p.10 #1 · Nightscapes using AstroTrac Tracking Mount
RobDickinson wrote:
Well I guess that proves a point? Also when are you buying an 800?
BTW what do you do when you cant see the circumpolar point?
And how does the auto guiding work?
Autoguiding sight + PC links to the astrtrac and controls its movements?
Hi Rob,
I'm not an expert on this as I have owned the Astrotrac mount for about a month. However, I'm glad to share my progress and what I've learned.
I'm sticking with my 400 f/5.6, 500 f/4 and extenders for astro shooting...
As far as auto guiding, it basically allows you to stay on your target. The auto guiding camera is connected to your computer and autoguiding software. It also connects to the Astrotrac mount using a special cable. It works quite well even though Astrotrac only corrects in RA.
It seems complicated but in about 3 minutes, you are ready to start your shooting sequence. I used BackyardEOS to connect to the camera. http://www.backyardeos.com
p.10 #3 · Nightscapes using AstroTrac Tracking Mount
Fred Miranda wrote:
Hi Dan,
The heaviest combination I've tried using a guiding camera was with the 7-pound Canon 500mm f/4L IS II lens on my Canon EOS 6D. The Astrotrac was attached to the "Wedge".
Awesome. Thank you for all the info Fred, your pictures look great!
Now to wait for the astrotrac to get back in stock.
p.10 #5 · Nightscapes using AstroTrac Tracking Mount
Here is s simple solution to keep that Polar alignment scope from falling out. Place a rubber band around the top or bottom, give it a twist and then up and over the other end. Then even if you bump it and knock it loose it does not fall.
p.10 #6 · Nightscapes using AstroTrac Tracking Mount
Mickey wrote:
Here is s simple solution for that Polar alignment scope falling out. Place a rubber band around the top or bottom, give it a twist and then up and over the other end. Then even if you bump it and knock it loose it does not fall.
Very clever Mickey!
I can see you already got the 'thumbscrews' to aid collimation.
An alternative to the elastic band is a 'Slip Joint Washer'.
Fred
p.10 #7 · Nightscapes using AstroTrac Tracking Mount
I've been following the thread to the point where I've finally ordered the AT. Peer pressure at its best! Has anyone found a source for "the wedge"? I'm striking out.
p.10 #8 · Nightscapes using AstroTrac Tracking Mount
There must have been a slight change in the design of the polar scope. The one I have has very little shoulder for the "Slip Joint washer" to grip to after the scope is put in place. Only maybe an 1/8th of an inch.
p.10 #9 · Nightscapes using AstroTrac Tracking Mount
Hi all,
I'm new to these forums, and am very happy to have stumbled upon this discussion! I am an astrophotography guy as well, and from my little experience can say that Fred's results with the astrotrac are really excellent. Especially after just one month!
As you can see from all the great images in this thread (though some might have been captured with larger-aperture optics and guided equatorial mounts) good deep-sky images have one thing in common: lots of total exposure time.
Image stacks with low total noise can be stretched further to show subtle detail. You get low-noise stacks by using many exposures. There is a point of diminishing returns of course, but generally you should capture as many frames as you have the patience / clear skies for.
Another consideration is aiming for the longest possible exposure for each indiv frame ... the time limits should be limited by star trailing (due to tracking error/polar alignment), and by overexposure due to the skyfog limit (light pollution or moon sky glow). For DSLRs, a great rule of thumb is to check the histogram after a test frame -- try to have the main peak of the signal about 1/3 to 1/2 away from the left side of the histogram. This helps to separate the signal from the dark noise floor. Too far to the right and you risk overexposing stars (leading to white, bloated stars) and losing some dynamic range.
Apologies for the unsolicited advice, of course there are many approaches. Earlier in the thread there was some great advice to check out Jerry Lodriguss' guides.
p.10 #10 · Nightscapes using AstroTrac Tracking Mount
Mickey wrote:
Here is s simple solution to keep that Polar alignment scope from falling out. Place a rubber band around the top or bottom, give it a twist and then up and over the other end. Then even if you bump it and knock it loose it does not fall.
Great idea. I thought of using gaffer tape to hold mine on, but the rubber bands will still allow the scope to be rotated. My polar scope doe not have the external thumb screws like yours does. Did you install them yourself? Are they used to align the reticle?
p.10 #11 · Nightscapes using AstroTrac Tracking Mount
Todd wrote:
Great idea. I thought of using gaffer tape to hold mine on, but the rubber bands will still allow the scope to be rotated. My polar scope doe not have the external thumb screws like yours does. Did you install them yourself? Are they used to align the reticle?
Todd
Todd,
Check out this PDF file written by Darryl Hedges.
It explains where to get the thumbscrews and collimate the polar scope.
p.10 #12 · Nightscapes using AstroTrac Tracking Mount
(East coast folks) The Rockland Astronomy Club is sponsoring a conference on astro photography in a few weeks that looks very interesting. Even some beginner workshops for us newbies. Jerry Lodriguess is going to be there and is conducting a couple of the workshops including a night one. I plan on going and wouldn't mind meeting up with anyone else for FM that might be going.
Here is the link.
p.10 #13 · Nightscapes using AstroTrac Tracking Mount
Fred -
Did you find it necessary to use a cable such as the DSUSB from Shoestring Astronomy to actuate the shutter on your T4i/6D when it is being controlled with Backyard EOS? I'm surprised that long duration (bulb) exposures can't be controlled via USB alone on these cameras.
p.10 #14 · Nightscapes using AstroTrac Tracking Mount
sky-candy.ca wrote:
Hi all,
I'm new to these forums, and am very happy to have stumbled upon this discussion! I am an astrophotography guy as well, and from my little experience can say that Fred's results with the astrotrac are really excellent. Especially after just one month!
As you can see from all the great images in this thread (though some might have been captured with larger-aperture optics and guided equatorial mounts) good deep-sky images have one thing in common: lots of total exposure time.
Image stacks with low total noise can be stretched further to show subtle detail. You get low-noise stacks by using many exposures. There is a point of diminishing returns of course, but generally you should capture as many frames as you have the patience / clear skies for.
Another consideration is aiming for the longest possible exposure for each indiv frame ... the time limits should be limited by star trailing (due to tracking error/polar alignment), and by overexposure due to the skyfog limit (light pollution or moon sky glow). For DSLRs, a great rule of thumb is to check the histogram after a test frame -- try to have the main peak of the signal about 1/3 to 1/2 away from the left side of the histogram. This helps to separate the signal from the dark noise floor. Too far to the right and you risk overexposing stars (leading to white, bloated stars) and losing some dynamic range.
Apologies for the unsolicited advice, of course there are many approaches. Earlier in the thread there was some great advice to check out Jerry Lodriguss' guides.
Welcome aboard Adam!
Thanks for the advice. I have been capturing long exposures at around 30 - 40% from the left of the histogram.
I have tested this and it seems that going further than this range will mainly record sky glow and not data from your target.
jhenderson0107 wrote:
Fred -
Did you find it necessary to use a cable such as the DSUSB from Shoestring Astronomy to actuate the shutter on your T4i/6D when it is being controlled with Backyard EOS? I'm surprised that long duration (bulb) exposures can't be controlled via USB alone on these cameras.
I use the original USB cable to connect the camera (T4i or 6D) to the computer (BackyardEOS).
No problems there.
If you are using the Canon 6D, you will need a beta version of BackyardEOS, which is currently not available for download. From my tests, it is working great and should be available soon.
p.10 #16 · Nightscapes using AstroTrac Tracking Mount
I am amused Fred has caught the astrophoto bug. I followed the opposite path.. I bought a DSLR for astrophotography in 2006 and got the photo bug!
I greatly enjoy imaging with the 400/5.6L - it is on par with most quality 80mm refractors and has the added benefit of autofocus and daytime use on my camera Here's a stack of 5 min exposures of M45/ Pleiades with a Canon 40D: http://astro.welsh-house.net/img/m45-5min-web.jpg
I am very interested in portable mounts, as my current setup is to piggyback on my 8" SCT, and moving it around and aligning is cumbersome.
A question for you, sir: you mention autoguiding your astrotrack mount.. what are you autoguiding with? My current autoguiding setup is rather involved, so I'm interested in hearing about simpler solutions.
p.10 #17 · Nightscapes using AstroTrac Tracking Mount
Similar to Andrew's interests. Mine have gone from Photography, to Astro (via modified DSLR) then to a full-blown CCD imaging system. However, my DSLR astro efforts lead me back photography, doing IR photography. It's all fun...
p.10 #19 · Nightscapes using AstroTrac Tracking Mount
JameelH wrote:
Has anyone tried using a mirror lens for astro photography?
If by "mirror lens," you're talking about the Maksutov-Cassegrain-type lenses which used to be fairly common, I wouldn't recommend it.
Unless you have a very fine mount (and by "very fine," I am talking about mounts that cost many thousands of dollars), you really want to image with fairly short focal length lenses (I wouldn't want to go over 400 or 500 mm with a budget mount), and it's a large benefit to have fast focal ratios. Mirror lenses tend to be very slow, and often artificially long focal length (the purpose of the mirror system is to pack long focal length into a short package).
Additional issues are that mirror lenses tend to have poor optics (not talking high-quality scopes here, but photographic lenses), and the central obstruction causes issues with the amount of light that reaches the sensor and the contrast of the images produced.
p.10 #20 · Nightscapes using AstroTrac Tracking Mount
+1 on starnut's comment. I've used one as a guide scope, with reasonable results. It was a 300mm f6.3. I also had a 500mm f8 that I tried, but the f# was too slow (dark) for my guide camera to reliably see stars, with out longer exposures (which defeats the purpose of the guide camera). Here's a shot of it on the 80mm Stellarvue refractor I used to have:
You'll also get better resolution with a refractor or regular camera lens (no central obstruction). That being said, if you have one, try it. However as a purchase, it might not be the best choice for astrophotography.
