Astrodon Ha and OIII not close to parafocal

[Adam J]

Hi all, 

I image with a newtonian reflector (so no its not my scope having CA) and so a am shocked to see that there is a huge difference in focus between my new Astrodon Ha and OIII filters, focus on one and the other is so far out I get doughnut shaped start.

Anyone else with Astrodon filters see focus shift between filters?

Adam 

[tooth_dr]

That’s a bit of a bummer! Auto focuser time?

[Adam J]

4 minutes ago, tooth_dr said:

That’s a bit of a bummer! Auto focuser time?

Astrodon claim all of their filters are parafocal......

[tooth_dr]

3 minutes ago, Adam J said:

Astrodon claim all of their filters are parafocal......

What have they said about it?

[Adam J]

2 minutes ago, tooth_dr said:

What have they said about it?

Astrodon? I have not contacted them yet only found out at 3am last night. 

The OIII is an older filter than the Ha, the Ha is one from after OSI bought out Astrodon so I dont know if they changed something in the specification. 

Adam 

[AngryDonkey]

Could well be a difference in the new spec as you suggest. The only other thing that comes to mind is CA caused by any flattener or reducer you may use? Not sure if this would make that much of a difference though.

[Adam J]

1 hour ago, AngryDonkey said:

Could well be a difference in the new spec as you suggest. The only other thing that comes to mind is CA caused by any flattener or reducer you may use? Not sure if this would make that much of a difference though.

No its a big difference in focus not a small difference, I used to image with a DSLR using this setup if it had that much CA the images would have been a complete joke lol.

[Adam J]

Here is the Ha in focus (tracking was not good so ignore that).

and the OIII at the Ha's focus

Same star field, 130PDS + Baader MPCMK3, ZWO filter wheel and ASI1600mm pro

From my perspective that is quite a way out.

OIII filter is older style the Ha is new post OSI purchase of astrodon.

 

Adam