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Collimating My TV NP-101

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#1 Jon Isaacs

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Posted 03 October 2010 - 07:14 PM

Hi: For those who had expressed interest, this is the story.

Collimating an TeleVue NP-101

This is a detailed description of the procedure I used to collimate my NP-101. In order to accurately collimate my scope, I decided to build a simple jig that slid over the objective cell and allowed me to accurately adjust the tilt of the objective cell. One should be handy with tools but nothing more. A screw driver, an allen wrench, a drill, a saw and a 1/4-20 tap are the only tools required.

Since you are reading this, I am assuming you have determined your scope needs collimation. This is the first step, testing the collimation by performing a star test. When I tested my scope I found that at 300x the diffraction rings were not centered on the airy disk and they were not full circles. I was not certain this was a collimation issue, it could have been a diagonal or thermal issue so I tried the tube in a number of positions to identify that the rotating the tube caused the off-centered diffraction rings to rotate as well. Once I established this, I considered it for a while, fooling with the collimation of a Newtonian is one thing, with an apochromatic refractor is quite another. I discussed it with John Biretta whom I know from Astromart and had advised me in the purchase of this scope, we talked over the various ways to build a jig and I decided to go ahead with collimating the scope.

The basic problem is that the objective in front and the Petzval elements in the rear must be accurately aligned. If they are not, the telltale signs of miscollimation are visible. My first step was to try collimation without a jig but it soon became clear this was hit and miss, the cell has no adjustment screws, only locking screws. I was not able to accurately position the objective so that I was happy with the collimation, it required a series of nudges and while I was able to get it close, invariably the attempt to make it perfect resulted in poorer collimation. You may want to try this, I don't recommend it, I liken it to collimating a fast Newtonian that lacks adjustment screws...

So, this is what I did, I can make no guarantees except to say it worked for me and I believe that if you have identified that your scope requires collimation and if you read this carefully so that you understand it, you too can achieve a well collimated NP-101 with little more than an hour's time and some care.

Materials: Acrylic Tube 6 inches long x 4.25" x 4.50" (0.125"wall)
4 1/4-20 Nylon Screws 1" long (Nylon helps to prevent marring the scope finish)
Hose Clamp 5 inch diameter

McMaster-Carr has the tubing in 12 inch lengths for $19.

Building the Jig:

- Drill and tap 4 equally spaced 1/4-20 threaded holes approximately 1/2" from one end of the tube. The Nylon screws threaded here will serve as the adjustment screws. This need not be precision, eyeballing it is fine.

- Using a saw, split the tube end to end so that it can be spread open and slipped over the front of the objective cell. Make sure you the cut is located so it will not intersect the drilled holes

- Remove the snap ring from the dew shield, it is wire and can be done without tools. The scope should be securely mounted. Slide the Dew Shield down the tube towards the focuser as far as it will go. Make sure there is sufficient room for the jig to fit, you may have to slide the scope in the clampshell.

- Spread the acrylic tube, slip it over the step in objective cell, the end with the screws should be towards the focuser.

- Identify the 3 collimation adjustment screws. Slide the tube towards the focuser until the distance from the non-threaded end to the screws is about 2.5 inches. Using the hose clamp, clamp the acrylic tube to the objective cell. Using a magic marker, mark the position of the three collimation screws, they are visible through the clear acrylic.

Remove the acrylic tube, drill three holes 3/8" diameter or larger centered on the marks. These provide access so you can loosen and tighten the collimation locking screws with the jig in place. Once this is done, the jig is finished and you are nearly ready to being the actual collimation.

First though, you must prepare the scope. The collimation locking screw heads are filled or covered and this must be removed so the allen heads are accessible. Mine had already been removed, someone had previously played with the collimation.

The actual collimation is simple. One will need a clear night with reasonably good seeing to perform the star test and an eyepiece combination capble of about 300x, I used a 3.5 mm Nagler.

- Slide the acrylic tube over the tube once again and position the 3 access holes over the collimation locking screws. Clamp the tube to the objective cell.

- Install the four 1/4-20 Nylon Screws and snug them up against the the OTA, they need not be tight, they just need to be tight enough to keep the Objective Cell from moving.

- Loosen the 3 collimation locking screws. These need to be loose enough to allow the cell to move easily but no looser.

- Perforn the star test, you will need to be able to see the diffraction rings so the star should be reasonable bright but not too bright.

- Using the 4 nylon screws, make the adjustments so that the infocus diffraction rings are centered about the star.

- Once you are satisfied, tighten the collimation lock screws. It is reasonable to do it in several steps as one would torque an engine head or other precision instrument.

- Once these are tight, loosen the nylon screws adjustment screws on the jig and repeat the star test to make sure the collimation has not shifted.

- Back out or remove the 1/4-20 Nylon screws so they allow the acrylic tube to slide freely against the objective cell, loosen and remove the clamp, slide the tube over cell to remove it.

- Slide the dewshield into position, replace the snap ring, making sure it is securely in place.

You are done.... Store the acrylic adjustment jig and enjoy your scope.

This is how I did it. Please feel free to ask questions or make comments. If it seems confusing or too much, I would advice against it. It is a simple procedure, the jig just provides positive adjustment screws. There are a number of different possible ways to do this, yours might work better for you.

Jon Isaacs

Attached Thumbnails

  • 4090522-NP 101 Collimation Jig.jpg


#2 Jon Isaacs

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Posted 03 October 2010 - 07:19 PM

Here is a photo of the jib in place.

Best to all

Jon Isaacs

Attached Thumbnails

  • 4090534-NP-101 Collimation Jig Photo.jpg


#3 mountain monk

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Posted 03 October 2010 - 07:51 PM

Thank you, Jon. Splendid explanation. Now all that is required is courage.

Dark skies.

mm

#4 johnnyha

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Posted 03 October 2010 - 07:57 PM

:applause: :applause: :applause: :bow: :bow: :bow: :bow: :bow: :bow: :applause: :applause: :applause:

#5 Eddgie

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Posted 03 October 2010 - 08:00 PM

Happy that this worked for you, but I would say that with some patience, an alignment fixture isn't really necessary.

The process I recommend is to break the screws loose, then snug them so that the cell does not move easily.

I used a nylon tipped hammer, (OMG a HAMMER!) and VERY gently tapped on the base and end of the cell a very tiny amount then checked the collimation. Just tiny little taps.

This allows great control. If the screws are kept very snug, the cell will move in tiny little jerks.

Using this method, it is a snap to quickly bring a Televue scope into perfect collimation.

Once the collimation is perfect, lock the screws down.

Now oh so very sadly, just the process of tightening the screws can cause the cell to shift.

For such an expensive telescope, it is a pity that Televue doesn't provide push/pull adjustments, ESPECAILLY on the Genesis/101 series scopes.

Anyway, I think it is good that you shared your design, but if it looks to complex for other readers to build, they may find the tap method to be easy and effective.

#6 Jon Isaacs

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Posted 03 October 2010 - 08:11 PM

For such an expensive telescope, it is a pity that Televue doesn't provide push/pull adjustments, ESPECAILLY on the Genesis/101 series scopes.

Anyway, I think it is good that you shared your design, but if it looks to complex for other readers to build, they may find the tap method to be easy and effective.


Eddie:

It is worth trying the collimation without a jig.

I tried the tap method, I guess I might have made it work but as you say, the collimation can shift just tightening the screws. With the jig holding it in place, this did not happen. The way I look at it, if I am collimating by tapping, it is literally hit and miss. With the jig, I can dial it in small tweaks as needed.

I agree that it is sad that TV does not include a push pull cell. It could be pretty simple, 3 or 4 small allen screws tapped in the objective cell that push on the tube. I considered removing the cell and having "my" machinist, drill and tap the cell.

Jon

#7 Bob Abraham

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Posted 03 October 2010 - 10:52 PM

Thanks so much for sharing this Jon!

Bob

#8 KerryR

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Posted 04 October 2010 - 08:30 AM

Great post! I'm glad someone finally made a jig for doing this. I considered doing this when my Genesis needed collimation. I tried hand and hammer collimating, with no success-- as mentioned, the cell tends to move when the bolts are tightened, a factor that appears to be even more prevalent on the older TV Petzvals (this from a TV tech at TV).

I ended up sending mine in, not only for collimation, but for cleaning as well. Next time, though, I'll build a jig like this!

#9 Jason B

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Posted 04 October 2010 - 08:38 AM

Great post, I am going to add this to the "best of..." links!

#10 deSitter

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Posted 04 October 2010 - 11:30 AM

Isn't this a Petzval? I would guess that Televue doesn't provide collimation because you need to do both elements. I'm astonished that the collimation was so bad that the diffraction rings were not even centered.

-drl

#11 Mike Clemens

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Posted 04 October 2010 - 11:37 AM

> Great post, I am going to add this to the "best of..."
> links!

Agreed nice contribution!

#12 KerryR

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Posted 04 October 2010 - 11:38 AM

Yes it's a Petzval.

The rear elements are not collimateable, and rely on the precision of the machining for their placement. The remaining elements (front objective, focuser) are aligned to the rear elements' location.

These scopes are VERY sensitive to collimation. Very small errors are easily visible at the ep.

Televue doesn't provide collimation of these scopes because NONE of their scopes do-- the ota, other than the rear element holder, is the same design they use on all the rest of their scopes, none of which are easily collimated, owing to the lack of push pull cell. On most of the scopes, it's not an issue, but on the Petzvals, it sure CAN be.

#13 Jon Isaacs

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Posted 04 October 2010 - 12:26 PM

Isn't this a Petzval? I would guess that Televue doesn't provide collimation because you need to do both elements. I'm astonished that the collimation was so bad that the diffraction rings were not even centered.

-drl


It doesn't take much to through off the alignment between the front and rear cells. I have heard that other Petzvals also have similar issues.

Jon Isaacs

#14 JoeBftsplk

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Posted 06 October 2010 - 12:01 AM

Thanks, Jon. Another excellent contribution to the hobby. It's been added to my favorites list.
Bob

#15 FirstSight

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Posted 16 November 2010 - 01:09 PM

QUESTION: Can the timid send their NP-101s to TeleVue for collimation, for a fee? If so, any idea what the cost for the service itself is, and what the typical shipping charges would be from the eastern half of the country?

At some point in the future, I hope to purchase an NP-101, perhaps used, or perhaps a demo model a vendor has, and that route certainly raises the potential the scope's collimation will need tweaking to get my money's worth of quality views out of it.

#16 KerryR

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Posted 16 November 2010 - 01:30 PM

QUESTION: Can the timid send their NP-101s to TeleVue for collimation, for a fee? If so, any idea what the cost for the service itself is, and what the typical shipping charges would be from the eastern half of the country?

At some point in the future, I hope to purchase an NP-101, perhaps used, or perhaps a demo model a vendor has, and that route certainly raises the potential the scope's collimation will need tweaking to get my money's worth of quality views out of it.


TV's service is about $200, but includes complete disassembly and cleaning, replacement of rusted parts if present, and, sometimes, replacement of the plastic bearing sleeve in the focuser. My 20 year old Genesis returned to me looking all sparkly new-like -- they even Armoralled the case. The price includes return shipping.

Note, though, that it's perfectly possible for the scope to loose collimation again in shipping, and TV does not guarantee the service, because of this. So, you could shell out the $200 and end up close to where you started. My Genesis was perfect when I got it back, though. While I don't fear collimating the objective any longer, my primary motivation for sending it back to TV was to get internal mold removed from the objective.

#17 johnnyha

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Posted 16 November 2010 - 02:48 PM

I believe Televue will send the telescope back after re-collimation in whatever shipping container you send it in, so part of the onus is on you to get it back still perfectly collimated. But this gives you a chance to come up with a bulletproof shipping container. Current NP101 service is $250.

#18 KerryR

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Posted 16 November 2010 - 02:57 PM

I had my Genesis professionally packed at a shipping store (in it's case). TV would not send it back to me in those boxes because it was slightly larger (not to mention more robust) than the boxes they use, and didn't fit their 'return shipping included' thing because of the size. I had to pay for TV boxes and boxing. Not sure why they wouldn't just let me spring a little extra for shipping the beefier setup I had done, but they wouldn't. No big deal, though; now I have 'official' Televue labeled boxes for future shipping, should I EVER (horrors!) decide to part with my beloved Genesis.

#19 FirstSight

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Posted 16 November 2010 - 08:55 PM

I believe Televue will send the telescope back after re-collimation in whatever shipping container you send it in, so part of the onus is on you to get it back still perfectly collimated. But this gives you a chance to come up with a bulletproof shipping container. Current NP101 service is $250.


I would probably expand on what I learned about crafting bulletproof secure packing of delicate optical items when I sent my mirror off on a three-legged transcontinental trip from North Carolina to Oregon for figuring, the Florida for coating, and back to North Carolina. Surely the same ideas about how to properly double-nest a mirror in a sturdy foambed inside a sturdy box inside more sturdy foam inside yet another sturdy box could be adapted to shipping a refractor to TeleVue in NY and back.

But first, now I must patiently accumulate enough funds to buy the NP-101 and THEN get around to the potential collimation and shipping aspect. However, you all are being very helpful in informing me well in advance what all I might be getting into, beyond just acquiring the scope.

#20 KerryR

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Posted 16 November 2010 - 11:39 PM

Chances are excellent that a) you're sample won't need collimating, and b) even if it does, it'll be fine in shipping. Most of these scopes arrive to their shops/and/or/owners in perfect collimation. No one's gonna post that, though, so all we hear about here on CN are the instances where collimation was needed. Some of the older Genesis's (like mine) don't hold collimation as well as the newer NP-101's do.

It's not THAT common to need to collimate them. It's nice, though, to be able to do it yourself (easily, as this thread shows).

#21 CarlDD

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Posted 17 November 2010 - 02:05 AM

Hi
This thread prompted me to star test my 11 year old TV®101, I hadn't done that for a long time, but as the scope is used every clear day for solar Halpha I thought the constant thermal cycling might have had a long term effect.

Over the last few years I've tended to use my Obsession at night and TV duing the day, star testing led to using it a lot more at night.

I've rediscovered just how nice the night sky can be at low magnification and wide field, so most days now, as the sun goes down, I convert from Ha to night time and enjoy the night sky with it.

Oh and my scope star tested just fine, I tried without diagonal using a three inch extension tube 7mm Nagler and Barlow, and with the diagonal in place.

Best Regards
Carl

#22 Jon Isaacs

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Posted 17 November 2010 - 08:09 AM

It's not THAT common to need to collimate them. It's nice, though, to be able to do it yourself (easily, as this thread shows).



I really don't know how common it is but before I purchased mine, I asked three friends about the scope. One of them told he had collimated several NP-101's and the second one said he had had to collimate his NP-101...

Given the nature of the objective mount, it is difficult to imagine that it would be permenent.

Jon

#23 KerryR

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Posted 17 November 2010 - 10:03 AM

Given the nature of the objective mount, it is difficult to imagine that it would be permenent.

Jon


That's for sure! I'm not sure why TV continues to use this method of mounting the objective-- it's difficult to collimate without push pull screws (unless you make a jig, as you did), and it relies on friction to stay there.

I, of course, also have no real idea how common it is to collimate these, but I assume thousands of TV Petzvals are out there, yet we don't hear about thousands of instances of lost collimation-- no one is saying 'don't by a NP 101-- they just don't stay tuned'. It could be that many are out, but that many observers don't know it (as is evidenced by the number of poorly collimated SCT's and Newts you see at star parties).

Either way, it's not difficult to do, and your jig is a much better design than what I came up with. Next time my Genesis gets out, I'll be doing it with your jig design.

#24 hudson_yak

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Posted 17 November 2010 - 11:28 AM

I'm not sure why TV continues to use this method of mounting the objective



While we can only speculate...it seems that one of TV's design-style goals is having the smallest OTA diameter they can get away with for the objective size. Their cell attachment design and the use of flocking paper instead of baffles both seem to be chosen with this in mind. The TV-85 is the most extreme example of this philosophy, where even the tube itself is smaller in diameter than the objective.

Mike

#25 KerryR

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Posted 17 November 2010 - 12:47 PM

I'd agree.

On the other hand, my Megrez 90 has a collimatable cell that's not of the bulkier push-pull variety. That said, I'm not sure that the radial screws it has change the pitch of the entire objective, or rather only affects the relative pitch between the elements, or, perhaps centering. In any case, those screws affect coma in the image, which is what most of us are after... Probably not as 'skinny' as TV's method.


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