3 replies to this topic

[Luis Abraham]

Hello!

 

A few weeks ago I bought a 2" L-Ultimate filter that I used for the first time the past weekend along with an Askar SQA55 and an ASI2600MC Pro Camera.

 

I set the exposure time to 300 sec and since the first image I noticed some kind of spikes on the brighter stars when checking the preview images, but I just ignored it since the previews in my phone were not very good, so I continued shooting.
Today I downloaded the images to my laptop and I found out that all the exposures have those weird spikes.

 

Below you can see a couple of portions of my image, as well as the Aberration Inspector where those artifacts are very noticeable across the entire field.

 

I have checked several reviews of the Optolong L-Ultimate filter and I didn't see anything like this before.

 

I have used this very same telescope and camera with the Optolong L-Quad Enhance filter and I got perfectly round stars.

 

I also thought it might have been a guiding problem, but I don't see anything wrong with the nebula, the issue is only with the stars.

Do you think I may have gotten a bad/defective filter? or is there something I may be doing wrong?

 

 

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Edited by Luis Abraham, 05 February 2025 - 12:00 AM.

[acrh2]

That looks like an obstruction to me. Probably a hair over the lens/filter/sensor? You won't see the obstructing object itself in the image because it would be too defocused, but I think that's the diffraction pattern it would create in stars. You often see these things when people shoot through power lines.

Edited by acrh2, 05 February 2025 - 12:07 AM.

[w7ay]

Hello!

Do you think I may have gotten a bad/defective filter? or is there something I may be doing wrong?

Loosen the filter and rotate it by 1/8 of a turn or so.  Did the spikes also rotate relative to the long axis of the image?

 

If so, look carefully around the retaining ring of the filter glass (and also the back side of the filter) with a magnifying glass to see if there is any tiny piece of dirt or metal filing sticking into what should be a perfectly circular aperture.  A single piece of dirt (odd number) will cause two diffraction spikes.

 

Chen

[Luis Abraham]

That looks like an obstruction to me. Probably a hair over the lens/filter/sensor? You won't see the obstructing object itself in the image because it would be too defocused, but I think that's the diffraction pattern it would create in stars. You often see these things when people shoot through power lines.

Thanks acrh2, I always use an air blower when assembling my rig, but still a hair or dirt can fall over the optics, specially when you are out in the field. I will take a close look to the scope, filter and camera to make sure everything is clean.

 

 

 

Loosen the filter and rotate it by 1/8 of a turn or so.  Did the spikes also rotate relative to the long axis of the image?

 

If so, look carefully around the retaining ring of the filter glass (and also the back side of the filter) with a magnifying glass to see if there is any tiny piece of dirt or metal filing sticking into what should be a perfectly circular aperture.  A single piece of dirt (odd number) will cause two diffraction spikes.

 

Chen

Thanks for the advice w7ay, I will try that.

I will check the glass retaining ring looking for any piece of metal or dirt.

I will also run a couple of tests with and without the filter just to make sure it has nothing to do with focus or scope optics.

I will compare it with my L-Quad filter as well. I don't have a filter wheel but I do have a filter drawer, so I can change the filter easily, refocus and take a couple of shots for comparison.