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How to remove objective lens in a TMB 115 LW Apo?

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18 replies to this topic

#1 Guilherme1

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Posted 01 July 2020 - 07:19 AM

Hi,

I need to remove the lens of my OTA TMB 115 LW, #201 lens.

There is some felt gone outside of the moving dewshield back. The dewshield no more slides softly...

Its out there any person who removed the lens? Any issues? A special care needed?

A recommended procedure?

Regards.

Guilherme


Edited by Guilherme1, 01 July 2020 - 08:07 AM.


#2 HARRISON SCOPES

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Posted 01 July 2020 - 08:31 AM

Most versions simply unscrew with those

#3 drd715

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Posted 01 July 2020 - 10:05 AM

Not sure on your scope, but I had to remove the dew sheild on my APM152ED to work on the dew sheild lock pin. I unscrewed the focuser end adapter from the back end of the tube and slid the dew sheild off the back end.  Had to strap the tube down to  a padded table and use a strap wrench on the end adapter to unscrew it. Put some duct tape on the end bell to protect the surface and it helps keep the strap from slipping. 



#4 mclewis1

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Posted 01 July 2020 - 10:30 AM

Guilherme,

 

I haven't done this on my scope but from some notes from another TM115 owner years ago ... 

 

Removing the 4 bolts around the bottom edge of the dew shield will allow most of the dew shield to slide off and is sometimes enough to repair any bits of felt but if you need to remove the bottom of the dew shield where the pressure bolt is you can push the dew shield back about another 100mm to expose the whole lens cell and you will see similar 3 allen/hex head bolts around the edge of the tube. Removing these will allow the lens cell to be lifted out, the dew shield ring to be removed and the felt repaired. Remember to mark the position of the lens cell with respect to the tube so it goes back into exactly the same position it was in.

 

This is my scope with the dew shield pushed way back to see the full lens cell and one of the attachment bolts ...

 

 

Attached Thumbnails

  • TMB with dew shield fully retracted 1.JPG


#5 Guilherme1

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Posted 02 July 2020 - 02:14 AM

Thank you very much, Harrison Scopes, drd 715 and Mclewis1. My scope has the lens #201 and has "TMB design" printed around the lens. The problem is indeed at the rear part of the dewshield, inside the rear collar were the fixing knob is placed.

The aspect of lens connection to tube is exactly the same as in the photo sent by Mclewis1. Near one of the screws I have une "small point", very circular that seems a kind of registering mark.  I have some other questions, please.

 

Is it better to operate with the tube in horizontal or vertical position?

Is the "fat" flange a simple connection between the lens cell and tube (with the lens cell simply screwed to the flange), or that flange is also a retainer of the rear (third) lens element? (beeing integral part of the cell).

Is it better to take off the set "flange+lens cell"), or first unscrew the lens from flange and, after this, take off the flange alone?

 

I hope the felt will be in good condition to glue again, with UHU glue.

Certainly I will register all rotational positions. So, as long as the lens is screwed, and setting correctly th 3 screws, the collimation will not change.

 

Thanks for all.

Regards.

Guilherme


Edited by Guilherme1, 02 July 2020 - 03:08 PM.


#6 Guilherme1

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Posted 02 July 2020 - 03:18 PM

Sorry McLewis1.

I misread your name at Cloudynights and I wrongly wrote "Mark" instead of "Mclewis1".

I trully appreciate your useful help. Could you give some more details concerning my last message?

My 115 scope is exactly as your 115. Looking to your photo, it is the same mecanical system.

Warmest regards.

 

Guilherme.



#7 mclewis1

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Posted 02 July 2020 - 09:51 PM

Guilherme,

 

You had my first name correct ... it is Mark.  wink.gif

 

I don't know the answer to your question about the flange. I believe it's all one piece when removed from the tube (and can then be unbolted from the rest of the lens cell) but since I've never had mine apart I can't say for certain. From the old comments that came from another TMB115 owner, they did not take the lens cell apart. They removed the three bolts and simply removed the whole assembly to allow the dew shield to be completely removed, new felt added, and then the whole thing re assembled. They seemed to work on the scope in the horizontal position.

 

I think for any discussion about the construction details of the lens cell itself I would talk directly to Markus at APM telescopes.



#8 Guilherme1

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Posted 03 July 2020 - 02:29 AM

Hi, Mark,
Thank you so much for tour help.
I already spoke (by email) with Markus Ludes (very kind and helpful as usual), but they have so many models and so many versions and batches, so they don't remember all situations.
One important question is to know if the mecanical connection between flange and tube end (after removing the 3 allen screws) is or not a very tight fit, making difficult the "extraction".
Warmest regards
Guilherme



#9 Kunama

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Posted 03 July 2020 - 03:50 AM

Olá,

 

Here is an image from APM which is the 115 LZOS objective cell that is collimatable  with push pull screws, is this like yours?

Attached Thumbnails

  • LZOS115CL.jpg

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#10 mclewis1

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Posted 03 July 2020 - 09:02 AM

Thanks Matt,

 

And that picture exactly illustrates Guilherme's questions to me. From my old notes the 3 bolts spaced radially around the top edge of the tube are affixed to something positioned below that flange and is holding the lens cell in place. That something isn't shown in the picture above and none of us really want to experiment with the lens cell given how valuable our scopes are. 



#11 Guilherme1

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Posted 03 July 2020 - 09:48 AM

I, Matt,

 

Thank you very much for your help and image.

However, my cell is not like the one shown in the picture you attached. My cell  is not collimatable.

 

The version you sent, has 6 holes in the plate (three sets of two holes) for push pull collimation screws (it belongs may be, to the heavier versions, weighting more than 10 kg, not the LW version).

 

My version do not has that screws. And it must have attached a sort of tube of thick walls, for the left (refering to your picture), and that extension needs to have three threaded holes, to accept the screws fixing it to the end of white tube to the flange.

 

Please see attached a image close up ot the interface cell-flange screws in my OTA (#201 lens). Very curious, near one of the screws (please see attached picture) there is a very small and round point that seems to be a register mark for some kind of reference, or it seems...

 

I dont know if the part of the flange inside the white tube(after removing the 3 screws) is a very tight fit or not.  Has someone experienced that?

 

May be in this excellent Forum we can have a large number of TMB 115 LW owners. And some of them could have the same problem of the felt of the sliding dewshield going outside of its place at the rear of the dewshield, increasing strongly the friction when we want to slide the dewshield back (to put the OTA in its case), or move it front (to begin an observing night)...

 

I dont know if I can use the same velvet (or felt) reglueing it with UHU tube glue.

 

 

Regards

Guilherme

TMB 115 LW_2.jpg



#12 Guilherme1

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Posted 03 July 2020 - 10:02 AM

Hi, again,

 

By the way, is it possible for you Matt/Kunama, to show a picture of the 115 lens viewed from another angle, specially from tilted rear? That is to show that 6 holes (3x2 holes) or a female inside thread, possibly to thread that flange to the possible portion of tube placed inside the end of white tube...

 

If the large diameter "dish" shown ot  Matt picture is integral part of the cell, to accomodate the screws we see at the white tube end,  it need to have a female thread inside the "dish", And the 3 screws we see outside, may be thread in a portion of thick walled  tube teminatinr, outside, with a male thread, to thread on the suppode female trad  inside that "dish".  These are only "maybe's", because I cant see inside that piece...

Regards

Guilherme



#13 Guilherme1

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Posted 03 July 2020 - 02:27 PM

Hi,

To make ideas clearer, and to share information easily, I made a picture (a draw), presenting several hypothesis possible for the coupling objective cell with flange in the Apo TMB 115 LW (D/7), in my case with the lens #201.

As long as I do not have X-ray vision,as Superman does, I put several possible hypothesis.

Certainly someone that already gad removel the objective lens in this model can make light and explain the right mecanical and correct design.

Perhaps, if I could speak to Mark's friend, the one that had exactly the same problem as myself, that insight  could be very very useful. Is it possible?

 

Now we can see my draw.

 

Regards

Guilherme.

Attached Thumbnails

  • 20200703_173344.jpg

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#14 Kunama

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Posted 03 July 2020 - 05:28 PM

Here is my TMB-LZOS 152 cell from 2007 manufacturing... you can see the cell threads into a fixed countercell and is not collimatable, nor is there any way for it to lose its alignment.

 

my guess is your cell is similar design.... although mine has the countercell and focuser adapter attached to the baffle system.  It appears that yours should be able to be removed after taking the three screws off the tube, 

 

however, I would prefer to remove the focuser and adapter instead, leaving the optics alone.

 

 

Attached Thumbnails

  • CD1E18DD-94A2-461A-9B6C-DD9AC9D50AE3.jpeg

Edited by Kunama, 03 July 2020 - 06:15 PM.

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#15 Kunama

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Posted 03 July 2020 - 07:06 PM

Here is another picture of 115/F7 from APM, it seems that the lens cell may screw into the collimation flange.

 

 

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  • LZOS115BL (1).jpg

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#16 Guilherme1

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Posted 04 July 2020 - 06:15 AM

Thanks Kunama,

 

If your 152 mm lens cell has the same attachment as my 115, so it is my hypothesis number 2 above. However, the rear of the flange  (in my 115) cannot be flat, because it needs a "short tube" to go inside the white tube to receive the three screws...

Thaking off the dewshield from rear is problematic because the finder bracket is on the tube, not on the focuser body as yours. And the dewshield, given the problem with felt, do not slides easily and makes a lot of fricion. So, the path is shorter moving towards front.

 

May be there is a TMB 115 LW owner, having the same version and also having the same problem...

 

Kind regards.

Guilherme


Edited by Guilherme1, 04 July 2020 - 06:43 AM.


#17 Guilherme1

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Posted 06 July 2020 - 05:40 PM

The work of repairing the velvet under the back part of dew-shield, in my TMB 115LW is finished.

At first sight I wanted to glue the same (original) velvet in place using UHU glue. I did the work OK , beeing very careful indeed, but the tickness of the glue film, despite very thin, made the dewshield back ring very tight on the tube, not sliding smoothly.
I took the velvet out and put a new autoglue velvet (selfsticking velvet), as we can see in the attached photo. I don't had the original velvet, the same type Markus Ludes puts at his shop (when making the OTA tube) and I expect it would last a good time.
Now the dew shield slides similar to the original fitting, may be slightly more tight, but may be with time and use it may became softer and smoother .
I had no black velvet and I put dark brown velvet, but it is hidden behind the dewshield back ring, it is not visible and works OK.
About collimation, I checked with my excelent Picostar artificial star, at 400X, and it is perfect.
Of course I registered carefully the rotational position of the flange relative to tube.
The lens cell has a male thread that screws into the flange.
When rescrewing the cell into the flange I tightened it softly, with a small torque.

If this can be of any assistance to you, I send some images attached. This includes photos of the flange (with registering rotational mark) and the UHU glue tube, clearly not recommended to this work.
Warmest regards.
Guilherme de Almeida

Attached Thumbnails

  • Auto_glue velvet.jpg
  • 20200706_114557.jpg

Edited by Guilherme1, 07 July 2020 - 06:28 AM.

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#18 Guilherme1

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Posted 06 July 2020 - 05:52 PM

20200706_114647.jpg The original self sticking velvet has a tickness of 0.38 mm (autoglue not included)
Concerning the objective lens of TMB 115 LW Apo, the total lens cell mass is 2.218 kg and the flange mass is 0.206 kg.

Please see attached another photo of the flange. The lens cell screws from the right ot this picture. The left side connects to the tube.

If this can be of some assistance to someone,I will be happy with that.
Regards.
Guilherme

Edited by Guilherme1, 07 July 2020 - 06:30 AM.

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#19 Guilherme1

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Posted 20 July 2020 - 10:57 AM

Hi,

May be this thread can be useful to someone who also as a TMB 115LW f/7 Apochromatic triplet refractor. A very good instrument, but time do not forgives, and some materials get old...

 

Nevetheless, there is another place in that telescope that also use felt ( I'm not considering the tube rings, that also have felt but it is not critical).

I mean the draw tube that supports the focuser. Very practical indeed: we shorten the tube to put it in a case (or to use a binovewer); we pull that tube all the way out for classical observation or photography. It slides easily... on felt (or, may be, velvet). But what if that felt came out, or becames loose, with lateral play?

The focuser will have lateral play, and "good by" accurate focuser alignement...  The focuser axis perhaps no longer points at the objective lens very center. This is not very relaxing...

Happily, I have not that problem... Perhaps someone who has (or had) the same telescope model has experienced and solved that problem. I'm asking that information contribution.  If someone has replaced the felt where the rear draw tube slides, please let us know...

This experience sharing is very usefull.

 

Thanks for all.

Guilherme


Edited by Guilherme1, 21 July 2020 - 07:33 AM.

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