Help on replacing Newtonian Secondary Mirror

[weixing]

Hi,
Something bad happen to my secondary mirror... my compress air can eject some form of liquid on my secondary mirror and after I clean the liquid, there are some brown colour "patch" on it. It is not very obvious, but is visible at a certain angle. Below is the image of the "patch"... it is better than this now after a few times of cleaning:


If I cannot clean off the "patch" and it affect the performance of the scope, I may have to change my secondary mirror.

Anyway, I've no experience in this (so this is a great chance to learn ATM), so I need help on what should I get if I want to change the secondary mirror. My secondary mirror is "paste" (using double-sided tape) on the diagonal holder... is that what they call?? The holder is then connected to the 4-vane spider via a centre screw and three push-pull screw for collimation. Below are a few image of my secondary mirror with 4-vane spider:



I'm thinking of getting a secondary mirror and a holder, but my concern is that will that holder fit my 4-vane spider?? Anyone know which brand holder can use on the above 4-vane spider??

All suggestion are welcome.

Thanks and have a nice day.

[VinSnr]

This is a simple problem.....in fact, it's a good problem.

Just go to fpi-protostar.com and select a curve vane that suit the id of your tube. Or talk to protostar and tell them your scope....a synta 6" f/5 is a size they are most probably familiar with and should have no problem recommending you a curved vane that suits your tube.

At the same time, buy a good secondary from them. And since you are buying from them, might as well get protostar flock paper and flock your tube also. Tkae this chance to upgrade your scope man!

After that, your scope would be wonderful! Next time, don't ever use compress air! Sometimes there are liquid that comes out with the air. Furthermore, I find the air pressure too strong.....if there are dust in the air, you are really sandblasting your mirror! Just use a bulb blower will do.

Ok..now my question to you. Do you know the hex screw size of the secondary push pull screws as well as the main primary push pull screws? Somehow my 8" f/5 didn't come with any hex keys.....do you know where to buy those hex keys? I aslo need a hex key to unscrew the two small hex screws at the back of the focuser....

[weixing]

Hi,

Ok..now my question to you. Do you know the hex screw size of the secondary push pull screws as well as the main primary push pull screws? Somehow my 8" f/5 didn't come with any hex keys.....do you know where to buy those hex keys? I aslo need a hex key to unscrew the two small hex screws at the back of the focuser....

The hex key use on my newtonian is the metric hex key and can be found on most DIY shop. The hex size for the three push pull screws on my 6" F5 newtonian secondary mirror is 2mm. The hex screw on my primary mirror is the locking screw not the push pull screws. For my newtonian, the push pull screw is the three Phillip '+' screws. Anyway, the hex size for the three locking screw on my 6" F5 newtonian is 2.5mm. I just try the two hex screws behind the focuser, it is 1.5mm size. Hope it helps.

Thanks and have a nice day.

[kayheem]

I'm thinking of getting a secondary mirror and a holder, but my concern is that will that holder fit my 4-vane spider?? Anyone know which brand holder can use on the above 4-vane spider??

All suggestion are welcome.

Thanks and have a nice day.

Hi,

My take on your happy problem:
1. Make your own curved spider from a steel ruler if you have access to a drill press. You can re-use your old holder. Just remove the mirror from the holder.

2. I do not know how much a protostar secondary is, but Sam's contact at Sky Instruments have secondaries with enhanced coating and 1/10 wave surface accuracy for reasonable prices.

Kay Heem

[MooEy]

tried cleaning that patch with any cleaning solution? might have a chance of saving it.

~MooEy~

[weixing]

Hi,
The secondary mirror seem to be ok... do a star test yesterday and the pattern seem to be identical to the pattern before the incident... that is not perfect .

Anyway, will test again on friday night when I go out for observation. Will check the image of Ring Nebula, M7, M8, Omega Centauri and Jewel Box to confirm that the secondary mirror is ok.

Thanks guys and have a nice day.