Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> Cats & Casses

Pages: 1 | 2 | (show all)
Itz marcus
Pooh-Bah
*****

Reged: 02/12/06

Loc: Brooklyn NY
Re: Why can't sct collimation be set permanently? new [Re: seawolfe]
      #6177136 - 11/05/13 10:52 AM

Hi,
Quote:

I don't understand the question.

Why would you want a scope that could not be user collimated? That would mean that if (when) collimation is required, the scope would have to go in for service. And then the system would have to be robust enough that it could survive shipping without disrupting collimation.
Quote:



My question was why can't it be an option. I myself have no problem collimating (anymore) but it is time consuming (20 minutes or so maybe I will get better and faster) and in 30 degree weather a real pain. Refractors with set cells (like my EON) do not cost anymore than collimatable refractors. In fact they many times cost less than an equal aperture and quality scope. Maybe they do lose collimation but that has not been the case with me and many other VERY happy non user collimatable refractors.
Clear Skies
Itz

Edited by Itz marcus (11/05/13 10:55 AM)

Post Extras: Print Post   Remind Me!   Notify Moderator  
rmollise
Postmaster
*****

Reged: 07/06/07

Re: Why can't sct collimation be set permanently? new [Re: Itz marcus]
      #6177402 - 11/05/13 01:31 PM

Again, if you are doing your SCT's collimation right, you have exactly what you are asking for: a telescope that can be collimated, but which rarely needs it.

Post Extras: Print Post   Remind Me!   Notify Moderator  
bicparker
Carpal Tunnel


Reged: 02/07/05

Loc: Texas Hill Country
Re: Why can't sct collimation be set permanently? new [Re: Itz marcus]
      #6177780 - 11/05/13 04:42 PM

Quote:

Hi,
Why don't scope makes make sct scopes with collimation permanent just as many refractors and mct are. The same question for reflectors. My refractor has remained in perfect collimation so why not these scopes?
Clear Skies
Itz




There is good design sense in making any optical train mechanism adjustable, not only in focus, but in collimation and other features, as well (mounting, rotation of focus, et al). This same logic extends to any mechanical system that is expected to operate within certain tolerances while maintaining a dynamic stance in a variable environment throughout its operations. The system needs to be adjustable so it can operate within its design tolerances under a wide range of circumstances. It would be a bad design decision to not have a collimation adjustment.

Perhaps a better question is, why can't a robust collimation adjustment design be put into place that isn't so easily changed by factors other than temperature, humidity, and atmospheric pressure? It is kind of a pain when the adjustment system is the primary reason the system is out of adjustment. This, of course, is the logic behind any push-pull screw system for collimation, but you generally have a straight set of screws in an SCT, and these simply loosen when shaken enough or bumped the wrong way.

Without respect to how well or not so well it was implemented, I think Meade was really on to a good notion when they introduced the electro-mechanical collimation system in their RCX 400 telescopes. Here was a system that was easily adjustable, and wouldn't (or wasn't supposed to) change due to bumps in the road or a loose screw. Those two criteria should be the fundamental criteria used for designing and making a telescope collimation system.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Asbytec
Guy in a furry hat
*****

Reged: 08/08/07

Loc: La Union, PI
Re: Why can't sct collimation be set permanently? new [Re: bicparker]
      #6178208 - 11/05/13 09:11 PM

Quote:

It would be a bad design decision to not have a collimation adjustment.



I agree. I hope they don't design scopes than cannot be user collimated in the field.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Gil V
professor emeritus


Reged: 09/09/12

Re: Why can't sct collimation be set permanently? new [Re: seawolfe]
      #6180941 - 11/07/13 12:23 PM

Backing up Rod 100%. Once collimated, there is virtually no need to re-collimate an SCT. If there is, it's because the scope was not properly collimated by the user (screws with improper tension/tightness). Even when shipped, collimation usually holds.

Best practice is to use an artificial star, IMHO.

They hardly ever go out. I really think part of the problem is people adding after market hardware. Total waste of money.


Post Extras: Print Post   Remind Me!   Notify Moderator  
orion61

*****

Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Why can't sct collimation be set permanently? new [Re: Gil V]
      #6181783 - 11/07/13 08:30 PM

if you dont have the secondary screws tight enough it can
go out, another thing that can trick you is mirror flop, always tweek your focus towards counter clockwise.
my scopes usually stay in for close to a year.


Post Extras: Print Post   Remind Me!   Notify Moderator  
MitchAlsup
Pooh-Bah


Reged: 08/31/09

Re: Why can't sct collimation be set permanently? new [Re: orion61]
      #6181916 - 11/07/13 10:00 PM

A couple of three points:

A) A refractor only has to hold alignment between the objective and the focal plane; while an SCT has to hold the corrector at the right spot, the primary at the right spot (a significant distance away), and the secondary at the right spot (another significant distance away), all the way to the focal plane. Its this distance which makes the difference.

2) I have a Top-end refractor (AP) that occasionally needs collimation (made in 1989).

3) My SCT came (circa 1990) miscollimated such that I had to change the spacings on the corrector to secondary holder to get the corrector plate and secondary in the right spots. This is WAY harder than aligning a Newtonian (even for the very first time.)


Post Extras: Print Post   Remind Me!   Notify Moderator  
corpusse
scholastic sledgehammer


Reged: 04/11/10

Loc: Mississauga, Ontario, Canada
Re: Why can't sct collimation be set permanently? new [Re: MitchAlsup]
      #6182060 - 11/07/13 11:46 PM

Not that it is really possible, nor would I even trust Celestron if they could offer it, but if there was an SCT that did not need collimation and I think that would be worth at least an extra $1000.

It's interesting to see how some people say you don't need to collimate for years and others say you should at least check if not adjust daily (mostly high resolution planetary imagers).

If you live somewhere where the seeing is always poor it can take months or longer to get a chance to actually collimate.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Spacetravelerx
Carpal Tunnel


Reged: 12/23/12

Loc: New Mexico
Re: Why can't sct collimation be set permanently? new [Re: corpusse]
      #6182084 - 11/08/13 12:10 AM

Quote:

Not that it is really possible, nor would I even trust Celestron if they could offer it, but if there was an SCT that did not need collimation and I think that would be worth at least an extra $1000.

It's interesting to see how some people say you don't need to collimate for years and others say you should at least check if not adjust daily (mostly high resolution planetary imagers).

If you live somewhere where the seeing is always poor it can take months or longer to get a chance to actually collimate.





I am one of those who hasn't needed to collimate my telescope for years, and certainly there hasn't been a need to collimate my 14" LX850 since I received it in the spring. Visually the views are stunning in the new unit. Planet views are wonderful too. Of course being in the high desert at over 5,500' helps too on the wonderful views,


Post Extras: Print Post   Remind Me!   Notify Moderator  
Footbag
Postmaster
*****

Reged: 04/13/09

Loc: Scranton, PA
Re: Why can't sct collimation be set permanently? new [Re: Spacetravelerx]
      #6182528 - 11/08/13 09:30 AM

I think it would be great if they could make collimation permanent... That is as long as I can adjust it if it goes out.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Why can't sct collimation be set permanently? new [Re: Spacetravelerx]
      #6182571 - 11/08/13 09:51 AM

Quote:

I am one of those who hasn't needed to collimate my telescope for years, and certainly there hasn't been a need to collimate my 14" LX850 since I received it in the spring. Visually the views are stunning in the new unit. Planet views are wonderful too. Of course being in the high desert at over 5,500' helps too on the wonderful views,




As someone who frequently observes in the high desert, generally the high desert is transparent but seeing is the issue. Also thermal equilibrium is a big issue because the temperature drops so quickly after sundown and continues to drop because of the transparent sky. What does the star test look like at, what do you think, is 600x is appropriate for a 14 inch?

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
vahe
scholastic sledgehammer


Reged: 08/27/05

Loc: Houston, Texas
Re: Why can't sct collimation be set permanently? new [Re: Itz marcus]
      #6182611 - 11/08/13 10:08 AM

Quote:

Hi,
Why don't scope makes make sct scopes with collimation permanent just as many refractors and mct are.





If one detects any amount of image shift while focusing that indicates that the primary position does not remain stable and in alignment as it moves back and forth and if that is the case then I do not see how critical collimation can be achieved in any system that can not maintain prefect alignment of its optics.

Zero image shift focusing mechanisms used in many high end Maksutovs are expensive to implement and will add to the price of instrument and it is just one more reason why quality Maks are generally more expensive than SCT’s, since vast majority of SCT owners are perfectly happy with what they get for the $$$ there is no incentive on the part of manufacturers to go beyond simple and inexpensive focusers supplied with these scopes.

Vahe


Post Extras: Print Post   Remind Me!   Notify Moderator  
Spacetravelerx
Carpal Tunnel


Reged: 12/23/12

Loc: New Mexico
Re: Why can't sct collimation be set permanently? new [Re: Jon Isaacs]
      #6182692 - 11/08/13 10:50 AM

Quote:

Quote:

I am one of those who hasn't needed to collimate my telescope for years, and certainly there hasn't been a need to collimate my 14" LX850 since I received it in the spring. Visually the views are stunning in the new unit. Planet views are wonderful too. Of course being in the high desert at over 5,500' helps too on the wonderful views,




As someone who frequently observes in the high desert, generally the high desert is transparent but seeing is the issue. Also thermal equilibrium is a big issue because the temperature drops so quickly after sundown and continues to drop because of the transparent sky. What does the star test look like at, what do you think, is 600x is appropriate for a 14 inch?

Jon




Jon,

When you say seeing is the issue, what do you mean exactly?

Yes, where I am the temperature does have a big drop, I want to say up to 30 deg after sunset. However, I have my LX850 under the Telegizmos 365 cover during the daytime, which tends to keep the temperatures cooler inside the cover (I will measure it when I get back home as I am on travel right now). This in turn seems to keep the cool down delta smaller. With a the metal OTA heat is also transmitted out quicker vs. say plastic or CF parts. Thirdly, I really don't start observing sometimes until 2-3 hours after sunset for a variety of reasons; things are a bit more stable at that point.

Besides the altitude (less air to look through), the other advantages in New Mexico: overall lower humidity and many clear nights (310+ a year). I never have to deal with dew, whew. Michigan? Total sogginess! Either way I find the view spectacular regardless if I am using the 14" ACF or my APOs in New Mexico. When I moved from the midwest to New Mexico the change in observing was profound. It was like I got a brand new telescope.

I don't do a whole lot of high magnification stuff, however I did observe the "double double" in Lyra with an HD-60 4.5mm eyepiece (632x). The view was wonderful and emotional - why do some objects invoke emotions when you view them? Jupiter of course looks impressive too. The views through my 8.8mm UWA look fantastic (323x) - I am looking at getting the 5.5 mm UWA when they become available (I think early next month).

I do occasionally check the collimation, but it so far has not been an issue.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Lew Zealand
Pooh-Bah
*****

Reged: 06/28/04

Loc: Pasadena, CA
Re: Why can't sct collimation be set permanently? new [Re: Footbag]
      #6185727 - 11/10/13 12:33 AM

I can assure everyone here that you really only need to collimate your SCT twice in the space of 10 years— a touch-up fresh of the box and once again when it takes a digger into the sand at Joshua Tree National Park.


Hey, at least the LX90 was in it's case when gravity got it's grubby mitts on it!


Post Extras: Print Post   Remind Me!   Notify Moderator  
orion61

*****

Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Why can't sct collimation be set permanently? new [Re: Lew Zealand]
      #6186290 - 11/10/13 10:43 AM

I always check mine, but something I haven't heard anyone mention is, Always fine focus Counter Clockwise when aligning, and checking optics. Mirror flop can drive you crazy

Post Extras: Print Post   Remind Me!   Notify Moderator  
Ed Holland
Carpal Tunnel


Reged: 06/16/10

Loc: San Jose, CA and Oxford, UK
Re: Why can't sct collimation be set permanently? new [Re: orion61]
      #6186702 - 11/10/13 02:15 PM

The counter clockwise rule is a good one.

What I would like to experiment with are some ideas I have to eliminate the mirror flop altogether, whilst retaining the neatness of internal focussing. To my way of thinking, this might (I stress the might) be achieved without costly additions to the design. There are some considerations:

1) The anti-flop system would have to be tolerant of temperature

2) It should not introduce undue resistance in the mirror motion, or shifts in focusing.

I'd retain the principle of two concentic tubes - it is a very good way to provide the starting point for aligning the optical axes of the mirror and image planes. What I am trying to conceive is a method to provide a higher tolerence bearing, or compliant interposer to maintain a more precise relation between the two cylinders than is provided by a grease film. I have some ideas for this.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Howie Glatter
Vendor


Reged: 07/04/06

Re: Why can't sct collimation be set permanently? new [Re: Ed Holland]
      #6186789 - 11/10/13 03:02 PM

> some ideas . . to eliminate the mirror flop altogether,
> whilst retaining the neatness of internal focussing.

The way to do it is simple in principle, but the mass-producers of SCTs don't seem willing to undergo the extra time, care, and quality control that would be necessary to machine the two linear bearing surfaces (mirror bushing bore and baffle tube exterior) to be true cylinders with a diameter difference of no more than 0.0005". Maybe they consider the cost to do this prohibitive, but it has been done by others, for example TEC on their Maksutovs, which have zero image shift. Even better would be three rows of pre-loaded rolling element bearings in grooves machined on the surfaces, spaced at 120 degrees. No doubt this would be expensive.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ed Holland
Carpal Tunnel


Reged: 06/16/10

Loc: San Jose, CA and Oxford, UK
Re: Why can't sct collimation be set permanently? new [Re: Howie Glatter]
      #6187329 - 11/10/13 06:51 PM

I was musing some simpler ideas:

.. an o ring at each end of the mirror tube, retained in a groove. Designed carefully, this could restrict off axis movement between the tubes. One would need to be sure how this held up to temperature changes.

.. make longitudinal cuts in the mirror tube ends to create compliant fingers - or add a spring collar to give the same function. These could be formed inward so that they are under preload when assembled with the baffle tube. Compromises would likely involve providing the necessary holding force without introducing undue friction.

... Collet type arrangements at each end of the mirror tube to allow adjustment of fit to the baffle.

These are just thoughts, not fully formed ideas, on methods that might be implemented without major cost impacts.

Ed


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | (show all)


Extra information
17 registered and 21 anonymous users are browsing this forum.

Moderator:  cbwerner, Starman27, kkokkolis 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 1822

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics