Astrophotography With The 8MP Raspberry Pi Cameras

Question

I will attempt to use the Raspberry Pi 8MP NoIR and standard v2 camera boards for capturing images of the night time sky, and also with specialized filters in the daytime.

My question for the E14 community,

Does anyone have experience in this application of the RPi 8MP v2 cameras?

DAB · Accepted Answer

Hi Trent,

Check the RPi website.

I have seen a number of projects attaching the Picamera to a telescope.

Depending upon what you want to do, there are ways to do eyepiece projection for high magnification using the camera or you can go prime focus for wide angle.

The first is just making a small tube to attach the camera to the eyepiece and use the lens on the Picamera for focus.

To do prime focus you will probably have to remove the lens from the Picamera, which I believe is fixed, so you will have to do some complex surgery on the Picamera.

See if you can purchase a T-adapter that fits your telescope.

Then you can experiment with different mounting ideas for the Picamera.

I hope this helps.

DAB

rcpettengill · Answer

The following information on building a RaspberryPi camera with a T-ring adapter and example images of the moon and planets may be helpful. Astro RaspberryPi Camera @ not so bad Astrophotography

rew · Answer

You know... There is something that I don't have the time to try, and I think it should work. So someone should take my idea and implement it. :-)

With astrophotography, there is always the problem that the stars tend to move during your (long) exposure.

The standard trick is to make your camera move along with the rotation of the earth. (or actually to counter the rotation of the earth).

My plan is to simply take say 1s exposures, but then say 300 of them to get a combined 5 minute exposure. Then in software, you KNOW that each image is rotated by 1/240th of a degree.

It's easiest if you start out by telling the software where the rotation point is. But you can optimize (with sub-pixel accuracy) for the rotation point if you have a few hundred images.

Next, instead of taking a canvas of say 8 Mpixels, you use 128Mpixels. Each pixel is blown up 4x in each direction. But now after rotation by those tiny amounts, you get some sensor pixels that overlap a different set of about 16 pixels in the canvas.

Next, instead of simply adding the results together you can run an optimization step (i'm explaining this in one dimension but of course it is easy to implement for two): suppose the REAL canvas has a single hot pixel. lets say 100. Now on the first image that means you get some value in pixel 25 of the sensor. Now suppose the sensor moves 1 canvas-pixel compared to the canvas. So next time you'll still get the value in pixel 25, only after 4 images does the measured value end up in the camera-pixel 24. So with the previous variant of the algorithm you'd be spreading the measured value out across 100-103 for the first image, and 101-104 for the second image, and only at the fourth image the 24-th pixel of the image would end up back on 100-103. So you would end up with a triangle of image intensity centered around pixel 103. Suppose we measure 100 in pixel 25 of the first image, and we spread that as 25-25-25-25 over 100-103 and add 8 images this way we'll get 50-100-150-200-150-100-50 in canvas locations 100-106.

But if we assume simply that canvas pixel 103 has intensity 100 then all measurements would be precisely identical. So we can sharpen the resulting image. This can be done by deconvolving or by an iterative algorithm.

So when we see pixel 25 with a value of 100 on the first image, we increase the values of 100-103 in the canvas, but when we measure 0 in pixel 24 in the second image this maps to canvas pixels 97-100 on the canvas and we'll decrease the running guesstimate of pixel 100 again. You should be able to reconstruct the original canvas with only pixel 103 bright much better than with the first iteration of the algorithm.

Some complications prop up in practice. So if one second of exposure is sooo little that when digitizing the digital version only has black pixels, then this of course won't work. You need some noise in the captured images for this to work. So turn up the ISO as far as possible without getting saturated pixels. The individual images will look like *** but the resulting canvas should be fantastic....

ninjatrent · Answer

Here is the Pi Camera with factory lense removed. This is my first attempt of constructing an adapter. I need a 3D printer or CNC to develop a better design.

DAB · Answer

Agreed, but for prime focus, my solution should work assuming you can get the chip perpendicular with the focus point. That is why my preferred solution is a T adaptor. The PVC approach would be a quick and dirty solution. It all depends upon what you want to do and how good a picture you want to take. A good mounting bracket is best for high quality. DAB

shabaz · Answer

Hi Enrico! I don't know the method Trent used, but since you have a 3D printer, there is some online design for a 'adjustment spanner', which partially helps: https://www.thingiverse.com/thing:1574661 As I understand some of them are glued slightly too. The removal tool isn't great (I ordered one from thingiverse, since I didn't have a 3D printer) but it did kind-of work. I think with hindsight I would have just made my own from filing a shaped hole in a small sheet of aluminium, it would have been cheaper (and faster to arrive) than the thingiverse order.

DAB · Answer

If the telescope eyepiece is 1 1/4 inch, go down to the hardware store and buy some 1 1/4 inch PVC tubing and maybe a cap. You can glue the cap on the tube after you drill a hole large enough to get the light to the camera sensor. Then you just stick the tube in the eyepiece holder and adjust the focus. QED! DAB

DAB · Answer

Hi Roger,

What you propose has been done.

There are a number of panorama pictures I have seen where photos were taken from dawn to dusk and then stitched into a all night sky view.

The problem is that the short exposure times does not capture a lot of the faint objects, but it would get you the main visible stars down to 6 or 7 magnitude, depending on seeing conditions.

DAB

DAB · Answer

I would get a T-adapter.

You want to place the sensor in the middle of the field of view to get the flat field over the entire width of the sensor.

You also want repeatability, so you want a robust mount for the camera.

DAB

ninjatrent · Answer

I used a razor blade and magnifying glass to carefully remove the glue. Then a pair of tweezers was used to unscrew the lens. The focus of the lens can also be adjusted this way.

defied · Answer

I'm late to the show. Setting multiple 1 second exposures won't do much to collect light for and take pictures of Deep space objects. It will be a series of shots with 1 second light collection. Stacking the images won't give you any proper increase in exposure (ie: 5 images with 1-second exposures stacked will create 1 image with maybe a hair more than 1 second exposure (Due to atmosphere shifting allowing more or less light through). Using the method you recommend for sun or moon, or other bright objects in the sky works fantastic. Most Stacking programs will software de-rotate images (They do an outstanding job with video). Ideally, using the Rpi and a motor controller to create a Goto mount and (if necessary) a derotator for stabilizing and capturing a long-exposure image would be far superior. D

DAB · Answer

I am not sure. If you get enough overlap to stack the images, then maybe.

Why not set up your camera and take a series of shots over say an hour or so and see what you get.

You can play around with the images to assess how easily they stitch and to see if you get enough overlap to do some stacking.

DAB