Cleaning Refractor Lens

[banjaxed]

I have a Meade LXD55EMC 5" refractor and was wondering why the images were not as bright and clear as my 8" dob and 5" Mak untill I noticed the lens was very dirty on the inside. 

I know it is not recommended to try and clean a lens but it is not really an option to leave it alone. It is not worth using as it is so maybe I should take a chance and try to clean it if I 

can figure out how to take the lenses out. Has anyone had any experience with this scope who could advise me please.

[mikeDnight]

You may be able to remove the entire cell from the tube assembly without removing the lens itself from the cell. Have you any images of the lens and cell assembly that may help in offering advice. Also, if you do remove the cell from the tube, it would be best to mark the tube and cell with a marker pen // so that when you screw the cell back on , the marks line up again. That way you'll know the optics should be aligned as they were before you began. I would steer clear of removing the actual lens itself from the cell, as the elements are factory aligned, and if you inadvertently rotate one element even slightly, you stand a chance of creating wedge issues. You will notice the lens itself will likely have alignment marks // on its edge, often in more than one position. These should match up perfectly after a lens has been dismantled otherwise the lens will not work at its optimum.

 

 

[Louis D]

Generally, if you can remove the dew shield by either sliding it off or unscrewing it, the screws holding the lens cell in place should become visible.  The trick is figuring out how the dew shield is attached.  For some, you need to unscrew the tube part from the rear reducer part by grabbing the two and twisting them gently apart.  Others, the entire tube and reducer unscrew from the main OTA tube.  Some are just slip fit and need wiggled off as a whole with some gentle back and forth twisting.  Do some online research to see if you can ascertain how yours is attached.

[banjaxed]

1 hour ago, Louis D said:

Generally, if you can remove the dew shield by either sliding it off or unscrewing it, the screws holding the lens cell in place should become visible.  The trick is figuring out how the dew shield is attached.  For some, you need to unscrew the tube part from the rear reducer part by grabbing the two and twisting them gently apart.  Others, the entire tube and reducer unscrew from the main OTA tube.  Some are just slip fit and need wiggled off as a whole with some gentle back and forth twisting.  Do some online research to see if you can ascertain how yours is attached.

I have tried to find on line research but am unable to find anything. The dew shield does rotate with difficulty so maybe I need to be a little more persuasive. Thank you for your input, I will keep trying and let you know how things progress.

[John]

The dew shield on those slides off. It is held on by three felt covered pads which are part of the objective cell. Have you got the type that has a collimatable objective cell ?

Once the dew shield is off, you can remove the cell that holds the objective from the counter cell that is screwed onto the scope tube by 3 screws with nuts on the inside. As I recall you can't get to the 3 nuts inside the tube that holds the counter cell in place without removing the objective in it's cell.

You need to mark the relative orientation of the cell that holds the objective to the counter cell so that you put it back in the same way. This should minimise the need for re-collimation.

I've owned one of these scopes and also the 6 inch version and the Bresser Messier 127L which is of the same design.

 

 

 

[John]

If it is the collimatable type, the objective end should look like the 2nd photo below:

[banjaxed]

9 hours ago, John said:

The dew shield on those slides off. It is held on by three felt covered pads which are part of the objective cell. Have you got the type that has a collimatable objective cell ?

Once the dew shield is off, you can remove the cell that holds the objective from the counter cell that is screwed onto the scope tube by 3 screws with nuts on the inside. As I recall you can't get to the 3 nuts inside the tube that holds the counter cell in place without removing the objective in it's cell.

You need to mark the relative orientation of the cell that holds the objective to the counter cell so that you put it back in the same way. This should minimise the need for re-collimation.

I've owned one of these scopes and also the 6 inch version and the Bresser Messier 127L which is of the same design.

 

 

 

Thank you for your reply, I am not sure how to tell if it has a collimatable objective cell or not but there are no visible signs on the scope to suggest it has. I did manage to rotate the dew shield a little but did not want to force it but now I know it is removable I will try a bit harder. Will keep you posted about my progress.

[banjaxed]

9 hours ago, John said:

If it is the collimatable type, the objective end should look like the 2nd photo below:

I was replying to your first message when you posted this one. It is not the collimatable type as it does not have those screws.

[John]

2 hours ago, banjaxed said:

I was replying to your first message when you posted this one. It is not the collimatable type as it does not have those screws.

Ok. I think the dew shield still slides off the objective cell but you will need to find a way to remove the whole objective cell from the scope tube to get to the rear of the objective lens.

Once the dew shield is removed, the objective sell should look like this:

There are 3 screws around the objective cell with nuts on the inside which I think hold the cell onto the tube - the trick is how to undo these without beeing able to get at the nuts. I don't think the objective cell in these threads onto the tube, which would make things easier.

If you really have to (not really recommended) remove the objective, the objective retaining ring around the front end of the objective cell will need to be loosened and removed and the lens elements gently taken out. If you can avoid having to do that though, I would. It is a delicate business.

 

[banjaxed]

Thank you John for your very clear instructions, I managed to remove the dew shield ( eventually) and removed the lens cell by undoing the 3 screws, then used my blower to remove all the bits and bobs from the lens and gave it a gentle clean. It is a lot better now but it probably would benefit from a good cleaning of all the cels but I think it would be better to leave it as it is, I don’t really want to go that far. Thanks again to all for your help.

[John]

No problem. Well done for getting the cell off and at least blowing the worst off.

[ollypenrice]

It actually is recommended that you should clean refractor lenses fairly regularly. Pollen can attack the coatings which are, mechanically, very hard. Baader Wonder fluid is an obvious choice of solvent. The 'don't clean too often' warnings apply more to the very soft aluminized surfaces of optical mirrors.

Well done on this job.

Olly

[Louis D]

3 hours ago, banjaxed said:

Thank you John for your very clear instructions, I managed to remove the dew shield ( eventually) and removed the lens cell by undoing the 3 screws, then used my blower to remove all the bits and bobs from the lens and gave it a gentle clean. It is a lot better now but it probably would benefit from a good cleaning of all the cels but I think it would be better to leave it as it is, I don’t really want to go that far. Thanks again to all for your help.

Having done all that successfully, I'll bet your confidence level has shot way up. 😁

[banjaxed]

Thanks for the comments. The reason I was a bit reluctant to try and clean it was the Meade manual clearly warned not to try it. Normally I would just get on with it as I have always been very practical and will try anything within reason. Cleaning all the cell lenses is far more tricky so they will be left alone ( for now) 😀

52 minutes ago, Louis D said:

Having done all that successfully, I'll bet your confidence level has shot way up. 😁

 

[Louis D]

42 minutes ago, banjaxed said:

Thanks for the comments. The reason I was a bit reluctant to try and clean it was the Meade manual clearly warned not to try it. Normally I would just get on with it as I have always been very practical and will try anything within reason. Cleaning all the cell lenses is far more tricky so they will be left alone ( for now) 😀

 

Yeah, I wouldn't open up the lens cell because trying to get all the spacings and orientations/rotations correct again could be problematic, even more so in a collimateable triplet.