One of the things that drew me to a quality refractor (TV102) was that it should not need collimation. So why is Astro-Tech making collimation a selling point in the advertisements for some of their refractors? It was my understanding that collimating a refractor is not something the average user should need or want to do.
Collimation
Started by davidcolton, 11/18/2008 10:06PM
Posted 11/18/2008 10:06PM
Opening Post
Posted 11/18/2008 10:19PM
| Edited 11/18/2008 10:19PM
#1
David Colton said:
One of the things that drew me to a quality refractor (TV102) was that it should not need collimation. So why is Astro-Tech making collimation a selling point in the advertisements for some of their refractors? It was my understanding that collimating a refractor is not something the average user should need or want to do.
If a refractor has an adjustable cell, allowing slight variations in the tip of the entire lens, then collimation is quite easy and something anyone can do. Normally, however, refractors hold their collimation well and adjustment is usually not required.
Some apparently have the ability to adjust the relation of the two lens elements. IMHO, this is a sign of poor cell design or tolerances that are set too low, either of which may be from a desire to keep the price low. I don't think it is something users should have to do - ever.
Clear skies, Alan
Posted 11/19/2008 01:09AM
#3
Collimation adjustments are very useful for the advanced end-user.
Prime example: almost every TV scope I have tested (7) was out of collimation
when first received either from the factory or purchased used. Unfortunately
they are difficult to field collimate, and require a trip back to the factory,
for what would otherwise be a 5 minute adjustment. Same is true for some
Astrophysics Travelers I have tested (new from factory) -- images at the field
center are sometimes comatic, and a 5 mintue adjustment would fix it, but there
is nothing you can adjust. Usually a coma-free area in the focal plane
can be located, so I know it is possible, but there is no way to move it to
the field center. The only high-end refractors I have seen that did not
need collimation adjustments were some of the smaller TMB lensed scopes
-- 80, 100, and some 130mm. From my experience most refractors would benefit
from having adjustments available. Just because there is no adjustment
or a claim "not to need adjustment" does not mean it gives the best
possible image. Adjustmens typically add some weight and size to scopes,
so there are indeed trade-offs. But I am pretty demanding on scopes --
I like to see text book Airy patters and 100x per inch on double stars.
A little coma, astig, etc. is not appreciated when it could be
so easily fixed.
Prime example: almost every TV scope I have tested (7) was out of collimation
when first received either from the factory or purchased used. Unfortunately
they are difficult to field collimate, and require a trip back to the factory,
for what would otherwise be a 5 minute adjustment. Same is true for some
Astrophysics Travelers I have tested (new from factory) -- images at the field
center are sometimes comatic, and a 5 mintue adjustment would fix it, but there
is nothing you can adjust. Usually a coma-free area in the focal plane
can be located, so I know it is possible, but there is no way to move it to
the field center. The only high-end refractors I have seen that did not
need collimation adjustments were some of the smaller TMB lensed scopes
-- 80, 100, and some 130mm. From my experience most refractors would benefit
from having adjustments available. Just because there is no adjustment
or a claim "not to need adjustment" does not mean it gives the best
possible image. Adjustmens typically add some weight and size to scopes,
so there are indeed trade-offs. But I am pretty demanding on scopes --
I like to see text book Airy patters and 100x per inch on double stars.
A little coma, astig, etc. is not appreciated when it could be
so easily fixed.
Funding Member
