Increase or decrease distance to camera query

[assouptro]

Hi knowledgeable folks!

I have recently purchased a Starizona Lf field flattener focal reducer which has a working distance of 55mm 

If used as advertised I should get a focal reduction of f7.

I am fairly close to that 55mm and using astrometry.net I can see I have achieved f6.8 with 0.45 arc seconds per pixel instead of 0.7 which should be 0.43 arc seconds per pixel

native focal length of my scope is 3048mm f10 (12” Meade lx200)

 The question is, do I reduce or increase the distance of the camera to the focal reducer to get the right spacing? Or am I “close enough”? 

Thanks in advance to anyone who can answer this

Bryan 

[michael8554]

Look at the star shapes in the corners of a sub.

If they're round then change nothing.

If they're elongated, pointing towards the centre of frame, try a few more mm of spacing.

If the elongation is circular about the centre of frame then try a few mm less spacing.

Michael

[assouptro]

35 minutes ago, michael8554 said:

Look at the star shapes in the corners of a sub.

If they're round then change nothing.

If they're elongated, pointing towards the centre of frame, try a few more mm of spacing.

If the elongation is circular about the centre of frame then try a few mm less spacing.

Michael

Thanks Michael 

That’s really helpful 

Bryan 

[newbie alert]

I'd say do as Micheal said first, if you need to adjust then I found that if I increased spacing I got a decrease in focal length, and visa versa...

Some run their systems at far further back, say at f5, look at JP Metsavano( may have spelled that incorrectly)  but depends what you want to do and your sensor size