Focusing on objects

[tibbz2]

Hey Guys,

I was just wondering about focusing on objects while I was out the other night (and just about every other night too). I'm not sure if it's me or my scope (it's 2nd hand and im only using stock ep's), but i'm having trouble with focusing. I can't tell when the object is focused as much as it can be, i'll slowly try to focus but I can never tell. Is this another skill im just going to have to practice, or is it me doing something wrong?

Thanks

[Qualia]

I guess focusing at night is always tricky, but I've learnt a little tip from WWII snipers - not sure if it is useful but it may help.

Snipers would make sure their focusing screws were snug tight, not over tight to damage threads but not too loose either. They would draw the focuser out until the image was blured and only then tune in, when the image 'snapped' into focus they'd have their kill in sights. It's this sniper tip of 'tuning in' that might be worth bearing in mind.

[keithatrochdale]

It is a "practice" skill; do bear in mind that ofter when focused the image will still "go in and out" of focus, so you have to guess/judge the "best" focus position.

[Scott]

I started using a Bahtinov mask for this exact same reason. I was always wondering if I could get the focus better. although it can be a bit of a pain for visual work when you're constantly changing eps, it does take the doubt out of the equation. with imaging it's almost an essential part of your kit .

HTH

Scott

[tibbz2]

Ah okay, thanks for the advice guys

[mason]

Have youj checked the scopes collimation?

[jabberwocky]

I've just invested in a SW auto focuser, bit of a misnomer, more a powered focuser. What it does do is stop you introducing vibrations to the scope whilst focusing, I think it's brilliant, may buy a bahtinov mask as well at some point. I find it much easier to see when I've achieved focus, and only 40 odd notes. Very easy to fit, but the controller box is badly designed, buttons are fine but the battery compartment is too small.

[Moonshane]

my focus method is thus:

get rough focus first

wait and look

am I getting sharp images at all? (this may be intermittent with the seeing conditions)

yes - leave it alone

no - tweak the focuser a little

wait and look

better?

yes - leave it alone

no - reverse above action and move a little the other way

wait and look

carry this on until you get images which ping into detail every now and again. this is perfectly normal. images are sharper for longer in better seeing conditions or with lower magnification

the lower the focal ratio, the less the field of sharp focus is. i.e. a f5 scope will need fine tuning more than a f11 scope.

I agree with Qualia about focusing in as well - it works.

[Moonshane]

ps

the above assumes the scope has been cooled for about 5-10 mins per inch of aperture and is collimated - although you should still get reasonably sharp images unless your collimation is well off

[Steve Ward]

Perfect answer from Moonshane ,

I wasted so much time when I first got my scope onto Jupiter by constantly tweaking the focuser to no avail .

I knew nothing at the time about the little details of atmosphere and seeing and was constantly frustrated . . .

Then all of a sudden the image went very still and the planet 'popped' into focus for a few seconds . . . all on its own . . .

There will be times when the view never seems to sit still at all , not much you can do about the atmosphere unfortunately , but stick with it and the rewards of the waiting will be well worth it.

Putting your scope out early to cool down is essential , it's amazing to think that the light you're looking at has travelled umpteen million miles only to be ruined in the last couple of feet ... !