Corrector Plate Cleaning - 8" SCT

[MarsG76]

Hi All,

For those interested, this is a follow up to my post regarding my 14" vs 8" comparison where the 8" showed ridiculously milky and low contrast views. "The Moon 8" vs 14" comparison and foggy corrector plate" in Observing -> Reports.

 

I got to the bottom of the hazyness.. at least in theory (theory because it wasn't tested yet)... The low contrast view looks like it was caused by a very filthy SkyLight Rear cell.

When I unscrewed it, it was visibly hazy even in low light... but I still bit the bullet and removed the corrector plate to try to clean it from the inside. Mainly out of curiosity at this stage.

I put of some rubber gloves and  followed the advise as written everywhere in forums and I marked the position of the corrector with two tape markers 120 degree apart before removing the plate.

 

I wrapped some glad wrap and held it in place with a rubber band on the secondary mirror not to touch or spray it and than sprayed the inside of the corrector plate, first with distilled water, than 100% Isopropyl Alcohol, than with distilled water again.

I used spray bottles and sprayed it with a misty spread. The fluid ran off and dried very clean, no dried streaks or spots.

 

After it dried I re-assembled the corrector onto the OTA and than cleaned the outside of the corrector using the same method. It definitely looks nice and clean.

 

Of course... just as I was ready to collimate and test the unit, I started hearing some rain droplets on the roof of the observatory, I looked out side and it was cloudy and sprinkling rain!!!! I thought "WHERE DID THAT COME FROM, TYPICAL NOW THE TEST WILL HAVE TO WAIT" more suspense... Literally 10 minutes prior it was mostly clear with a few clouds here and there.

The whole procedure was not as daunting or hard as I though it might be, but of course I should wait until I do a collimation and a focus/star/moon test before I call it a success.

Update on the real life performance test to come.

 

 

[Stu]

Good stuff. Hope it fixes the problem. I took a somewhat sick C925 apart and cleaned it up, the corrector plate had snail trails all over it!!

Lookinging forward to hearing your C8 performs next time out.

[MarsG76]

7 minutes ago, Stu said:

Good stuff. Hope it fixes the problem. I took a somewhat sick C925 apart and cleaned it up, the corrector plate had snail trails all over it!!

Lookinging forward to hearing your C8 performs next time out.

Thanks... I'm looking forward to seeing the results....

[Astro_king]

Great post!

 

I bought a used C8 and it needs cleaning but was wondering where to start.

 

isn't alcohol meant to be bad for the corrector plate?

[Peter Drew]

7 minutes ago, Astro_king said:

Great post!

 

I bought a used C8 and it needs cleaning but was wondering where to start.

 

isn't alcohol meant to be bad for the corrector plate?

No, bad for the liver. 

[Astro_king]

1 minute ago, Peter Drew said:

No, bad for the liver. 

Why didn't you take the chance and clean the primary as well mate?

[MarsG76]

40 minutes ago, Astro_king said:

Great post!

 

I bought a used C8 and it needs cleaning but was wondering where to start.

 

isn't alcohol meant to be bad for the corrector plate?

I hope not!!!!

Than it was washed away with distilled water... 

all of lens cleaning fluids are alcohol based so I think it'll be fine.... Of course until I look at it tonight when I get back from work to collimate and test and see all sort of weird lines and cracks through it :-/

[MarsG76]

34 minutes ago, Peter Drew said:

No, bad for the liver. 

Yeah, but I find that when I add alcohol to my liver, all of the theories in make up about aliens become more and more plausible.... ;-)

 

[Stu]

Pretty sure the corrector plate coatings are quite resilient. I used slightly soapy water, Baader Wonderfluid, even saliva (!) to get the snail trails off mine, then rinsed off with distilled (actually reverse osmosis) water. It's pretty good now although there is still some residue from the snail trails which shows up when there is dew on the corrector. Goodness knows what is in that stuff! Doesn't affect the view though.

Because mine was a bit of a recovery job I had to be a little more thorough than would normally be the case.

[MarsG76]

34 minutes ago, Astro_king said:

Why didn't you take the chance and clean the primary as well mate?

The primary was spotless... absolutely perfect, and didn't need a clean...

If you're going to attempt to clean your C8, the corrector plate is easy enough, use distilled water and as pure isopropyl to do it (98% or better... 100% is available and cheap enough) this way you might even not need to touch the glass... when I cleaned the front of the corrector after re-installing, I sprayed the distilled water on it, literally drenched the glass in it (while the scope was pointing 30ish degrees down for the run off) than sprayed with alcohol, than washed it all off with distilled water again... when dried, it dried clean, no streaks or spots... as in the pic, touchless cleaning. 

The primary on the other hand is different... apparently it doesn't have much of a coating on it and is easily damaged, not as rugged as, for example, the mirror in a dob. This is where alcohol might not be a good idea and generally people use detergent, than wash it with distilled water. Personally I would first use nothing but distilled water, spray the heck out of it than wait for it to dry and see the result.... I'd avoid touching it...

If I'm wrong about it's delicateness, someone please correct me, I'd love to be corrected and not worry too much when and if the time come to clean it.... but as it stands now, my primary was clean.

SCTs being closed up, internal cleaning should never (or very rarely) be necessary if taken care of... I read a post by someone in Cloudy Nights, who tried to blow a few specks of dust from the inside of his corrector with some kind of an air compressor, totally filthying up his corrector and mirror with more particles that were blown inside the OTA... I bet the words that came out of his mouth were quite descriptive of the circumstance.... BUT if one doesn't do something like that, a internal won't be necessary.

 

[MarsG76]

9 minutes ago, Stu said:

Pretty sure the corrector plate coatings are quite resilient. I used slightly soapy water, Baader Wonderfluid, even saliva (!) to get the snail trails off mine, then rinsed off with distilled (actually reverse osmosis) water. It's pretty good now although there is still some residue from the snail trails which shows up when there is dew on the corrector. Goodness knows what is in that stuff! Doesn't affect the view though.

Because mine was a bit of a recovery job I had to be a little more thorough than would normally be the case.

Snail slime might be very slightly acidic, and depending on for how long you glass had it on there, it might have started to react with the coatings??? I'm only guessing but that would explain to why you can still make out where the slime was after a thorough clean...

[Astro_king]

6 minutes ago, MarsG76 said:

The primary was spotless... absolutely perfect, and didn't need a clean...

If you're going to attempt to clean your C8, the corrector plate is easy enough, use distilled water and as pure isopropyl to do it (98% or better... 100% is available and cheap enough) this way you might even not need to touch the glass... when I cleaned the front of the corrector after re-installing, I sprayed the distilled water on it, literally drenched the glass in it (while the scope was pointing 30ish degrees down for the run off) than sprayed with alcohol, than washed it all off with distilled water again... when dried, it dried clean, no streaks or spots... as in the pic, touchless cleaning. 

The primary on the other hand is different... apparently it doesn't have much of a coating on it and is easily damaged, not as rugged as, for example, the mirror in a dob. This is where alcohol might not be a good idea and generally people use detergent, than wash it with distilled water. Personally I would first use nothing but distilled water, spray the heck out of it than wait for it to dry and see the result.... I'd avoid touching it...

If I'm wrong about it's delicateness, someone please correct me, I'd love to be corrected and not worry too much when and if the time come to clean it.... but as it stands now, my primary was clean.

SCTs being closed up, internal cleaning should never (or very rarely) be necessary if taken care of... I read a post by someone in Cloudy Nights, who tried to blow a few specks of dust from the inside of his corrector with some kind of an air compressor, totally filthying up his corrector and mirror with more particles that were blown inside the OTA... I bet the words that came out of his mouth were quite descriptive of the circumstance.... BUT if one doesn't do something like that, a internal won't be necessary.

 

Great Thanks for the advise.

Unfortunately, the primary has some floating dust marks on it. By floating I mean something that is lying on top and a blower might blow it easily and I was thinking about it.

This has clearly happened because the eyepiece novel was not always in closed state. 

It is not too dirty like the corrector so I might hold off to it.

 

[MarsG76]

2 minutes ago, Astro_king said:

Great Thanks for the advise.

Unfortunately, the primary has some floating dust marks on it. By floating I mean something that is lying on top and a blower might blow it easily and I was thinking about it.

This has clearly happened because the eyepiece novel was not always in closed state. 

It is not too dirty like the corrector so I might hold off to it.

 

Good idea... Do the corrector.. and if you decide to clean the mirror, avoid touching it.. blower first... 

[Stu]

The primary is definitely a different proposition to the corrector plate, much more delicate and to be cleaned with utmost care. In my experience, the primaries in sealed tube scopes like maks and SCTs generally stay in excellent condition, it is normally the correctors which get dew or sap marks on them for example.

Using a compressor is a bad idea, they often chuck out muck of some sort so a hand blower is much safer. @Astro_king I would either leave well alone (best option), or if you are going to remove the corrector, just use a hand blower to see if the dust specs move. If they don't I would just leave them, they won't affect the view in any way.

[Astro_king]

6 minutes ago, Stu said:

The primary is definitely a different proposition to the corrector plate, much more delicate and to be cleaned with utmost care. In my experience, the primaries in sealed tube scopes like maks and SCTs generally stay in excellent condition, it is normally the correctors which get dew or sap marks on them for example.

Using a compressor is a bad idea, they often chuck out muck of some sort so a hand blower is much safer. @Astro_king I would either leave well alone (best option), or if you are going to remove the corrector, just use a hand blower to see if the dust specs move. If they don't I would just leave them, they won't affect the view in any way.

Sound advise!

Thanks All

[MarsG76]

32 minutes ago, Stu said:

The primary is definitely a different proposition to the corrector plate, much more delicate and to be cleaned with utmost care. In my experience, the primaries in sealed tube scopes like maks and SCTs generally stay in excellent condition, it is normally the correctors which get dew or sap marks on them for example.

Using a compressor is a bad idea, they often chuck out muck of some sort so a hand blower is much safer. @Astro_king I would either leave well alone (best option), or if you are going to remove the corrector, just use a hand blower to see if the dust specs move. If they don't I would just leave them, they won't affect the view in any way.

Completely agree.... 

 

[MarsG76]

I just went through the collimation process, and even though the seeing wasn't the best I managed to get the secondary shadow centered using the dmk41 at various focus positions and it seems to be symmetrical or mirrored on either side of the focus.

That is a good sign since corrector plate mismatch sign is where the star looks collimated at one side of focus but skews on the other.

Moon views comparison with the 14" and a imaging session is in order now.

[MarsG76]

Oh, and also no Laptop issues so far...

I connected the 7D to APT and the DMK21 to setup for my next image... a nice little Galaxy near M74 that doesn't seem to be on any of my star maps or software except StarmapPro. 

After playing with it and the OAG trying to find a guide star for about a hour, there were no problems with the laptop... hopefully none will materialize.

I didn't find a guide star at F10 do next time I'll attempt it again at F6.3. But the next target has been chosen.

The plan is to run it through a couple of nights using my unmodded 7D, say 10 min subs, than a few nights capturing the Galaxy using the modded 40D to catch some of the HII...

[MarsG76]

UPDATE:

Last night/this morning (1am) when I got back from work, I noticed that the sky was clear, dark and stable, so I had to do another test on the corrector plate/collimation....

Good news is that the mirror collimated perfectly, perfect concentric circle in and out of the focus, and when in focus, the star was crisp, stable and beautiful, with slight movement on the edges when magnified 10X in the DSLR live view... the star I was using to collimate was Canopus via Canon 7D.

Now for the BAD NEWS... I don't want to but I have to take the corrector off AGAIN. I noticed that after collimating on Canopus and slewing the scope to the north to set up for imaging of NGC1055, I LOST COLLIMATION!!! On further investigation I noticed that the secondary mirror is loose and moves, so I have to get to the inside of the corrector again, but this time to tighten the secondary mirror housing....