OCAL Electronic Collimator

I just wanted to share my experience with the OCAL collimator. In the time I've had my ONTC I haven't found collimation to be too difficult of a task using just a concenter eyepiece, laser, and cheshire. Generally I can have collimation done in 5 minutes or less and while fast, the exercise of bending at awkward angles to look down into the focuser to make adjustments is never fun. Especially at my height. I once tried the Catseye wifi cheshire for easier collimation of the primary mirror but it only worked well if the center spot on the primary is reflective which mine isn't. Connecting to the camera using the Android app was also hit or miss but in the end it didn't matter because the battery swelled during charging after only a few days of ownership.

So back to the old method I went. I have known about the OCAL for a while but it showed as unavailable on Amazon here in the USA and there were no other domestic retailers selling it. I eventually found it available at FLO and was able to order one. It always amazes me how I can order stuff from Europe and get it within 3 days but ordering things (from some places) domestically takes over a week. Anyway... the scope has been sitting in my sunroom waiting for the green light to drive it up to its new dark site home so I have downtime to play with the OCAL.

The device itself has female T2 threads on the front for attaching an appropriate adapter for your focuser. My 2" Feathertouch focuser uses a compression ring so that means threading in a T2 to 2" nosepiece which I ordered separately from Amazon. The device then slides straight into the focuser tube and I locked down both screws. It was not difficult to get the OCAL flush with the drawtube and it remained flush after locking it down. YMMV depending on what focuser you use. I would love to be able to thread the device onto the focuser but it is not possible with this focuser. The device then connects to your PC via an standard USB A cable for power and data which is awesome because it means you never have to charge it.

In the software you are able to change exposure, focus, zoom, and manipulate 3 rings + crosshair. It's essentially an electronic concenter eyepiece and cheshire all on one device. With it you can accurately center your secondary mirror under the focuser, align the secondary to the focuser, and align the primary to the focuser all without any additional devices. Not to mention it can be done more accurately since there is no double that the camera is always looking directly down the center of the focuser. Its important to mention that the OCAL works best with Newtonian telescopes and has a proven track record with them. While it is officially stated that it also works with RC, DK, and SCT, results are inconsistent at best. I've done a lot of reading about user experience with those scope types and to be honest, I wouldn't personally purchase the OCAL unless it will be used on a Newt.

This post wasn't meant to be as full guide on how to use the OCAL. Instead, this is just an overview of how I use it and the results. Though, if there are any questions drop a comment and I'll be happy to answer. I will say these few things though:
- Focus of the camera can be changed depending on the surface being worked on.
- Camera exposure can be changed depending on your light conditions and/or the surface being worked on.
- The rings can be manipulated to be different color, size, and thickness to match the element being worked on.

I will also say that prior to use the telescope hadn't been collimated after being moved inside, but the secondary was already in good position from previous usage of the concenter eyepiece.

Step 1: I focused the OCAL on the end of the drawtube, set exposure time so that I can clearly see, then used the offset and size settings match the green ring with the inside edge of the drawtube. This step is very important. The rings (regardless of their size) are all aligned to the center of the OCAL view so in order for them to accurately judge alignment of the mirrors they must be concentric with the focuser. 

View fullsize

Step 2: I change focus, and exposure time, zoomed in, and used the collimation screws on the secondary to make the reflection of the primary mirror concentric with the red ring. Note that the alignment is not absolutely perfect but remember we are zoomed in pretty far. The size of that misalignment is extremely small and won't show in images. Not at F4. One can become obsessive about it and get it exactly right if one wishes to but this is much more accurate than someone can reliably get by eye with even a good laser.

View fullsize

Step 3:  I zoom in even more (100% in fact), change exposure time so that the body of the OCAL is clear inside the focuser, and use the blue circle to align the primary mirror. Simply use the outside edge of the OCAL itself as the surface to make concentric with the blue l circle.

View fullsize

So now we have a fully illuminated primary reflection hitting the middle of the focuser, and the reflection of the drawtube centered on the primary mirror. That essentially is the goal of Newtonian collimation. This process takes less than a few minutes depending on how out of collimation your telescope is. This process can be done at any time of day indoors or outdoors and the camera is sensitive enough that one does not need an extremely bright light source. You may be tempted to use the crosshair to align with the camera sensor. This would be a mistake because the camera sensor is not mechanically centered in the OCAL body. This is why part of the OCAL setup is to enter a code based on the camera serial number to correct that offset in the cameras FOV. The body of the OCAL inside the drawtube is absolute so use that as your reference for aligning the primary mirror.

One thing to keep in mind is that it can becomes very easy to nitpick very small errors and chase your tail trying to fix them. We must remember that when zoomed all the way seeing a sliver of misalignment translates to fractions of a millimeter of error and likely wont have any impact on image quality especially when using a higher focal ratio telescope. Errors of that nature wouldn't even be detectable using more traditional methods such as lasers and cheshire. They may be noticeable with a mirrored autocollimator but again unless youre running at f2 fractions of a mm of error are inconsequential.

I'd also like to point out something the OCAL revealed to me. During my first session with the device I noticed the crosshair (which is perfectly in the center of the OCAL view) was not lining up with the center mark on my primary mirror. That indicates the center mark itself is not actually centered on the mirror and any adjustments made using that mark as a focal point will result in misalignment. It is for this reason that I use the body of the OCAL and the silver square around camera sensor as my focal point because those are guaranteed to represent the center of the view every time. Here's a photo where I purposefully misaligned the primary mirror to show the error in the mirrors donut.

View fullsize

Lastly, just for reference here is a screenshot from the official OCAL Youtube video showing the end result of collimating a Newtonian telescope.