Focus on TEC 140 and Atik 460

[kirkster501]

Further to a discussion ealrier I have just done a test on this with my Baader LRGBHa filters.  They all look parfocal to me. This was done on Vega high up in summer obviously with one second looping exposures, all done within a few seconds of each other.  Hope this helps anyone wondering about how parfocal the Baader LRGB is on this excelent scope.

LUM CHANNEL

RED

GREEN

BLUE

Ha

[swag72]

Looks good Steve - I wish any of my Baader filters were parfocal!!

The issue with the blue on the TEC and Sony sensors wasn't about parfocality, but specifically blue bloat. I've added the link to the CN thread here in case anyone thinks they may have an issue as they have found some useful ways around it.  

[ollypenrice]

Those look very close but in my view blue is a tad out, as is Ha. In both cases I think the central 'cat's whisker' wants to go towards the top left hand corner very slightly. It seems odd that this should apply at both ends of the spectrum, though. Did you shoot them in that order? If so, could this be a cooldown effect?

In any event they are very close. I'm confident enough in parfocality to scroll RGB, RGB, RGB in our TEC. However, that's at a less resolved pixel scale (1.8"PP, Atik 11000) so our focus is more tolerant. And, to be honest, you can get away with very small imperfections in the colour layer. I prefer to prioritize 'getting it in the can,' especially for guests who might only be here for a week.

The other thing that makes the TEC focus-tolerant is that, with flattener, it is working at F7.25. The plate solved focal length is 1015mm rather than 980.

Tom is having a ball with ours at the moment. It's such a nice scope to use.

Olly

[PatrickGilliland]

Agree with all of Olly's comments - colour is more forgiving which is a bonus and Lum needs to be spot on.  That said it's very hard to really tell via a bhatinov, certainly very close but some variance there.  Software based focusing would really be required to see the detail.  May be the cause of the colour fringing but at these levels can be processed out.

Certainly close enough not to be too worried by anything though  

Paddy

[kirkster501]

I agree - I think the Ha is slightly out and that's to be expected. Before using Ha I would always refocus.  But I think the LRGB are pretty darn close...  Cooler was on and they were done in that order - LRGBHa.

[MrsGnomus]

To our collective eyes, the Blue and Ha are quite significantly out.  We find Bahtinov Grabber quite useful .... most of the time.  But there is a lot to be said for robofocussing.  Feathertouch do a unit ...   In for a penny ......

Mr & Mrs Gnomus

[kirkster501]

i think the Blue could do with a slight, slight tweak, yes agree.  I will do more tests on this and report back.

[kirkster501]

I'm going to look into Robofocus at some point.  However, at the minute I have enough IT related stuff in my obs that keeps going wrong as it is without introducing yet another variable into the equation!

[ollypenrice]

8 hours ago, kirkster501 said:

I'm going to look into Robofocus at some point.  However, at the minute I have enough IT related stuff in my obs that keeps going wrong as it is without introducing yet another variable into the equation!

A man after my own heart!

Olly