Seben AP3 90° star diagonal 1.25 in

What the maker does say

Ninety degrees, 31.7 mm at both ends, suitable for refractors, Schmidt-Cassegrains and Maksutovs, and not suitable for Newtonians. That last exclusion is worth the whole listing: it is the commonest mistake a beginner makes with a diagonal, and few sellers mention it.

What the maker does not say

Whether the element is a mirror or a prism. What its coating is. What orientation the image comes out in. Those three would decide how it performs and how a chart is read with it, and none appears.

Where it belongs

On a small refractor, replacing a diagonal that was lost, broken or never supplied. At this price it is a component rather than an upgrade, and the more expensive diagonal on this shelf publishes rather more about itself.

The one thing to check on arrival

Which way the image comes out. Point it at a distant sign in daylight, note whether the text reads the right way up and whether it is reversed, and write it down. That single observation makes every future star hop easier.

Availability

German and French Amazon stores ran from 6 € to 8 € on the day of the survey.

British Amazon store lists it in local currency, which the euro range above sets aside.

Italian and Spanish Amazon stores stood above 1.6× the cheapest country. A gap that size normally means stock forwarded from abroad rather than a seller on the ground, so those figures are left out of the range above.

American Amazon store gave no result whatever, so the buy button there opens a search rather than an empty page.

Figures as Keepa reported them on the day this page was last updated. Stock and pricing shift without warning.