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Meade 152ED: How to access interior?

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#1 ccwemyss

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Posted 15 September 2021 - 02:17 PM

Meade APO - 3.jpeg

 

What is the best way to access the interior of a Meade 152ED APO EMC refractor? I'm interested in repainting the baffles, which I believe are just held in by friction. The contrast of my other 6" was significantly improved with that treatment, and this one doesn't come up to that level.

 

Given the lens centering and collimation issues inherent in the model (this one doesn't have any, and I'd like to keep it that way), I'm reluctant to try anything with the objective cell. It's not clear to me how the rear cell comes off -- there is one screw near the bottom, and two screws for the finder bracket, which are not positioned in an even pattern that I would expect for serving the purpose. I also know that Meade liked to glue things in place. 

 

So I'm hoping that someone here has already figured out how to get inside and can offer their advice (I've read posts about repositioning the baffles after they've slipped, but didn't see anything about how it was done). 

 

Thanks,

 

Chip W. 


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#2 junomike

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Posted 15 September 2021 - 02:52 PM

Gonna be tough to access the baffles with the lens cell still installed (but possible I guess).

The Focuser removes via three screw attached to the visual back


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#3 dron2015

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Posted 15 September 2021 - 03:18 PM

Chip,

 

I would advise to have a look at the article "adventures in refractor collimation". It is quite a good skill for any refractor owner to check if the objective and focuser collimated and if not good - to collimate them. Obviously, one will need some extra equipment - collimation mask (about 50 USD), laser (prices vary depending on Howie Glatter Laser or some others) and perhaps a collimation EP (I am using takahashi collimating scope).

 

However, here might be some peculiarities with Meade 152 - I am not aware of. My apologies if this piece of advice is completely out of the context if Meade is a way different.

 

I have no fear at all removing focuser and the objective and to recollimate everything back. I have LSOZ 152F8 - its objective has push and pull bolts. Initially focuser flange was glued - so it was not easy to reach baffles. I changed the focuser, but still.... baffles are also glued to the best of my understanding in my case. not just by friction.

 

why do you want to repaint the baffles? due to mold?

 

Best,

Andrey



#4 ngc7319_20

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Posted 15 September 2021 - 03:31 PM

 

Given the lens centering and collimation issues inherent in the model (this one doesn't have any, and I'd like to keep it that way), I'm reluctant to try anything with the objective cell. It's not clear to me how the rear cell comes off -- there is one screw near the bottom, and two screws for the finder bracket, which are not positioned in an even pattern that I would expect for serving the purpose. I also know that Meade liked to glue things in place. 

 

Given the collimation is OK as you say, I'd be super-tempted to leave well enough alone.

 

Why do you suspect the baffles need painting?  What do you see at the eyepiece end that indicates a problem?


Edited by ngc7319_20, Yesterday, 09:33 AM.

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#5 ccwemyss

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Posted 15 September 2021 - 04:11 PM

Chip,

 

I would advise to have a look at the article "adventures in refractor collimation". It is quite a good skill for any refractor owner to check if the objective and focuser collimated and if not good - to collimate them. Obviously, one will need some extra equipment - collimation mask (about 50 USD), laser (prices vary depending on Howie Glatter Laser or some others) and perhaps a collimation EP (I am using takahashi collimating scope).

 

However, here might be some peculiarities with Meade 152 - I am not aware of. My apologies if this piece of advice is completely out of the context if Meade is a way different.

 

I have no fear at all removing focuser and the objective and to recollimate everything back. I have LSOZ 152F8 - its objective has push and pull bolts. Initially focuser flange was glued - so it was not easy to reach baffles. I changed the focuser, but still.... baffles are also glued to the best of my understanding in my case. not just by friction.

 

why do you want to repaint the baffles? due to mold?

 

Best,

Andrey

I've collimated at least a dozen achromatic doublet scopes in just the last few years. They don't bother me in the least. But the Meade EDs are known for needing extremely precise centering of the two elements, due to the high curvatures they used. Later versions had a modified cell with three set-screws for adjusting centering. Mine is very early, and lacks those, but it is still perfectly centered (and collimated). So, unless there is some secret way to remove the cell without disturbing the centering, I prefer to leave it in place.

 

I've also built my own baffle sets for several refractors, so I'm familiar with the geometry of the reflections that they are meant to stop. The main goal is to eliminate reflections from the interior of the tube. But also important is that they be very dark so that they are not sending light back up the tube, where it can reflect from the objective.

 

When I look down the objective end, the baffle paint is not very dark (more of a dark gray than black), and it is thin in places so that the aluminum reflects as bright spots.

 

The baffles are just held by tabs that are pressing out agains the tube, and are known to slip out of place sometimes. So my hope is that there is an easy way to remove the entire rear cell, which would allow me to slide them out, paint them, and slide them back in. 

 

I know that the focuser comes off of the rear cell. But that doesn't create an opening large enough to remove the baffles. Although it would probably be enough access to straighten or reposition them if they slip.

 

I'm hoping that someone here, who has dealt with the peculiarities of the old Meade APOs, can share their experience.

 

Chip W. 


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#6 HARRISON SCOPES

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Posted 15 September 2021 - 04:47 PM

Just remove the push pull screws on the cell and remove the outer cell with lens noting rotation and check with a Cheshire after reinstallation (normal refractor collimation).
From memory once off the countercell is held to the tube with three black screws outside and three black nuts in the tube. Then you have full access, none of the above will risk the lens centering

Edited by HARRISON SCOPES, 15 September 2021 - 04:50 PM.


#7 ccwemyss

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Posted 15 September 2021 - 05:49 PM

Have you done this specifically on a Mead 152ED? There is only one exterior screw on the outer cell, on the bottom. 

 

Chip W. 



#8 CHASLX200

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Posted 15 September 2021 - 05:59 PM

I never heard of the 6's having a problem with holding center. Seems it was just the 7" like mine.



#9 Sol Robbins

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Posted 15 September 2021 - 06:19 PM

Other than what was said about removing the lens cell in post #6,

 

I'm posting this link to KerryR's post. Its a simple DYI improvement when using a Cheshire for greater accuracy.

 

You can first use a Chershire sight tube with cross hairs for centering the focuser on the objective in the usual way.Then you can use a regular, without crosshairs, type of Cheshire that can show a bright reflection using KerryR's method described in the link below. You'll achieve very good alignment after you're finished with darkening the inside of the OTA.

 

https://www.cloudyni...limation-trick/

 

Best,


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#10 ccwemyss

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Posted 15 September 2021 - 10:18 PM

I did find a thread about a 178ED that needed to be disassembled:

 

https://www.cloudyni...iewfirst-light/

 

Unlike the 152ED's single screw, it does have 3 screws holding the outer cell to the tube. So the 152 may have something else, like glue, holding it in place.

 

And it talks about how removing the rear cell involves taking off the focuser, removing the handles by unbolting them from the inside, and then heating up the glue and beating it off with a wood block. So that doesn't seem like a good route to attempt. 

 

I also found another thread about a 178ED focuser that wouldn't come off. Unlike the later ones that have three screws, it's glued on. Mine also lacks the three screws, and is from the same year (1992). The advice for replacing it with a Moonlight was to heat it up and bash it with a rubber mallet, but there wasn't any followup as to whether that worked. 

 

I may be stuck with the shiny baffles, and hoping that they don't move. That's not going to make it any less usable for students in my classes. I was just wanting to see if there was an easy way to get at them, as I'm a compulsive tinkerer for making improvements. 

 

Chip W. 


Edited by ccwemyss, 15 September 2021 - 10:53 PM.


#11 CHASLX200

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Posted Yesterday, 05:45 AM

I did find a thread about a 178ED that needed to be disassembled:

 

https://www.cloudyni...iewfirst-light/

 

Unlike the 152ED's single screw, it does have 3 screws holding the outer cell to the tube. So the 152 may have something else, like glue, holding it in place.

 

And it talks about how removing the rear cell involves taking off the focuser, removing the handles by unbolting them from the inside, and then heating up the glue and beating it off with a wood block. So that doesn't seem like a good route to attempt. 

 

I also found another thread about a 178ED focuser that wouldn't come off. Unlike the later ones that have three screws, it's glued on. Mine also lacks the three screws, and is from the same year (1992). The advice for replacing it with a Moonlight was to heat it up and bash it with a rubber mallet, but there wasn't any followup as to whether that worked. 

 

I may be stuck with the shiny baffles, and hoping that they don't move. That's not going to make it any less usable for students in my classes. I was just wanting to see if there was an easy way to get at them, as I'm a compulsive tinkerer for making improvements. 

 

Chip W. 

I don't remember  Meade making these ED scopes in 1992.



#12 ccwemyss

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Posted Yesterday, 04:21 PM

The inspection sticker, on the inside of the lens cover, is dated 9/29/92. The manual states that they began development of it in early 1991. And here is a thread with a picture of the cover of a 1992 catalog with a 102ED.

 

https://www.cloudyni...og#entry8803436

 

So it was probably introduced that year, and likely had some unique "features" that were ironed out later in production. What were the odds that both of my 6" refractors would be among the first ones of their series? 

 

Chip W. 



#13 CHASLX200

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Posted Yesterday, 06:18 PM

The inspection sticker, on the inside of the lens cover, is dated 9/29/92. The manual states that they began development of it in early 1991. And here is a thread with a picture of the cover of a 1992 catalog with a 102ED.

 

https://www.cloudyni...og#entry8803436

 

So it was probably introduced that year, and likely had some unique "features" that were ironed out later in production. What were the odds that both of my 6" refractors would be among the first ones of their series? 

 

Chip W. 

I was thinking 1997 for the 7" i had. I know they could never get it right after 3 trys.  I was thinking the LX200 came out around 1993 and then the ED's in the later 90's



#14 ccwemyss

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Posted Yesterday, 08:38 PM

Meade's corporate page says the LX200 was introduced in 1992. I've been in touch with someone who has a 1992 catalog, and they said it has multiple pages describing the ED refractors and a comparison page. One history of the company says that when Diebel bought the company back in 1991 it had no new products in development, and he and his partners invested over $2M in R&D to jumpstart new products with improved quality control for 1992 introduction. 

 

I've read several horror stories about the 178. One reviewer sent it back five times before it was right (and noted that the last objective had different coatings than the original). Another sent it to an optical systems machinist to rework the cell. Other people seem to have gotten lucky, but even then, some let them go because of the size.

 

I'm hoping that HARRISON_SCOPES will jump back in and confirm, from experience, that the inner cell of the early 152, which has a different counter cell than he described, will come out without affecting the centering. I've seen a post elsewhere from him that's he's done it while making the centering screw mod on the version of the 178 that has the three-screw counter cell. 

 

Chip W. 



#15 teashea

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Posted Yesterday, 09:12 PM

Unless the baffle problem is substantial, you might be better off leaving it alone.



#16 HARRISON SCOPES

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Posted Today, 01:40 AM

Once you remove the the main cell via the normal collimation screws you can then remove the countercell from the tube. The lens cell tself is then at no risk, a threaded ring (glued to) holds the doublet within the cell and does not need touching.
There is a chance yours could be different as in the countercell glued on to as they did change build a bit on these but it should still be fairly straightforward to disassemble.

Edited by HARRISON SCOPES, Today, 01:44 AM.


#17 CHASLX200

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Posted Today, 06:34 AM

I would never fool with a ED and collimate it.  I will stick with Newts and SCT's. 




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