43 replies to this topic

[dothead]

True quadruplet onjectives have reportedly been made by Zeiss and also by Lichtenknecker, many decades ago. They may be revived by APQ, though those have not been seen in the wild yet as far as I can tell.

Don't forget the Astreya quadruplets /Super APOs:

 

https://www.cloudyni...t-astreya-lens/
 

[Jon Isaacs]

Are we 100% sure of that, or has anyone ever tried it?

 

I'm not 100% sure of anything. 

 

It would be quite a project. Without the rear elements, the F/11.5 light cone would clipped, the focal plane would more than 20 inches beyond the end of the OTA.  Probably the easiest thing to do would be to build an objective cell and build a telescope around it.

 

Jon

[Terra Nova]

I'm not 100% sure of anything. 

 

It would be quite a project. Without the rear elements, the F/11.5 light cone would clipped, the focal plane would more than 20 inches beyond the end of the OTA.  Probably the easiest thing to do would be to build an objective cell and build a telescope around it.

 

Jon

Yes, comparing the TV 101mm instrument’s rear Petzval unit to an off the shelf flattener/reducer is apple to oranges. Typical after-marker reducers shorten the native focal length of the objective by only 10 to 20 percent. They are intended to work with telescopes that are designed to operate with the objective at it’s native focal length. The TeleVue and Vixen rear Petzval units are entirely different animals. They shorten the objective’s focal length by half, effectively doubling the optical speed of the instrument, while correcting the resultant image to yield a flat field. BTW, some of the Vixen Petzvals utilized a triplet rather than a doublet rear element (the Vixen 120S for instance). I don’t know of similar triplet situations in some of the TeleVue and Takahashi designs. I do know that TeleVue used a fluorite lens element in the rear in some of it’s scopes like the SDF, (SD = Special Dispersion (in the objective) F = Fluorite (in the rear unit)).

Edited by Terra Nova, 11 April 2025 - 10:32 AM.

[ngc7319_20]

It is my understanding that triplets are very sensitive to miscollimation, centering.  The tolerances on centering can be less than 10 microns.  They go back to the factory for that.. 

Jon

 My 3 are OK. The TOA and LZOS have big heavy cels (making OTAs heavy), so I feel they will stay good. 

Triplets do have sensitive spacing and centering, but that stuff is hidden away in a strong metal cell, and is protected by the dew shield, etc.  The triplets I have seen with collimation problems all had dented / bent lens cells (I didn't ask for details) or had been disassembled by the owner (maybe trying clean something).  They can be fixed, but a 4 inch might have 18 screws and 6 spacers to adjust, so it gets complicated.

 

The Petzvals (in particular TeleVue) have the collimation stuff hanging out there exposed.  On the plus side there are only 3 screws, so a competent user can adjust it for themselves without too much effort.

 

Part of my personal skepticism stems from trying different scopes at star parties.  I'd take a 3-6mm zoom eyepiece in my pocket and go star testing.  The majority of the TeleVue Petzvals, including the ones Al was schlepping around, would be out of collimation.  Of course, this is a terrible way to do a survey -- cause I'm only testing the ones that have been schlepped to star parties.  In proper collimation they make beautiful images across a wide field.

[25585]

This the FSQ-85

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[25585]

FSQ-106

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Edited by 25585, 11 April 2025 - 01:28 PM.

[CMS1288]

My FSQ-85 is the sharpest scope I've looked through, and handles imaging incredibly well.  I always lusted for one, and it does not disappoint. I travel with it often, and collimation stays spot-on.

[Jon Isaacs]

Triplets do have sensitive spacing and centering, but that stuff is hidden away in a strong metal cell, and is protected by the dew shield, etc.  The triplets I have seen with collimation problems all had dented / bent lens cells (I didn't ask for details) or had been disassembled by the owner (maybe trying clean something).  They can be fixed, but a 4 inch might have 18 screws and 6 spacers to adjust, so it gets complicated.

 

The Petzvals (in particular TeleVue) have the collimation stuff hanging out there exposed.  On the plus side there are only 3 screws, so a competent user can adjust it for themselves without too much effort.

 

Part of my personal skepticism stems from trying different scopes at star parties.  I'd take a 3-6mm zoom eyepiece in my pocket and go star testing.  The majority of the TeleVue Petzvals, including the ones Al was schlepping around, would be out of collimation.  Of course, this is a terrible way to do a survey -- cause I'm only testing the ones that have been schlepped to star parties.  In proper collimation they make beautiful images across a wide field.

 

My friend had an ES triplet that fell.  There was no sign of damage but it was definitely out of collimation.  It had to go back to the factory but when it came back, it still had issues.  

 

Some triplets have metal cells precisely made but I believe a substantial number have sets of centering screws.  

 

The TeleVue objective cell design could include a second set of adjustment screws that would make adjusting the tilt straightforward.  I thought about doing it when I collimated my scope but decided just to built the simple collimation fixture instead.

 

Jon

[ngc7319_20]

My friend had an ES triplet that fell.  There was no sign of damage but it was definitely out of collimation.  It had to go back to the factory but when it came back, it still had issues.  

 

Some triplets have metal cells precisely made but I believe a substantial number have sets of centering screws.  

 

The TeleVue objective cell design could include a second set of adjustment screws that would make adjusting the tilt straightforward.  I thought about doing it when I collimated my scope but decided just to built the simple collimation fixture instead.

 

Jon

Sorry about your friend's ES.  I haven't worked on those, but at least there is a factory to send them to, though it still has issues.... Hmmm.

 

Yes TeleVue could use some sort of push-pull screws, in addition to, or instead of, the minimal 3-screw design.  I guess their design minimizes the tube diameter -- maximizes portability -- but they need something more clever IMHO.

[Mike W]

Sorry about your friend's ES.  I haven't worked on those, but at least there is a factory to send them to, though it still has issues.... Hmmm.

 

Yes TeleVue could use some sort of push-pull screws, in addition to, or instead of, the minimal 3-screw design.  I guess their design minimizes the tube diameter -- maximizes portability -- but they need something more clever IMHO.

Televue doesn't want you messing with the collimation, in the long run would cause more trouble than not.

[Terra Nova]

My friend had an ES triplet that fell.  There was no sign of damage but it was definitely out of collimation.  It had to go back to the factory but when it came back, it still had issues.  

 

Some triplets have metal cells precisely made but I believe a substantial number have sets of centering screws.  

 

The TeleVue objective cell design could include a second set of adjustment screws that would make adjusting the tilt straightforward.  I thought about doing it when I collimated my scope but decided just to built the simple collimation fixture instead.

 

Jon

Both of my AT triplets have fixed metal cells without centering/collimating screws and aren't meant to be user collimated. I’m thankful for that because they are both spot on perfect and I figure the collimatable ones might have more play or be more prone to get out of collimation. It’s the same with my older Vixen apo (doublet), it has a threaded and fixed cell that’s not meant to be messed with.

Edited by Terra Nova, 12 April 2025 - 09:14 AM.

[Jon Isaacs]

Televue doesn't want you messing with the collimation, in the long run would cause more trouble than not.

 

The current three screws are covered with epoxy, the same could be done with the adjustment screws. With the three additional screws, it would be more robust, less likely to be knocked out of collimation.

 

TeleVue would also benefit, from what I understand, they collimate by hand rather than using a fixture. One advantage of a fixture is that the objective cell is held in place while tightening the current three screws.

 

I believe there is room in the current cell to drill and tap a set of adjustment screws. As I said, when I built my collimation fixture, I considered it. At that time I had a close relationship with some highly skilled machinists who would have done the actual work.

 

I agree with NGC 7319-20, a more "clever" solution is needed. As he said, the majority of TeleVue Petzvals he has tested at star parties are not collimated.  

 

If a trip to a star party is too much for the collimation, that's not good. My NP-101 has traveled over 15,000 miles in the bed of a pickup, suffered one nose first tumble, it's still in collimation.

 

I attribute that to the fact that it was collimated using a fixture so the collimation could not shift while the screws were being tightened.

 

Jon

Edited by Jon Isaacs, 12 April 2025 - 09:31 AM.

[Mike W]

Yes but, Televue doesn't want you messing with the collimation! They use an MPT scope to collimate AND check collimation before it goes out the door. I've had this conversation with Al Nagler in person so why should I listen to you?

[ngc7319_20]

Yes but, Televue doesn't want you messing with the collimation! They use an MPT scope to collimate AND check collimation before it goes out the door. I've had this conversation with Al Nagler in person so why should I listen to you?

Well that's not entirely true.  I know Al has explained to people how to pick the epoxy out of the screw heads and collimate it themselves.  He's explained it to me and others.  I know the latest user manual says to contact them for collimation.  Maybe TeleVue has changed policies...  dunno...  That is one huge plus for TeleVue these days -- you can easily send it back to the factory for service.  Not so with many other scopes.

Edited by ngc7319_20, 12 April 2025 - 12:33 PM.

[Astroman007]

Not everyone has the ability financial (a real concern nowadays) or otherwise (lost shipping boxes?) to send their scope back to the manufacturer for service that could be done themselves as long as all necessary care is taken. And who knows how long the manufacturers will be around with the way things are going? That is why we thank Jon for sharing his method here. If one has the fine motor skills and inclination, so be it. If they would rather pay for TV to collimate (as I probably would) so be it. Always good to have options. The more one can do for oneself the better, and another skill learned.

[Mike W]

The current three screws are covered with epoxy, the same could be done with the adjustment screws. With the three additional screws, it would be more robust, less likely to be knocked out of collimation.

 

TeleVue would also benefit, from what I understand, they collimate by hand rather than using a fixture. One advantage of a fixture is that the objective cell is held in place while tightening the current three screws.

 

I believe there is room in the current cell to drill and tap a set of adjustment screws. As I said, when I built my collimation fixture, I considered it. At that time I had a close relationship with some highly skilled machinists who would have done the actual work.

 

I agree with NGC 7319-20, a more "clever" solution is needed. As he said, the majority of TeleVue Petzvals he has tested at star parties are not collimated.  

 

If a trip to a star party is too much for the collimation, that's not good. My NP-101 has traveled over 15,000 miles in the bed of a pickup, suffered one nose first tumble, it's still in collimation.

 

I attribute that to the fact that it was collimated using a fixture so the collimation could not shift while the screws were being tightened.

 

Jon

So you're saying Televue collimates their scopes with the MPT, doesn't tighten the screws enough and doesn't re-check collimation? Quite a bold statement!

[25585]

Long short, if in doubt buy a doublet.

[Jon Isaacs]

So you're saying Televue collimates their scopes with the MPT, doesn't tighten the screws enough and doesn't re-check collimation? Quite a bold statement!

 

I am not saying that.

 

Jon

[25585]

My fsq106 had to go back to Japan because the rear elements needed to be reset. They are not collimatable and they are set in place, not sure if they are cemented or how they are fixed.
I don’t think that the fsq is diffraction limited but after the trip to Japan I get excellent stars to the corners of the imx461.

Cross section of a FSQ-106

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