Take extra care of your scopes! (1 Viewer)

Just wanted to chime in.

My scope has for no obvious reason at all totally lost collimation, I've been taking such good care of it and have never had a bump to the lens cell. Been trying out if it was sitting in the wrong threads but it didn't, noticed it the first time looking at Jupiter through one of my eyepieces, and then began searching for faults with the camera. Focus can't be reached really sharply, and a small double image is shown on photos with objects in distance.

Now it's a matter of sorting this out.

I thought collimation was only a problem with reflectors. Could it be a reflection issue? Have you flocked the tube and extensions? Does anything rattle if you shake the lens element? What about the atmospheric conditions when you looked at Jupiter? Nothing like a bit of air to screw up sharpness.

Yes collimation is mainly a problem with reflectors, but it is possible on refractors as triplets also, I don't think it is common for doublets with no adjustment screws like this one to become misaligned. The cell feels solid when shaken, I haven't changed anything in the setup from my last picture so reflection is ruled out. I thought about conditions in the beginning as well, but since then I've been testing it on stars and such two nights in a row as well as trying it in daytime conditions. I've thought about if the focuser has become misaligned, will have to do some adjustment tests on that one.

I find it very strange.

Could be the focuser. My scope has an adjustable focuser that some times needs to be re-aligned for some reason or another. First thing I'd do is get a cheshire collimation eyepiece to see if your scope is in fact out of alignment.

Hopefully the focuser is the issue, it wasn't such a long time ago since I adjusted it but it could loose tension with weight putting pressure. I will have opportunity to make a proper adjustment tomorrow, and if that doesn't work will have to get a cheshire, been wanting one of those for a while.

Are you getting infinity focus? Can you adjust the mount for the extension tubes on the end of the focuser. Mine has a lock ring and there is a certain amount of adjustment possible. Is the halo or doughnut around a star nice and round when it is out of focus, both front and back? If so, it is not a collimation problem.

Think I might have jumped the gun on this one. Just sat down and did a thorough adjustment of the focuser, it seems to have decentered itself quite a bit. It's a cloudy night so no stars to test, but from taking a photo of the street lightning and looking through eyepieces it seems better. But it's very dark and hard to decide so I will have a final answer in the morning, looks promising though.

Well it turns out I did! Stupid focuser.. but such a relief though.

Glad you got it sorted. I don't think there's much that can go wrong at the glass end with regards to a doublet. I've had my lens cell off loads of times and also took the glass right out of the cell on a few occasions. The focuser can go wonky though. |=)|

Paul.

Oskar,
Can you tell us exactly what you discovered and how you adjusted your focuser, and then how you checked it?

I added a numbered picture to make it a bit easier. Well I discovered that 1, 2, 3, 4 had become loose, that must've caused the tube to point at an angle not centered with the lens.

I start off by loosening every screw except number 8. Then I begin to tighten screw 1 to 4 diagonally, trying to tighten the same amount for each screw. Going round a little at a time to get it precise, like 1 & 4 to 2&3. These screws need to be tightened a fair amount, to get more feel for the pressure using as few fingers as possible when tightening is advised.

Then I move on to number 8, loosening that and trying to feel when the shaft is centered and then tightening again. If the shaft is not centered it will be noticed when trying to spin the knobs. This screw I tighten after preference, more pressure will result in more force required to turn twist the focusing knobs.

The tube should now slide without much friction, it should be able to move it in and out just using one finger. It should roll ind and out if you angle it in either direction.

Then I begin tightening number 5 until I feel first resistance, then tightening it bit by bit as I check the friction on the tube by drawing it outwards. I tighten it enough so that it has enough friction to hold against the weight of a camera and accessories.

The last step is number 6 & 7, these should just barely touch. I tighten these so that they just sit safely without unscrewing themselves, very little force is needed on these.

The adjustment should now be complete, if done thoroughly the tube should now slide with a nice and even friction when focusing. I'm sure some people do it differently but this works for me. I plan to add some grease to the bearings in the knobs later on as well, when I opened it up previously they looked a bit dry. I unfortunately don't have any before and after pictures for comparison, but it was just enough that when looking through an eyepiece the eye was straining all the time trying to adjust itself.

No scientific procedure to check the after result at all, it just snaps into focus now.

Thanks Oskar,
1,2,3, and 4 are the mounting screws and I can see that if they were really loose it would have an effect, but they would have to have been so loose that the tube would have been flopping around.
It seems that the other screws adjust the pressure on the flat part to the focusing tube, but I fail to see how they could affect the alignment enough to be that noticeable. I can see though, how proper adjustment could make it much easier and accurate to focus, that is, more of a mechanical problem than an optical one. Star tests are still the easiest and best method for testing. Let us know what you see of the North Star both in and out of focus.

I agree that by logic it shouldn't have such an impact, it was mostly fine tuning but the difference was apparent straight away. The tube seemed to sit nicely before, but no matter how hard I tried to find focus (in horizontal position so tube could not slip) it was always slightly off, my cameras focus confirmation had problems as well.

As soon as I get some clear skies I'll do a star test. Hopefully will show nice circular rings, but as the focusing problem is gone now it can probably be expected.

Good, smooth focusing is a must, no mater what lens. I had an Olympus 50mm/2 macro for a while, and although it war sharp as a tack, it was a real pain in the proverbial butt to focus manually. Had focus-by-wire, and all you had to do was have the lens pointing down, and really accurate manual focusing was very difficult. It would jump one way and lag the other. I sold it and stuck with my nearly 40 year old Leicaflex macro. Tight and smooth as silk.
I found a huge difference between the stock Skywatcher focuser and the Lacetra 1:10 I have on it now. It is basically the same as yours, but without the two extra adjustment screws, 6&7. I also fine polished the edges of the "flat" surface, (actually slightly concave), and now it is butter smooth.