7 replies to this topic

[stephenws]

Do small, thin, lens multicoating sleeks (very small, thin scratches in the multicoating only observable by shining a bright flashlight at the lens) really cause any noticable problems for visual observing?

 

My experience is they are just cosmetic defects that are so far out of focus that they have no impact on the view through the scope.

I would suggest they only affect resale value.

 

Any thoughts?

[matt_astro_tx]

I think you're right on target.  Unless they're huge blemishes, they shouldn't affect anything, especially if you're only doing visual.

[hyia]

Do small, thin, lens multicoating sleeks (very small, thin scratches in the multicoating only observable by shining a bright flashlight at the lens) really cause any noticable problems for visual observing?

 

My experience is they are just cosmetic defects that are so far out of focus that they have no impact on the view through the scope.

I would suggest they only affect resale value.

 

Any thoughts?

For the main objective, I think the conventional wisdom is that they don't matter.  If they are in the coatings of the eyepiece, I think it is more debatable.  A scope with a sleek wouldn't bother me much, but I wouldn't want an eyepiece with one even though I have no proof it would be detectable.

[vtornado]

I have a scope with a few sleeks in the coatings.  It delievers exceptional lunar/planetary views.  

 

I suppose a high level of sleeking (whatever that means) may cause scatter, and reduce contrast.  

[TOMDEY]

Yeah --- very very meh in the great scheme of things. This is why the professionals (both fabrication and use) refer to such things with words like "cosmetics" and "beauty". Telescopes are meant to be looked through... not at. I bought this crazy expensive brand new binocular for $6400 (+ $15 shipping heh and $512 NYS sales tax Auugh!)  I noticed a couple of sleeks on the external surface of one eye lens (not the other) and said, "Geesh... you would think that for $7K... Aw, meh" and proceeded to enjoy the bino for approaching 2 years this coming spring!    Tom

Edited by TOMDEY, 27 November 2022 - 05:26 PM.

[ngc7319_20]

For the main objective, I think the conventional wisdom is that they don't matter.  If they are in the coatings of the eyepiece, I think it is more debatable.  A scope with a sleek wouldn't bother me much, but I wouldn't want an eyepiece with one even though I have no proof it would be detectable.

Agreed, objectives are more forgiving.  The light beam covers the entire aperture, and the sleek has very little area compared to the entrance aperture area.

 

I think very fine sleeks won't effect eyepieces.  But it is more sensitive.  The light beam for a star or planet through an eyepiece will be smaller -- maybe a millimeter or less at high powers.  So the sleek will affect a greater percentage of the light beam.   I know scratches -- wider features -- can definitely effect eyepiece views.  Sometimes you see a diffraction spike from an eyepiece scratch, and the spike rotates as you rotate the eyepiece.  Probably you would need to test the eyepiece on some bright planet to know exactly what the impact will be.  Try to move the planet around the field, etc.

[donadani]

If you search long enough on different angels with a really strong LED lamp you can find sleeks on nearly every scope of every brand.

 

Some more then others but none will affect your views.

[Jeff B]

Sleeks and outright scratches on objectives can only be seen by looking through the front of the scope.  

 

I don't observe that way.