Boros

As a follow up to my previous thread re 'focuser issues with Skymax 127 Mak' I have tonight discovered a possible contributory factor. I decided to do a 'star test.' First one I did using a pin hole in a black disk taped over an led torch came out like this: Which I thought looked okay, but later on this evening I decided to try it on a real star and I was slightly taken aback at the result. I didn't manage to get a photograph, but I've altered the image below to be as close to what I saw as possible. Can anyone explain what might be going on please as this doesn't look like any pics of uncollimated scopes that I've seen. Could the difference between them be due to the fact that for the first one, the focuser was wound almost as far back as it would go as my artificial star was just up the garden a bit, so presumably the mirror would be 'locked up' at that point. The second one was unfocused on a star, just thinking it might be something to do with the position of the mirror in relation to the rod, and that something is happening to the mirror as it travels up the rod, causing the distortion!! I don't know just a complete guess on my part! But something definitely looks amiss.

I tried the sponge thing, but have to confess didn't like the soft feel, just felt a tad vague to me.

Hi I've found like others that the small diameter focus knob on the Skymax 127 is not conducive to achieving accurate focus. I fully intend to add an auto focuser but in the meantime decided to make my knob bigger, er hmm, you know what I mean! I've seen various methods, using clothes pegs, Nutella caps etc, but I wanted something that didn't look quite so 'Heath Robinson' so briefly here is what I did. The idea was to use the existing knob to form a female mould using car body filler inside a larger diameter cap. I managed to find an old Tamron adaptall mount cap, and a spare cap which I think came off an old diagonal, this proved to be almost an exact fit inside the Tamron cap. I decided to cover the knob in clear tape to protect it and make it easier to remove from the filler. I then filled the diagonal cap with the car body filler, inserted the focus knob, centered it, then set aside to harden. Once hardened it was easy enough to remove the knob, then remove the excess filler, tidy it up and make black. I also added some black electricians tape around the central part of the cap, not necessary but I think it looked a tad tidier. After that it's just a matter of securing it inside the larger cap with epoxy resin. It's a nice snug fit over the knob, but with a slight smear of vaseline on the rubber it slides on and off more easily. Overall, functionally I think it's a big improvement and it doesn't look too bad either, although I may add a plain plastic disc over the 'Tamron' printing just to tidy it up a bit.

Hi Magnus No I don't intend to do it now, it was just for future reference, but very interesting to know that it's okay to use acetone on the mirrors.

Thanks so much for that information Magnus, your post/thread on the 180 is superb, such a lot of time and effort into producing it, I'm sure it's been great help to many with questions or issues with these scopes. If I do eventually decide to venture inside the tube, these instructions will be invaluable. One question at this point, not related to the focuser but the secondary mirror, I've been led to understand that it's best not to try and clean these, so can I ask what your method, cloth and cleaning fluids were to complete that task? Many thanks for your help.

Hi Thanks, I had already done that, I removed the knob, shaft had small indents where the screws had been tightened onto, so rotated and tightened in to fresh section of the shaft. But that hasn't made any difference. Thanks for the link, it seems a task not to be undertaken without good reason, especially without the accompanying photographs! However I did try to unscrew the back plate just to see if it would move, but failed miserably. Also I did find this article : http://scopeviews.co.uk/SW127Mak.htm Where it does touch on the same issue I'm experiencing, unfortunately he doesn't explain or delve into this problem any further than the following: The focuser is typical of a Maksutov – a knob protruding from the back-plate moves the primary mirror. This arrangement gets a lot of bad press because in some cases you get a lot of image-shift when changing focus direction That being the case I'm surprised there is not more to be found documenting the problem or reports of others with the same issue.

Since I've had this scope which I bought s/h I've felt that the focus adjustment wasn't quite right, but it seems to be getting worse, and it's proving more difficult to nail focus than I think it should be. If I go past focus then wind it back, I seem to have to turn the knob back much further than where focus actually was to get past focus and bring it back again, so I get the impression that the position of the knob in relation to it being in focus seems to change. Also sometimes the change from being out of focus to being in focus is more of a step than a smooth transition. I have checked that the knob is not moving on the shaft and the grub screws are tight. Have to say it's quite annoying and getting critical focus isn't the easiest task at the best of times anyway. Any ideas or remedies greatly appreciated.

Thanks for suggestions, another option has cropped up, if I fit tube rings I should be able to rotate the scope to the correct orientation, I think I quite like that idea, it's non invasive and can be changed back in the future if required. So just need to find a set of rings to fit. From what I can gather from other posts the Skywatcher 140mm rings 'might' fit. Bit of debate as to what the actual inner diameter is 140- 143mm? I have measured my tube and it's 142.8mm so if they are 143mm+ they should be okay. Anyone actually tried to fit these rings?

Yes I was aware that is the case, but as I said I had intended to do the mod which rotates the rear plate and that would alleviate the issue, but I now can't find the article explaining the procedure. I don't know if it's straightforward and don't want to risk messing up the collimation. Really was hoping someone would have done it and could explain the process. I have a decent red dot sight, so spending on another one is not an option. Thanks Rob

Hi all Hoping I can get some questions ironed out relating to the mounting of my 127 on an AZ GTi which I've just bought (separate purchase). I have searched the subject but am left with a few questions. When the 127 is mounted on the AZ GTi , it's on the left side of the mount, which is fine because I am left handed and prefer it being on the left, but it does pose a problem for me, my 127 has the mounting rail on the underside, so when it's mounted on the AZ, the focus knob is now directly behind the diagonal, which is a tad inconvenient, but worse still is that my Baader red dot sight would be in an impossible position down to the left about 7-8 o'clock. My intention was to hopefully rotate the backplate by slackening the screws so it could be rotated to the right, bringing the focus knob and sight mount back to their normal positions. I read an article somewhere about doing this, I can't find it now, but am having second thoughts anyway, just concerned I'd be opening the proverbial 'can of worms' by attempting it and upsetting the collimation . Has anyone done this 'mod' is it easy enough to do, and does anyone have a link to the article? Or any other suggestions how to get round this issue. Thanks

Hi The diagonal it came with is a rubbish plastic 90 degree mirror, not a prism, I alternated it with the one from the 102GT which is a 45 degree prism, and on checking it is indeed an amici prism, so that probably explains the vertical black line, thank you Vlaiv. I'll try rotating focus knob to it's extremes a few times, although it's had a good workout already, but I suspect that this is where the focus/ soft image issues are stemming from. If so and the focus racking doesn't help, then it looks like I won't be buying it! Thanks again Vlaiv and White Giant.

Hi I talked to my neighbour about his Bresser, he's not in a hurry to have it back so says I'm okay to do a few more tests on it. I had really clear skies this morning about 2am so had a good opportunity to try it on a proper subject. Did the star test and to be honest it all looked fairly concentric, but one thing I did notice was that the out of focus disc had a thin black line running vertically through the centre, this moved to either side if the disc was moved away from the centre of the frame, is this normal? Also I'm not sure about the focuser (is that a word?) First of all I never felt the images of Saturn and Jupiter ever got truly sharp and when trying to achieve focus if I went too far and had to bring it back a tad, it went way out of focus so had to wind it back really far then try again, so I basically have to wind it to achieve focus first time, can't just get it close and jiggle it a bit. it's impossible to fine tune the focus, it can be almost there, I'll move it just a tiny bit, but it jumps out of focus to almost a doughnut, so have to wind it way back and go in again. Anyone had any experience of these issues?

Okay all thanks for your advice, I'll update when I have made some progress.

Hello Gfamily, thanks for your thoughts, I totally understand what you mean and I will try what you have suggested, but just taking the results from the mak on their own, they are not good. Some Maks like the Celestron C90 are used as spotting scopes presumably during the day, this is unusable for that purpose. I've read that Maks are supposed to have very sharp optics, this is far from sharp. But as I say I'll give it another chance tomorrow, redo the star test and use different lenses as you suggest, but I've a funny feeling I'll be handing it back to my neighbour. Shame really as I'd hoped it could have been a more user friendly scope than the 102GT. Thanks for all the input from everyone.

Hi Yes I tried it with 2 different diagonals, the one that came with it, a mirror one(cheap rubbish plastic) and the one from the 102GT which is a prism, not much to separate them to be honest. And both diagonals with 2 different eyepieces. The camera was prime focus using a barlow (without the lens) Image was soft viewing through eyepiece and the camera lcd and the camera images are also soft and just look slightly out of focus. I went back and forth with the same setup between the 102GT and the Bressier and each time the image from the 102GT was noticeably superior, more contrast and distinctly sharper, the Bressier just looks soft no matter what I did. Conditions were fine, daytime and viewing brick chimneys about 100yds away.