locking/adjustment screws on 250px primary

[sunshine185]

Please can anyone shed some light on which are which? I posted 2 pictures.

[Pete Presland]

i think the large ones are the adjustment screws and the small ones locking screws.the adjustment screws will be spring loaded.

[Moonshane]

I am sure bunnygod is right. personally, I tend to do anway with locking bolts as they can cause astigmatism and undo the collimation work you have just done.

[sunshine185]

These are the screws that the last owner put on the dob, moonshane, do you think I should replace them?

[Moonshane]

they look as though they will work well with 'no tools' so I'd leave them in place - pointless spending on new ones that will do the same thing!

the ones for the secondary can be replaced with (probably) M4 thumbscrews, just check the length.

[sunshine185]

Wonderful! Many thanks.

[Hals]

Those screws look exactly like the standard ones fitted to the 250px.

The larger ones are indeed the collimation adjusters, the smaller slotted ones the lock screws.

As Moonshane says, you don't really need to use the locking screws but if you do use them be very light on your touch.

[sunshine185]

I noticed this, get it all collimated then tighten up the locking screws and it all goes pear shaped. So you guys just don't bother tightening the lock screws?

[Moonshane]

I have a 10" mirror in the same sort of cell (slightly different but the same really) awaiting a portable dob makeover and I just took them out. store them as they may be useful for something else in the future (or for putting back if you ever sell the scope).

[Moonshane]

really you need to collimate the primary every time anyway so they just get in the way.

[Tinker1947]

When you have collimated, the locking screws need to be just biting the back of the Mirror Cell, that's like you feel the thread tighten as it touches, then give it 1/8 of a turn then check you haven't moved the mirror......or as said take them out....

[sunshine185]

Now I'm up to 10" I plan on doing collimation every time anyway,I believe its more critical than in a 8", this will save me faffing about every time I do it. Respect

[Moonshane]

it's more the speed of the scope (f5 rather than f6) that makes it more important but even at f4 it's the same process.