Twisted Vanes

[Stephen]

Another plea for help

More shiny bits have arrived to go on my 200P, namely Bobs Knobs (primary & secondary.) I've fitted them and was about to embark on collimation (as it's well out all over...)

When I noticed all four vanes on my secondary spider are twisted. They appear to be fixed like that as releasing them generously doesn't let them snap back to straight.

How concerned should I be regarding this, will it cause problems visually / imaging? If needed, what are the possible fixes / replacements?

Cheers,

Stephen

[NGC 1502]

Hi Stephen, I expect you realise the spider vanes should be edge on, as viewed from

the front of the scope. If they are not, they will give stronger diffraction spikes on

bright objects, and lower contrast a bit.

You have tried the first possible fix by losening them up to see if they will spring

back. As they have not, then I would try some persuasion, by using finger pressure

to straighten them. If it's no go with that, then you may have to resort to removing

the spider, so you can get at them better. Two adjustable spanners in opposition

should do the trick.

As you say collimation is currently off, then you have nothing to lose by dismantling.

It's best to work with the tube horizontal, so if anything is dropped, it won't fall down

the tube onto the primary mirror. Be careful of the secondary mirror too. When

replacing the spider, the nuts on the ends of the spider legs don't have to be super

tight, just enough to get a "twang" when you flick the spider leg.

Good luck, Ed.

[Stephen]

Hi Stephen, I expect you realise the spider vanes should be edge on, as viewed from

the front of the scope. If they are not, they will give stronger diffraction spikes on

bright objects, and lower contrast a bit.

You have tried the first possible fix by losening them up to see if they will spring

back. As they have not, then I would try some persuasion, by using finger pressure

to straighten them. If it's no go with that, then you may have to resort to removing

the spider, so you can get at them better. Two adjustable spanners in opposition

should do the trick.

As you say collimation is currently off, then you have nothing to lose by dismantling.

It's best to work with the tube horizontal, so if anything is dropped, it won't fall down

the tube onto the primary mirror. Be careful of the secondary mirror too. When

replacing the spider, the nuts on the ends of the spider legs don't have to be super

tight, just enough to get a "twang" when you flick the spider leg.

Good luck, Ed.

Cheers for the advice.

I agreed with your "what the hell" conclusion and removed the whole spider / secondary assembly

The vanes were pretty ugly but under finger pressure I managed to get them back into what I consider pretty good shape.

Then came the stroke of genius / luck - whilst putting the assembly back in I did two screws at a time, and would you believe it - perfect centring of the secondary mirror without adjustment

I think I spent longer cutting out the cardboard mask for the end of the tube to verify the results than actually doing anything .....

Much appreciated! Now onto centring it in the focuser ....

[NGC 1502]

Hi Stephen, pleased you had success .........Ed.