Help with lack of focus

[Ziggy135]

I’ve just resurrected my Skywatcher MAK 90 and was disappointed to find that I can’t get a focus on anything. The primary mirror is moving but all I see is a blur. It has been stored inside safely for a few years and I didn’t use it a lot before. Now about 5 years old. Can anyone tell me what may be wrong and more importantly what I can do about it? I am reluctant to just take it to my nearest telescope repair if it’s something I can do myself. No shortage of tools just telescope maintenance knowledge.

Thanks.

[ronin]

What are you focusing it on?

More relevantly how far away is it?

They are a pain to get a good focus, as you can go through it easily and quiclkly, so just miss it. I spent ages getting a decent focus on mine when aligning the finder.

Assuming the mirror is OK then the corrector should be easy to check, just take a look at it. Next comes the diagonal they can get mucky so have a look at it through the focuser tube.

How good is the actual eyepiece?

[opticalpath]

The moving-mirror focusing mechanism provides a very wide focusing range, from a few metres to infinity. Are you trying the full range of adjustment and still not coming to focus?

I don't have this scope.... but a couple of things to suggest if you haven't done this already:

1. Rather than pointing at the night sky, aim the scope at a distant daytime target (keeping well away from the Sun) and try to focus on that

2. Keep the scope mounted firmly and stationary, avoiding wobbles.

3. Check that you're using the same elements that you know worked OK previously: eyepiece? extension tube? diagonal mirror?

4. Go through the full focus range, making adjustments quite slowly in case you shoot past sharp focus without realising.

Adrian

[Alfian]

Hi Ziggy,  I have the 102 Mak and I find the focussing smooth and easy and I'm  surprisedyou have that problem. If everything is a blur, have you checked the rest of the optics train - diagonal/eyepiece?

[Ziggy135]

Thanks forthe three who have offered advice. Before I posted this problem I had checked all the obvious. The eye pieces are good as is the diagonal. I have tried astonomical focus and terrestrial. Both no good. I am not missing the focus as it passes and am using the scope as I did before when all was OK. I can see objects very tiny when looking through the wrong end and taking off all from the focus end lets me see objects albeit too small to comment on focus. The blur is a total blur through the eye pieces no matter what it is pointed at. It occurs to be that the focal point is either too short or too long but if so I can work out why.

[Alfian]

Hi ziggy thats a teaser. I've never had to collimate my Mak, nor tried, or particularly want to. I suppose it would have to be a long way out to give that issue?

[Leo.A]

This may be of no use to you but I do know some scopes are designed where the Barlow must be used to obtain focus. Were you previously using a Barlow when focus was achievable but perhaps forgotten about it?

I can't obtain enough in focus with a couple of my smaller scopes for photography purposes but using the 2 X Barlow moves the focal point back and corrects the problem. I was also given a small reflector which couldn't achieve visual focus without the Barlow, that was the way it was designed to be used.

Worth dropping a 2X Barlow in and trying I say.

[Cornelius Varley]

I can't think of an optical reason why the telescope shouldn't focus. Maks have a wide focus range and it takes many turns of the focus knob to go from lock to lock. The telescope should focus with the stock eyepiece / diagonal so long as you are not trying to focus too close. Can you confirm that the primary mirror does move when the focus knob is rotated and that the secondary mirror (silvered disc on the rear of the meniscus) is not obstructed / damaged.