8 replies to this topic

[Daniel Dance]

From my limited research, I'm told this star artifact is due aperture vignetting as opposed to pinched objects which usually has a 3-point diffraction pattern.

 

Has anyone had this issue with the FRA500 (or similar scopes) and how have you dealt with it?  I'm told its fairly common, and could be a result of the dew shield, but it hasn't been clear here for me to test that aspect out of it.

Thanks in advanced.

 

 

 

2024_1111_aperturevignetting by Daniel McCauley, on Flickr

[ShortLobster]

This doesn't look like vignetting to me. I'd say it's either pinched optics or an obstruction in the imaging train. 

 

Suggest taking the imaging train off and looking at a bright star through an eyepiece. If it is is still distorted you can rule out the imaging train. 

[Daniel Dance]

This doesn't look like vignetting to me. I'd say it's either pinched optics or an obstruction in the imaging train. 

 

Suggest taking the imaging train off and looking at a bright star through an eyepiece. If it is is still distorted you can rule out the imaging train. 

It's definitely aperture vignetting.  Pinched optics doesn't present itself such as this.

Its caused when the edge of the field doesn't see full circular opening of the aperture.  I'm just not sure how to correct it which is what i'm asking.

[Jim Waters]

IMO this is pinched optics.  I have seen and corrected this on two scopes I owned in the past.  If the scope was just purchased send it back, get a replacement or a refund.

Edited by Jim Waters, 11 November 2024 - 12:39 PM.

[B 26354]

Gotta disagree. I'd say it's definitely pinched optics. Read this, and look at the "original O-ring / no O-ring" photo, about a third of the way through the article:

 

https://interferomet...ml?view=sidebar

 

Pinched optics don't always form a three-sided defect.

[Daniel Dance]

Gotta disagree. I'd say it's definitely pinched optics. Read this, and look at the "original O-ring / no O-ring" photo, about a third of the way through the article:

 

https://interferomet...ml?view=sidebar

 

Pinched optics don't always form a three-sided defect.

If you read the article, especially about the part of the o-ring, or no o-ring, that describes aperture vignetting where something is making the "aperture hole" non-round.  Pinched optics is something different entirely where the optical glass itself is distorted, which i don't think is the case. 

The author of the document himself doesn't seem to understand what he is writing about.  A notch in the o-ring doesn't cause pinched optics, but it *does* create an imperfect circular aperture hole.

 

At least the image still looks somewhat okay if you zoom out.

 

The Great Orion Nebula, M42 by Daniel McCauley, on Flickr

[Daniel Dance]

I just want to give a shout out to Agena.  I don't know if they browse Cloudy Nights, but A+++++ service.

 

I contacted them with this issue this afternoon, and I already have new scope being shipped out to me.

 

That is A++++++ customer service.  Special thanks to John over there for assisting with this!

[licho52]

An opinion that Tommy Navratil has no clue what he's talking about is not something one expects to see, even on Cloudy Nights.

[Jim Waters]

I just want to give a shout out to Agena.  I don't know if they browse Cloudy Nights, but A+++++ service.

 

I contacted them with this issue this afternoon, and I already have new scope being shipped out to me.

 

That is A++++++ customer service.  Special thanks to John over there for assisting with this!

My experience with Agena has been different to the point where I will not buy expensive stuff from them.  Its been a pain to return scopes with bad optics.  YMMV