Focus Question

[Neil McRae]

Can someone explain the benefits of the more expensive type of focussers advertised. I understand that collimation is essential and brings better quality to the image and that better quality lenses make a difference but my simple way of thinking says using my Bahtinov mask once I have focus what else do I need to do and what do these focussers bring bearing in mind their cost .

Neil

[rfdesigner]

Better focusers hold the camera better (more consistantly) centred. If you're using a fast newtonian collimation is quite precise, so if your focusser allows the camera/eyepiece to move to one side or the other then the sweet spot will no longer be in the centre of your field of view, resulting in poor images.

This gets more important if you're using coma correctors, which expect the light path to be distorted in a particular way at a particular position, if the distortion is different then your spot size grows and you get ugly stars across the whole field of view despite good focus and good initial collimation.

HTH

Derek

[johninderby]

The drawtubes in cheap focusers tend to move about a bit (focuser slop) which affects collimation. A better focuser holds the drawtube better which means collimation isn't affected as much as the drawtube is moved. Also better focusers don't slip as much with heavy eyepieces. The better focusers are usually dual-speed and the fine focus makes focusing much better as well. Less telescope vibration as the fine focuser knob can be adjusted with a fingertip.

Finally once you've used a good focuser you just can't stand a cheap one afterwards. It really makes using the scope so much nicer.

John

[Moonshane]

for visual use, I genuinely feel that the basic R&Ps with a little tweaking can give perfectly satisfactory results. I feel you have to work a little harder with them to find focus though and using a 10:1 fine focus crayford makes it a much more enjoyable experience. also, there's less settle down time after adjusting the focus point. for imaging it's possible a whole different ball game and I know nothing about that!

like buying larger aperture a good focuser works well with all your current eyepieces, finders etc and makes the whole experience more pleasurable.

for me though, if it's a choice financially of more aperture, a better focuser or more eyepieces, I'd go for more aperture every time.

if you just want to make your current gear more pleasurable to use then a new focuser.

[Neil McRae]

Thanks for your replies it was something I was not too sure about.

Neil

[Moonshane]

I think another option for standard focusers is a battery controlled auto focuser.

this apparently really smooths out the focus and reduces shakes etc. I believe that Skywatcher do one - in fact yes First Light Optics - SkyWatcher Auto Focuser

[Neil McRae]

Hi Moonshane

I built a battery free electric focuser last week and have it mounted on the scope and it is great. No shakes while focusing. Cost around £10.

Neil

[Nexus 6]

When using my cpc 925 mirror shift was a pain so I went for a Moonlite, very nice it it too ....no more image wobble

[Moonshane]

Hi Moonshane

I built a battery free electric focuser last week and have it mounted on the scope and it is great. No shakes while focusing. Cost around £10.

Neil

is there a thread? this sounds great!

[Neil McRae]

Moonshane look at a thread I posted on 20th June No more shake while focusing.

If you need more info then let me know

Neil

[chemtom24]

moonshane - http://stargazerslounge.com/beginners-help-advice/146333-no-more-shake-while-focusing.html

[Moonshane]

nice one! - cheers both