pictures

if you need a hood use something that is far wider than your lens,a plant pot with the bottom cut away does to stop dew

Link to comment
Share on other sites

I use Gimp (free) and adjust the output file from DSS. The file in DSS looks hopeless but Gimp sorts it out rather the tools you have to use

If the shield shows it is too long. If you have one of those collapsible ones collapse it a bit more and test where it needs to be in day light.

If you raise your iso right up and use live view it might help you find a star. Member Ronin (or it might be alien 13) has a neat trick on using a ISO to find the focus sweet spot.

Link to comment
Share on other sites

I've heard this a few times now, but I can't really picture it. I wonder if anyone on these forums has a picture to demonstrate the plant pot technique?

Also, regarding DSS, I get the full picture now that I'm using the other version, so that's sorted. And I've managed to create a stacked image, which does look quite nice actually, i.e. the sky looks properly black as opposed to light-polluted. However, in the original RAW files, I could see a lot more stars than just those that formed Ursa Major, but in the stacked image only Ursa Major is left, and to be fair, a few of the other stars look just as bright to me.

But I notice that when I import just one of RAW Lights into DSS, it's already been made to be quite a bit darker than the actual RAW as viewed in "Digital Photo Professional" (the Canon software RAW viewer), and in fact, the single Light in DSS basically just looks like the stacked image in "Digital Photo Professional", but not quite as good. So is there a way that I can get the RAW Lights into DSS without DSS automatically making them darker without even stacking?

Also, I have a question about the "Star Detection Threshold". The tutorial says:

"Generally I’ll start at 5% and click “Compute the number of selected stars” and look at the result. If
the number is above 50, I raise the percentage until I get it below 50. If there are below 10, I lower the
percentage and reclick the compute button until I’m happy. You can’t go lower than 2% though, so if it
can’t detect stars at 2%, you’re hosed. Of course, that probably means the images aren’t very good."

My results were:

5% - 74 stars

10% - 40 stars

8% - 50 stars

2% - 566 stars (just to see what it said)

So I went with 8%. But I'm not sure on what the tutorial author meant. If it's above 50, do you try to get it just below 50, but staying as close to 50 as possible? If there are less than 10, then do you just experiment?

Link to comment
Share on other sites

I usally just leave mine at 2%, i have 60000 stars before today to process with dss just play with the sliders the first set you come to just slide them up into the curve of the graph, on the second tab the middle set of settings set the top row at 5 and the btm row at 39.2 then on the saturation tab set the slide at 18% the press ok while it's changing if you don't like what you see just press reset  and redo the sliders.

When you do the middle row on the second tab you will see the curve tighten up  so go back into the first tab and move the histogram so the btm half of the graph is in the btm half of the curve hope this helps 

Link to comment
Share on other sites

Thanks, maybe with a combination of turning up the ISO and zooming into the preview image I might be able to focus better.

And I'll try a more collapsed lens hood before I abandon it altogether.

And I'll bear those DSS settings in mind.

I have GIMP too, but at the moment I can't see a way to restore the lost stars in the stacked image, having fed it through DSS.

So does everyone find that their RAW images are too dark when imported into DSS?

Link to comment
Share on other sites

As I am learning I go for speed and simplicity and work with jpeg.

I'd be happy to go with jpeg except that presumably I would still need to stack them, which would mean putting them in DSS, which I guess would mean dark images again.

Link to comment
Share on other sites

the plant pot idea

post-30122-0-36230500-1406395766_thumb.j

take one plant pot,select lens to fit to (model shown is an upmarket M&S trifle dish :tongue: )

post-30122-0-75461400-1406395772_thumb.j

draw around end of lens on bottom of pot,and cut out  (Blue Peter..if your reading this call me)

post-30122-0-48120800-1406395778_thumb.j

pot then slides onto lens,cut inside your drawing line for a tight fit (paint if you wish :grin: )

post-30122-0-06847100-1406395783_thumb.j

now hood is well clear of bieng caught in the frame

post-30122-0-41648500-1406395789_thumb.j

tune in next week where we build an observatory from a few bin bags and a bucket :p

Link to comment
Share on other sites

Thanks for that! The main thing I wondered with this is how it would stay on (it could really mess things up if it tilted during a long exposure), but it seems like it would be ok.

Regarding the Darks, are they supposed to look like that, with those coloured pixels? Anyone know what they are? And it doesn't mean there's anything wrong with my (new) camera does it?

Link to comment
Share on other sites

I think most of your problems have been answered but i will elaberate on a few.

The vignetting you are getting with the lens hood normally occurs with the kit lens when its being used at 18mm but as sugested the rubber hoods normally have 3 positions so you should find one thar works,

Focussing with live  view can be very accurate but it needs to be quite close initialy to see anything at x1 but thats one of its benifits once you can see an image zoom in and focus again you will see the bright stars blur a little but the fainter stars will start to switch on/off (you may have to set the ISO quite high initially but can be backed off) you can repeat at x10 until you can get a faint star just a the point of being visible. I would also make sure that the star you are focussing on is about 1/3 to 2/3 away from the center.

When starting out dont be afraid to run the ISO at 1600 so you can get some usable data it can allways be reduced later when you have some practice.

The coloured pixels in your darks are normal "hot pixels" and nothing to worry about there is a method of remaping that can reduce them that involves runing the manual sensor clean routine and powering down then removing the battery but i cant remember the exact process.

Found it

1) Remove the lens and place the cap on the camera
2) In the menu functions find the Sensor Cleaning menu
3) Select "Clean Manually"
4) Let it sit for 30 seconds and then switch the camera off
5) When you power back on all pixels should be remapped
 

Alan

Link to comment
Share on other sites

Great, thanks for that!

The only thing I'm left wondering about now is why it is that when I import a raw into DSS it's really dark, but when I import a converted jpeg of the same image it's the correct brightness. But like Kat says, with a PC as old as mine maybe jpegs are the way to go for now anyway

Link to comment
Share on other sites

Great, thanks for that!

The only thing I'm left wondering about now is why it is that when I import a raw into DSS it's really dark, but when I import a converted jpeg of the same image it's the correct brightness. But like Kat says, with a PC as old as mine maybe jpegs are the way to go for now anyway

Hi

That's simply down to dynamic range - cr2 files are 14 bit data (2^14 levels) whereas jpegs are only 8 bit (2^8 levels) - that's a big difference! Astro CCD's use 16 bit data which is one reason they are better :) 

Louise

Link to comment
Share on other sites

But why does that mean that they are darker when imported into DSS? The jpeg lights have lots of stars visible (stacking them now, it takes a while), so hopefully some of those will still be visible when stacked with the darks. But with the raws, they are so much darker to begin with that lots of the stars have already disappeared, so it seems to defeat the object of having the better-quality raws.

Link to comment
Share on other sites

As I am learning I go for speed and simplicity and work with jpeg.

You really don't want to be suing jpegs for astrophotography I'm afraid. Jpeg using 8 bits of data per channel while the RAW files are 16 bit. Using RAW files makes it possible to adjust the histogram without losing any detail.

But why does that mean that they are darker when imported into DSS? The jpeg lights have lots of stars visible (stacking them now, it takes a while), so hopefully some of those will still be visible when stacked with the darks. But with the raws, they are so much darker to begin with that lots of the stars have already disappeared, so it seems to defeat the object of having the better-quality raws.

You don't need to worry about that, the data is there in the RAWs even if it's less visible. Converting to jpeg always changes brightness and colours slightly.

Link to comment
Share on other sites

I only use dss to basically create me one final image I then use gimp to manipulate it and bring out the image. My image in dss looks almost unusable and after watching a video it said don't worry about what it looks like in dss.

Link to comment
Share on other sites

I only use dss to basically create me one final image I then use gimp to manipulate it and bring out the image. My image in dss looks almost unusable and after watching a video it said don't worry about what it looks like in dss.

Have you got any tips and/or links for processing images in GIMP?

Also, I managed to stack my RAW 10 Lights and 10 Darks in DSS, and I also had a go at stacking my JPEG versions as well, and I've attached a JPEG conversion of the TIFF of each result. I'm well aware that RAW is much better than JPEG (although my computer does seem to struggle with RAW's - even stacking the ten JPEG versions took a good 2.5hours or so), but as you can see, there are a lot more stars visible in the JPEG result.

But like I said before, even when I put a single RAW Light in DSS, it's already quite a bit darker, and that's how it comes out when stacked. So I must be doing something wrong, because it must be possible to get a better result than the JPEG one if I have the RAW's available (and if my PC can handle it).

post-35725-0-00379000-1406457936_thumb.j

post-35725-0-38647200-1406457956_thumb.j

Link to comment
Share on other sites

What time of night did you have to stay up to take these? I admit to not trying at all in the summer as I don't do late nights.

I have no tips for Gimp I just played with levels.

I watched that guy who images using camera and static mount as his video covered a bit of everything. I have shared it before I think.

And read lots on this site when other members post.

Next time I have a go I will take raw and jpeg to see what a raw is like in dss. I guess using RAWS for me will be down to if my pc can cope.

Link to comment
Share on other sites

I started moving the stuff downstairs at about 10:30pm (I'm on the second floor!), so it was about 11pm by the time I had got everything outside, worked out what I was doing, and got to a stage where I could take some Lights and Darks. I'm quite pleased with the results actually, considering it was my first ever try, apart from the trees and the corners, but I could always crop the picture a bit, and remove the trees. I'm lucky enough to work flexitime (and I will be in my new job too), so I can stay up late one night if the whether permits.

I'll have a look for that guy's tutorial videos then, I'm sure they'll help.

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.