One Time Use Astrophotography – CVS PV2 and your Telescope

This evening, Mars will be as close to Earth as it'll get until 2018. Incredibly, just in time for weekend viewing, Mars decided to put on a show with a dust storm that should be visible with the backyard telescope.

I'm going to try and capture a few pictures with my hacked CVS camera. Grab your CVS cam and your telescope and I'll show you how you can snap a few pictures too. (Make sure to post back your best images here for others to see).

Astrophotography Overview

Firmware Adjustments

Firmware Adjustments

The first thing you'll need to do is disable the camera flash. BillW released pv2patch version 0.3.2 a little while ago that allows you to do just this. Unfortunately, some of the other adjustments that it allowed were too buggy and were destroying cameras, so that revision was pulled from the download site.

I did a search and was able to find the download here.

I'll walk you through safely disabling the flash, but be advised that this may turn your camera into a paperweight. You have been warned.

PV2Patch 0.3.2 Options

PV2Patch 0.3.2 Options

When you've downloaded the firmware from your camera and run pv2patch on it, here are the values you should choose:

  • unlock camera patch: yes, choose option 2 (unlock_camera)
  • camera pid patch: your choice, I use flatfoto2 for iPhoto support
  • mute patch: no
  • piclimit patch: no
  • flashbulb patch: yes, choose option 1 (flash_disabled)
  • timelapse_enable: NO (this is known to make paperweights)
  • timelapse_value: NO (this is known to make paperweights)

When you upload the patched firmware, your camera will no longer flash when a photo is taken. The capacitor is still charged, however, so if you turn your camera off and on the flash will sometimes go off and scare the hell out of you. This is normal.

The capacitor issue also has some safety implications for when you are digging around in the camera internals.It's now more likely to be charged than not, so be _extra_ careful in there and keep your left hand in your back pocket.

Camera Adjustments

Firmware Adjustments

There are basically two ways that you can connect your CVS camera to a telescope. You can entirely remove the camera's optics and position the ccd in prime focus with telescopes that support this. Alternatively, you can go the less permanent route and carefully position the camera's optics to be at the focal point of the the telescope's objective lense.

I chose to do the latter so I can continue using my camera for other things, but I'll show you how to set up the prime focus hack as well (which should give you more reliable, better photos).

The Less Invasive Method

The Less Invasive Method

For this to work, your camera needs to be focused at infinity. You'll use an objective that you'd normally use for looking through. You then position the lense of the camera where your eye would normally be. The result will be nice photographs that use the magnification of the lense you are using, but with some image degradation due to all the lenses the light has to go through (this includes the IR filter in the camera lense).

The other downside is that you have to hold the camera up to the optics manually, which incurs a bit of vibration.  You could also develop some sort of rig to support it, but you might as well do the full blown prime focus hack if you are going to go to that much trouble.

Focus Adjustment

Focus Adjustment

The camera should ship focused at infinity, but it never hurts to fine tune things, right? Note: this step is entirely optional if your camera appears to focus well on things at a distance. Note #2: reread the last sentance because this is entirely a pain in the ass.

To adjust the PV2s focus, you'll have to take the camera apart.

The shutter has to be removed first.. It's attached with a little ring of tape, so you can just carefully pull it off. Be careful with this, it's easy to damage. If yours does malfunction, just adjust it so that it's always open. It serves no purpose other than to keep dust out of the camera.

The focus ring that holds the lense is glued to the barrel in which it rotates in, so you'll need to scrape off what you can with an exacto and then use manual force to break the seal.

I recommend first removing the whole lense assembly from the camera before breaking the glue bond, or you might risk slipping and damaging something.

Once you are able to adjust the focus, screw it in a half turn. Re-assemble everything and take a picture of something far away. Then unscrew the ring 1/8th of a turn, re-assemble, and take another picture of the same thing. Compare the pictures and repeat until you've found the optimum focus.

Infrared Filter Removal

Don't bother with this. The filter is actually a coating on the lense. Some people have reported success with polishing it off, but this seems like an easy way to mess up your lense. If you want to take better photos without the IR filter, use the prime focus hack (below) instead.

Telescope Focusing and Alignment

Telescope Focusing and Alignment

It's easier to test everything on a terrestrial object during the day. Just pick something far away and and start experimenting with the focus adjustment on the telescope. Instead of focusing by eye, I find it a little easier to look through an SLR camera (focused at infinity) into the objective. Otherwise, it seems like my eyes play tricks on me and do some automatic focus adjustment on their own.

Now position the camera right up to the lense and take a photo. It has to be exactly centered and aimed straight, or you will see a black ring around one edge of the image as in this image:

After a bit of re-adjustment and some focus fine-tuning, you should be seeing nice results.

The Prime Focus Method

The Prime Focus Method

If you really want to take even better photos, you'll need to completely remove the camera optics and position the CCD at the camera's prime focus. Thus, you will be basically using the telescope as a big telephoto lense.

Remove the entire lense assembly from the camera. I'd also recommend using a dremel to make the opening a little wider in the front part of the case.

It turns out that a 35mm film case is about the same diameter as a typical objective lense. If you cut a hole in the bottom and glue this to the camera body, you can then insert the camera into the telescope instead of an eyepiece.

You may need to adjust the depth of the film tube before you'll be able to focus correctly. This is also a process of trial and error.

Post Your Pictures

I'm going to try and snap a few pitcures of Mars this evening, and if I'm successful, I'll post them here. You should do the same. Whether you add an image gallery here or post them on flickr, make sure to leave us a comment with a link and any tips you might have!

Written by Jason Striegel

C/C++, Java, Python, Linux developer for 18 years, A-Tech enthusiast love to share some useful tech hacks.