ghosting!

[philj]

Coma is different to ghosting Louis, coma is a streak from the image ghosting is just that a ghost of the image. The more misalignment the further away it will be from the main image.

[Louis D]

6 hours ago, philj said:

Coma is different to ghosting Louis, coma is a streak from the image ghosting is just that a ghost of the image. The more misalignment the further away it will be from the main image.

Yes, and steviebee was first describing a classic ghost image, but then started describing a classic comatic image.  It's certainly possible both can be caused the objective being spaced incorrectly and/or tipped.

[steviebee]

Just an update, I am writing this red faced with embarrassment . Well after having the lens's out again yesterday and putting them back in order It was worse. I was at the point on giving up on it and asking SWMBO for an advance on my salary so I could pop out today and get a new scope. Last week I found an article on the net to show you how to strip and clean a refractor. I followed the instruction (or so I thought) to the letter. I re read it last night, and the penny dropped. I had put the front lens in back to front. I had put the large convex side facing out instead of the small convex side. Put it in the right way round and a Happy bunny again. Thank you all for the help you gave me ( heaven knows I need it).

Steve.

[CaelumVidentis]

Conversation with Google Bard:

 

Do amici prisms in astronomical telescope diagonals (RACI) exhibit inherent aberrations when viewing a bright target, such as the moon?

 

 

 

Yes, amici prisms in astronomical telescope diagonals (RACI) can exhibit inherent aberrations when viewing a bright target, such as the moon. These aberrations include:

 

• Diffraction spikes: These are bright lines that appear to radiate from bright objects in the field of view. They are caused by the diffraction of light around the edges of the prism.

 

• Secondary spectrum: This is a slight blurring of the image due to the prism's inability to perfectly separate the different colors of light.

 

• Spherical aberration: This is a type of optical aberration that causes the image to be blurry at the edges. It is caused by the fact that the prism does not bend light rays equally at all points.

 

These aberrations are most noticeable at high magnifications and with bright objects. For this reason, amici prisms are not generally recommended for astrophotography or for viewing very bright objects. However, they can be a good option for general observing and for viewing faint objects.

 

Here are some tips for minimizing the effects of aberrations when using an amici prism:

 

• Use a lower magnification.

 

• Use a dark sky.

 

• Avoid viewing bright objects.

 

• Use a high-quality prism.

 

If you are concerned about the effects of aberrations, you may want to consider using a mirror diagonal instead of an amici prism. Mirror diagonals do not exhibit the same aberrations, and they are generally considered to be a better option for astrophotography and for viewing bright objects.

 

 

Could the aberration be a ghost image of the moon at the opposite side of the apparent field of view?

 

Yes, it is possible that the aberration you are seeing is a ghost image of the moon at the opposite side of the apparent field of view. This is a type of optical aberration called grating ghosts. Grating ghosts are caused by the reflection of light off of the surfaces of the prism. The reflection of light can cause a secondary image of the object to be seen at the opposite side of the field of view.

 

The ghost image of the moon will be fainter than the actual image of the moon, and it will be slightly blurred. The ghost image will also be inverted, meaning that the left side of the moon will appear on the right side of the ghost image, and vice versa.

 

Grating ghosts are most noticeable at high magnifications and with bright objects. They are also more noticeable when the prism is not perfectly aligned. If you are concerned about the effects of grating ghosts, you can try to minimize them by using a lower magnification, by aligning the prism more carefully, and by using a dark sky.

 

Here are some additional information about grating ghosts:

 

• They are caused by the reflection of light off of the surfaces of the prism.

 

• They are most noticeable at high magnifications and with bright objects.

 

• They can be minimized by using a lower magnification, by aligning the prism more carefully, and by using a dark sky.

 

•

[bosun21]

This thread is 7 years old 🙂.

[John]

2 hours ago, bosun21 said:

This thread is 7 years old 🙂.

It started before AI became so accessible 😁

Edited August 1, 2023 by John

[bosun21]

38 minutes ago, John said:

It started before AI became so accessible 😁

A sign of the times I reckon.