GEAR · IN USE

76 mm f/4.6 Newtonian

350 mm focal length reflector. Small, and honest about it — the diffraction limit is the binding constraint on everything.

Brendan, Goolwa SA

Aperture: 76 mm
Focal length: 350 mm
Focal ratio: f/4.6
Dawes limit: 1.53"
Lunar resolution: ~2.8 km
Image scale: 0.853"/px
Field: 46.4' x 30.7'

Recorded as a 114/500 for the first session, which made every derived number wrong. It's a 76/350 — measured and corrected 30/08/2026.

The lunar disc is 2188 px across at this focal length, which overflows the 2160 px sensor axis by 28 px. That clipping breaks any measurement that assumes a whole circle.

Slightly under-sampled at 1.8 px per Dawes limit. A 2x Barlow is the obvious next purchase.

The AstroDMx equipment profile is named "NG Reflecot" (pre-existing typo, left alone) and still carries the old 500.0 / 114.0 figures.

Used on these nights

SESSION 5 · 09/26 · DIDN'T WORK

A new tube, two nights, and not one frame of sky

Got the 76/700 on the mount and pointed it at nothing successfully. Cloud, a finder I never aligned, and a field of view the size of a keyhole. The morning's daylight testing is where the actual…

SESSION 4 · 08/26 · DIDN'T WORK

First planet — Venus, low in the west, and nothing to see on it

Pointed at Venus instead of the Moon on the rebuilt mount. Three short runs so far. Learned that most of what limits a low planet has nothing to do with the telescope.

SESSION 2 · 08/26 · WORKED

Three analysis methods, all wrong — and the reason was in the frame the whole time

Built a processing stack and tried to rank the night's runs by sharpness. Every metric disagreed with my eyes. The bug wasn't in the metrics — it was that the lunar disc runs off the edge of the…

SESSION 3 · 08/26 · PARTLY WORKED

New swivel, a focus lever, and a darker patch of yard

Three changes at once before tonight: the mount is rebuilt onto a friction-loaded roller-bearing swivel, the focuser has a long lever instead of a knob, and I'm setting up out the back away from the…

SESSION 1 · 08/26 · PARTLY WORKED

First light — and a cable that lied to me

Got the SV205 talking to AstroDMx and the Moon onto the sensor. Burned most of the session on two failures that both presented as camera limitations and were neither.