Seating a dovetail fully

[gregbradley]

I have had it happen a few times now that dovetail fittings with grub screws to tighten and hold it have not been fully seated. The FLI cameras have a dovetail at the front for mounting, the MMOAG has one both front and back and so does the Atlas focuser.

So I smeared a small amount of Teflon grease on them and they feel a lot better when engaging.

I think sometimes little dings from past tightened grubs screws can cause a slight catch and the dovetail does not slip into a fully engaged position. This can cause the camera to not be square to the scope or perhaps slip a tad when the scope is pointing fully up and go out of focus.

I had a large number of subs get wrecked the other night by exactly that. About 20 or more 10 minute subs had one side out of focus and had to be trashed.

I thought I would pass the observation on. A little bit of misalignment you can get away with at F8 or F7 but at F3.8 you can't get away with anything.

Greg.

[SpaceNoob]

I found a similar problem, even at f8 it can cause issues.... more so with the 16803. Actually it was with the 16803 that I have found all of these type of tilt problems become a nightmare, add a rotator into the mix and its even more of an issue. Hopefully at the end of the problems and I should be able to start using the damn thing.

[niharika]

Yep, this was one of the negative of the FLI FW design for me too.

[SpaceNoob]

On my train there are quite a few dovetails, if that's what they're called.

The FLI one has proven to be the least concern and was extremely easy to seat flat/flush. The FW also bolts firmly through the camera body.

Issues for me have been MOAG->precise parts adaptor -> Pyxis rotator -> optec to PW Hedrick focuser adaptor. All of which are those damn pinch bolt dovetail things. The whole thing requires very careful assembly on a bench before lifting the train onto the back of the scope. If I keep struggling with adapters I'll be ripping off the rotator and just going directly to the focuser using the secure fit adapters which are much better, so I hear at least. Rotator is nice to have but not really needed given the field size/shape of the 16803.

[gregbradley]

Perhaps that is why they came up with the zero tilt adapter. I am using one on the Atlas and its a nice piece of gear. But its only for the Atlas and the Centreline filter wheel at present.

Greg.

[gregbradley]

Unless you are doing remote I don't see a massive gain in using a rotator on the CDK. I was just using my CDK last night with the reducer and its so easy to simply loosen the 2 tightening bolts and rotate the camera. But if you are using a MMOAG and PWave MMOAG adapter then yes you have to loosen the grub screws and rotate the camera on the MMOAG and then retighten. A careful process, if you loosen it too much the camera can fall off. So I think a little lubrication here would help as it would turn more easily with less back off of the grub screw. I haven't had tilt issues with the CDK17, MMOAG and PL16803 except right at the beginning when the MMOAG prism was too far forward and was preventing the adapter seating properly. But then no problems after that.

Greg.

[SpaceNoob]

Sounds like a good idea. I probably will remove the rotator and just go with the secure fit option. Removing the rotator would probably reduce the weight of the train by a fair bit too. Regarding the grub screws..... I think I'll leave them alone and loosen the focuser assembly, seems less prone to tilt issues :)

[LewisM]

I negated the FLI dovetail issue by having a 2" SCT thread (FLI side) to M72 (Tak side) adapter made up.No brainer really. No need to mess with those silly dovetails.

FLI kindly shows a whole plethora of schematics too to help with the design.

[gregbradley]

Planewave also sell an integrated focuser and rotator.

Greg.