TS OPTICS 2X ED BARLOW 2" Optical accessory Dust on the sensor window

Dust on the sensor window (seen as 'donut' shaped spots on the image)

so adding this adapter will increase the thickness of the ARCO 3" from 23mm to 24

ASI2400 Optical thickness 5mm Internal thread M54 x 0

5 mm Connection side A

The Losmandy bar 350mm belongs to the PLUS system (Prima Luce Universal System) that includes a large variety of telescope rings

TS OPTICS 2X ED BARLOW 2" Optical accessory Dust on the sensor windowThe TS Optics 2x ED 2" Deluxe Barlow lens is high quality yet affordable and features an ED (extra low dispersion) element for better colour correction and contrast. The brass compression ring precisely locks your eyepiece or accessory. Its large aperture of 37mm gives a fully illuminated field without vignetting with any 2" eyepiece. The Barlow lens element can be removed and screwed directly into the 2" filter thread of any eyepiece or adapter,