My EAA rig for SeeStar S50

EAA stands for Electronically Assisted Astronomy. Its primary difference from the classic hobby is that you are looking at an image on some screen instead of directly at the object in the sky. There are multiple EAA options from obvious sensitive camera and fast image stacking options to military night vision devices and scientific image intensifier tubes re-emitting the light after the signal is passing high voltage cascades. I prefer the good old wide field eyepiece view. The 100 deg. AFOV is an unbeatable joy. I have made a very similar experience possible with my SeeStar S50 EAA rig.

Aside from designing, procuring the optics, and 3D printing, the project requires some additional mobile software and phone tricks to make it a real joy to use.

EAA Eyepiece

Essentially, my EAA eyepiece is a simple 3D printed box with the phone holder and a loupe. But it's not that trivial to engineer. Here is the list of primary features I have implemented in its design:

• The lens is a cheap 42 mm in diameter single piece with 70mm focal range. That combination provides a relatively good flat view of my rather large smartphone screen providing the venerable 100+ degrees AFOV (Apparent Field of View) just as I like. It is possible to calculate the lens parameters needed for a particular screen size. The good "specimen" can be procured from so called "Google Cardboard" VR glasses of the past still sold around. Otherwise you can struggle finding a lens with the flat enough AFOV (VR lenses are aspheric to handle exact that).
  
  
• The two-piece 3D printed box is reducing the stray light on the screen and provides following features:eTight glove fit  slot for my smartphone while it's in the protective plastic case/sleeve which I'm using most of the time on it.

1. The box is fully open on the bottom (behind the screen) so the camera and attachments on the back of the phone are not interfering with sliding it in/out or in use.
2. The fit is tight enough to hold the lens over the screen in the desired position reliably, but also allows moving it up and down along the screen when desired with enough force applied. That's desirable as the good field of view of the lens is circular (within a square) while the phone screen has a long rectangular shape (but see also the software section below helping with that).
   All of the above is provided by the simple but efficient rail system design with optional stopper side screw.
3. The height of the lens in the box is fixed above the screen to provide the perfect focus for my a bit myopic eye. So no glasses required, and no focusing mechanism required either. As a result, it's ready to view as soon as attached to the phone, but works best for me (my eyesight) only.
4. The screen is enclosed on 3 sides to reduce the stray light from the environment, but semi-open on one side to allow touching the screen with fingers to control the app (ambidextrous, right or left handed). I had a design iteration with 3 sides open (lens on the arm), but it defies the purpose of using it in the well lit environment, while adding almost no benefits.
5. Edges of the box at the screen level are only 0.4 mm thick (the minimal thickness my current printer nozzle provides). That allows content and controls on the screen outside of the box to remain almost unobstructed for use if needed (without sliding the box up or down).
6. The lens is covered by a separate soft rounded plastic ring (TPU) piece matching my eye socket size for convenient eyepiece-like feel and also can be printed with the lip for a standard rubber eye guard, or replaced with any other material ring as its connection design is very simple. Its inner depth is also matching my eye geometry individually so I would not get in contact with the lens by accident, but still close enough to see the 100 degrees view unobstructed.
7. The overall "inflated" and "rounded" shape of the box promotes comfortable grip by the box when the device is operated singlehanded. The inner wall is starting vertically for about 2 cm to allow enough space for fingers when reaching any UI controls at the edges of the box far from the side opening when needed. 

Software

I'm using a few tricks to have the SeeStar app convenient to use with this "eyepiece" without sliding the box up and down all the time:

1. The main trick is using the SeeStar app in the "Split Screen" mode of my Android smartphone (iPhone users are out of luck with that, a.f.a.i.k.t. as of 12.2024). 
2. In the top square window under the lens I have the SeeStar App view which is totally functional though might flip into the less convenient landscape mode, so I make sure the top window in the split screen is a bit taller than the phone width (which is natural due to the screen having a bezel of a nonzero width. I can manipulate all controls through the side opening on the right side with one or two fingers just fine. Left side controls are less accessible, but still doable due to the "bell" shape of the box.
3. In the bottom window (outside of the enclosed box), I'm running my favorite astronomy planetarium app, as the SeeStar SkyAtlas is too trivial for my observing tasks). Not all such apps would work well in such a small window which is also considered to be in a landscape shape (forcing that app into landscape mode). Some apps will fail to launch upwards as they don't support that mode or a windowed view (the latter can be forced from the phone settings sometimes). Gladly my planetarium-like app (not naming it here as it's actually custom made app) is fully adjustable, so it works even with very odd screen dimensions. You can also control SeeStar from some of these apps so it's a win-win combination solution. Or you can use any other app on that bottom screen as needed for your astronomy work. Afterall, the primary goal of the split screen mode use is to limit the SeeStar App screen to the physical boundaries of the EAA eyepiece box. But the secondary app window is extremely handy for me too.
4. Recently, I have also rigged the virtual touchpad app to cover that screen entirely when needed. It's adding even more convenient way of controlling the SeeStar app without using the side window in the eyepiece box as it's showing a mouse cursor over that screen and providing additional buttons for various common touch operations (like zoom). The app is so well made and so useful in general that I don't hesitate to advertise it here with the link to the PlayStore.
   I have rearranged all its buttons and their color scheme to be convenient to use up close (without looking at it much) and with "night" colors. It's easy to custom tailor that app to satisfy any personal use style. It can be minimized by a single touch to reveal my planetarium app behind it when needed.

My EAA eyepiece can be held and controlled two- or single handed in various ways. It's also fully ambidextrous as you can switch that any moment by inserting the phone upside down. I consider it being an AR ("Augmented Reality") device, and also "Bionic" as it's deliberately custom tailored to my body, as well as to my current hardware features. With the 3D printer at hand it's easy to adjust the design to any other hardware or other body shape/eye prescription whenever the need arises and print another glove-fit version in about 2 hours.

Potential improvements

1. Find a better, aspheric lens for improved clarity in the corners of the view.
2. Design a quick replacement mechanism for the eye-rest ring for even easier changing of experimental designs. Potentially switching to the separatable from the box eyepiece design (DONE).
3. Play with the phone settings to reduce the size of the SeeStar interface elements (DONE).
4. Program Tasker scripts/screens to provide more convenient app control panel. E.g. to replace the "full screen" tap control of the app to sit on the right side of the screen or at the bottom of the split screen.
5. Add wearing strap hole, hard case, try smaller phone sleeve or the holder replacement mechanism.

Conclusion

The EAA eyepiece is a joy to use whenever I setup the imaging session or monitor the stacking progress. When well designed, it's resembling the real high grade eyepiece view quite nicely. You just need to get used to the unavoidable phone screen pixelation at the magnification needed to stretch the display to the 100 degrees AFOV view. Thus it might be wise investing into a high ppi screen phone (surprisingly not top tiers). 

Such an EP is considered being a gimmick on some dedicated EV scopes. But that's only because the screen on those is rather just a tiny low resolution, low fidelity cheap TFT screen which you need to approach from an awkward position to see, also risking to shake the telescope taking subs as you look. Imagine a 100 degrees wide view (read a 300 inch TV screen from 10 ft) 8K AMOLED screen conveniently watched on top of your couch or form inside of the sleeping bag.

The EAA eyepiece is also more Star Party compatible (than a laptop screen typically used in EAA), as the phone screen is small when seen from the side and mostly fully enclosed (in a lit room it cuts the room lights, in the darness it cuts the light of the screen). Just use a black background image or properly dark adapted dedicated for visual astronomy app on the bottom split screen. In one of the models I have 3D printed a special thin flat overlay piece, filling the phone case border to the rim, with the fixed square window.