Polar Alignment Part 3, Finding True Celestial North.
How to find true celestial north.
Find Polaris. Polaris is actually the last star on the little dippers handle (ursa minor) Trace back along the path of stars untill you reach the star Kachob, (see picture). If you draw an imaginary line between Kachob and Polaris, the NCP (north celestial pole) is on this line, approcimately 45 arc seconds out from polaris. Arc seconds? WTF? ok, if you dont know arc seconds, the moon is approximatly 30 arc seconds across. So you want to trace from Polaris TO Kochab one and one half moon widths length, and you are pretty much dead on polaris.
If your tracker is moving at the correct rate, pointing right there with the laser is going to get you some pretty good accuracy. With my current rig i should be able to do….
200mm at 3 minutes,
400mm at 1.5 min,
800mm at 45 seconds,
1600mm at 22.5 seconds.
Polar Alignment Part 2, The LASER
The laser should be a 100mw laser, and you want to use something tactical like a laser site for a sniper rifle, this should be bright enough to see (100mw is perfect) and should have elevation and windage adjustments which are CRITICAL to center the laser.
To center the laser you just need to find a way to rotate the laser without adjusting its pitch. The method i used was to drill a hole the exact same diameter as my laser (the housing not the beam) into a 2x4. Then i secured the 2x4 to my work bench and put the laser into the hole so it was shooting at the far wall, then i rotated the laser and sure enough the dot went in a circle. I adjusted the windage and elevation screws untill i could rotate the laser a full 360 degrees without the dot moving. then i knew the laser was pointing perfectly straight,.
Next, i attached a rail mount (the same kind that scopes mount to on rifles) onto my tracker right along the hinged side taking time to ensure it was perfectly straight.
Now i know when i attach my laser that it is in perfect alignment with my hinge.
Next, i need to find Polaris. This is the north star, you should be able to find the north star, if not, well, go read up on some astronomy. Here is a clue, whatever your current latatude is, look north and the same angle up as your latitude, in colorado i think im at 39 degrees, so if i look north and up 39 degrees, i should be looking almost right at polaris.
But polaris is not TRUE celestial north. it is just real close. Depending on what you are shooting. If you plan to image wide angle star fields you can just point the laser at polaris and that is “good nuff”. if you want to zoom in and image real faint deep space objects “good nuff” just wont cut it.
Polar Alignment
(sorry, most of this applies to northern hemisphere only)
This is an important one to learn, when i first started looking into this i saw all kinds of information about drift alignment, the kachob wheel, etc, and a lot of it seemed to be over complicated.
In a nut shell, in porlar alignment you want your movement of rotation to be perpendicular to the axis of earths rotation. Say what?? its not that complicated. With my tracker shown here i want the hinge of the tracker to line up with the rotational axis of earth, meaning the hinge needs to be pointed to celestial north.
My method of achieving this is rediculously easy. I use a laser, its like having a straight edge ruler that shoots out 5 miles. I point the laser at celestial north, and presto, i have instant polar alignment. Last time i had my setup in my yard and was testing there were clouds in front of polaris, finally they parted and in under 30 seconds it was clouded over again, but i already had polar alignment nailed down to whe point i could shoot 3 minutes at 200mm with no visable error. Keep in mind at 200mm stars start taking a pill shape in 3 seconds. Not bad for 30 seconds!
Things to keep in mind, i get the impression that astronomy clubs dont allow lasers at thier viewing locations, if you plan to go out with your local astronomy club, check thier rules, they may not allow you to use this.
Mixed success last night, i managed to get what i was looking for which is accurate tracking at 200mm, but not jut 2 minutes i got 3 minutes!
On the image you can see tracked vs untracked and see the amount of correction the tracker accomplishes.
However, that wheel wobble is still present, albeit far less pronounced i have to zoom in at the pixel level to see it. What is happening here is the nut that pulls up the threaded rod is not 100% centered in the gear, so it causes the rod to wobble ever so slightly. Note this is only seen when zoomed in, at 100mm this is hardly noticable, at wide angles 24mm -10.5mm this is undetectable as the star is the size of a single pixel.
So telephoto work is still out untill i cant find a way to correct that wobble, i think the entire desgin is the problem. i may need to re-invent the wheel on this.
For wideangle work thi tracker is perfect. here is a estimated exposure i time i can manage at the following focal lengths
200 = 3 min
100 = 6 min
50mm = 12 min
24mm = 24 min
12mm = 48 min
10.5 = over 50 minutes.
that is awesome!!!!! Once the outerband of the milkyway is visable i should be able to get some very low noise and extremly stunning images. :) Im very excited!
Google Sky map App
I think they have this available for iPhone, but this is definatly available for the Droid. I use this, it is about the best app you can possible have for astrophotography. Basically it turns your phone into a window in a planetarium, it knows your location, the time, the year, everything, you can hunt for various messier objects like star clusters, nebulas, galaxies, etc, and it even has a night mode where all it shows is red lines and the stars as to not mess with your vision at night.
this has been crucial for getting proper polar alignment. It is a free app, if you have a droid get it.
The next writeup will probably be on polar alignment.
Here is an example of what can be done in a white/red zone. This is the orion nebula, in an earlier post i show the same nebula that was taken in dark skies and stacked. This is just one single image, this is actually the first image i ever took of a Nebula. This was done in my backyard, and has been processed with photoshop for maximum effect. If i had stacked with with 20-30 images i have no doubt it would look much better, but probably not as good as the one i took in the dark skies.
Light Pollution = Bad M’kay?
Light Pollution is your enemy, you should try to get as far away from it is possible. this causes problems for the people on the eastern side of the us as there is TONS of light pollution, but even in areas with light pollution all is not lost.
The website below is a very handy tool, you can find areas near you with the least amount of light pollution.
http://www.jshine.net/astronomy/dark_sky/
There are various filters and such i have seen for astronomers that supposedly eliminate some light pollution, i have no idea how they work, and the idea behind them seems a bit sketchy, and i am pretty skeptical that a tinted $200 piece of glass is going to do much. To be fair, i have never used one.
One of the best tools for reducing light pollution is photoshop. I dont really have an established workflow, but i always shoot RAW and in Adobe Camera Raw you can adjust the black level and that really seems to help. I also spent time in Levels and Curves and playing with exposure masks. Check Youtube it is a great resource for post processing AP images. It is tricky sometimes but you can get somewhat decent results. As for the filters, i dont see how they do anything that can not be done in photoshop. the good thing about using digital imaging software for post processing over a filter is you can either add the effect or remove it, shooting through a filter it is always there.
So my best tips, try to get out as far as you can. Once you get out to green zones the outer band of the milky way becomes visable. the purple areas are pretty much pitch black and perfectly good for astrophotography. If you are anywhere within 100 miles of a city the glow will show up on the horizon, this can be good or bad, sometimes it looks nice to have the city glow defining the horizon. or you can shoot in the opposite direction and not see it at all.
My house is right on the border between the White and Red zones, meaning it has tons of light pollution. However im butted up against the mountains, if shooting west in the direction of the mountains i can still fare pretty well. The shot of the Pleadies shown earlier was done in a red/white zone in my back yard.
STACKING, yes you need it, it will be your best friend
This will become your best friend. it will take your astrophotography to a new level. IF YOU ARE NOT STACKING YOU ARE WASTING YOUR TIME
Stacking will virtually eliminate high ISO and long exposure noise, and it will pull out an incredible amount of detail out of your images. The way it works is to take multiple images, overlay them on top of eachother, average out each stack of pixels, do some fancy math and based off the values it will pull out detail that you cannot see (the pixel data sees it, but the resulting image does not untill you stacK)
I have seen stacked DSLR images that look like they were taken by the hubble space telescope.
Here is the awesome benefit. Say you want to take a shot of a distant galaxy, and you have a 300mm zoom, and seeing as how you dont want tons of high iso noise you shoot at 200 ISO, however to get the proper exposure you need to shoot for 10 minutes. Short of having a high priced ($1,500+) self guided scope with a DSLR piggybacking it this is nearly impossible. I have been tweaking my setup for the last several months trying to get the most performance out of it, i can barely do 1 minute at 200mm unguided.
STACKING TO THE RESCUE! This will allow me do get the image with my current setup.
The shot that requires ISO 200 for 10 minutes can gather the same amount of light in 45 seconds at iso 3200, or under 25 seconds at ISO 6400. That means as long as you can accurately track at 300mm for about 30 seconds you can get the image. You just have to spend the time getting the Lights and Darks. You want as many as possible, i usually got for 30-50 light frames, and 10-15 dark frames.
Lights - Light frames are the images of the cosmos you have taken.
Darks - taken with identical(exact same settings) settings with the lens cap on. Yes, with the lens cap on.
The lights are fed into the stacking program. it will align the images, crop off the excess, and look at it pixel by pixel through the stack to obtain the averages that will be used in the final output. The Darks are also fed into the stack, these black images are averaged together to create a noise profile for the image sensor, this is what eliminates the noise. So the lights bring out the detail, the Darks eliminate noise.
I use DSS (Deep sky stacker), it is free, google it. There are many youtube tutorials, it is not hard to use. There is another free program called registax but i cant seem to figure it out, other people dont seem to have a problem. Nebulosity is NOT free, but seems to get excellent results.
Once you stack the images in DSS, the best bet is to do the post processing in photoshop or whatever your favorite editor of choice is, once again, there are many youtube tutorials on this stuff.
When you are done you will likely have a far far more detailed image using multiple high iso images stacked than a single low iso image, plus you dont have to rip out your hair trying to get a 10 minute exposure at 300mm.
UNTRACKED
This is one of the first astrophotography shots I took.
shot on D90, 12mm tokina at f/4, 30 second exposure at ISO 3200.
Looks ok from a distance, as you get closer you can see all the noise and grain from the high iso. If i had used a tracker at ISO 200 for 4-5 minutes it would have been much cleaner. Check out the high res version and you will see all the grain/noise
Also, if i had known of stacking, i could have gone that route and really helped the image by eliminating the noise and bringing out the detail.
Unfortunatly the dark rift is not showing yet, i need to wait a few more months before ill be able to find it again in the night sky.
This is a tracked/stacked image. Notice the very nice pinpoint stars, if you look over the “S” in “chris” you will see the andromeda galaxy. This was taken i believe at 24mm. Click on the high res.
Here is another example of un-tracked astrophotography to give you a better idea of what i mean
this is in a area with lots of light pollution (my backyard) when i was working on my tracker, in this image the tracker is actually shut off.
This is one of the frames taken by my timelapse robot (that will be another blog), about 70 miles east of denver in a near total blackzone. you can see the laser shooting into the sky, and if you notice the stars they have taken a pill shape, this is 24mm focal length for 25 seconds.
Page 1 of 2
