100mm Mak repair

[Richard]

[attachment=0]100 mm Mac broken lens.Hi all so I went to a garage sale and purchased this unknown Mak for 13 US including mount and 2 rubbish eyepieces it came with a Meade correct image finder 8x21 as well as a 45 deg correct image diagonal so I assume was used as a spotter , the mount is an eq 1 or 2 and actually works well after a clean and grease job.
The front corrector lens has a clamshell damage in one corner but it does not affect the view too much . It needed collimation as the view was terrible but now after collimation one can see the bands of Jupiter nicely . Unfortunately there is quite a lot of focus shift , the primary mirror is held with a spring on to the backing plate which can be tightened by turning it , When loose there is a lot of focus shift compared to tight.
any advice ? and does anyone know this scope , I used to have a similar one was an ultaoptic?
I was quite surprised that a broken corrector does not really affect the view.
This scope will be given to the kids that cant afford one

[Richard]

So I replaced the sticky glue with some white Lithium grease on the spring that holds the primary to the backing plate just to try it out , massive difference virtually no focus shift , makes me wonder why the manufactures use that for that particular use, its fine for focusers to take up slack but not for this application , I think it sticks and then lets go and thats why there is a focus shift, that stuff as we know is like glue, something I learned today

[Don Quixote]

Whatever the defect there may have been it seems that you have acquired a useful tool at a very good price...plus, you got some edikation.
Congratulations.

[yobbo89]

nice scope,what's clamshell damage ?

[notFritzArgelander]

nice scope,what's clamshell damage ?

A fracture patter that is clam shell shaped I trust? I think I see it in the pic.

[Richard]

Yes the scope must of taken an impact sometime in its life and the corrective lens took a knock , I have a meade ETX 90 that bent the metal around the corrector but no damage to it , the corrector was loose in this scope so perhaps thats why the lens chipped ,these small Maks are otherwise bullet proof

[Lady Fraktor]

If you see any flare/ scatter from the chip just cover it with black paint or nail polish.
It will not affect the views afterwards.

[Richard]

Thanks Gabby have not noticed any scatter on bright planets , its not a great scope but the mount works well and it works now hopefully will put a smile on someones face, I have a spare 90Deg diagonal that works so much better with this scope so it will go with that , I did think of black paint , but nail Polish ? what colour :smile:

[notFritzArgelander]

Thanks Gabby have not noticed any scatter on bright planets , its not a great scope but the mount works well and it works now hopefully will put a smile on someones face, I have a spare 90Deg diagonal that works so much better with this scope so it will go with that , I did think of black paint , but nail Polish ? what colour :smile:

Ah.... well black. Find a goth fashion boutique. Maybe, if lucky, you can find it in flat black?

[yobbo89]

could stop it down with a mask on the front ? that's if you come across glaring

[notFritzArgelander]

could stop it down with a mask on the front ? that's if you come across glaring

The mask would unnecessarily cut off uninjured parts of the corrector though.

[Richard]

So after I changes the grease around the spring and the tube all was well but short lived ,focus shift is back , not bad as a 15mm eyepiece at least keeps the target view, its a F14 , now I dont know what else to do seems like some Maks are built better than others , pity I did not take some picks of the cell but it was identical to a meade ETX 90 that I stripped some time ago , but I suppose tolerances cant be seen, I still wonder who made this scope , the only Mac that is 100mm and a focal of 1400 is made by Ulta Optec from Google

[Lady Fraktor]

Do you know if the Bresser/ ES 100mm f/14 is the same telescope?

[Richard]

Do you know if the Bresser/ ES 100mm f/14 is the same telescope?

Probably but no markings on this scope , the finder is a Meade 8x21 correct image (has a prism) perhaps the scope was resprayed , I dont really want to give anyone a bad scope I would rather trash it and use some parts for spares, I must say the mount is great a simple EQ 1or 2 but so smooth , The RA movement is perfect just as good as my EQ 5 , unfortunately the original owner is not with us and the last owner just wanted it gone .Apparently its 20 + years old
It cost nothing in money terms but I would still like to try and fix it as best

[Richard]

I must add that if the scope was resprayed it was a fantastic job no markings of a respray visible

[yobbo89]

it's still going to be a good little usable scope, i've seen mods with a corrector totally destroyed and they have put in a spider vein like a newt with functioning results

[Richard]

So I was not happy about the focus shift not being able to get any info on the tolerance of the shaft movement where I think the problem is I disassembled and and I think thats where the problem is , coat with Epoxy paint , or Teflon tape ? original was the glue type grease as there will be a lot of movement with time teflon tape will not work

[Lady Fraktor]

You may have to go back to a heavier grease to help keep it under control.

[pakarinen]

If you see any flare/ scatter from the chip just cover it with black paint or nail polish.
It will not affect the views afterwards.

Wow. I don't own a Mak (yet?), but I never would have thought of that.

[Richard]

If you see any flare/ scatter from the chip just cover it with black paint or nail polish.
It will not affect the views afterwards.

Wow. I don't own a Mak (yet?), but I never would have thought of that.

I have had many Mak's some have had a bit of focus shift at high power (like 200+) but this is the first that you loose the target at 100x grease any form does not work due to the forces involved , the scope is just a bad one , if you are moving a heavy mirror off center on a tube that is not made properly , teflon tape did work to take up the tolerance , just needed 2 coats of the plumber type which I sealed with some small glue dots , seems to work , still some shift but one does not loose the target , will try for a few days and see
One can always get a SCT/Mak focuser to eliminate this problem but they are expensive and really only good for the large SCT or MAK I used to have one on my 150 Mak as there was a bit of focus shift , but I think its only really good for AP as the cost is terrible and in my opinion not worth it for visual