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Carton 60/910 and lens spacers problem

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#1 LukaszLu

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Posted 24 March 2021 - 04:31 PM

A very rare bird has just arrived ... Courtesy of Dietmar from Germany, I have just received a shipment containing the Carton 60/910 refractor. Thanks a lot Diddy! This beautiful, elegant telescope, the design of which is definitely ahead of its time, seems to be in pretty good condition. The copy comes from 1976, it is most likely the Carton 619-A model, although the manual signed by Neckermann is silent about it. I have already started cleaning, I have repaired larger paint losses on the tripod, I have cleaned the mount (although I decided not to change the greases because they still seem quite functional). The work progresses quickly and everything would be fine if it wasn't for the lens.

 

The lens was clearly disassembled. On this occasion, the spacers were damaged. One has survived, and the other two are in a rudimentary form. In such a state, it is not possible to maintain the correct distance between the lenses, perhaps they even touch each other, which is dangerous for the lens. I'll find out soon when I take it apart. I will then be faced with the question of how to recreate the spacers. This is the question I would like to ask my more experienced colleagues. How to make new spacers, so that they do not become a source of scratches on the optics or a habitat of fungi and molds? How to stick them to the surface, and maybe stick them not to the face but to the sides of the lens - even with adhesive tape?

 

Thanks in advance for any advice. Do you recognize this model? Is it 619-A?

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Edited by LukaszLu, 24 March 2021 - 04:32 PM.

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#2 LukaszLu

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Posted 24 March 2021 - 05:06 PM

A few lens pics...

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#3 Piggyback

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Posted 25 March 2021 - 02:54 AM

Nice scope with great looking Carton mount.  I can feel your pain, though. Seems you are struck by some form of bad luck, ending up with yet another 60mm problem "child". Hope you will get this one right.


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#4 LukaszLu

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Posted 25 March 2021 - 05:35 AM

This is what the fun is all about :-) I am particularly interested in restoring this optics to full functionality, because the telescope - apart from stylistic differences - seems to be almost a clone of the Kenko TA 910. If I had the opportunity to reliably assess the quality of its optics, I would also have a benchmark for optics evaluation in Kenko.



#5 davidc135

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Posted 25 March 2021 - 08:33 AM

I suppose if Newton's fringes can't be seen (as it is now) the lenses aren't touching. I would measure the spacer in good condition and replicate that thickness. Sometimes tabs of adhesive backed paper are used if the spacers are very thin. After reassembly the objective can be tested for spherical and chromatic aberration and the spacer thickness adjusted if necessary.

 

Vla Sacek in 'Telescope Optics.net' gives the recommended air space for his example of a Fraunhofer doublet as .001x f.l ie .9mm, although I'm not sure if that is a reliable guide to your scope. Maybe there is a bit of tolerance for small, slow achromats.

 

David


Edited by davidc135, 25 March 2021 - 08:42 AM.


#6 clamchip

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Posted 25 March 2021 - 10:16 AM

You can assemble the lens as best you can and slide a feeler gage in next to

the good spacer to gage it's thickness.

A preferred method will be to carefully remove the good spacer so you don't

distort or alter the thickness and measure it's thickness with a micrometer. 

Then find a material same thickness and replace all three spacers.

I've been using aluminum foil and Elmer's glue sticking the spacers on the

flint.

In the past I've used self adhesive aluminum duct tape that's pretty close

to .005" for Edmund lenses.

For the past 400 years or so postage stamps were used. Some say paper

isn't a good idea, its ability to absorb moisture, etc. but more than once I've

gone into my stamp collection for vintage lick N stick stamps to cut up and

I wet and stick on the flint and I like these for absolute originality on a few

brass scopes I've had apart. It may be the self adhesive stamps are in the

range of correct thickness.

 

Robert 



#7 DAVIDG

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Posted 25 March 2021 - 10:34 AM

 Spacer thickness is going to be between 0.003" and 0.005" for a lens of this size. For it's aperture and focal length the exact spacing is not super critical. It is not like if your off by 0.001" the image will be a fuzzy mess and full of color,  it won't. What is more critical is that the spacing between the elements is uniform in thickness. If not the elements will be wedged with respect to one and the other. This will cause lateral color at high magnification , ie  stars will turn into short spectrum being red on one side and blue on the other. Lateral color will smear out fine detail at high magnification. 

 The easiest and most precise way to check the uniformity of the air gap is to shiny monochrome or semi-monochrome light on the lens. You should see interference rings. If the air gap is uniform the rings will be round and centered.  Here is a picture of typically what you should see. I'm using my desk lamp which CFL bulb in it. The light from a CFL is semi monochrome so you the interference rings in multiple colors.

 

                   - Dave  

 

 

 

lens interference pattern CFL bulb.jpg



#8 LukaszLu

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Posted 25 March 2021 - 12:53 PM

Unfortunately, the elements that I found after dismantling the lens do not look original, so measuring their thickness may turn out to be misleading. They appear to be made of a wrapped strip of aluminum, with the end of the strip falling out in the middle of the spacer, which means that its thickness is not the same along the entire length. It is hard to imagine something like this coming from the manufacturer.

 

I removed all these residues, washed the lenses, which are waiting for ideas clean and ready for further service. I found a self-adhesive aluminum foil to seal ventilation systems. I don't know how thick it is, but it is thinner than the spacers I removed. Most likely it can be 30-50 microns, which is 0.016 inches. This is three times more than what the clamchip suggests, and still less than the thickness of the spacers that were used in this lens.

 

I had a plan to wrap the end of the foil strip once so that it does not stick directly to the lens, leaving only glue on the end that I would stick to the sides of the lens. What do you think?

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#9 clamchip

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Posted 25 March 2021 - 01:15 PM

If you don't think the spacers are correct thickness maybe a search of Carton Optical lenses here on

cloudy nights and a general search might turn up information of Carton spacer thickness.

As Dave mentioned it will probably be in the 0.003"-0.005" inch range for a lens of this size.

Sticking gluing the spacer on the lens edge is risky, if clearance is insufficient the glass may get pinched

depending on the temp.

 

Robert



#10 LukaszLu

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Posted 25 March 2021 - 03:10 PM

OK, I did the quick test because I really wanted to look at the Moon which is just visible despite the slight haze of the sky. I made spacer out of ordinary baking foil, which should be within the limits mentioned here. I taped them to the sides of the lenses.

 

A very distinct rainbow Newton ring appeared, but with a very short range - less than a quarter inch in diameter. It is off-center, but very sensitive to touch - each contact of the lenses causes it to begin to move across the surface. The same applies to pressing the retaining ring - the slightest turn means moving the center of this figure.

 

I hope the lenses do not touch despite the thickness reduction of the spacers. Does the presence of Newton's rings mean that there is a space in their center?

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#11 LukaszLu

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Posted 25 March 2021 - 03:14 PM

Ah, I forgot the most important thing - the Moon! Great! The image is great, sharp, precise, sharpness is easy to achieve without torturing the focuser knob. Very encouraging - next to it I put my unfortunate Kenko TA 910. To say that there is no comparison is like saying nothing ...



#12 clamchip

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Posted 25 March 2021 - 03:23 PM

The lens elements may be touching in the middle if you can make Newton's rings

change by touching the edge.

Aluminum foil is only .016mm .00063" inch, heavy duty foil .024mm .0009" inch, way

too thin.

Try a postage stamp and repeat tests.

 

Robert



#13 mitsos68

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Posted 25 March 2021 - 03:31 PM

http://yumarin7.saku.../Carton1971.pdf

#14 Kasmos

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Posted 25 March 2021 - 03:50 PM

I've taken a bunch of them apart and several had original foil that looked folded or layered for the correct thickness. If you can't find something, double the foil and tape it to the side or maybe just use some tape. I've taped some of the originals that hang over the side when they came off with no worries. BTW, here in the US our adhesive stamps come on a sheet with a border so one can use that without even costing you a stamp. grin.gif


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#15 LukaszLu

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Posted 25 March 2021 - 04:17 PM

The lens elements may be touching in the middle if you can make Newton's rings

change by touching the edge.

Aluminum foil is only .016mm .00063" inch, heavy duty foil .024mm .0009" inch, way

too thin.

Try a postage stamp and repeat tests.

 

Robert

This is exactly what I am afraid of, which is why I have already disassembled this lens because even if the lenses are not touching at the moment, it does not mean that they will not touch and scratch when the temperature changes. I have to work on it because what I saw on the Moon showed that it can be one of the best optically classics in my collection - it's definitely a keeper!

 

Thanks a lot. I don't speak Japanese, but my sister does - maybe she'll help :-) My model seems to be the very first in the row and it's name according to this folder i T-620...

 

I've taken a bunch of them apart and several had original foil that looked folded or layered for the correct thickness. If you can't find something, double the foil and tape it to the side or maybe just use some tape. I've taped some of the originals that hang over the side when they came off with no worries. BTW, here in the US our adhesive stamps come on a sheet with a border so one can use that without even costing you a stamp. grin.gif

In this case, the cell is quite tight and sticking the spacers to the sides of the lens is troublesome, and as the clamchip rightly points out - it can also be risky due to pressure on the lens.

With all due respect to the US Post Office, but if you tell me that these stamps are printed on fungus-resistant paper, I won't believe it ... :-)

 


Edited by LukaszLu, 25 March 2021 - 04:19 PM.


#16 davidc135

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Posted 25 March 2021 - 05:25 PM

Congratulations on the objective. As said above the lenses are centre touching if the rings move towards you when the objective is pressed at the edge. It also explains why the Newton's rings appeared off centre.  I'd try 50 microns or two thou.

 

I expect spacer thickness could be worked out by measuring the diameter of the Newton's rings, two fringes being one wave length of light. Eg minimum spacer thickness will need to be 100x number of fringes in centre 1/4in.  David


Edited by davidc135, 25 March 2021 - 05:33 PM.


#17 LukaszLu

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Posted 25 March 2021 - 05:39 PM

Thanks David! I temporarily reverted to the concept of duct tape for ventilation systems glued to the side of the lens. After smoothing this side surface of the foil with a nail, the lens entered the cell relatively easily, so it has some reserve. Netwon's ring appeared, but centrally, slightly larger, softer and slowly fading towards the edges. It is only visible under fluorescent lighting (previously it was also visible under LED lighting), so I assume this is the correct situation.

 

I did not deny myself the pleasure of putting the instrument outside again, especially as the sky cleared a lot. The image of the moon has remained very precise, sharp - just the one that invites you to look and enjoy finding details. Now I can also add that it is nicely contrasting. With the ortho Zeiss 10 mm eyepiece the chromatic aberration becomes noticeable in the case of weaker lenses. Here it remains almost invisible. The shadows of the craters do not show traces of purple or greenish discoloration. Even with off-axis viewing, the aberration does not increase in the way that it does with worse quality lenses. The diffraction rings are round after defocusing.

 

I think that's it for today, It's almost midnight in Poland. Thank you very much for all the comments and advice!


Edited by LukaszLu, 25 March 2021 - 05:43 PM.

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#18 RichA

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Posted 25 March 2021 - 07:43 PM

A few lens pics...

Got a six-inch achromat in a similar way.  I noted the orientation of the blanks, took them apart, cleaned off the adhesive residue with acetone, then replaced the spacers with new ones and put the lens back together.  This re-aligned the Newton rings so they are now centred.



#19 LukaszLu

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Posted 26 March 2021 - 05:45 AM

In my case, the lens was additionally inserted upside down, with the crown inside the tube.

 

In my opinion, the retaining ring was the source of the problems. Usually, access to it requires unscrewing the entire cell, and unscrewing the ring requires a special tool. In this case however, the ring is at the front, easily accessible and can be easily unscrewed without tools. It could therefore be unscrewed many times for no apparent reason, the lenses were probably pulled out many times, which not only damaged the spacers but also chipped the Flint edge.

 

Conclusion: don't trust your customers too much and don't give them all the keys :-)


Edited by LukaszLu, 26 March 2021 - 06:21 AM.


#20 DAVIDG

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Posted 26 March 2021 - 08:27 AM

 You said the rings only appeared in the middle  of the lens. As stated by others that indicates the centers of each lens element is very close. Having worked on hundreds of lens and made many optics that indicates to too me that the crown element is flipped. The two inner radii are close  to the same value but not the same so even without the spacers and the elements in direct contact you should see interference ring that goes completely out to the edge since the gap between them is almost uniform   With the spacers  in place the rings will  fill the area of the lens  like in my picture.  Since you said you only see rings in the middle that indicates the air gap is not uniform and much larger at the edges. 

 A lens that has front  element flipped  will still give  an image that many will say is good especial at low to medium power that is used to view the Moon, so people are fooled that the lens is assembled correctly. 

    

               - Dave 


Edited by DAVIDG, 26 March 2021 - 08:30 AM.


#21 LukaszLu

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Posted 26 March 2021 - 08:38 AM

Judging from the condition of this lens and considering its possible history, flipping the Crown element is of course possible. At the moment I folded it with the more convex surface inward, because I thought that this is how the correct design of the achro lens should look like. Perhaps this lens is just so designed that the gap is not uniform?

 

I will try to observe these rings in the evening, under fluorescent light, because you cannot see them in daylight. Maybe I can photograph them.


Edited by LukaszLu, 26 March 2021 - 08:38 AM.


#22 starman876

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Posted 26 March 2021 - 08:48 AM

I have always loved doing what is needed to get those beautiful newton rings.  Like getting a reward for doing things right.


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#23 DAVIDG

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Posted 26 March 2021 - 09:11 AM

 Here is another example of what you should see when the spacers are in the correct position, the correct surface of the crown is against the flint and the air gap is uniform in thickness.  In this picture I'm using a true monochrome light source, which is Mercury source filtered to only allow 546nm green light to be emitted.

 

               - Dave  

 

unitron lens.jpg

 


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#24 LukaszLu

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Posted 26 March 2021 - 09:17 AM

In the meantime, I finished cleaning the mount. Structural black paint was polished with Tempo car body polish.

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#25 LukaszLu

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Posted 26 March 2021 - 09:18 AM

Chrome and aluminum elements were polished with a special agent for the renovation of metal surfaces. I cleaned and replaced the grease in the focuser - now it works perfectly.

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Edited by LukaszLu, 26 March 2021 - 09:27 AM.

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