focuser sideways movement

[mike-h]

I have a skyliner 250px dob with the standard crayford focuser. When collimating recently I noticed some slight sideways movement (left to right with reference to the drawtube) of the laserbeam dot on the primary when the focuser is wound in and out. It is very slight except when the focuser is wound fully out or particularly when it is wound in its final couple of mm.

I thought it may be that the secondary was not directly facing the drawtube or that the focuser was not square with the tube.

I tried playing around with the alignment of the focuser but the same pattern of movement occurs.

I'm guessing now that it is the focuser mechanism itself rather than any alignment issues. I haven't gone to the trouble of removing the secondary to square the focuser yet-I wanted to ask for ideas first before I mess around with it.

I doubt it is too detrimental but is there anything I can do to improve it (besides buying a better focuser). I already collimate with the focuser wound halfway out which helps.

Thanks in advance if you have any tips.

Mike H

[Keithp]

Hi Mike, I've got the same beast, I did have a similar type problem that manifested it self while I was imaging.

Make sure the 2 to 1.25" adapter is locked up solid, try rotating it around while scewing the two screws down. I found it locked better in some positions than others.

Also when using the laser to collimate I wound some sellotape round the end so it would not fit the ep holder, then unwound bit by bit until it would just slip in to the holder, then lock it up with the screws. See if that helps.

Regards

Keithp

[mike-h]

Thanks Keith.

I think you are describing what people call "focuser slop". I get that too. I'll try the 2" adapter in different positions and see if it helps.

However, in this case, the sideways movement isn't caused by movement of the laser in the focuser. It seems more like the drawtube changes angle ever so slightly as I wind the focuser -particularly fully out or in.

Mike

[Keithp]

Could well be Mike, not had mine that long (since Christmas) but I must admit the next thing on the shopping list is a new focuser. I've spent abit upgrading my kit already, but everytime I get something new it goes cloudy and rains:o.

Might be looking at getting one of these shortly:

Focusers - Dual-Speed 2” Low Profile Crayford Focuser for Skywatcher & Celestron Newtonian Telescopes

I'll wait and see if the weight of everything I've got so far makes it any worse though.

Regards

Keithp