How do you know when spacing is correct?

[AndyUK]

DOH! - That's way too simple Pete...! Which is probably why I never thought of it! I'll see if I can give that a quick go when the Equinox is next on the mount...

The reason I put the reducer on is that due to the small size of the 314L chip, the larger nebulae seem to want a bigger FOV than I can get... So Mosaic's become the order of the day. Not that I mind them, but they seem to either take months, or become a "roll-over" project for next year (I have a few of these already!)

I must admit though, it's also very nice imaging at f5. Mind you, I guess FOV's not a problem for you as you can use your 383...

[i'll be interested to see how you get on with the quad - I've been toying with moving to a triplet for many months, but the funds have always disappeared just as I've been getting close!]

[Interested]

lol, simple!......would have preferred the word 'practical' (if it works ok ).

I haven't bought the quad yet. I did buy a Skywatcher Esprit 100ED Quin but it had collimation problems and had to be returned (collimation is 'factory set'). Williams Optics are supposedly bringing out a 5 element quad in the very near future so I might look at them, but I do rather fancy a Tac FSQ 85ED.

I'm not sure the small chip of the 314 will utilise the 'flattener' part of your F/R Andy. Ian King did mention to me that when imaging at f5 or faster, distances might need to be extended, anything up to 68 mm. Just a thought...

Regards,

[ollypenrice]

I find this "add a mm" biz quite interesting. I've also read a slightly different rule which is add a 1/3 of the filter thickness. But no-one ever seems to mention the thickness of the glass window in front the CCD camera ???

I said a mm because I think most are about 3mm thick. You are right to say it should be 1/3 of the glass thickness. I was being idle!

Olly

[AndyUK]

Cheers again Pete - I have a couple more extension tubes which I can always try to see what the effect is, but I must admit the results around the edges I have now with 56mm is a LOT better than it was before...