Tilt /tip adapters

[gregbradley]

I am thinking about putting a tilt tip adapter in my imaging setup just in front of my camera filter wheel. At the moment I have 2 packers packing out the top of my camera as it flexes slightly downwards.

Does anyone know of an adapter on the market for this? The FLI Filter wheel has about a 75mm opening.

Greg.

[Joshua Bunn]

Hi Greg,
Optec make one...http://www.optecinc.com/astronomy/catalog/19380.htm

Josh

[cfranks]

I made a very similar device to the above, a couple of years ago. The two plates are spring loaded together and forced apart by tapered screws. My springs were 35Kg load but there was still a movement of the plates with different telescope position. I subsequently made one similar to http://www.optcorp.com/telescope-accessories/collimate/opt-focuser-collimation-ring-rc6-and-8.html where the two plates are locked together and thus no variable sag, as it were. A much better design. There are various sizes at Optcorp, Telescop-express.de and Bintel (I think) and you should be able to get something suitable for your rig

Charles

[gregbradley]

Thanks Josh. Looks to be almost perfect but no longer made. Also too thick. I only have 8mm to spare.



Thanks Charles. Perhaps I should make my own.2 plates with adjusting grub screws may do it. The lacking out is working but I think th eflex is slightly variable with the angle but not by much.

Greg.

[LewisM]

There is this one: http://myastroshop.com.au/products/details.asp?id=MAS-005K4

[niharika]

Hi Greg, are you getting some sort of flex somewhere in the imaging train? Does the tip/tilt change across sky if you measure through ccdinspector? what's the back focus of the adapter between FLI FW and MOAG (assuming that's how the setup is). Few people found that getting a 0 length adapter between FLI FW and Moag allowed them to shave off some backfocus and reduce the flex due to thin front plate of the filter wheel. Just some thought.

[rally]

Greg,

Niharika is on the right track

If you have tilt - you have a measurable problem.

Can you identify the source of the problem and solve that first.

If there is a fault, then fix it, if there is flex in an adapter or fitting then its either faulty or not suitable for the loads involved - get a better one.
I will assume that its in the optical train as opposed to mirror alignment ?

That would be my approach

Rally

[gregbradley]

Thanks for that Lewis.



Hi Raki. Thanks for that. I'll check that out. Astrodonb has a zero length adapter for the MMOAG?



Thanks Rally. It appears to be at the junction of the filter wheel and the adapter to the MMOAG. That adapter is only 2mm thick. If I grab the camera and flex on it I can see some slight movement under stress at that point. Raki's suggestion may be spot on. Definitely not the mirror as I have gotten perfect round stars to the corners many times.

Greg.

[niharika]

If you ask Ashley of preciseparts he will know about it as he already made a few including mine. He may initially complain that its a bit risky and stuff but i think its quite ok. This way the whole body of the Moag is supporting the weight and pressure is spread out on a larger area compared of having a adapter sticking out in between.

But if the tilt is constant on different part and orientation it might well be coming from somewhere else.

This is overall an interesting area. For example when I got my 3nm filters from Astrodon I saw that their edges were blackened with paint. My initialy thought was would they still sit "Perfectly square"? I don't know and thankfully I don't have a f 3.8 :P scope. Overall I don't think its coming from Scope or the CCD itself. So it can be from anything else in the imaging train and it can be hard/expensive to figure out what exactly is causing it. I believe Peter Ward once posted something on how he could measure required shimming thickness based on some calculation derived from auto focusing. I know he uses quite high end component like you so does that indicate tilt is unavoidable time to time when you have few items sitting in between? One thing for sure once you start getting perfect stars in all corners you would be reluctant to touch it.

[gregbradley]

Thanks Raki. I'll email Ashley about it and see what he's got. So the adapter has a plate that covers a larger part of the filter wheel face?

I increased the shim thickness from .27mm to .34mm and it seemed to make a difference. Not 100% perfect but probably not worth chasing any further.I'll wait til I finish the current imaging project (I consider it operational and ready for imaging and have been) I may experiment with a few different thicknesses. Perhaps a tad thicker than even this.

I'll also be imaging with smaller sensors at times so it won't be an issue with them.


Greg.

[niharika]

In zero length adapter the the dovetail end finishes exactly where the threaded part ends for the filterwheel. So the body of the moag will sit flush against the filterwheel plate. I have the adapter for mega moag, I believe you have monster moag. The opening are the same so no problem there. Just check the guider port is fine and won't get on the way if you reduce that 2mm backfocus of current adapter. I will try to take a picture later tonight to show what I mean.

[PRejto]

This is too thick, but seems quite sturdy and precise:

http://www.gerdneumann.net/english/astrofotografie-parts-astrophotography/ctu-camera-tilting-unit.html

Peter

[gregbradley]

Thanks Peter. That looks very good. Expensive but good.

Greg.

[gregbradley]

Come to think of it the measurement of th etilt could be done by having the centre of the image in focus and noting the focuser step number. Then refocusing the corner where the tilt is until its in focus. Subtract that from the original position (1000 steps = 1mm) and express it in mm.

The only problem with that is the tilt cause radial stars on the Honders in the corner affected and I don't think it would necessarily come to focus and change that. It might but I don't think so.

Greg.

[niharika]

Zero Length Adapter in between moag and the FW

[gregbradley]

That's very good. I'll definitely talk to Ashley.

Greg.