Bikeman55

Excellent, thank you guys very much for your response. Weight will probably be something for me to keep in mind and something I didn't think about although that barlow above intrigues me. Thanks again, much appreciated.

I am getting into visual observing and am planning an eyepiece kit for my soon to arrive dobsonian. My question is, is there a distance the eyepiece needs to be from the glass of a barlow? I am wondering if I get a 2" barlow and want to use a 1.25" eyepiece in it, will using the required 2" to 1.25" adapter for the eyepiece, space the eyepiece too far back for it to function properly or will there be negative affects like vignetting, aberrations or inability to focus? Any help would be appreciated. Thank you.

Thank you all for the responses. Seems as though there are several different opinions on where the backfocus should be measured from. I did end up talking with Explore Scientific about it and they told me the same thing as Fredmt in that it is technically measured from the glass but they said point B from the pictures. I am currently waiting on a variable spacer to come in where I can do some star tests and figure it out once and for all then get a more permanent spacer afterwards. And thank you Waldemar for that diagram. That is fantastic and very helpful. I will definitely be referring to that the next time I'm out. Cheers

I posted this in another section but perhaps it better belongs here. The title pretty much says it all... Where do I go about measuring the 55mm of back-focus on the Explore Scientific 3" field flattener/reducer. I have attached a couple pictures for reference so we can refer to the same locations. I thought from the research that I have done I should measure from point A but after last night's first use it seems as though I got something wrong and I wanted to make sure I was measuring from the correct spot before I really start to scrutinize my spacing to sub-millimeter or perhaps my imaging train is not quite "plumb". Any insight would be greatly appreciated. Thanks.