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Nightscapes using AstroTrac Tracking Mount
  
 
harshaj1
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p.14 #1 · p.14 #1 · Nightscapes using AstroTrac Tracking Mount


danws6 wrote:

Oops. I forgot to reply. To answer your question, yeah I have the astrotrac wedge. I ended up going back out to try again the next day after my last post. I took my time with the polar scope. I ended up getting fairly decent alignment, although it wasn't perfect. I attempted a few shots with the 70-200mm + 1.4 III but didn't really get anything that I found interesting. As I was packing up my stuff at 2am I decided to try using the wide angle for a Milky Way shot.

Here is the result. I think the post
...Show more
You got very nice details in the center. Trailing at the edges will get better with practice. Great job.
Harsha



Jun 27, 2013 at 12:42 AM
dgdg
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p.14 #2 · p.14 #2 · Nightscapes using AstroTrac Tracking Mount


Your polar alignment looks just fine at this focal length, so congratulations!
The lens (16-35 f 2.8 II??) has some coma at the edges/corners when used wide open even on a crop body. The milky way core is not centered at polaris, so you should not have the appearance of rotation around the corners of your image. You'd have to crop the coma out, or try something like the inexpensive samyang 14mm if you like this focal length. Alternately, try stopping your lens down to f4 - you've got a great tracker, set iso to around 800 and enjoy. The need to use your lens wide open for a great wide angle astro photo faded away once you bought the tracker. Agree, it is blown out in the milky way core on my monitor. Maybe you can still recover the highlights. Make sure your histogram on the first image shows the spike about 25% to 33% from the left. If you have skyglow, then you'd have to account for that when reviewing the histogram and your test image.
Contrary to what I thought intuitive, most astrophotographers using dslrs recommend the ISO sweet spot of 800 instead of something like 100. I haven't researched it heavily to give a scientific explanation.

Good job!



Jun 27, 2013 at 12:24 PM
dasams
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p.14 #3 · p.14 #3 · Nightscapes using AstroTrac Tracking Mount


dgdg wrote:
Contrary to what I thought intuitive, most astrophotographers using dslrs recommend the ISO sweet spot of 800 instead of something like 100. I haven't researched it heavily to give a scientific explanation.

Shooting at 800 or 1600 is preferred over 100 for several reasons. First of all, the higher ISO means a shorter exposure time which allows for more shots in a given session. Secondly, stacking images improves the S/N ratio as hot and variable pixels are removed. Shooting multiple darks also gives a reference for subtraction of high ISO noise. Finally, shorter exposures also reduces tracking errors. I'm sure there are other reasons I've missed so please chime in. Dave



Jun 27, 2013 at 05:09 PM
Guari
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p.14 #4 · p.14 #4 · Nightscapes using AstroTrac Tracking Mount


tag for follow up


Jun 27, 2013 at 11:43 PM
danws6
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p.14 #5 · p.14 #5 · Nightscapes using AstroTrac Tracking Mount


dgdg wrote:
Maybe you can still recover the highlights. Make sure your histogram on the first image shows the spike about 25% to 33% from the left. If you have skyglow, then you'd have to account for that when reviewing the histogram and your test image.
Contrary to what I thought intuitive, most astrophotographers using dslrs recommend the ISO sweet spot of 800 instead of something like 100. I haven't researched it heavily to give a scientific explanation.


I was trying for that range on the histogram. It's amazing how quickly time flies by when you're taking test shots with long exposures. I can probably recover those highlights but I think I'd rather try to get a better picture to spend my time working on. The higher ISO for shorter exposures makes sense when it comes to stacking images, which is something I need to read up on. Determining how many frames to take might just require lots of practice.

dasams wrote:
Secondly, stacking images improves the S/N ratio as hot and variable pixels are removed. Shooting multiple darks also gives a reference for subtraction of high ISO noise. Finally, shorter exposures also reduces tracking errors. I'm sure there are other reasons I've missed so please chime in. Dave


Something I definitely need to get a handle on is figuring out the sweet spot for exposure lengths and the number of darks to take. I'm really new to the concept and am trying to learn if offset/bias and flat frames are required too. I have Backyard EOS which will should me keep track of the different frames.

I'm planning to go out again over the July 6-7th weekend so it looks like I need to do a lot of research. I'd like to get a handle on drift aligning with the autoguider since I might have access to a super telephoto that weekend. I was playing with the setup during the day time this past weekend and I think I've got the basic idea down.

Thanks everyone for the replies, you are a great resource.



Jun 28, 2013 at 04:12 AM
dgdg
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p.14 #6 · p.14 #6 · Nightscapes using AstroTrac Tracking Mount


I'd take an equal amount of lights, darks, bias frames. You don't need many to vastly improve your IQ compared to a single photo done at high iso. If you ever get a big telescope and like nebulas, that is entirely different. Those people can have many hours of total exposure time. I have one nebula photo I'm still learning to process, but due to light wind causing micro vibrations, I had to throw out about 7 of my 20 lights. So if you have the time, extra lights can't hurt.
Deep sky stacker's website has some good short tips on this. I haven't bothered with flat frames. I suppose if vignetting were a problem, I'd add those too.



Jun 28, 2013 at 03:53 PM
Lincoln Harrison
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p.14 #7 · p.14 #7 · Nightscapes using AstroTrac Tracking Mount








22 x 71sec f2.8 iso1600
D800E, Sigma 35mm f1.4, Vixen Polarie

larger version: http://www.flickr.com/photos/hakka69/8659236354/sizes/o/



Jun 28, 2013 at 07:42 PM
dgdg
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p.14 #8 · p.14 #8 · Nightscapes using AstroTrac Tracking Mount


wonderful photo there - iso 1600. For wide angle stuff and normal ranges, the vixen rocks. Only niggle I have is sometimes when I try to set up my composition, I get misaligned and have to take the camera off.


Jun 28, 2013 at 07:56 PM
astro-ep
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p.14 #9 · p.14 #9 · Nightscapes using AstroTrac Tracking Mount


Nicely captured, stacked and processed, Hakka.
Thanks for sharing it with us.

Eric



Jun 29, 2013 at 02:47 AM
astro-ep
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p.14 #10 · p.14 #10 · Nightscapes using AstroTrac Tracking Mount


That reminds me. I wrote a little piece a while back that might be appropriate here. Although there are no photos, it's specifically about that very topic. Hope it's OK to post this here

------
Look Up
by Eric Chesak

Ever look up? As an astrophotographer, most folks would certainly think so. Recently, I have found myself looking more at a computer monitor than the sky. With more and more automated & robotic scopes, I believe that I am not alone.

Working for a small Government contractor, I regularly travel to very remote sites. Here we offer our wares by day, but have little to do at night. There is nothing for miles. No TV, no internet; not much of anything!

2008 was my first year on this project. After darkness fell, I looked-up and was astonished. The view caught me a bit off-guard. I found myself hunting for the familiar constellations, but the background starfield was so bright, this task was more difficult that I imagined. During the duration of this project (~2 weeks) we experienced perfect weather. With no distractions, my spare time clicked-off under the stars.

So taken by this, I spent the next year assembling a portable imaging system, that would allow me to capture some of the incredible views that I experienced. As the project approached, I was excited at the prospect of having extended lengths of time to image the wide-field swath. In hindsight, it became evident that I must have violated one of Murphy’s laws of astronomy. During the duration of the 2009 project, we experienced weather of apocalyptic proportions; No stars, no sky, just gale-force winds and 100% coverage of salt spray from the Sea below.

2010 rolls around, with the memory of the 2009 event. I was forbidden to bring anything remotely associated with astronomy. Disappointed, I planned to just stargaze… What I experienced during the 2010 project was nothing short of magnificent. I spent countless hours just staring at the galactic depth. I naked-eye star-hopped to M31, which was clearly visible. I was also amazed to easily see M15. As an added bonus, dozens of Taurid and other meteors displayed their brilliance. After I tired of sitting, I climbed into my tent, into bed and spent many more hours with my head hanging out the door. In the morning, I typically arose several hours prior to the rest of the team. As a reward, I witnessed a week’s worth of Zodical Light. Never having previously seen this phenomenon, I was astonished at the intensity & clarity.

At times, I wished I had some gear to photograph these sights. But knowing I didn’t, allowed me to just enjoy the sheer splendor. I’ve previously been to dark skies, but never with such extended, uninterrupted viewing time. I witnessed 10 year’s-worth of normal dark sky observing. But most important of all, I was looking up…

------


I'm certainly no writer, but hopefully you enjoyed reading it. These days of Techno-everything, sometimes we loose sight of the simple pleasures.

Eric



Jun 29, 2013 at 03:25 AM
 

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dgdg
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p.14 #11 · p.14 #11 · Nightscapes using AstroTrac Tracking Mount


great reminder eric for all of us. thanks for sharing.


Jun 29, 2013 at 03:41 AM
danws6
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p.14 #12 · p.14 #12 · Nightscapes using AstroTrac Tracking Mount


dgdg wrote:
I'd take an equal amount of lights, darks, bias frames. You don't need many to vastly improve your IQ compared to a single photo done at high iso. If you ever get a big telescope and like nebulas, that is entirely different. Those people can have many hours of total exposure time. I have one nebula photo I'm still learning to process, but due to light wind causing micro vibrations, I had to throw out about 7 of my 20 lights. So if you have the time, extra lights can't hurt.
Deep sky stacker's website has some good short tips on
...Show more

Cool, I'll check out the website. If I'm using a zoom lens does it make sense to turn off IS to save battery and avoid any vibrations?

Another question for the Backyard EOS users, does anyone have any tips for using the focusing feature?

Hakka wrote:
22 x 71sec f2.8 iso1600
D800E, Sigma 35mm f1.4, Vixen Polarie

larger version: http://www.flickr.com/photos/hakka69/8659236354/sizes/o/


Amazing shot, I love the amount of detail.



Jul 01, 2013 at 01:55 PM
dgdg
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p.14 #13 · p.14 #13 · Nightscapes using AstroTrac Tracking Mount


definitely turn off IS (zoom or prime)


Jul 01, 2013 at 02:04 PM
astro-ep
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p.14 #14 · p.14 #14 · Nightscapes using AstroTrac Tracking Mount


I'm one of those that take images with many hours of exposure time. Typically my images are from maybe 5-30 hours. Each night that I shoot, I also take calibration images (Flats & Bias). You should also take dark frames. My astro CCD has regulated temperature control, so I can take one set of darks for a particular temperature and re-use them for 4-6 months. But for DSLR's you'll need to take Dark frames on each outing.

Getting these right, will help your images significantly. I usually shoot 20,20,20 of Bias, Dark and Flats. One calibration frame will help, but averaging more will help much more. Take a look at this page. It gives a really good quick overview on why these are needed, and the benefits of larger numbers of calibration frames:
http://starizona.com/acb/ccd/advimcal.aspx

You might also give some of these a read:
http://www.hiddenloft.com/notes/acq.htm

Also, You'll definitely want to turn off your IS. This is more likely to cause harm than good. It will also tend to use more power than with it off. You might also be aware that Zoom lenses tend to creep, under changing temperatures. When I first got started, I was shooting with a EF70-200mm f2.8L, on a Losmandy G11 Equatorial mount. Although the flattness and color correction of professional lenses are great, the changing temperature caused the zoom internals to change dimension slightly. I thought zoom ring was slipping, but even taping this ring, I still experienced this creep. This was occurring after several hours of Winter night shooting. Different lenses will have different characteristics, in this respect. But it is something you might want to watch. On one image, I had more than 50 light frames, over several hours. They were mostly unusable, as the zoom factor was slightly different on each frame. This made stacking them impossible (with the software I ad at the time).

FWIW, this temperature creep is a major concern with many small f# telescopes also. Many use temperature controlled focusers to help this. My scope is a 530mm f5. I typically shoot 30 minute exposures. But I was experiencing enough focus shift, during the length of a single exposure, to make the image un-usable. I came-up with an innovative solution,( http://tinyurl.com/8ppa9ss ) but this is an issues for nearly every astrophotographer out there.

Hope this is useful,

Eric






Jul 01, 2013 at 02:32 PM
danws6
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p.14 #15 · p.14 #15 · Nightscapes using AstroTrac Tracking Mount


Eric, thanks for the info. I used it to make this heavily cropped picture this past weekend.


5 x 140 seconds, 280mm, f/4, ISO 1600

I stacked the images using Deep Sky Stacker and adjusted the curves in it.

I ended up with only 5 usable light frames out of the 10 that I was attempting before clouds rolled in and ruined my plans. One of the interesting struggles I'm running into is the large amount of time it takes to find objects and center in on them. My current process is using backyard eos to capture a preview, adjust the camera, take another preview. There isn't enough light with the live view to be able to see anything. I'm tempted to mount another camera on the same rail with a 24-70mm f2.8L to use as a spotting scope.

As for the focus creep, one of the problems I've been running into is dew. I'm planning to get a few of the dew heater bands so I can control the temperature of the lens. I'm wondering if that would do an adequate job of avoiding the focus creep.



Jul 08, 2013 at 04:30 PM
astro-ep
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p.14 #16 · p.14 #16 · Nightscapes using AstroTrac Tracking Mount


Not a bad start. More time and better guiding/alignment will really help this a lot. You're right about finding targets, especially in skies that are light polluted (fewer stars to help locate). Before I had a Goto mount, I used to spend an hour+ locating and framing. The problem, as you've no doubt seen, is that most of the targets are so dim that you need to shoot a test exposure to see if it's in the frame. Then adjust, shoot, adjust, shoot...you get the picture (no pun intended :-) ). Many of my targets are so dim that they are barely visible, even after a 30 minute soaking. So locating targets like this visually is impossible.

With a Goto mount, I can now align the mount and locate any target in the sky within a few seconds. I then take a test shot and see which stars I want located where, in the frame. I generally know what the framing should be, from previously framing in catalogs called Uranometria. But many planetarium programs will also help with framing. The Goto mount allowed me to get another hour+ of imaging time, each night. So besides the frustration, that alone was worth it.

Dew is definitely an issue for a lot of locations, but is rarely a problem, here in the Desert Southwest. Dew strips will help with the Dew, but in order for it to help with the focuser shift, you'll need to warm the entire lens, and control the temperature with a regulated controller. Dew strips me be better than nothing. It all depends how constant the dew strips will control the temperature. My closed-loop system can usually hold the temperature within about 1 degree F. But the critical focus zone (CFZ) on my scope is about 55 microns. So small changes in the temperature can create enough dimensional change to throw the system out of focus.

Keep working on it. The learning curve for all this is pretty steep and the only way to make progress is to experiment and see the results. I'm in my 4th year of serious imaging and still learn something every time I spend time with my set-up.

Eric



Jul 08, 2013 at 04:57 PM
dgdg
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p.14 #17 · p.14 #17 · Nightscapes using AstroTrac Tracking Mount


excellent image
the rigel site finder can be an easy 'spotter scope' for you. It mounts on your hot shoe. Calibrate the site using a bright star, then star hop to your target.
I found with a 400mm lens, a dew heater in moderate temperatures works just fine as far as any focus shift.
For fine adjustments across the sky, consider experimenting with a geared ball head.
You are testing the limits of your gear, but it is fun.



Jul 08, 2013 at 06:57 PM
danws6
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p.14 #18 · p.14 #18 · Nightscapes using AstroTrac Tracking Mount


I've been using Stellarium for helping find objects which has been working well.

I managed to collimate my polar scope this past weekend which helped with the alignment but I can tell it's still not as accurate as I want. I think on my next outing I will spend time getting comfortable with drift aligning using the orion auto guider. I wonder if it would well as a spotting scope too.

I've been trying to decide what route to go with the dew bands. I guess I'll get one of those 4 port controllers so I could use two on a lens and one on the autoguider.

Thanks again to the both of you for the helpful information.



Jul 09, 2013 at 10:37 PM
MikeW
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p.14 #19 · p.14 #19 · Nightscapes using AstroTrac Tracking Mount


Fred Miranda wrote:






Here is the gear I'm using for auto guiding with the Astrotrac mount:

I have tried the LVI Starshooter but was unhappy with the results. It would not lock on dimmer stars and when it did, it would lose the lock during shooting. Very frustrating.

I did a little research and most shooters are happy with the Orion Startshooter guiding camera. That is the one I'm using. You need a laptop to operate it and the PHD guiding software with special drivers is included (PC and Mac)
The Orion 50mm scope works great. Orion created a bundle (50mm scope with the
...Show more

Bump -

Do you need the astrotrac polar scope if you have the Orion-Magnificent-Mini-AutoGuider?



Jul 14, 2013 at 08:10 PM
astro-ep
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p.14 #20 · p.14 #20 · Nightscapes using AstroTrac Tracking Mount


I'm not an astrotrac user, but the question is relevant to any astro set-up, so I'll comment.

The two parts that you mention are for different functions, as you are probably aware. The polar scope is for aligning the mount, to the Celestial North Pole. The Autoguider is for making adjustment to the Astrotrac, to insure that the unit stays locked on target, regardless of where it's pointed in the sky.

You can take images and autoguide without polar aligning, but depending on the amount of error, focal length of the lens/scope and the length of the exposure, you will begin to get some field rotation, and some streaked stars in the image. The more error in the alignment, the faster this will occur. If you're using a wide angle lens, the polar alignment can be fairly rough and there's little need for an autoguider. But the longer the lens, the more precision that is needed for both the mount alignment and the autoguider actions.

As an example, I shoot with a full frame Astro CCD with a scope, not much longer than one above (530mm) and I aim for the polar alignment error to be <1 arc-minute (1 arc-minute is 1/60th of a degree). Obtaining very accurate polar alignments are more difficult with the Astrotrac. That's why many folks that want to shoot with longer lenses should eventually buy an equatorial mount.

I hope this answers your question. If not, shoot me a PM and I'd be glad to chew it over some more...

Eric



Jul 14, 2013 at 09:12 PM
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