Bahtinov Mask - Dew Shield On or Off?

[Steve789]

Until recently I've always taken my dew shield off my newt' before using my bahtinov mask to focus but recently I've got a bit lazy and started hanging it off the front of my dew shield. So my question is; will doing so affect the accuracy of my focus? Does the extra distance of the dew shield in front of my scope affect how the bahtinov mask performs?

I have no real idea of how the bahtinov mask works, other than employing some form of dark magic so am clueless to whether I still get perfect focus with it hanging off the dew shield.

[psamathe]

My thoughts have been that the light entering the scope should be parallel (or so close ...) and thus a dew shield distance away from the scope should make no difference.

But that is my thought and I'm not experienced to say what the situation really is so would welcome somebody correcting (or confirming) my own thoughts.

Ian

[Uranium235]

You can leave it on, it makes no difference at all.

[SteveNickolls]

Never thought about it but have always had a dew shield in place, both on an SCT and a refractor. No problems focusing or out of focus stars. Hope your mind is put at rest.

Cheers,

Steve

[Stub Mandrel]

I use one on my Newtonian so it's metre from the first optical element and it works fine...