Hello all
I would value some opinion on what might be causing the artefact shown in the attachement.
It appears on all bright stars, and if I recall correctly, I have seen this using 2 different CCD cameras, so most likely an optical issue.

Would it be possible that I am pinching the FSQ Optics?

thanks
Martin

Hi Martin,

This looks like a very small occlusion in the optical train. Something like two small tabs or clips at the edge of the objective cell, dew shield, or on the focuser/rotator extension tube. Could also be something more natural (spider web, dirt, etc.)

Look through the front of the objective to see if you notice anything. Also, look at all the tubes/attachments after the focuser to see if there's anything protruding into the optical path.

Regards,

-Paul

Hello Paul
thank you for that.
You are right. Just about every FSQ106N image I have looked at on the web has this effect. I emailed someone who confirmed it is the clips holding the objective. So, basically, you cant do anything about that.

cheers
Martin

Hi Martin,

Here is an explanation of what you are seeing that I found on another group.

The artifact you are seeing with your FSQ is normal. The FSQ-106 is a petzvel optical design and as such it has an internal field stop. This design allows for a flat field and virtually no astigmatism over a wide field. But there is a cost. The field stop causes a fair amount of vignetting off axis as it does not allow the full aperture of light to
reach the off axis image plane. The off axis image is really an oval or cat-eye section of the 106 mm aperture. It's the field stop that's also responsible for the dark spikes you see on bright stars off axis. On axis stars up to about 25 mm will not exhibit this affect The dark spikes are the diffraction results of the field stop. Basically the third lens in the system is the field stop.
Hope this helps,

John Laborde

Thanks Frank

did you also see the other reply to this. I think it mentioned another Petzvel design telescope (Pentax?), which does not have this problem.

I also read that the AP refractors do not have this issue either. Such a pity you have to wait 18 months for those!

cheers
Martin

It sounds like a mechanical design problem with the FSQ. The middle Petzval element has to be pretty large (near the size of the objective) to not vignette the light path. Sounds like Takhashi did not make it large enough.

There's a new scope coming out from TEC that promises to be a nice imaging platform: APO110FL, F/6. It'll need a field flattener, but with a dedicated FF, this sounds like it'll be an awesome wide-field imaging machine. And it's airline-portable, to boot.

Regards,

-Paul