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 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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Im no expert, but if everything worked fine before adding the L-ultimate and is doesn't now, I'd send it back for another. Maybe it has an optical irregularity. Good luck.
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Hey Luis,
how cold was it during your imaging? This looks a bit like pinched optics. Just a guess.
CS Ben
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Hello, I have this filter too, and I get perfect results.
Some ideas to help you.
- There may be a problem of sharpness due to the temperature of the tube, which needs to be refocused after an hour's exposure.
- Maybe a condensation problem, do you have heating strips?
I hope you solve your problem as soon as possible.
Best regards
Jacques
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Successfully used (and using) the L-Ultimate filter with various optical tubes and focal lengths without any issues with the stars.
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Ben Schubert-Ludwig:
Hey Luis,
how cold was it during your imaging? This looks a bit like pinched optics. Just a guess.
CS Ben Hi Gen, It was not very cold, it was like 11°-12° Celsius. I was also thinking in a pinched optics problem with the filter. I will take a closer look to the glass retaining ring looking for any piece of metal or dirt. Jacques Bocquet:
Hello, I have this filter too, and I get perfect results.
Some ideas to help you.
- There may be a problem of sharpness due to the temperature of the tube, which needs to be refocused after an hour's exposure.
- Maybe a condensation problem, do you have heating strips?
I hope you solve your problem as soon as possible.
Best regards
Jacques Hi Jacques, About focus, I got those diffraction spikes in every single exposure, since the first one to the last and I didn't notice any difference in sharpness. It was a very low humidity night and I was also using a dew heater strip so, I'm pretty sure it was not a condensation problem. I will 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 also compare it with my L-Quad filter. 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. Thanks!
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did you try turning it around?
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Check for scratches on the filter. I experienced a similar diffraction spike when I had a scratch on my camera window.
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Jeff Bennett:
did you try turning it around? Not jet but that's one of the things I'm going to do when I test it again 👍🏻
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Lorenzo Massimi:
Check for scratches on the filter. I experienced a similar diffraction spike when I had a scratch on my camera window. I checked the filter this morning and I didn't notice anything wrong with it, no, dust, no burrs in the retaining ring, no scratches
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We have this filter and its been perfect on all of our imaging systems, from 135mm to 2500mm. We occasionally get spikes just like this however and its usually due to high cloud, mist or excessive moisture in the air. Slight dew on any of the optical surfaces (including the camera window) can do similar. Make sure its not the filter by changing to another like you've said and if it isnt check these other causes. Do you use the dew heater on your 2600?
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Stargazers SA - Andrew:
We have this filter and its been perfect on all of our imaging systems, from 135mm to 2500mm. We occasionally get spikes just like this however and its usually due to high cloud, mist or excessive moisture in the air. Slight dew on any of the optical surfaces (including the camera window) can do similar. Make sure its not the filter by changing to another like you've said and if it isnt check these other causes. Do you use the dew heater on your 2600? Hi Andrew, I used a dew heater strip on the scope but not on the camera, however I didn't check if the Anti-dew was turned on in the camera settings. I'm pretty sure I have the "Turn on Anti-dew while cooling" option enabled in the Advanced Settings but I recently read about a new bug introduced in the latest ASIAIR firmware version, it appears that even when this option is enabled the Anti-dew is not turned on. I'm planning to run some tests tonight without the filter and also with other filter in order to see if I still get those spikes, I will make sure the "Anti-dew" option is enabled.
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Probably not this, but I do get something similar when my target get behind the clothesline. Do you have any obstruction in your telescope line of sight in a portion of your sky? Even if really small, it'll make diffraction spikes.  |
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After several tests targeting different stars, rotating the filter and using a telescope as well as a camera lens we finally concluded the issue was caused by the filter.
Until now I don't know what is the cause, I don't see any scratches in the filter, dirth or metal burrs in the retaining ring.
Yesterday I got a new filter and ran some quick tests and this time I got perfectly round stars, no more diffraction spikes, so I'm happy I was able to get a replacement.
Thanks to all who came up with ideas and possible causes to the problem, I hope I can finally take some real images with this new filter.
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