More Bahtinov mask questions

[bigal1]

Hi all , so i've been reading up more on imaging and found a lot of people use a Bahtinov mask to get focus . Getting good focus is always the hardest thing for me and wondered if using one of these masks would help on my skywatcher 127 mak with a toucam pro2 . One thing i want to know is if i get good focus on a bright star using the mask then slew to saturn will i still have correct focus ? only asking because at the moment i'm only doing planetary imaging also i will be using a netbook so will i be able to find good focus using the mask and reviewing on the screen ? thanks .

[rwg]

You may need to turn the exposure and gain right up to see the spikes from the grating on the screen, but it does work - I've used a bahtinov with my 127 Mak, barlow and LifeCam. At worst, you might just see the base of the spikes near the star, but that should be enough to get you a better focus than you can by eye.

Robin

[Glider]

I do what rwg does and it works fine for me.

What can happen is that as I slew from the star to the planet that the weight of my camera sags in the rack and pinion focuser. So pick a star close so the slew is minimised, otherwise it's OK.

[Glider]

And the other thing that everyone has done, don't forget to remove the mask before you start slewing and/or imaging!!!!

[bigal1]

Great thanks guys , i,ve looked into making my own but found one made from good quality plastic for £18 guess i'll be making that purchase .

[Glider]

I use StayFocused.

[Breakintheclouds]

Does anybody have any tips for using a Bahtinov to focus on the moon? I tried focusing on a star and then slewing to the moon but that left me out of focus.

[Glider]

Did something move in your setup, was the star much higher/lower in the sky than the moon at the time?

[Breakintheclouds]

I'm pretty sure nothing moved, and the star was pretty close.

I suppose the question I need to ask is whether the moon is at exactly the same focal point as a star? I mean, it IS physically a lot closer, but is that enough to make any difference to focusing? If it is focused at infinity then I guess something must have moved when I tried.