telescope angle for collimating?

[mura_gadi]

Hello,

I normally collimate at 0 degrees - tube level, should I be collimating at 45degrees?

If I only view from 35degree and up should I have the angle of the tube even steeper when collimating? Halfway between 35degrees and 80+ degrees?


Thanks
Steve
assuming that my bulk standard 8" newt will have some degree of play since the mirror cell is fairly average.

[EpickCrom]

Good question Steve, I sometimes wonder the same thing as I also collimate at 0 degrees. I look forward to the replies you get.

[bojan]

Hmmm..
If there is a difference in colimation when scope is hor or vert, then you have a mechanical problem with optics (something is moving..). So you have to fix that first, IMO.

[mura_gadi]

I agree Bojan, but that would be on a mirror cell separate to the mirror box, with whiffle bars (or the old slings) and the mirror supported on corked tip triangle pads hopefully based on a PLOP calculator.

None of which is present on a standard SW/GSO newt that I have, the collimation bolts are untipped single bolts and at the edge of the mirror. Without using the retainer pads to fix the mirror and cause optical flex I am assuming I will have movement above 1/4 wave lengths. The current SW/GSO designs seems to be the same design as mentioned in telescope books from 70+ years old...

But I could be wrong, so, best to ask I thought.

*********

I seem to remember one of our more talented amateur scope tinkerer's remade the back of the cell to accommodate a 3 point support system more in line with modern designs and report a good improvement.

https://www.iceinspace.com.au/forum/showthread.php?t=188532&highlight=mirror+cell

Something I can see a lot of sense in, but not able to progress with atm.

[OzEclipse]

Steve,

Small mirrors of reasonable thickness ratios don't need fancy cells. Only necessary for thin mirrors. I have always collimated my scopes comfortable for my eye which is usually pointing up slightly. My 6" mirror is a 1:6 ratio. It sits on three 4mm brass screws machined down to a point on the tip.

It sits loose in its cell, that is, it can rattle when pointing horizontally. However, it is mechanically restrained so that it can't fall out but that looseness keeps the mirror free of stresses and the figure true.

So I would always point the scope up in a direction that the mirror is siting in it's observing orientation. The style of mounting cell really depends upon mirror size and thickness ratio.

I notice you haven't posted for a long time about the mirror you were making? Have you finished using my Foucault tester? Can we arrange a return at some stage?

Cheers
Joe

[mura_gadi]

Hi Joe,

Thanks for the reply, I was thinking the best approach would be to have a list of targets and collimate at the halfway mark of my highest and lowest visual objects for the night.

Re Tester:

I have only just started on my mirror again after a winter hiatus due to the cold and damp weather and doing most of my grinding in the garage.

I had a double curve and gone back to 120-220 and starting 400 again. I am more than happy to drop your tester back at any stage however, just seeing one and using one was a great resource.

Let me know when your home and I can be there as quickly as I was to pick it up.


Many thanks
Steve
I had a good finish and was a few inches out on my F/l, so went again, got a bad finish and had to restart all over just about, think my 25mm thick glass is approaching sub 20mm soon... /sigh. At 205mm by 20mm I'm at 10:1 ratio, so, I'll be needing all the hints and tips I can find for the mirror cell on the home made scope.

[Rainmaker]

I collimate with the OTA between 40 and 60 degrees inclination and usually view between 20 and 80 degree altitudes. Seems to work well enough…

[mura_gadi]

Thanks Matt, I have read a few web sites about collimation and can't remember anyone mentioning the preferred position of the scope tube. Good to hear the mirror is not affected by such a wide range in the alt. I think I'll go with something around the 50degree mark then.

[OzEclipse]

Steve,




Once it gets hot, the pitch won't hold it's press. You're better off polishing in the cold. But yes, get any polishing done now. If it gets hot over the summer, you'll need to stop.



It's only an 8 inch diameter mirror. So even at 1:10, I'd think a nine point floatation cell should be plenty of support. You can build you own or I'm sure somebody sells them. Speak to the owner at Kunama Optics.

Joe

[Stonius]

I collimate at 45 degrees, but mostly because at that angle I can actually reach the screws :-)

[evltoy]

Its has taken me a good part of a year to sort out my method of collimation on the 8" SCT.

I collimate on a star that is in the same location (highest point) of the target I'm imaging as I have to factor in mirror flop.

[Tulloch]

Collimate at the same (or similar) elevation angle to that of your target. This is especially important for planetary imaging.