Straightening spider veins

[CapturingTheNight (Greg)]

Hello,

I have an 10" F/4 newtonian inwhich a couple of the spider veins are noticibly bent/warped. What is the best way to straighten them??? I have tried by hand but I don't think I achieve much. For most of my images it does not make a noticible difference but when I come up against a bright star I am getting double diffraction spikes, which I am certain is caused by the spider viens being out. Please see attached image (and yes I know I have got a reflection off the coma corrector there as well)

Cheers

Greg

[tilbrook@rbe.ne (Justin Tilbrook)]

Hi, Greg.
I don’t know how you’ve tried to straighten the veins?
But here’s how I’d go about it.
1. Make a card board template of the exact centre of the spider.
2. Make sure the veins are tight, if not go around and tighten a quarter turn at a time. ( Do not over tighten!! )
3. Check for centre with template.
4. Have two sets of flat nosed pliers at hand, ( use card board packers with pliers to protect the veins). Grasp as close as possible to the inner and outer edge of the vein as possible, twist in the desired direction. Do this a little at a time!!
5. If this works, check with your template re-adjust if needed.

Hope this helps.

Cheers,

Justin.

[RobF (Rob)]

The other trick if you're trying to deal with twist is to try tightening/loosening the outer screw on the OTA. Has to be done very carefully of course in case you upset your secondary position, but I have found a mixture of "hand tweaking" and screw repositioning useful in the past. Chinese Newt reflector vanes tend to be pretty light on, so care required.

[CapturingTheNight (Greg)]

Thanks for the tips Rob and Justin. I'll see how I go.....

[bmitchell82 (Brendan)]

maybe a little bit of twist but more likely your secondary holder is pulled slightly to one side!

Grab a straight edge or a ruler and lay it across the top quickest way to check if it may be that

[Shiraz (Ray)]

hi Greg. Also check that the bent ends where the vanes attach to the central block are actually at right angles - if they do not start out pointing directly at the locating holes in the OTA, the vanes will be forced to curve slightly under load. My GSO ones are fairly soft metal and it was easy to get the correct angles - wouldn't like to flex them many times though, it's thin metal. Regards Ray

[multiweb (Marc)]

Originally Posted by bmitchell82

maybe a little bit of twist but more likely your secondary holder is pulled slightly to one side!

+1. That's exactly what it is. Your spider vanes are not at right angle so the diffractions don't overlap. Nothing to do with twisting.

Bit more reading here and here . Whole thread here.

[CapturingTheNight (Greg)]

Awesome! Thanks for the information Brendan, Ray, and Marc. I'll get right onto it, and see if I can sort out that secondary.

[bmitchell82 (Brendan)]

If you have a look at my last image of the running man you will see if you look up close i have the same issue, though unlike your issue mine is only just off and if your not looking closely you will miss it.

After doing some reading i believe that with twisted vanes all it should effect is the width of the diffraction spike as your mirror sees a larger vane than it actually is (because it presents a larger surface area) so you may be able to see this as the diffraction spikes getting larger and smaller. Though i cannot speak from experience and somebody else may be able to give you a much more informed reasoning behind the physics and resultant diffraction pattern.

Regards
Brendan

[CapturingTheNight (Greg)]

Originally Posted by bmitchell82

If you have a look at my last image of the running man you will see if you look up close i have the same issue, though unlike your issue mine is only just off and if your not looking closely you will miss it.

After doing some reading i believe that with twisted vanes all it should effect is the width of the diffraction spike as your mirror sees a larger vane than it actually is (because it presents a larger surface area) so you may be able to see this as the diffraction spikes getting larger and smaller. Though i cannot speak from experience and somebody else may be able to give you a much more informed reasoning behind the physics and resultant diffraction pattern.

Regards
Brendan

Cheers for that Brendan I have not had a lot of time of late to have much of a play with my setup to try and correct this issue. Hopefully get a chance this weekend.

[bmitchell82 (Brendan)]

not a problem mate. Last night i decided to have a little look to see if mine where infact out because im going out about 3hrs from Perth city for 3 days so the scope was out i grabbed a piece of white A4 paper, and sure enough its out by about a mm. a quick adjustment will render this issue solved and once again give perfectly square and straight diffraction spikes.

Good luck

Brendan