1. Raw Photon Collecting Power (Focal Ratio & Sensor Size)

Larger sensors and faster focal ratios collect more photons from extended objects like nebulae and galaxies. This is the “raw photon collection” starting point.

Despite the S30 Pro having slower optics than the Dwarf (f5.3 vs f4.3) the S30 Pro’s huge sensor means it will catch 40% more photons than the dwarf and a whopping 350% more than the regular S30. However the Dwarf is a couple of hundred quid cheaper so it looks like quite a good deal. Thing is you can’t trust the marketing bumf because astrophotography is about more than just raw light-gathering power; it requires precision. Cheap rigs often have to compromise, and it turns out that a lot of the Dwarf’s photons are wasted due to poor tracking.

2. Photons Lost to Poor Tracking

If your mount can’t track accurately, stars trail and exposures get thrown away. My test kept only exposures with acceptably round stars. Scopes with poor tracking waste the majority of collected photons.

All 3 smartscopes tracked stars near the celestial equator (the hardest part of the sky to track) simultaneously from my roof in London. The Dwarf 3 tracked poorly. I’ve used 3 different Dwarf 3’s now and each one seems to track badly. The Seestar S30 and S30 Pro are both pretty good. I believe the mechanics of them are identical. BTW when shooting Andromeda which is high in the sky the tracking of the Seestar S30 was at about 80%. I would expect all three smartscopes to perform significantly better when their targets are far from the celestial equator.

3. Photons Lost to Poor Optics

Bad collimation, excessive chromatic aberration, or severe corner distortion blur your images. Blurred photons aren’t useful photons – they’re just spreading light around instead of forming sharp points. There is also question of quality control too as my initial dwarf had crooked optics.

Collimation Test

Collimation is arguably the most critical optical test for any telescope. If the optical elements aren’t perfectly aligned, the entire instrument becomes useless – an expensive paperweight. To test collimation, I use an artificial star setup in my optical dungeon. The light from the artificial star reflects off a 16-inch parabolic mirror, creating parallel wavefronts that simulate a star at infinity.

When you take a star out of focus, a properly collimated scope shows beautiful, concentric rings (known as diffraction patterns). The first Dwarf 3 I tested showed a concerning asymmetry – the donut around the central spot was brighter on one side, indicating a collimation error making this telescope next to useless. However I tested an alternate Dwarf 3 and it’s collimation was flawless. I suspect mine was a dud and it probably should have been sent back. Lucky I was able to test other units which were optically excellent (see sharpness test below).

Sharpness Test

A good way to test overall sharpness is simple to take a picture. To replicate stars that are hundreds of light years away my biscuit logo image is being reflected off my 16 inch parabolic mirror. All the properly collimated telescopes were extremely sharp.

Chromatic Aberration and Flat field Test

Chromatic aberration occurs when a lens fails to focus all colours at the same point. You can easily spot chromatic aberration with a bhatinov mask as the diffraction patterns lines of either the red, green or blue sections veer off from straight.

I also use a bhatinov mask to check for a flat field. A flat field is a fancy way of saying that the image stays in focus all the way to the corners of the sensor. If the corners are out of focus the bhatinov mask’s central diffraction line will not be centered.

I found that the Seestar S30 did not have a flat field. 20% of the photons hitting its sensor (those in the corners) were not in focus (see red circle in above picture) and would produce egg shaped stars. Although the edge of the field is the least important area of the sensor when shooting objects that fit nicely inside the sensor I deducted 20% from the S30’s useful photon count as this aberration will impact multi panel mosaics and I feel that mosaicking is something most S30 users will end up doing.