Addendum - Telescopes and Lenses

TS-Optics 90/600 APO Triplet

updated: 2022-11-14

TS-Optics Apochromat (APO) Triplet 90/600 (out of stock!)

Lens: APO906-O (Replacement part)

Link to TSO 90/600 APO Triplet (Astroshop)

Link to APO906-O (Teleskop-Express)



90 mm

Focal length:

600 mm

Focal ratio:



Multi-coated APO triplet lens - FPL53


CNC metal tube with 2 additional tube segments

Limiting magnitude:

12.3 mag

Resolving power:


External diameter of dew cap:

116 mm


500 mm


4 kg

Dew cap:

extendable - can be locked with a screw


2.5" CNC focuser

Connection on eyepiece side:

2", 1,25" and M63x1 female thread

Connection from tube to focuser:

M88x1 female thread on the tube

Outside Dimension of the case:

570 x 225 x 290 mm

Image Quality of the TS-Optics APO 90mm Objective - SPOT diagram and star test

The Spot Diagram is ideal for judging the colour correction of a telescope, not only on the optical axis, but also off axis. The black rings are the airy discs. As you can see all wavelengths between 500nm and 700nm are kept inside the airy disc. Off axis (second line: 1/4°, third line: 1/2°) the colour is still very well corrected - just compare this with some very expensive APO Objectives.

The Star Test on our artificial star is equivalent to the image of a real star at a magnification around 200x. But please note that our artificial star works in autocollimation. This means that whatever optical defects there are, you will see the effects twice as strongly as on a real star!

Images from left to right:
♦ far inside of focus
♦ slightly inside of focus
♦ a focused medium magnitude star (around 5-6 mag)
♦ a focused bright star (e.g. Vega)
♦ slightly outside focus
♦ far outside focus

As you can see false colour is virtually nonexistent in focus. You can also see that the star is well centered. This also shows that the lens is not pinched inside its cell.

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