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OpenAstroTracker: A cheap 3D-printed tracking mount for DSLR astrophotography

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Re: OpenAstroTracker: A cheap 3D-printed tracking mount for DSLR astrophotography

#21

Post by LeifCarrotson »

dylan604 wrote: post #8
dukeofdoom wrote: post #7

How does this compare to something like move-shoot-move? I think that one costs only $200. Is it even worth it to DIY.

Shoot-move-shoot does what it sounds like. It moves the platform, allows time for the movement to settle, snaps the shot, then moves again. Astrotrackers like this are constantly moving at the same rate that the earth spins on its axis. This allows for the subject to remain in the same poistion in the frame during super long exposures. Depending on the accuracy of the polar alignment and the focal length of the lens,…

One benefit of shoot-move-shoot is that when combining/compositing the images together in post, you can remove and adjust for temporary artifacts like satellites or terrestrial lighting that would otherwise ruin a long exposure. You can also compensate for motion platform inaccuracies by shifting the location of each layer to keep the object you're trying to image at the same location in the frame. Minutes-long exposures mean you're just ORing all the photons together, and you get what you get.

Re: OpenAstroTracker: A cheap 3D-printed tracking mount for DSLR astrophotography

#24

Post by spfzero »

dylan604 wrote: post #15
andrewxdiamond wrote: post #9

Earlier quoted context omitted.

What is the benefit of using robotics to move the camera over image stabilization software in post? Is it simply image quality? Or are there more trade offs?

The is a common question, but there are certain things that are just better done in camera than post. Then there are situations where a combination of in camera + post provides optimum results. Astrophotography is one that can and does use both. The longer you can expose, the more information obtained. For ultimate long shots, you need to compensate for the earth's rotation. You continue to snap away all night, and t…

Taking short exposures and stacking also can help by removing the effects of periodic error in the mount gear-train (or belt-train).

Re: OpenAstroTracker: A cheap 3D-printed tracking mount for DSLR astrophotography

#25

Post by wtallis »

emptybits wrote: post #20

This is quite brilliant. Here's another approach to tracking, employed by Pentax and maybe others: Use 5-axis sensor movement to track stars (i.e. use the motors which move the sensor for in-body stabilization) Given GPS coords, software can do this to the limits of sensor movement afforded by the camera body. I don't have a Pentax but modern models can apparently track for at least 4 minutes.[1] (!) In theory, offic…

I think this requires not just a GPS fix but also fairly accurate heading information from an electronic compass and tilt information from the camera's accelerometer, because shifting the sensor in the right direction requires knowing which part of the sky the camera is pointed at. (I haven't bought the astrotracer add-on for my Pentax because it's crazy expensive for what it is, but it should be at least a bit more than just a GPS receiver.)

Re: OpenAstroTracker: A cheap 3D-printed tracking mount for DSLR astrophotography

#26

Post by martyvis »

wtallis wrote: post #25
emptybits wrote: post #20

This is quite brilliant. Here's another approach to tracking, employed by Pentax and maybe others: Use 5-axis sensor movement to track stars (i.e. use the motors which move the sensor for in-body stabilization) Given GPS coords, software can do this to the limits of sensor movement afforded by the camera body. I don't have a Pentax but modern models can apparently track for at least 4 minutes.[1] (!) In theory, offic…

I think this requires not just a GPS fix but also fairly accurate heading information from an electronic compass and tilt information from the camera's accelerometer, because shifting the sensor in the right direction requires knowing which part of the sky the camera is pointed at. (I haven't bought the astrotracer add-on for my Pentax because it's crazy expensive for what it is, but it should be at least a bit more…

Surely in camera, it is just a matter of taking a shot, wait an interval, take another shot, then shift/rotate the two images until X number of bright spots line up and then form a new composite, rinse and repeat. If you have a motor in the camera for stabilising you can use that shift/rotate parameter to move the sensor for the next shot.

Re: OpenAstroTracker: A cheap 3D-printed tracking mount for DSLR astrophotography

#27

Post by astroflask »

LeifCarrotson wrote: post #21
dylan604 wrote: post #8

Earlier quoted context omitted.

Shoot-move-shoot does what it sounds like. It moves the platform, allows time for the movement to settle, snaps the shot, then moves again. Astrotrackers like this are constantly moving at the same rate that the earth spins on its axis. This allows for the subject to remain in the same poistion in the frame during super long exposures. Depending on the accuracy of the polar alignment and the focal length of the lens,…

One benefit of shoot-move-shoot is that when combining/compositing the images together in post, you can remove and adjust for temporary artifacts like satellites or terrestrial lighting that would otherwise ruin a long exposure. You can also compensate for motion platform inaccuracies by shifting the location of each layer to keep the object you're trying to image at the same location in the frame. Minutes-long expos…

For sufficiently dim targets, you absolutely need minutes long exposure. If you go for shorter bursts, you face two main challenges:

1) Not enough photons reach the sensor to distinguish the object you are trying to photograph from the noise floor of the sensor. This is by far the biggest reason to go for a tracking mount.

2) You bog your computer down in post processing. 50x1 minute images are far simpler to align than 500x6 seconds images.

Combine (1) and (2), and there's barely any reason to go for untracked shots. As for satellites, planes, clouds, or other kind of transient phenomena that can potentially ruin a shot, that's where you apply some kind of clipping over data (usually sigma clipping or some variation of it) and problem solved.

Re: OpenAstroTracker: A cheap 3D-printed tracking mount for DSLR astrophotography

#30

Post by TaylorAlexander »

martyvis wrote: post #26
wtallis wrote: post #25

Earlier quoted context omitted.

I think this requires not just a GPS fix but also fairly accurate heading information from an electronic compass and tilt information from the camera's accelerometer, because shifting the sensor in the right direction requires knowing which part of the sky the camera is pointed at. (I haven't bought the astrotracer add-on for my Pentax because it's crazy expensive for what it is, but it should be at least a bit more…

Surely in camera, it is just a matter of taking a shot, wait an interval, take another shot, then shift/rotate the two images until X number of bright spots line up and then form a new composite, rinse and repeat. If you have a motor in the camera for stabilising you can use that shift/rotate parameter to move the sensor for the next shot.

Modern cameras can physically move the sensor inside the camera. It is called IBIS or In Body Image Stabilization.

Taking one long exposure I imagine would better pick up on faint sources of light compared to multiple short exposures.

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