OAG star shape

[Ken82]

Is using an OAG likely to cause diffraction spikes in an SCT ?

im thinking to get a combined OAG and filter wheel like the starlight express maxi as I have a bit of flexure. 

[Davey-T]

No, it's behind the mirror, what you can get is funny shaped guide stars on the PHD screen, like seagulls or bananas but these don't seem to bother PHD.

Dave

Edited October 14, 2019 by Davey-T

[vlaiv]

Actually you can if you are not careful.

OAG prism contains straight edges, and if you push prism too far into light path so that it casts a shadow on sensor, which can be corrected with flats - it will cause single spike perpendicular to OAG edge that is causing (not X type like in reflectors with spider support).

Here is an example of it:

Or maybe this one shows it better:

or this one

I was not careful enough, so OAG prism did shadow a bit of sensor, and only stars in that part of frame were affected (and only bright ones).

Luckily this can easily be sorted out by moving prism out of the light path that hits main sensor.