34 replies to this topic

[Jon Isaacs]

I recently rejoined the ranks of the Classic Telescope owner in earnest.  A Craigslist add for a 60mm F/15 for $50 and my wife wanting to go for a drive resulted in this 60mm F/15 Carton.  It's in reasonable shape, everything seems to work. It only came with straight through porro prism and one eyepiece but the draw tube seems to standard 36.4 mm Vixen and I found a visual back so everything was under control.  

 

 

 

 

I was able to get first light the first night. It was inconclusive, just a quick look.   The objective looked like it might have a mold issue between the lenses, it was certainly quite dirty and looked like there could be mold. I was able to get the objective apart with the aid of strap wrenches and some hot water under the kitchen sink spout. It actually cleaned up quite nicely so that was good.

 

When I disassembled it, two of the spacers stuck to one element, the third spacer to the other. This at least served as alignment marks so I knew which side was which and how they had been aligned.  

 

The issue:  Astigmatism  There's classic astigmatism, best focus is a cross rather than a point and passing through focus the image is a line that rotates 90 degrees. 

 

It didn't look like the lens had been disassembled so I am in a holding mode while I think about possibilities. It's possible the one lens is tilted somehow due to the spacer, it came off and was positioned again where it had been. 

 

Any thoughts would be appreciated.  I may try rotating the elements but I am not hopeful.

 

Jon 

 

 

[eyeoftexas]

Best of luck.  It looks nice.

[davidc135]

I suppose you might try varying the thickness of one of the three spacers to see if there is an effect. Similarly, the tilt of the whole objective. Also check if the objective isn't being supported only across one diameter and whether the retaining ring is too tight (but I know you know this). I doubt if it's the cause but the objective should be supported at three points corresponding to the spacers.

 

Probably those checks will draw a blank and so it could be that one or both of the objective lenses are faulty. The crown could be rotated relative to the flint. If nothing changes then it's likely the flint. If it gets worse or improves both lenses have a problem. If it is in either the crown or flint the air-space could be annulled with oil to show which surface is bad; just for interest's sake. 

 

For completeness there's always the diagonal and the eye at low power.  David

Edited by davidc135, 21 November 2020 - 02:37 PM.

[PawPaw]

Jon..........Very nice Carton and it looks complete.  Here is a very informative thread on Vintage Lens and spacers etc:

 

https://www.cloudyni...?hl=lens spacer

 

Show us a picture of the lens.

 

All the best

 

Don

[MisterDan]

Hi, Jon.

 

My Carton has the same issue.  While I have not confirmed via trial and error, I suspect axial tilt may be the primary problem.

 

David's notes are valid, of course.  I tried the element-rotation scheme years ago, but no clear results were seen - granted, it was a very tedious process, so if you do try it, you may wish to seriously consider a makeshift optical bench, rather than chugging through the removal-rotation-reinstallation method I tried with the objective and cell.

 

Another thing to check for is axial tilt - in either the objective or the focuser (or both).  A quick "eyeball" method will catch significant misalignments.  Mount the scope in a manner which allows for a long line of sight towards the front end of the objective (say, in your yard).  Using the clear aperture, the dew shield's edge and the focuser drawtube at the other end, your line of sight (perhaps 30-40 feet) should reveal any significant tilt, if it's there.  A similar check via line of sight towards the focuser can help confirm.  If you remove the visual back, the shiny chrome edge of the drawtube provides a nice annulus "target."

 

Sometimes, one end (or maybe both ends) of the optical tube is simply not-quite-square.  If you do find axial tilt, you may try a simple rotation of the focuser 120 degrees (to the "next screw hole") to see if tilt is lessened or worsened.  If there's no improvement via focuser rotation in either direction (clock- or counterclockwise), then trial-and-error shimming of the objective (ugh...shudder) would be my next (and hopefully final) check.  In this case, work will likely need to be done while the o.t.a. is assembled.  Make your shim/tilt adjustments at either end of the "astigmatic oval's" major axis.

 

I sincerely hope it's nothing more complicated than a simple case of focuser tilt.  Even in an f/15 refractor, it can be easy to "find" and see through simple visual alignment over a long-enough sight line.

 

Let me know if I can clarify any of my babble.

Best wishes and luck.

Dan

[Kasmos]

Checking the objective for centered Newton rings should give you an idea if the lenses are equally spaced. Even when they are a little off, the images should be decent. That said, you may have another problem all together.

 

On one objective I have, I had to take it in and out of the cell many times to get it to work well and I never found out why most of the times it performed poorly (lots of CA and soft focus). I inspected and retraced every aspect of the lens and cell and it's fit on the tube. Once it went back to working very well, I've left it alone, but now I'm afraid of ever taking it apart again.

Edited by Kasmos, 21 November 2020 - 07:48 PM.

[MisterDan]

I should have thought of this before:

 

Ensure the scope is solidly mounted, and loosen the objective cell (from the tube) by about a half turn.  Mark a "baseline"  with two small strips of masking tape.

 

Now, view a distant "point" source and defocus to induce a few-to-several wavelengths of astigmatism (you don't need a true point source, so long as it's "point" enough and distant enough).  Note the orientation of its major axis (ala, "2 o'clock/8 o'clock").

 

Rotate the entire cell a quarter turn (mark your stopping point) and check the orientation of the astigmatic major axis, again.  Did the axis rotate within the eyepiece view?  Did the major axis elongate? shrink?  Was there no apparent change, whatsoever?

 

Rotate the cell back to its "starting point" and make sure your defocus and original "o'clock" orientation are re-established.  Now rotate the cell a quarter turn in the other direction and check your new results (i.e. astigmatism axis rotation, extent, et.al).

 

If there's no change in the orientation of the astigmatic pattern, then the objective's alignment and the elements' relative orientations are almost certainly fine.  What's left is to check the focuser.

 

All of this can be done during daytime.

 

Best wishes.

Dan

Edited by MisterDan, 21 November 2020 - 07:26 PM.

[Jon Isaacs]

Dan:

 

I checked the alignment with my Howie Glatter laser collimator, it was dead on, right in the center.

 

I disassembled the lens cell, did a final cleaning and carefully assembled it. I'm going to give a try to night.. if it's still astigmatic, I'll probably put it on the back burner for a while.

 

Thanks for your help and encouragement.

 

Jon

[Pete W]

Jon, another thing to check are the tube baffles.  I’ve had one tilt crimping the light cone.  

Edited by Pete W, 21 November 2020 - 09:03 PM.

[Jon Isaacs]

An quick update:

 

It was clear enough last night to do some testing.  There's plenty of astigmatism to go around, whoever wants some, there is plenty.  It clearly focuses to a relatively large cross, worst I have even seen. 

 

I did try rotating the front element, no change in the amount of astigmatism.  Very disappointing.  

 

At this point, I am not sure what to do.  I may try to find a good objective for it or I may try to find someone who wants it.  For me, a 60mm refractor like this is for some casual fun, an easy scope that just performs.  I have already paid for Chucks 60mm x 800 mm Asahi-Pentax which is a known top performer.  

 

Jon

[MisterDan]

I'm sorry to hear that, Jon.

 

I suspect I'll be in the same boat, once I re-test and evaluate my own C.O.C.  I expect to find that the focuser is aligned and fine, and I expect no change in the aberration's major axis (beyond orientation) when rotating the cell.  If, indeed, that's where I end up, I will likely start from scratch and check the spacers for wedge and the cell "seat" for obliquity.

 

If it's objective tilt, I will find it and cure it.

 

If it's "in the glass," I'll try one or two systematic intra-element rotations and check for changes.  (If I get to this point, I don't expect a cure.)

 

If, after all that, I look down and see the same darn boat, I'll curse a few times and try for a replacement objective.

 

Cheers and best wishes.

Dan  

[memento]

Hello Jon, sorry to hear that your long 60mm refractor is underperforming like that.

 

 

My Dai-Ichi Kogaku 60/910's lens cell is visibly tilted when mounted to the scope. I would say that if you follow the center line of the dew shield (which is in line with the lens itself) until the rear of the tube where the focuser sits, that dew shield / lens cell's center line will be maybe 5 centimetres off! Now that I know what to look for, I can see that tilt of the lens cell / dew shield actually just by looking at the scope.

 

Nonetheless I don't see any significant problem in a star test. It focuses to a nice airy pattern. Surely there are better 60mm scopes out there but my scope's optics are absolutely good and don't show any visible astigmatism as you describe. Maybe your lens does have a problem in the spacers? Or the lens cell is too tight or something like that?

 

Thomas

[Kasmos]

You really don't hear about bad Cartons, but I suppose every brand has sold a few dogs.

[clamchip]

Astigmatism is a interesting aberration.

I witnessed it once when I mounted a 4 inch Brandon lens in a piece of PVC tube.

I didn't have the lens square with the optical axis. My fault, trying to cut corners.

Try unscrewing the lens cell 90 deg and see if the aberration follows.

If it does there's something wrong with the objective and or it's cell.

If it doesn't then it's after the objective lens.

Of course I'm sure you are not using a star diagonal during this evaluation.

 

Robert 

[Jon Isaacs]

An update:

 

I decided to try to find a replacement objective because the one I had is clearly astigmatic.  I contacted Sheldon, he didn't have one.  There was one on Astromart and it seemed like I had a deal going but somehow the seller dropped our conversation and did not reply to a couple of my Emails.  Oh well.. 

 

Then along comes a Christmas Miracle.  I get an PM from Tony Spina.  In the process of looking for his Christmas lights, he found a 60mm F/15 objective.  

 

"Did I want it?"

 

For sure... 

 

It arrived a couple of days ago. It was beautifully wrapped, perfectly clean, a real beauty.  I was still concerned it might not fit.. 

 

I broke out All About Telescopes and looked up the element order to make sure I installed it correctly on my first try.  I got a fresh pair of gloves and removed the old objective.  To install the new one, I placed the cell on the kitchen table and then put a pill container with a Kimwipe on it, set the objective on Kimwipe and raised the objective.  

 

It slid right in, a perfect fit, the retainer was just wright, almost flush but maybe a millimeter or so left.  

 

It was cloudy, of course.. But I woke up about midnight, I could see Arcturus rising in the east.  I could see Algieba, wow, a double.. 

There I was in my PJs in the backyard, a nice split of Algieba and no astigmatism..

 

It was clearing, still lots of clouds but enough sucker holes to do some observing.  I was using my Paradigms and I was getting some good views.  Even the Pleiades nearly fit in the field  I had forgotten just how special a small long focal length refractor can be.  The Orion nebula was surprisingly bright considering I was observing from my urban backyard.  

 

That view of Orion reminded me of my first view of Orion.. I was out on the Arizona desert early one fall morning with a 60 mm long focal length refractor I had resurrected, $5 at a garage sale, one two element eyepiece, no finder, a mount so broken the scope was lashed to a $5 garage sale photo tripod.  Somehow I stumbled on Orion.. I didn't know what I was seeing but whatever it was, I knew I had to see more, I was hooked.  

 

This Carton is a far better scope than that and I was a far better observer.. That first view was a tiny glimpse, this view was a testament to how far I can come, the trapezium and real structure.. and from my backyard with the moon up.  

 

I reflect back on the night more than 30 years ago.  I had no ideas or goals.. I just wanted to go out there and see what there was to see.  That bit of nebulosity had a magic that has never subsided, that's about what I am doing these days.  Just going out there to see what I can see, hoping to see a bit of fuzzy something magical.

 

Jon

[tony_spina]

Jon,

I'm glad the transplant operation worked. The objective is now in use again and collecting photons that will be turned into new memories and enjoyment 

 

I too started with a 60mm refractor,  from the sounds of it mine was in better shape tripod wise so at least I didn't have those struggles. Like you I pointed at various objects and saw wonderful stuff for the first time

 

Fast forward a few decades and despite all the other bigger and better scopes that I have, I still get a kick in using my 60mm refractors.   I admire the simplicity, and I can truly appreciate what I'm seeing.  All the years of observing has taught me to really see and not just look. I'm constantly amazed at what I can see with a 60mm telescope 

 

If only I had this ability and knowledge back when I first looked up with my 60mm refractor 

Edited by tony_spina, 11 December 2020 - 12:30 AM.

[Senex Bibax]

Just rediscovered this thread. It sounds very similar to a problem I am trying to resolve in my old Polaroscope. In my case, the scope is also 60mm x 910mm f/15, with the cover on the focuser stamped "C.O.C", the objective is marked "Yamatar". I am using a Vixen 1.25" adapter, and I have not been able to achieve a satisfactory view at any magnification. The focus is soft, and I cannot resolve Jupiter, for example to a clean round image. On examining the objective, i noticed that the elements had rotated a few degrees from the original location of the spacers, apparently because the retaining ring was loose. The elements separated easily, and I cleaned them and reassembled the objective with the proper alignment of the elements, but there is little change in the image quality.

 

I will check the alignment of the objective and focuser with respect to the OTA next, and try rotating the focuser 120 degrees in the tube to see if there is any change.

 

It is rather disappointing, I have had much better viewing experiences from Towa and Tanzutsu 60 mm scopes, but hopefully there will be a straightforward cause and resolution.

[Kasmos]

Just rediscovered this thread. It sounds very similar to a problem I am trying to resolve in my old Polaroscope. In my case, the scope is also 60mm x 910mm f/15, with the cover on the focuser stamped "C.O.C", the objective is marked "Yamatar". I am using a Vixen 1.25" adapter, and I have not been able to achieve a satisfactory view at any magnification. The focus is soft, and I cannot resolve Jupiter, for example to a clean round image. On examining the objective, i noticed that the elements had rotated a few degrees from the original location of the spacers, apparently because the retaining ring was loose. The elements separated easily, and I cleaned them and reassembled the objective with the proper alignment of the elements, but there is little change in the image quality.

 

I will check the alignment of the objective and focuser with respect to the OTA next, and try rotating the focuser 120 degrees in the tube to see if there is any change.

 

It is rather disappointing, I have had much better viewing experiences from Towa and Tanzutsu 60 mm scopes, but hopefully there will be a straightforward cause and resolution.

I had a problem with a Swift that needed new spacers and it turned out I had flopped the crown when putting back together. In my haste to check it, I accidentally did it again!. Since some load from the back and others from the front you can get a little confused when reassembling them. Also, rotating one element in regard to the other should not make a big difference.

[Bonco2]

Jon, Glad you found a solution. Too bad tho it seems Sheldon doesn't have objective lenses like he did a few years ago. I think I bought his last two 80mm f/15 Carton lenses. I too have had some recent great moments with my 60mm f/15. Took me back to the 50's to when I first discovered M42, open clusters, Jupiter and Saturn. I remain impressed with what these small scopes can do.

Bill 

[Terra Nova]

Jon, Glad you found a solution. Too bad tho it seems Sheldon doesn't have objective lenses like he did a few years ago. I think I bought his last two 80mm f/15 Carton lenses. I too have had some recent great moments with my 60mm f/15. Took me back to the 50's to when I first discovered M42, open clusters, Jupiter and Saturn. I remain impressed with what these small scopes can do.

Bill 

I have a 60mm x1000mm Carton objective that I dropped in an RAO tube that had a damaged lens. It gives super sharp images.

[Tenacious]

Jon, Glad you found a solution. Too bad tho it seems Sheldon doesn't have objective lenses like he did a few years ago. I think I bought his last two 80mm f/15 Carton lenses. I too have had some recent great moments with my 60mm f/15. Took me back to the 50's to when I first discovered M42, open clusters, Jupiter and Saturn. I remain impressed with what these small scopes can do.

Bill 

 

I may be the lucky one who bought Sheldon's last Carton 60mm x 1000mm objective a few years ago......

[eric_zeiner]

I have one of Sheldon's 60/1000 objective's as well and it is a winner.  I had also bought the cell and tube from him and that scope was my first foray into ATM.  This is one scope I will never part with.

 

As for you Jon, I am happy to hear that your problem is fixed.  To me 60 mm scopes rule and the long ones are especially good.

[Senex Bibax]

I had a problem with a Swift that needed new spacers and it turned out I had flopped the crown when putting back together. In my haste to check it, I accidentally did it again!. Since some load from the back and others from the front you can get a little confused when reassembling them. Also, rotating one element in regard to the other should not make a big difference.

Pulled it apart again yesterday, I backed off the retaining ring a touch. I was worried before because it rattled noticeably an I might have over-tightened it. Now it makes the barest sound when shaken lightly. I also re-shimmed the draw tube in the focuser and everything looks straight.

 

There are two baffles in the OTA and two more in the draw tube. Should I remove any of them if using a 1.25" visual back adapter - if I flock or blacken the interior?

[Tenacious]

 

This illustration has been around for a while.  I wish I knew who made it so I could credit their work when referring to it.  I think it is someone on CL.

 

@ Senex Bibax

 

In my limited experience, flipping the crown makes an enormous difference in the image quality (Wrong orientation produces a very soft image.  See image #2.) and yet it is so easy to do because it is often hard for the eye to distinguish one curve from the other while cleaning.  On the other hand, it is easy enough to try the other way, like image #1, and see if the image improves.

 

Baffles are a tough call.  You could make a full-scale drawing of the light path with real-world measurements of the baffle locations and with the draw tube at the focused position.  This should give you an indication if the baffles are cutting into the light path. 

[Kasmos]

AchromaticLens.jpg

 

This illustration has been around for a while.  I wish I knew who made it so I could credit their work when referring to it.  I think it is someone on CL.

 

Badback is the member that made it  He was always finding interesting scopes but he doesn't post much anymore