Photographing the Stars
 

Following the posting of some stunning Asto photographs I fancied giving it a go.

As there is no thread running with info that might be useful I thought I would get one going.

I have absolutely no idea of the techniques required or this, but faced with a forecast of cloudy skies for the next week I had one window of oportunity on Monday night.

A bit of research suggested I needed to cobble together a means of tracking the stars over a series of exposures. From Alex's comments and a quick read through Stevies astronomy magazines it seems that ' stacking ' a series of exposures is the way to go. So comming up with a means of tracking the night sky reasonably accurately over a long period was an important consideration.

Tracking over a long period seems to require the orientation to be set reasonably with regard to global altitude. A quick net search for images of telescope mounts confirmed this. By logging into http://www.heavens-above.com/ and entering my location I was given this info. Observer's Location: Swaffham ( 52.6520°N, 0.6840°E).

Until I had some idea if I was going to be able to get reasonable pics then it was a NO SPEND situation. I have several tripod heads. So by attatching a ball head first, platform angled at approx 50 deg and attaching a 501 fluid head reversed to that I had roughly the means. The 501 will not give vertical unless used in reverse. A rifle scope with cross hairs was the metod I chose as a tracking scope. To allow the camera to clear the rifle scope I used a 701 head locked up as a spacer. No time to make anything as the clock was ticking on the only clear night for 1 week plus.

As condensation was likely to be a problem, a dew shield from a bit of plastic drain pipe was made for the tracking scope and a larger lens hood attached with electrical tape to the metal hood af the 28mm lens.

At dusk the tracking system was checked against a bright star and found to be accurate over 15 mins, the time taken for the star to move from the centre along a crosshair to the edge. The riflescope is 4x so it showed how far stars move in quite a short time.

All geared up and ready then the skies clouded over. Skies started to clear around 11:00pm so kit set up. I only allowed about 20 mins for the rods in the eyes to kick in before starting to take pics for fear of more cloud comming in. That did allow the camera to cool down. About 3 deg C at this point.

I have yet to process the images to see the results. With the 28mm f2.8 lens wide open I took 19 frames at ISO 400, 30 sec exposure, and 33 frames with 12-24 f4 at 17mm with 30 sec at ISO 400 wide open. The D2X is not a high ISO camera hence limiting ISO but hopefully taking lots of images instead will compensate.

Total time taken was 1 1/2 hours. At the end of that the camera was soaking wet from the heavy dew. A well sealed camera needed in these conditions if used without protection.

I need to look again at the guidance method, as I found the crosshairs difficult to see even after an hour with my eyes recieving no exposure to white light. I hope any missalignment can be sorted by an image stacking program. I also need to make a plastic/polythene dew cover for the camera before another attempt.

I attach a couple of pics of the set up for info, pending processing of the images.

Don

Don: Your engineering mind is a joy... Excellent set up... I will be participating in the is thread as soon as I get some errands done.... I think we will cover a lot of sky in this thread.... Registax is an outstanding stacking program for astro work....I think your 30 second timed exposures stacked will produce excellent results provided you are getting away with little to no star trails... One of the key elements to a succesful stack... The more distortion you have the more pronounced it becomes when images are stacked.... Your scope idea with crosshairs for tracking alignment is brilliant...... I'll be back.....Alex

Well I have some stuff to show for demonstration but of course I don't know how to add the shots in thumbnail form.... Some would say how do you get dressed in the morning..... To that I reply, I have no idea....So I guess I will forget it for now....Alex

Im going to follow this thread with interest and maybe even give it a go.

Alex to add the photo, go to advanced which is just below where I am typing now, move down to manage attachments and load your picture as normal. It creates a thumbnail in the thread.

Alex,
I have now downloaded Registax V4 and the 48 page manual. A lot of reading here in order to understand something of what is going on. I have got a few days to get some handle on the program as the weather forecast for the next 7 days are not too encouraging for a repeat shoot.

Info for uploading an image into a post is in my post #4 in the ' Manual macro on the cheap ' thread.

Superb images in the gallery btw. Something not quite right with my pc settings. Unable to add a comment unless someone else has.

Unlike yours, my scope Nikon ED82A is a fieldscope, well corrected for Astro viewing at 1/10th wavelength, but not good for this sort of thing. See attached pic and laugh :D . With the camera adaptor on it is effectively f13. So at the moment I am limited to photographic lenses. 12mm - 300mm, so widefield is the better route.

Don

Don, your ingenuity never ceases to amaze me. I'm assuming that you are using the cross hairs to align the target and tracking manually to ensure a consistently repeatable image to stack?

Duncan

Got it in one Duncan. Now if I can find a cheap one with illuminating reticule I will have it made. :D

Got a tiny led torch yesterday to see if I can come up with a mod to save buying the proper job the guy tried to sell me.

It is great for anything as at 4x is wide field and when set up with just the scope on I can be on anything faster than most with an angled scope. Stevie uses it with the scope when cruising the skies at night.

Don

Don: What a beauty of a fieldscope that is.......Your set up is anything but laughable.... You have an excellent engineering mind my friend... Widefield work is a fabulous option as well...Now that I have the info on posting thumbnails I will get involved with the thread in a show, tell, ask, and share kind of way:)... I will start tomorrow... I am going to take a quick look for conditions for some shooting tonight....Orion is in view at about 3:00am to the east of me and gets perfect for shooting at about 4:00 am right now..... I will help with the fast track to using Registax... It will do most things automatically including choosing the stackable images, aligning them, and stacking....It is actually a lot more straight forward than it appears in the beginning... I will also show how to set up and use a Webcam for imaging, using a laptop and a program called KCCD which allows you to do everything from the laptop once webcam is attached to scope and mount is aligned...Extremely high quality images with very little noise.... I spent some time playing with it and it is what I was playing with at the time I started wanting to get some sleep at night. I didn't go as far as I did with shooting the DSLR but I learned some basics and the results once you get a good handle on it are fantastic! Talk about best bang for the buck... Great imaging using a 49 dollar webcam :D :D....Take care pal...Thanks for getting me fired up with this again.....Alex

Thank you Christine... I knew it had be something simple I just can be dumb at times:D :D....Thanks a lot.....Alex

Here is one of my scopes that is wonderful for imaging.....Celestron Schmidt Cassegrain C8.... I just picked up a C9.25 which I will be doing my newest series of astro imaging with....I am including one of my last M42 shots from last year which includes The Running Man Nebula......Alex

Well I cannot cope with that lot Alex.

In case you are wondering I am still here, but trying to get my head round a few things.

As previously posted I downloaded RegiStax v4 but seem to be having a few probs. Starting simple I tried a few exposures of the moon but program only seems to recognise the last image loaded. Downloaded v3 but still the same. Also a bit of a problem with image size dimensions as the D2X exceeding program limits. Had a play with wavelets on a single moon exposure and that is something I will definately go back to next time the moon appears.

I have downloaded DeepSkyStacker and that does work. Long processing times though, 20 mins to stack 10 frames and subtract the darkframe and that is on top of image registration time.

Next problem is exposure. I did a stack of 30 frames with a 30 sec f4 exposure taken the other night. Result looks underexposed in terms of the number of stars captured. Luckily last night we had a lull in the high winds and by midnight clear skies as well so I had another go. Starting with 6mins at f4. Totally overcooked. 3mins at f4 the same. The length of those exposure did show up the limits of my manual tracking system. A bit of a rethink and I decided on the 50mm at f1.4 at a dramatically reduced exposure of 4 secs at f1.4. A test stack of 10 frames showed we were now in the ballpark but still suffering from tracking errors. I then took a series at 2 sec f1.4 and have just downloaded to pc and things are looking promising. Just got to process now. I have not worked out a link yet between exposure and each frame added to the stack so it will be a bit of trial and error.

I think something else I will need to look at is sensor sensitivity at low temperatures. Comparing the image I posted the other day taken with a warmed up D100 that 30 sec exposure, although delibrately containing more noise has also recorded the planets better than the 30 stack from a cooled down D2X ( approx 3 deg C ) . Last night it was 8 deg C and I did not allow a cooling down time and was achieving better results at same ISO. Previous exposures f4 - 30sec, last night f1.4 - 2 sec. 3 stops difference.

Guess you do not have the same temperature problems in the Bahamas luck devil. :D

Don

Stevie has just had a droole. :rolleyes:

Certainly looks a big beast with high magnification. I noticed the TWO finders on top. You should get some impressive results from that.

Well I just lashed out as well. Managed to replace my recyled coke bottle converter with a Nikon TC201 mint for £69. Just got to do some tests with it various lenses. Hoping for better results with the moon. :)

Don

Here is my pic from last night.

Taken with 50mm f1.4 lens at ISO 800 exposure time 2 secs.

35 frames + 1 darkframe were taken and stacked using DeepSkyStacker set to select the best 80%. During that stack I noted the best 10 frames ( the program gives points to each image ), copied each 4 times and stacked that lot. The stack was then copied 16 times and re-stacked. The result from that stack, was copied a further 16 times and stacked again. Each stacking operation took the computer 1 1/2 hours.

I have not tried taking the single best frame, multi copying that and stacking to see if it works.

From these pics I see I really need the exposure down to 1 sec as there is still some star trailing. On a wide angle ie 18mm you can probably get away with 15 secs exposure without an equitorial mount. For my 200 f2.8 to get in closer, I may have a problem as the X does not like ISO higher than 800. Hopefully the darkframe is a method of noise reduction, so I may be OK, as no NR was used on these images.

Pic 1 is the full frame shot.
Pic 2 a crop of pic 1
Pic 3 a 100% crop from a 4 sec exposure stack of 10 frames to show star trail over that time.

Don

Don: You get great results from that 50mm.. One thing to be said for the Canon DSLR's is they really have excellent noise reduction and shooting 3200 is not too bad.... I generally try to use 800.... The dark frame does remove a substantial amount of noise... Hot pixels are another issue that happens with to many timed exposures one after the other as the CCD or Cmos Sensors do heat up.... We need to get you more magnification... The images you get are fantastic and with more mag I think what you will be producing with stacking will be mind bending.... I would consider getting Stevie the Orion ED80 with the CG5 mount.... It has motorized tracking and so it will do a wonderful job for both of you.... As long as you can decide how to split up the use;).... I was thinking about your birding scope but it would be very difficult to focus with the aperture limit and you really need to have a mechanized tracking solution to get the 30 second and above timed exposures... Now none of this holds true for widefiled shooting as in the Milky Way, but to get the deep space Nebula you really do need it to get consistent images for stacking to build it up to its potential.... I will go through Registax work flow and write it down so that I can post it.... It has been a while since I have been actively shooting Astro stuff so I went through a number of previously shot M42 frames today and stacked them with Registax.To get back into the groove... Once you get the flow and logic of the layout it is a nice simple program to use... I will go through it again in the morning and write up the procedure and post it tomorrow... I would give the 200 a go with 15 second exposures with a cool down in between every 2nd shot. With the results you got with the 50mm on Orion, It would be interesting to see just how much more image size the 200 will give you..... Don: You make me wish I had a Nikon:),,,,, When I see your images.... Noise reduction goes to Canon but oh how nice the rich images of the Nikon are.....Take care Don.....Stevie..... Get after your Dad.... We need to get the both of you that scope......Alex

Alex,

Having seen how stacking brings out detail, I have to understand exposure, then relate that to size of stack required to produce the final image.

Equally I need to do some tests to establish the effects of sensor warm up on long exposures.

I will look around at motorised mounts but will stick with photographic lenses for now. The ED82 is a great observing scope and any advance on that should logically be in the direction of 102 - 105. :rolleyes:

A workflow for Registax would be very handy in view of my initial experiences. I would also very interested to see the results from a 200mm on a tracking mount as that is the next logical step up for me.

Don

Don

I have been watching this thread with interest, thanks for getting it going. I am a little puzzled about your stacking technique. As I understand it when you stack say 10 images, then they are averaged but as the noise is random it gets averaged out giving a better signal to noise ratio. If you stack identical images then there should be no improvement as 10 lots of identical noise added together and divided by 10 gets you back to where you have started. Have I misunderstood what you have done or the process?

I am (rather impationately) waiting for a clear night to have a crack at M42 with a 200mm lens or even 400mm. I am fortunate that I do have a drive.

Dave

Dave: If I might..... This is where the darkframe is used by the software... It is shot during the same session with the lens capped off for a total darkframe... When this is used with the stacking program it takes all the dark background with included noise and uses the dark frame for cancelling the noise and turning the background black. I hope this made sense....It dramatically improves the shots by replacing the actual background of the stacked shots with the dark frame.At least that is how I understand it to work.... I can tell you it does work:D :D....Alex

Don: Though the extent of money that can be spent on quality scopes is outrageous and aperture fever is a common affliction, the reason I love the ED80 is massive bang for the buck.... Though I have and use my other larger scopes, so far none of them have beaten the image quality of my cheap but very good little grab and go Orion.....Anyway there are many ways to enjoy this particular hobby:D :D..... Good tracking is the key to good stacking;).....Alex

Hi Alex

You are correct about the use of dark frames but as I understand it the stacking is a separate issue. I have been using ImagesPlus to process my images and the dark frame subtraction is done to each image before the stacking process. Using a dark frame removes the fixed element of noise from the image but not the random thermal noise, if I understand it correctly. Images will be slightly different e.g. due to fluctuations in the atmoshere, so the stacking process will average these fluctuations out and give a cleaner image. Stacking many identical images will do nothing to improve the quality.

Does that make sense?

Dave

Hi Dave,

I am in the dark as to the absolute way stacking works. The assumption I made after reading comments from Alex was that the greater the stack the more very fine detail would be shown in the final image.

I used DeepSkyStacker ( freebee on Sky at Night magazine ) and loaded say 35 frames plus 1 darkframe. You cannot see all the frames you have loaded which is a bit of a miffer. After loading, the light frames are registered. During that process each frame is given a score and the program uses say the best 80% for the stack. During the registration process you can see the star count for each frame. I started with a count of about 530 max and ended up with a count of around 1200 by the time I was stacking previously stacked images. Darkframe subtraction only takes place during the stacking process and I included a darkframe ( same one ) for each stack operation.

I have attached the first stack I made. This was from 35 frames plus 1 darkframe using the best 80%.

Don

Dave,

I have just put in a stack of first and last images to read the star count. Image 1 of the first stack 530 stars. Image 2 taken from my full frame posting 1815 stars. I put that down to the totally massive stack I did.

Don

Hi Don

I have used Deep Sky Stacker but gave up on it as with my images I was getting in some cases double stars that were not there. That may well be due to my inexperience using it rather than the program. Some people do use it with success. I am not sure that the number of stars used is any indication of image quality.

I have just done a quick Google search on image stacking and there are many results. Here is a link to just one of them which seems to explain the process clearly and in particular the need for truly random noise for stacking to be effective.

http://www.rocketroberts.com/astro/ccdnoise.htm

I hope that helps.

Dave

Hi Dave,

Thanks for that. I will read in a minute. I am just cobbling together a single image compaison of my fist stack with the first image. Will post in a minute once I have added explanitory text.

Don

Hi Dave,

Side by side comparison. Quite a difference in the level of extra detail in the stacked version.

Don

With 35 images there should be quite a remarkable improvement (Look at the images further down the page of that reference). You first image seems to have double stars? The second image is so similar to the first but more sort of blurred. There is no extra detail visible that I can see. Sorry!

I am firmly convinced that there is no short cut to taking real multiple images. It is then very worth while. I'm sorry I don't personally have any examples that I have taken that I can post, my astro images so far are quite long exposures and so have not taken many to stack. (I believe it is also good practice to let the camera cool down between shots which extends the time taken.)

Here are two shots of M27 (the dumbell nebula). The first is a single processed image and the second is using a dark frame and stacking just 3 images. I will at the next opportunity take many more images to stack.

Dave

Dave,

I processed my images as jpegs due to file size. So image does suffer from multiple process jpeg blocking as well as star movement and frame registration with my primitive kit. Next opportunity I will try a longer exposure time and stack a lot fewer tiffs.

All down to processing power. 35 light frames + 1 dark as jpeg = 120.24 mb as tiffs this would have been 2519.64mb. Each jpeg run took an hour and a half so I have no idea what a tiff run would take.

All down to Alex now if he has some samples with his new fancy kit. :D :D

Don

For those that might be unfamiliar with jpeg blocking here is a screen capture.
This is 400 magnification of the image from the end of the first stack operation.

Don

Ooops
 

Better issue this as a correction. Or I'll get jumped on by Rob. Seems I am looking at individual pixel wells here.

Left hand is a tiff from the first stack. Right hand is a tiff from the raw file of the first image of that stack.

Don

I have just found this link http://www.astropix.com/

Huge amount of detailed info on processing in Photoshop. A lot more than a 5 minute read.

Don

Jerry Lodriguss is quite an authority on the subject. I have copies of his two e-books (A Guide to Astrophotograpy with digital SLR cameras and Photoshop for Astrophotographers) and am currently on a very steep learning curve.

Last night it was unexpectedly clear so now have an example of the power of stacking. It is not up to Alex's standard but was taken through a 200mm lens on a driven mount that was decidedly shakey and not properly polar aligned so decided that 10s was all I could manage. One is a single 10s exposure and the other is 33 stacked 10s exposures. I hope it is obvious which is which.

Next opportunity I will mount the camera on my driven telescope and should be able to cope with longer exposures.

Dave

Excellent job Dave. Nice to see a stack with details as you have given here. If conditions with you were similar to here in Norfolk then you get extra bonus points.:) Decidedly windy.

Don

Don said "Now I just have to figure out tracking as I have a 200mm lens."

Hi Don

There a few methods of tracking the stars in order to get photos. Probably the easiest is to mount the camera on top of a driven telescope. If you don't already have an astronomical telescope then this would be the most expensive option. It is still possible to track with an undriven telescope provided a way to mount a camera on the telescope can be devised and the scope has slow motion hand controlled drives. It is better, but not essential if the scope is on an equatorial mount. To keep the camera accurately pointing you would have the scope looking at any star in a southerly direction and using the hand controls keep the star centred in the eyepiece while the camera is taking the exposure.

Most astro photos that I have taken are with the camera mounted on top of a driven scope. However, the Orion Nebula photo (see earlier post) was taken using a small driven mount that only takes the camera. Again it is not a cheap option but I have chosen it because I am taking it to Australia next April and it needs to be light enough to fit in my airline baggage allowance. I wouldn't recommend it as a method in other more normal circumstances as I am sure that for the same price (~£500) a small driven scope could be purchased which of course means you can look through it at all the wonderful sights there are in the sky.

A much cheaper option is to make (or possibly buy) a barn door mount (sometimes called a scotch mount). Here are a couple of URLs where there are full details. The photos taken with them are very impressive.


http://www.tucsonastronomy.org/barndoor.html
http://www.astronomyboy.com/barndoor/

I hope that is of some help.

Dave

Dave: You did a great job with the shots and the stack.....I am in awe that you got the shots with a 200mm lens..... I may have to give my 400 a go with my telescope mount.... The stability would be outstanding, and obviously these lenses have plenty of resolving power with great optics. I know my 100-400 has a fluorite element and it shows no false color or CA so I would love to give it a go.... Once again very nicely done.....It has been a while since I have astro imaged and my bet is you have done a better job on these than I will manage for a while until I am back in the groove...... Skies have been hazy with large batches of clouds going through, and so seeing is less than nice and of course we have a 3/4 moon right now so even with the breaks in clouds there is more light than I want to deal with:D..... Hopefully in the next week or so we will have clear skies..... You guys really have me itching to get at it again.....Take care.....Alex

Alex

Thanks for your comments. I also have a 100-400 lens and am itching to give it a go. What did you use for your Orion Nebula picture? It is an amazing shot. Am I right in thinking that it is a single shot? I am deducing that from the file name which contains a number.

Dave

Dave,

Thanks for those links.

I had heard the term but failed to find an example. My solution in post #1 works well as long as there is enough light to see the cross hairs. These are exceedingly fine in the centre and it is highlighting these in total darkness that is my current challenge. My 35 exposure example was not tracked during exposure but each frame alinged before pressing the shutter. I am going to check out scopes with illuminating reticule as probably the cheapest solution for now.

Don

To give an idea of the view through my telescopic sight, I took a pic today. I also took a pic of this evenings moon and scaled it to fit. To ensure accurate scale I took one through the sight itself, but that image quality is poor so I downsized a larger version.

I have set this up in dusk conditions locked onto a star just above dead centre. The star was observed for 15minutes and it held true to the cross hair until it exited view to the right. I also tracked a star quite easily over a reasonable exposure time, The 501 is quite a chunky fluid head. Easy in dusk conditions, but until I can light the crosshairs, a very tricky job in total darkness.

The crosshairs are gold and my intention is to figure a way of lighting these. I have taken advantage of glancing a mini torch beam and the effect is similar to the view in the second pic. In terms of scale, Orions belt occupies nearly the full width of the scope, unlike in this image, so manual tracking is a serious option for occasional use.

Don

Orion ED80 600mm focal length f7.6 Apo...300D IR screen modified, with Celestron CG5GT mount.... Has electronic tracking and Go To,,,, Interfaces with laptop and GPS for precise location calibration, And I use DSLR focuser which will interface with the mounts tracking electronics and the camera for precise automated tracking correction as well as focusing the image on the screen.... The mount was 650 US and the little ED80 was 500. I shoot Prime method with camera body mounted with adapter direct to the visual back on scopes focuser tube. I looked at Losmandy mounts and love the G11 and even the smaller GM8 but it is overkill with imaging with the smaller scopes and I am happy as a clam with the capabilities of the little 80..... I have several scopes...4 Refractors ranging from 80mm to 6" 2 Schmidt Cassegrains, 8" and 9.25 1 8" Dob and an 8" newt with several different mounts of different styles, and a full set of Televue Nagler Type 2's, a few widefields in 1 1/4" along with a couple of Televue Panoptics for the gazing portion of this madness My best images were with the little 80, and the Celestron mount.... It is high enough tech, high quality imaging, low enough cost, light weight enough to move around and so it has served me well as a proper imaging set up withouit going to the Bentley end of the spectrum.... We would all love nothing but Takahashi gear but I for one work for a living..... As always it is the photographers eye, technique and understanding how to get the best out of his gear that makes a great shot, not the amount of money thrown at it....... My images all end up with numbers thrown in at the save as stage as I usually save several different variations of each and rarely actually designate a name for my images.... My last M42 shot was stacked with (to the best of my recollection) 12x 1.5 minute exposures, stacked with Registax along with one dark frame for noise reduction and dark background contrast, saved and then processed using Photoshop..... I hope with all of this babbling I have answered at least something in the original question;) ;).... I have been out of it for a while so I don't recall everything as far as exact settings and or all of the details of each shot..... I should have logged everything but of course I never did and probably never will:).... I have a lot of different astro imaging software programs that I have used and loved but it will take time playing again to refresh my use and techniques with them.....I hope this is some help.......Take care Dave....Alex

Don: I love the scope idea... It is a great way to maintain good alignment.... If you can slew smoothly to keep it where it is originally set up it a winner in every way... I think as long as you can calculate your longest acceptable exposures with out trailing.... that is the key to a good clean stack... With auto aligning in Registax and I assume others, as long as the subject is approximately in the same location in each frame the auto align feature will accept or reject the stackable images and if the exposure has to be short to be clean just shoot more frames.... The fewer frames involved with the stack the easier it is to get stellar results, however without solid, smooth, and accurate tracking capabilites the longer exposures aren't possible so you use more frames to build the image..... I am sure you already know all of this but I thought it was worth mentioning again....... You guys are an inspiration and are proving that minimalism is an excellent option once the needed technique is sorted out..... Thanks Don..... I need to get my stuff outside and start getting reaquainted with everything again.... I have an injured rotator cuff at the moment and need to be careful for a while, and with the bright moon and less than clear skies I think it may be a little while before the heavy artillery is utilized......Alex

Phew, thats some kit Alex.

US prices are nothing like here in the UK.

Stevie has read your previous posts and has reminded me to mention she is my wife. Does this mean I also have to play the role of ' sugar daddy '. :D :D
In her astro mode she tends to be a ' space hopper ' so there has been no previous need for a tracking mount. She has drooled over bigger scopes but not really suited to her style of instant set up and go.

Excluding the camera I tend to adopt a minimalist approach to lots of my photography. If I get hooked then I may buy kit. I enjoy the challenge of working with not a lot, or ancient bits of kit that most would dismiss.

I have had another play with RegiStax, and have worked out importing multiple images. Now I have to have a further play with the interface. Never too sure when program is actually doing something without watching ' task manager ' for a bit.

Don