Eyepiece influence on collimation

[Mark in Macc]

An interesting question to ponder. A friend of mine recently mentioned that eyepiece type can affect collimation. He had his C8 collimated at his local astro shop but when he tried a star test whilst observing, the collimation was clearly out. He was informed that it may be down to the eyepiece type that he used. Is there any sense in this?

[Sirius Starwatcher]

Good question Mark I hope some experienced members can answer the question.

[YKSE]

I wouldn't expect type of eyepiece to be the most possible reason, 

The more common sources are: if the diagonal used well centerred and tightened, if the eyepiece used well centerred and tightened, if the collimations screws were raasonably tightened when collimated, etc, also the scope should be properly cool when checking for collimation.

[spaceboy]

Given the amount of elements thrown in modern eyepieces it sounds feasible but I'm guessing highly unlikely ?? There are many variables in getting what appears to be a perfectly collimated scope like temperature of optics, temp in OTA, focuser and draw tube being aligned and remaining aligned through the whole travel, droop in the focuser, slop in the mirror in SCT, MAK's and similar, distortion in the tube depending on rotation, clamping of eyepiece in focuser, temperature of eyepiece so on and so on..... everything has it's play and as long as your enjoying the views I think that's all that matters IMHO as seeing and transparency in my eyes plays a far more damming effect on the views than any miss-collimation I have ever had.

It is also a good idea to star test on several stars as I have seen terrible collimation on one star become perfect on another just by taking the flex out of my Newt (more an issue on my EQ mount than AZ)

[John]

I can't be sure about this but I'd have thought that the eyepiece is just a passive receiver of the light cone from the primary. If the scope optics are out of collimation the damage has been done before the optics of the eyepiece are involved. I have seen eyepieces with lens elements out of place where the eyepiece added aberrations such as false colour, astigmatism etc but no collimation errors.

C8's can have issues with mirror flop where they go out of collimation as the scope reaches a certain angle. It could also be a residual air current within the tube affecting the image.

There are a number of other candidates I'd suspect before the eyepiece.

[Mark in Macc]

That's essentially what I was thinking too. It sounds a bit fishy to me.

[ronin]

If the collimation depends on the eyepiece then seems little point in collimating the scope as one eyepiece may be OK the next awful, so why bother.

It does sound like an excuse.

However collimation is a case of mechanical alignment - everything on the axis and orthogonal to it. There are several bits in any scope that can therefore be a bit off.

Still suspect an excuse however.

[marcopolo]

_{I think hte only way an eyepiece could effect collimation is if the weight of a large eyepiece caused the focuser to deflect in some way fro mthe optical axis. But by it's very definition a field of view is everything off axis so all it would do is shift the optimally placed portion of the field of view. Which is to say .....no!}

[Scott]

I'd be more inclined to think the trip home has messed up his collimation or it wasn't done right in the first place?

[alan potts]

Something I have noticed on collimation is with scopes like Maksutovs the defocused star is affected by where you view it. If you collimate and using this method on this type of scope and Sc's, it is about the only way without spending loads, the secondary shadow should appear in the middle of the light circle from the defocused star. Now, and it is more noticeable on my Mak, move the star to the edge, now the scope looks out of alignment. The shadow only appear in the centre when the star is in the centre of the FOV, within reason.

It is also there a little on the SC but nowhere near as obvious, this could be what is being seen by your friend. It makes no difference as far as I see with eyepiece choice though I have never used an Ethos to do this .   

[Lowjiber]

I can't be sure about this but I'd have thought that the eyepiece is just a passive receiver of the light cone from the primary. If the scope optics are out of collimation the damage has been done before the optics of the eyepiece are involved. I have seen eyepieces with lens elements out of place where the eyepiece added aberrations such as false colour, astigmatism etc but no collimation errors.

C8's can have issues with mirror flop where they go out of collimation as the scope reaches a certain angle. It could also be a residual air current within the tube affecting the image.

There are a number of other candidates I'd suspect before the eyepiece.

I can't be sure about this but I'd have thought that the eyepiece is just a passive receiver of the light cone from the primary. If the scope optics are out of collimation the damage has been done before the optics of the eyepiece are involved. ...

Bingo!!!

The collimation ensures that an image is delivered in front of the eyepiece.  The focuser simply moves the eyepiece to the point where the image has converged.

If someone is blaming your eyepiece, tell them "Thank You" and never go back.

Clear, Dark Skies