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Tasco 152x - (old Royal Astro?) 60mm Refractor- Coma?

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#1 DIYDarren

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Posted 19 July 2020 - 12:12 PM

Hey everyone- so 6 months or so ago, I snagged an old Tasco 152x Refractor, 60mm x 900mm f/15. We believe its provenance is early royal astro from the late 1950s.

 

ANYWAY, so I finally have it with me out in southern Utah, dark sky, ~5500ft. Last night I was looking at the comet, and trying my first tries looking at various stars, planets, etc. with it.

 

Basically, I feel like something is "messed up" with it (with the objective). I really couldn't get much practical magnifaction more than about 100x out of it before everything was super-soft and fuzzed out. I believe the type of errors are "Coma"-esque, as everything was kind of fuzzy and had ghosting/skewage to one side. If i had something perfectly in the middle it would get better, but still tended to be skewed.

 

I know that someone has "messed" with the objective before- it has at least one small clam chip in the edge. (Not sure if the inner or outer lens). But to me I think that would only happen from someone trying to clean it or something...?

 

Anyway, so where is the best place to start in terms of troubleshooting this? I am up for dissecting the lens as as it stands I don't think its in good working order.

 

Course I didn't check it without a diagonal in place- maybe it is related to that? Can a diagonal introduce a coma-like effect?

 

Any thoughts are appreciated, I can check this out over the next week or so weather dependent.

Thanks in advance!!!

Darren

 

 


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#2 starman876

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Posted 19 July 2020 - 12:29 PM

sounds like one of the two elements is in wrong.  Have you tried to take them out of the cell and look at the orientation of the two lenses.  Make sure you place a mark on the side of the lens before you take them apart from each other to make sure you can orient them correctly putting them back together. On the other hand there should be some marks on the lenses already indicating proper orientation.   Make sure you wear surgeons gloves to not get body oils on the lens. Would also be a good time to clean them with some rubbing alcohol if you do not have lens cleaner. Also, make sure not to disturb the spacers.   The flint (rear lens toward the focuser should be flat.  The crown lens should have a curve that fits the flint lens rather well.  Hopefully you should be able to tell which one goes where.  You can try the different positions.  Also, sometimes someone puts the lens back into the cell wrong with the flint forward and the crown towards the foucser.  Good luck.


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#3 Garyth64

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Posted 19 July 2020 - 12:35 PM

Try it  straight-thru without the diagonal.

 

Are the foil spacers in place?

 

I don't think RAO made a 60x900 lens.

 

Can you show some pics?  It will help to see what you have.  Does it have an equatorial mount or an alt-az?


Edited by Garyth64, 19 July 2020 - 12:37 PM.

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#4 Bomber Bob

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Posted 19 July 2020 - 12:48 PM

My first star tests with a refractor are always straight-through, even though all of the diagonals in my collection have been collimated.

 

I agree with the advice posted so far.  You never know what's been done to these used scopes...


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#5 DIYDarren

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Posted 19 July 2020 - 12:49 PM

Oops- a couple additions/corrections:

 

1. Garyth you are correct regarding lens config- it is 600x910. I'll put a couple pics at the end (ones I took when I first bought it, don't have it set up right now). It is equatorial.

2. I looked at the retaining ring and it definitely has been opened at least once, there is wear/scratches around the spanner slot.

3. Yes, the foil spacers are still in there.

4. I can't quite tell the orientation (without taking it apart), both the surface facing the sky and the surface facing the focuser are pretty "flat"- with the part facing the sky probably the flatter of the two. Again can't get a great look without further dissection.

5. Yup I will try without the diagonal later on tonight, just to be sure

 

Thought I had a pic of the objective cell, but I guess not. I'll add some more pics when I get a chance.

 

 

IMG 20200313 174613897
IMG 20200313 174525429
objective3
 

 


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#6 starman876

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Posted 19 July 2020 - 01:44 PM

Oops- a couple additions/corrections:

 

1. Garyth you are correct regarding lens config- it is 600x910. I'll put a couple pics at the end (ones I took when I first bought it, don't have it set up right now). It is equatorial.

2. I looked at the retaining ring and it definitely has been opened at least once, there is wear/scratches around the spanner slot.

3. Yes, the foil spacers are still in there.

4. I can't quite tell the orientation (without taking it apart), both the surface facing the sky and the surface facing the focuser are pretty "flat"- with the part facing the sky probably the flatter of the two. Again can't get a great look without further dissection.

5. Yup I will try without the diagonal later on tonight, just to be sure

 

Thought I had a pic of the objective cell, but I guess not. I'll add some more pics when I get a chance.

 

 

is it my imagination or do I see a lot of very small surface scratches.  Almost, like someone cleaned the lens a few too many times?



#7 DIYDarren

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Posted 19 July 2020 - 01:48 PM

is it my imagination or do I see a lot of very small surface scratches.  Almost, like someone cleaned the lens a few too many times?

Yeah there is some light scratching for sure, but that was a pic where I was intentionally trying to find an angle where the scratches would show... I think there's a little fungus in there too. So yeah, its definitely seem some use... but I don't think my issues are related to that. (I'm guessing)

 

Darren



#8 Terra Nova

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Posted 19 July 2020 - 04:02 PM

Hey everyone- so 6 months or so ago, I snagged an old Tasco 152x Refractor, 60mm x 900mm f/15. We believe its provenance is early royal astro from the late 1950s.

 

ANYWAY, so I finally have it with me out in southern Utah, dark sky, ~5500ft. Last night I was looking at the comet, and trying my first tries looking at various stars, planets, etc. with it.

 

Basically, I feel like something is "messed up" with it (with the objective). I really couldn't get much practical magnifaction more than about 100x out of it before everything was super-soft and fuzzed out. I believe the type of errors are "Coma"-esque, as everything was kind of fuzzy and had ghosting/skewage to one side. If i had something perfectly in the middle it would get better, but still tended to be skewed.

 

I know that someone has "messed" with the objective before- it has at least one small clam chip in the edge. (Not sure if the inner or outer lens). But to me I think that would only happen from someone trying to clean it or something...?

 

Anyway, so where is the best place to start in terms of troubleshooting this? I am up for dissecting the lens as as it stands I don't think its in good working order.

 

Course I didn't check it without a diagonal in place- maybe it is related to that? Can a diagonal introduce a coma-like effect?

 

Any thoughts are appreciated, I can check this out over the next week or so weather dependent.

Thanks in advance!!!

Darren

Well Coma only occurs in reflectors so it’s not coma per sé. And it’s not coma-like because if it were that, the distortions would be radial in all directions around the center. Since you cay It’s in one direction it could be astigmatism, but it sounds to me more like ‘wedge’- ie. the plane of the objective Is not at right angles to the walls of the cell and the axis of the tube. Since it has a chip, as you acknowledge, someone has probably messed with it and had it out and putting it back in and wedging it is a good way to get a chip at the edge. This can also produce a ghost. Since as you say, it is ‘fuzzing out‘ at higher magnifications, the objective itself or at least one element May also be ‘flipped’ (placed backwards when reassembled). At any rate, it needs to come out (the glass come out of the cell). 



#9 Kasmos

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Posted 19 July 2020 - 04:47 PM

Sounds like the crown lens is flipped, or maybe the whole lens assembly.

Take it apart since it has quite a bit of fungus and needs a cleaning anyway.

On longer focal lengths it's sometimes visually hard to tell which side has more curvature.

Lay the crown on a padded but flat surface.

Lightly press on the edge to tilt the lens.

Check it on both sides.

The side that tilts the most has the most curve and should face the flint.

 

I take it that you know the proper way to remove and install the lenses from the cell.

 

Badback created this handy little chart showing all the possible ways they can be in the cell.

Only #1 is correct.

Lens arrangement.jpg


Edited by Kasmos, 19 July 2020 - 04:48 PM.


#10 DIYDarren

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Posted 19 July 2020 - 05:06 PM

Hey there! Wow that diagram is very helpful, thanks!

 

At an observational level, both sides that are facing out are fairly flat... So if I had to guess, I would say that if something is wrong, then the whole assembly is probably in backwards. Darnit I don't have a set of spanner wrenches (ordered one already) or else I would jump on this and let you all know the outcome. If I can think of a crafty (but safe) way to get the retaining ring out in the meantime, I will give that a try.

 

Here's another question- is the curvature of the surface where the crown and flint come together identical on both sides? I see that one of the spacers is a bit (not much, like .5mm) farther from the edge than the others. Could that be enough to "tilt" the orientation between the two? (But if the curvature is the same then that shouldn't make any difference...)

 

As far as proper way to remove/install- I have seen the "wine glass", or in my case "beer can" method. Is this what you are referring to?

 

Meanwhile I am starting to suspect my diagonal also- I can test straight-through and I do have a nice .965" diagonal that'll fit in too that I can try. I wonder if the softness is coming from the objective, and the weird off-center ghosting thing is coming from the diagonal..

 

Anyway I'll take it a step at a time as soon as I get a chance!

 

Thanks all,

Darren



#11 DIYDarren

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Posted 20 July 2020 - 12:29 PM

So just a quick update to the story for now...  kinda coincidental and kinda funny. Not haha funny, but ironic funny.

 

I have one other "classic scope" that I brought with me- a Meade 300 (Towa 339). Anyway, I also suspected that this one had been messed with. It has an easy-to-remove retaining ring on the objective, so I took it apart and had a look. Per your drawing above, I could see that the crown glass was backwards on this one! Rather than fix it right away, I decided to try it out with the crown backwards. The views it gave were similar to the views I am getting out of the Tasco 152x. (including the ghosting off to one side) I then proceeded to flip the crown on the Meade 300 and re-test it, and the view was quite sharp! I was able to see the bands on Jupiter. Anyway, so that gives me hope that I may be able to do the same process on the Tasco and correct my issue. (It didn't seem like the diagonal was the culprit though I will do some further testing.) I still need further work on the Meade to get it to perfection I'm sure- collimation, and looking at orientation of the lenses. There were no markings, and of course given that the crown was backwards I'm doubtful that that is in factory position. But that's another story...

 

It'll probably be a week or so before I get back with the next chapter on this one between getting the spanner wrench and having time to play with it.

Darren


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#12 Kasmos

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Posted 20 July 2020 - 03:03 PM

Hey there! Wow that diagram is very helpful, thanks!

 

At an observational level, both sides that are facing out are fairly flat... So if I had to guess, I would say that if something is wrong, then the whole assembly is probably in backwards. Darnit I don't have a set of spanner wrenches (ordered one already) or else I would jump on this and let you all know the outcome. If I can think of a crafty (but safe) way to get the retaining ring out in the meantime, I will give that a try.

 

Here's another question- is the curvature of the surface where the crown and flint come together identical on both sides? I see that one of the spacers is a bit (not much, like .5mm) farther from the edge than the others. Could that be enough to "tilt" the orientation between the two? (But if the curvature is the same then that shouldn't make any difference...)

 

As far as proper way to remove/install- I have seen the "wine glass", or in my case "beer can" method. Is this what you are referring to?

 

Meanwhile I am starting to suspect my diagonal also- I can test straight-through and I do have a nice .965" diagonal that'll fit in too that I can try. I wonder if the softness is coming from the objective, and the weird off-center ghosting thing is coming from the diagonal..

 

Anyway I'll take it a step at a time as soon as I get a chance!

 

Thanks all,

Darren

The more curved (convex) side of the crown should exactly match the (concaved) curvature of the flint. 

 

Yes the wine glass/beer can method.

I use a small jar of paint covered with a piece of paper towel or lens paper.

Something with a bit of weight is best so that it doesn't topple over.

9TE-Lens-removal.jpg

 

BTW, a spanner wrench is ideal but I don't have a spanner wrench and have worked on many.

I've used a fingernail, or on stubborn ones carefully using a small blade screw driver.

Covering the lens can be a good idea if it's really tight. I sometimes use a tooth pick just to spin them faster once loosened, or to close them up.

You don't want them too tight anyway as it can pinch the optics.


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#13 DIYDarren

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Posted 24 July 2020 - 04:16 PM

Good news folks! I got my spanner wrench and was able to take a quick look at the objective. YES the crown lens appears to be in there backwards. I haven't had time to fully clean and reassemble, but will hopefully do that over the coming few days. Let's hope it works out!!

Darren


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#14 DIYDarren

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Posted 24 July 2020 - 10:07 PM

One more update for now! So, I finally did the full cleaning and flipping of the crown glass... I was going to put it back together and was like... Wait a minute!!  The whole objective was flipped as well- the flint was facing the sky!  So, it seems like it was backwards and with a backwards crown glass.

Unfortunately a storm just rolled in, so I won't be able to test it tonight. Fingers crossed for a clear night one of these nights...   I'll report back once I've had a chance to test it.


And quick question (if you guys have a minute). There were no markings on the glass as far as orientation, and with everything being mixed around, I'm assuming that they were just in there randomly. I recall seeing some sort of test using a certain type of light where you can find the best orientation? Anyone know what that is called so I can google it?

Thanks for all the help!

Darren



#15 DreamWeaver

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Posted 24 July 2020 - 10:43 PM

None of my objectives had orientation marks on them.  And for the lightbulb test, here's a post from earlier today in another thread... https://www.cloudyni...ngs/?p=10364490



#16 DIYDarren

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Posted 27 July 2020 - 11:40 PM

Hey everyone,

 

Just another brief update.... So tonight I finally had time to get the scope out and take it for a spin. My easiest target is Jupiter, so I used that. YES, I had a nice sharp image... I would say I was able to stay reasonable sharp up to about 5mm (182x)  4mm was going soft (227x). Now mind you it was still early in the evening here, about 10pm so the seeing wasn't the greatest either. I could tell with my 5mm and 7mm eyepieces that I was seeing atmospheric waves interfering with the view. But I figured that was still a testament to the sharpness that I could tell that much. Of course maybe some of you experienced folks will say that pushing the magnification that high is "false" magnification anyway, too much for my brain to handle right now!

 

A couple other points-

1. I did not have a CFL on hand, so I had no way to inspect for Newton rings... I have one on order I'll let you all know what I find

2. I am still trying to get my head around the whole star test thing- I sort of get the general idea but I haven't had time to fully delve into this. So maybe I'll be able to do some more evaluations at a later time!

 

Thanks for all of the help!

 

Darren


Edited by DIYDarren, 27 July 2020 - 11:40 PM.

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