what is your focusing technique?

[DannyHarvey]

How do you guys focus? I mean what is your exact technique? Mine is to focus roughly then go backwards and forwards beyond the focus point both sides of exact focus and try to find where the focus peaks. Two or three tries normally gets a good focus. I also try to wait for a moment of good seeing to do this.

Dan

[Digz]

A 'Y' mask and zoomed live view. Simple and works well for my DSLR.

[cantab]

I read that a better way is to approach from one side and stop as soon as things become sharp. Seems to work well enough for me, though it can take some trial and error at high power.

[jimmyjamjoejoe]

I read that a better way is to approach from one side and stop as soon as things become sharp. Seems to work well enough for me, though it can take some trial and error at high power.

I read a similar thing, at least for terrestrial, you should focus to infinity then draw back till whatever you're looking at is focused, rather than the other way. Personally i do the old back and forth...

[jimbooz]

Back and forth for me!!

[ollypenrice]

Back and forth, though I do try to remember the infinity then back technique and discipline myself to follow it. With SCTs you should focus only by pushing the mirror up the tube, not up and then back down, because the mirror may lag on the way down and then settle gradually.

Olly

[DannyHarvey]

I have just bought a Crayford focuser for my SCT, but its only a single speed model. I was kind of wondering it that would make it harder to focus, but in practise have found that is not the case. Then I got to thinking about the exact technique I use focus (which I had never thought about before, it just came naturally). I like the fact that I haven't got far to turn to de-focus and thus helps me judge the point at which the focus peaks.

For an planetary imaging session I keep re-doing the focus after a movie is taken, unless it is good seeing and I know for certain its bang on, then it stays at that position for say 3 or 4 movie clips.

[acey]

For eyeballs there's no rule, just rack back and forth until you get what's most comfortable. As you carry on viewing, your eye will possibly accommodate differently, in which case you need to refocus.

[Welrod50]

Dan, I use a Newtonian and focus with Bahtinov mask, but before I did this I put a sticker on the focus tube of my OTA and in daylight and with a pylon about three or four miles away on the horizon, I marked a graduated scale (with line marks every millimetre) on the sticker and made a note of where the pylon came to focus both afocaly with DSLR + EP and also with prime focus. Then, out in the field at night, I fine tune from this with the mask and as I'm already nearly there with focus, it usually only takes me two or three test shots to get bang on.

I also find that, if I approach focus from one direction it is quicker than going to and fro. Once its focused, lock the focus tube and leave well alone! Of course if you're just using the good old eyes for viewing, the bahtinov way is also most accurate but can be a faff just for viewing. Also, as acey points out, your eyes may adjust, so focus will also need to be adjusted, if only a tiny bit.

HTH

[Double Kick Drum]

I try focussing from both sides until I am happy I am at peak sharpness.

[Superdavo]

Same for me, but with my DSLR, I often have to take about 100 photos and adjust them into focus-a very frustrating technique!