AstroFinder released… by me

[Peter Santangeli]

(I know we try to keep TAC non-commercial, but since a few people here gave me feedback on this product, I don’t have all their contact info, and it’s most certainly a visual-observer product, I thought I’d post)

There have been some amazing advances in telescope pointing in the last few years with devices like PiFinder and Hopper - developed by our own local astronomers.  Incredible work, great products.

But being a mobile developer by profession I always wondered if there was a simpler alternative. Today I released AstroFinder on the app store to provide just that. (Android version is identical, finished and just needs publishing).

https://www.santangeli.net/astrofinder/

https://apps.apple.com/us/app/astrofinder/id6790024890

AstroFinder takes gyro pointing fused with plate solving and does it completely with your phone. No hardware required except a simple phone mount (3D printable file downloadable on the link above). The result is a dark sky adapted, push-to ‘heads up’ dashboard for your telescope.

I spent most of GSSP exercising its functionality. The only change I had to make was to deepen the catalogs it offers, as I was running out of objects in parts of the sky. It’s that easy. For me, the ergonomics make it a game-changer.

Should work on any reasonably modern iPhone (also works great on my 7 year old Android phone - releasing soon). One month free trial. Feel free to give it a try, and of course send me feedback at peter+as...@santangel.net. It’s super fun.

pete

[Richard Navarrete]

That’s really cool, Pete! I wish you great success.

Richard

Sent from the all new AOL app for iOS

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[Steven R.]

Congratulations!

-Steven

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[David Kirjassoff]

Very cool.  Firing up the 3d printer already!

David

Sent from my iPad

On Jul 20, 2026, at 7:58 AM, Peter Santangeli <pe...@santangeli.net> wrote:



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[Peter Santangeli]

Oops!

Mis-typed my feedback email address in the above:

peter+as...@santangeli.net

pete

[Paresh Khanapurkar]

Awesome Peter! Best of luck!!

[Alex]

Hey Pete. Congrats! And thank you for sharing the news here!

I have a similar functionality implemented in my app in 2021 following the Celestron Starsense Explorer (CSE) idea but with the same direct phone mount (without the mirror as the CSE). It was fun until I discovered the problem with the very low accuracy (same as the CSE, b.t.w.) due to the standard phone camera lens' low resolution back then. Have you solved that problem? (so folks could use a dedicated old phone for the sensor, keeping the main one for the primary Planetarium app handheld use convenience). Later on, I had the idea to leverage new telephoto lenses on newer phones to mitigate that problem, but then was obsessed with my ARhopper app (the one with the bino attachment I showed again recently) to cover the last star hopping/push-to leg problem which all these plate solving pointers still suffering from (frankly the target FOV id).

From my past experience, I would suggest the app tested for:
1. The partial sky view (with dark and lit terrestrial obstacles, like trees, buildings, lights).
2. Bright unevenly light polluted sky views.
3. Sky regions with the Moon and bright planets in the view.
4. Directional sensitivity (e.g. if there is an accuracy change when you push from one or the opposite direction to the same target).
5. Target Altitude sensitivity (refraction effect mitigation).

6. The device mount rigidity (or lack of it) effect on the accuracy. As I have a doubt about the magnetic mount stability at the swinging wide UTA top. Though it might be stronger on a modern iPhone being integrated in its chassis, I would still recommend just printing a sturdy enclosure/clamp (or repurposing a good commercial one) for the dedicated phone, as after removing and replacing the phone on the scope you will have to star-align it all again (newer phone camera might provide around 30 arcsec accuracy, you don't want ruining it with a flimsy phone mount).
7. I will definitely test it on my Portaball to see how the random roll is handled (I recall we had it discussed here before, I wonder if you have managed to apply proper quaternions to the gyros data?).

At any rate, I'm looking forward to trying your app when the weather permits!

Cheers!
Alex

[Tim Lorz]

what a great idea and neat way to implement it. Along with Pete's great comments around the durability/resolution/light sensitivity of cell phone cameras, I would be curious what impact you have seen on the battery life of the phone by running the camera in the background the entire time (I may have misunderstood the part around the "sleep mode"). 

I have tried to just take nightscape photos with my Google Pixel 9A, and was not too impressed so far. the iPhone I was given for work purposes is a #15, so it's a couple of years old now - would that be adequate?

Again, what a fantastic idea!

Tim

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[Peter Santangeli]

I'll be very interested in your Portaball experience. It's all quaternion math internally, but portaball is definitely a different challenge.

'ground lights' and bad skies will always be a challenge to the software that isolates stars prior to plate solving. One thing I have done is limit the field of view used (it's also adjustable). Much of my testing has been in dark skies though. I have not seen sensor resolution be an issue. I do allow the user to select any of the enumerated lenses on the camera, but the main lens is typically the fastest, and that's what it defaults to. 

The modern cameras are quite amazing though. A big challenge was really getting full manual control. For an iPhone I can now do (typically) 1s exposures, and have good control over ISO (typically running at about 3200). At that I'm getting 70+ detected stars in a 20 degree field (I really just need 4 for the solver). The solver itself is written in Rust so it can use a large database.

I did try custom printed phone cases but there were a few issues - too many models to support being the primary, and also you really would want a TPU case with more solid mount, and that combination of materials is tricky. In practice I have found the magnetic mount to be at least as solid, so I went with that. For phones that don't have a mount, the magnetic mount I recommend also comes with a thin magnet ring you stick to the back of an older phone. But there is nothing specific to the mount - any mechanism that holds the phone in the desired orientation will work.

As for phone generations, I haven't released Android yet (waiting for some Play Store stuff), but my test phone is a 7 year old Pixel 4XL and it performs quite well.  The biggest challenge is not the camera - I can go up to 10s exposures on Android - it's the relative inaccuracy of the orientation sensors in older phones (plus apparently they lose accuracy as they age). But that's what the solver is for :-)  You just get more 'jumping' at the end of a slew with an older phone.

pete

 

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[Peter Santangeli]

I've been surprised at the lack of battery drain, but clearly that could be an issue (particularly with older phones with weak batteries, and you might have to plug it in to something (a small power bank strapped to the scope might be fine). My main phone is modern/top-of-the-line (iPhone 17 Pro max) and it easily lasted an evening. But my other phones, including my aging Android with much smaller capacity, also surprised me with how long it went (many hours).

Battery life on a phone is governed by many factors. A poorly written UI loop can kill your battery as quickly as a naively written compute engine. So far it's been ok but I'd love feedback with others results.

The 'sleep' value in the settings is specific to the app. I didn't want the imaging pipeline to keep running (and burning battery) when you walked away from the scope for a while, so it turns it off after a specified period of no motion (default to 3 minutes). As soon as the scope moves, the gyro's wake it back up.

Keep the questions coming. I'm building an FAQ on the support site :-)

Your iPhone 15 should be totally fine. I have a 15 pro max and test on that as well.

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[Steven R.]

Which solver are you using? I know there are multiple Rust ports of Cedar Solve.

-Steven

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[Peter Santangeli]

It's not Cedar. Cedar has commercial restrictions.

pete

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[Steven R.]

Cedar Solve is open source (Apache 2.0) with no restrictions. It is a fork of Tetra3, so licensing it under similar terms seemed appropriate. Cedar Solve as published is in Python, but as I mentioned there are at least two published Rust ports. I don't know how they are licensed. Hopper uses its own non-published Rust port of Cedar Solve.

You might be thinking of other Cedar components such as Cedar Detect or Cedar Server, which do have a commercial restriction.

Cheers,

-Steven

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[Peter Santangeli]

(we should probably take this off the observing list :-)) 

These things get messy :-) I use a Rust port of a derivative of Tetra3 specifically, which was partially derived from cedar-solve (by the author's notes). 

I avoided Cedar-detect or any other encumbered software. I use the Gaia database for solving, but that required reaching out to ESA separately for use (and had a backup database if that was rejected).

Trying to be careful :-)

pete

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[Alex]

Thank you for the details, Peter. I'll wait for the Android release to test on the Portaball.

Regarding the mounting. I had great success with the off the shelf "vise-style" phone clamp with 1/4x20 to a short selfie stick, clamped by another 1/2x20 "claws" clamp right to the OTA rim. With that the phone is like "hovering" in front of your eyes, thus you can directly compare the screen with the stars in the sky. No 3D printing required. The stick is optional, but helps to get in focus the chart and the real thing simultaneously, creating a cool AR effect when you push it around, and helps avoid interference with your head. It's also quite nice on your neck strain, and immediately fixing the "staring into the screen all the time" problem. The disadvantage is that you need a good counterweight for the balance. I miss my steel OTA with the magnetic 6lbs weight sliding on it.
 

(I believe I had this one posted here already after having a blast with it at the Spring Binge'21).

Also, for in-depth subject matter conversation, perhaps, consider creating a product Discord group eventially.

Alex.

[Peter Santangeli]

Anyone interested in testing the Android version should be able to join the test with this:

https://play.google.com/apps/testing/net.santangeli.astrofinder

or on their phone with this:

https://play.google.com/store/apps/details?id=net.santangeli.astrofinder

pete

[Alex]

Pete. I believe you need to add the dedicated google group or individuals' emails to the testing board first for that facility to work.
E.g.,for the first link I see:

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[Peter Santangeli]

Yup. My bad. 

Send an email if you want to be a part of it.

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