strutsinaction

That's what I was thinking and something I will try. It just seems odd though. Regards John

FSQ85 offset focussing mentioned here (courtesy of sharkmelley): https://groups.yahoo.com/neo/groups/UncensoredTakGroup/conversations/topics/59070 I'm going to try this next time I'm out imaging. Regards John

If it's any consolation Steve I think my corner star elongation/distortion is worse than yours See my latest image here: http://stargazerslounge.com/topic/256830-ngc281-pacman-hoo/ Jury still out on this for me (at least, nothing from Mr King or Takahashi yet), although I have my suspicions that in my case it could be due to poor focussing. Regards John

I sent Ian King a few subs and he thinks this type of radial distortion at the corners is a collimation issue rather than mechanical tilt. He's sent my subs off to Takahashi Europe for further investigation. If they suspect a collimation issue then I'll have to return the scope to Ian for replacement or repair. In the meantime I still intend to do the zenith test when the skies clear. Regards John

Yes, smaller chip and, yes, I was happy until I started reading your thread and started pixel peeping I will try the zenith test the next time it's clear. Regards John

No, I use a QSI690 (which was returned to QSI to get the Sony Glow fixed). Hoping I don't have to return my Tak! Regards John

Just an idea. Maybe rotate your camera 90 degrees and repeat the test. If it's always the same bottom right hand corner that shows the most distortion then would that indicate sensor tilt? I've been taking a closer look at some of my earlier images taken with the FSQ85. Coincidentally, I have elongated stars in the bottom right hand corner, more so that the other 3 corners. The other corners show some elongation but in different directions - radial I believe. This does not appear to be a PA issue. E-mail sent to Mr King for advice! Regards John

Hi Steve Elongated stars in the corners may also be due to play in the CAA (camera angle adjuster). I assume you have the CAA in your optical train? See here for more info and a possible fix (if you are brave): https://groups.yahoo.com/neo/groups/UncensoredTakGroup/conversations/topics/43074 The following may help too: https://groups.yahoo.com/neo/groups/UncensoredTakGroup/conversations/topics/44706 http://www.skyimager.com/FSQ-MMOAG/Using%20an%20Astrodon%20MonsterMOAG%20with%20a%20Tak%20FSQ-106N-2.pdf I also have a Tak FSQ85 and have noticed elongated stars in one corner of my images and suspect the CAA, focuser slop or sensor tilt is the cause. It hasn't concerned me so far so haven't done anything about it but I may follow up with Ian King just in case this is a known issue. Regards John

Congratulations, thoroughly deserved! Regards John

Yes, almost, as in lacking the laptop and a cloudless, dark sky

Here's my Baby FSQ, almost ready for action.

Fantastic achievement, well done and congratulations to you both. Looking forward to your next collaboration! Regards John

If you're interested, there's a similar thread on CN asking the same question: http://www.cloudynights.com/topic/475406-considering-filter-thickness-when-calculating-backfocus/ Look for the post with the parts list where the supplier has quoted the backfocus contribution of the 3mm filter as -1. Regards John

Steve - isn't that what QSI are saying though? They state that the backfocus of the camera should be adjusted by -1mm if a 3mm filter is fitted. So, when you do the arithmetic to maintain the 72.2mm backfocus distance the contribution made by the camera is now reduced by 1mm to 49.2mm so you need to add a 1mm spacer to compensate, thereby moving the' optical distance outwards to maintain the status quo'. Regards John