Field Flattener adjustment

[69boss302]

Ive spent the last 2 nights trying to adjust m field flattener. I have a William Optics Zenithstar 73 and the 73a adjustable flattener (not reducer). It is asking for a 55mm back focus, so I add the two extensions it comes with, add it up, and Im 19mm short. So I screw it in to the 73a at the 19mm mark and it should be OK. Well its not.  I tried a half turn one way, then a full turn the other way and was making no difference.  So I went to the extremes and went all the way out and took a picture (at the 20mm or so mark) and then screwed it all the way in to the 5mm mark... and there was absolutely ZERO difference. Apparently thats not where you adjust a field flattener?  The two shots below are at the extremes, but show no difference. What am I doing wrong?

 

 

[69boss302]

Note Their docs say 11.4mm but it didnt seem to help anything.

[GoldTop57]

So you have the two ZWO spacers which are 16.5mm + 21mm 

+ 17.5mm from the top face of the ASI2600 to the sensor giving you the 55mm back focus.

I have the same flattener and I set it to 11.4mm + 55mm to my ASI294MC Pro. Are you sure the elongation is not a guiding issue?

[69boss302]

I currently have 16.5 and the 21mm on it now and have it set to 11.4mm on the flattener but still getting the images above.  I dont think its tracking as the center of the images are crystal clear

[69boss302]

here are two almost full size images I took this week, maybe it helps to show whats going on.  Youll have to remove the s from the https since its my server at home.

https://maxboostracing.com/astro/andromeda.jpg

https://maxboostracing.com/astro/orion.jpg

[69boss302]

update: It seems I was missing one of the extensions on the camera. I remeasured everything, got some help from the ZWO forum and found I forgot to add one of the extensions on. Ill give it a try tomorrow night if the weather cooperates!

 

[Phillyo]

5 hours ago, 69boss302 said:

update: It seems I was missing one of the extensions on the camera. I remeasured everything, got some help from the ZWO forum and found I forgot to add one of the extensions on. Ill give it a try tomorrow night if the weather cooperates!

 

I was just about to comment and say it looks to me like your sensor is still a little too close to your final lens element. All the stars are pointing in towards the middle which is a very good indicator of this.

This is a useful image to show what I mean...

Phil

[69boss302]

thank you @Phillyo. I added the extra extension last night, and today I will test and report back I hope this does it!

[69boss302]

Just to follow up with you, I added that extra extension and last night I did some shots. Although the skies werent great, it was enough to see that it fixed the issue!  A VERY quick and dirty NGC7000 shows the corners as being much better. Thank you all for your amazing advice.

Bob

 

[newbie alert]

That looks better but think it still needs a final adjustment

[Stefek]

Yes , this looks close, but it looks that there is also some tilt present . Perhaps some small fine tuning of distance and than tilt .

[69boss302]

Thank you guys, yes, still a little bit left to go, but at least I know Im on the right track now! Im sure itll take me several nights to get it dialed in.