Resolved SBIG 16803 - image train rigidity

Thanks Colin,

I just removed the outer guard to inspect the fan and to make sure all the blades are there and that there was nothing that might be impacting the free rotation. All looked good.

The trials I did on set back distance largely removed the field curvature issues in the corners, but if you look at every image, even the best ones they are elongated in the y direction and it is right across the image. This seems to be worse now than when I started out. The direction of the elongation does not align with the RA or Dec axes. It is this elongation or more precisely double stars that has stopped me getting to eccentricities of less than 0.6 and in more recent trials they are consistently worse than 0.7, even though there are no particular issues with distorted stars in the corners due to field curvature. I am almost certain this is a vibration issue.

The "fan off" test will tell it and I will do the test as soon as I get some clear skies

Has this issue arisen before?

Thanks,

Niall

 

In my case I had a fan with a bearing that had, somehow, gone bad. This is not somethings that happens a lot.

When I did replace it, it was a straight-up replacement with the same model etc.

So, it is not too likely you have the same issue, but I figured I would at least mention it as a (slight) possibility.

Thorsten

 

Thanks Thorsten.

When I turned the fan off the stars were round. When the fan is on they are highly elongated. It is clear that vibration from the fan is causing the elongated stars. I will write a small report with the details including pictures, but fundamentally when the fan is "on" the average eccentricity is ~ 0.8-0.85, which means the stars are nearly twice as long as they are wide. When the fan is off the average eccentricity was 0.4 - 0.55 which means the stars are on average 10% to 20% longer than they are wide and they look good to me....recognising as Colin pointed out to me that the sensor is bigger than the maximum image circle that Celestron specifies to have perfect stars.

I ran the "fan on" and "fan off" trials for the Luminance and Red filters and got the same thing. I then rotated to the SII position. I had previously removed this filter. This was a check to ensure that the fan wasn't jiggling the filters causing the issue. But no, the results were exactly the same. So with the fan on and no filter the stars were elongated as before and with the fan off they were basically round. The filters are not an issue.

So Colin, please advise what I need to do from here. This is a huge surprise. I have been barking up the wrong tree for months because frankly, even though I knew vibration was a possible cause of elongated stars, I had dismissed that possibility from my mind given the pedigree of this camera. In hindsight, this was a foolish omission.

Thorsten, thank you so much for your feedback. Of course, in the meantime, my searches on elongated stars show multiple posts where elongation and double stars have been cause by fan vibration, but none that I could find for the SBIG 16803.

Regards,

Niall

 

Many years ago (in 2013) I had a similar problem. Spent a lot of time to understand what was happening and it turned out that the problem was in the camera fans. I had a FLI camera, but it doesn’t matter, as I see it. I replaced standard fans with more expensive ones at a lower speed and with a special anti-vibration mount, and since then this problem has disappeared.

 

Thanks Andrei. This has taken me a long time to understand and frankly I am a bit annoyed with myself for not doing a better job of the root cause analysis. I was fixated on field curvature and just dismissed the vibration possibility, until I saw Thorsten's post.
May I ask what fan you actually bought?
Thanks Niall

 

Thanks Doug, as I looked back on my results, it seems to me that the eccentricity has been getting worse as time goes by. I was getting 0.6s then 0.7s now 0.8s. It made me wonder whether the fan is defective and whatever is causing the vibration....bearing? is getting worse over time. I am worried that that replacing the damping foam won't correct the issue. Is there a way to determine this?
Thanks, Niall

 

Noctua - https://noctua.at

 

Thanks Andrei,
I have made a note of that.
Regards, Niall

 

Hi Doug,

The fan makes a lot of noise, but I have no reference point to know what is reasonable and normal, however, you can hear for yourself. I made two videos the other night before I started the fan on/ fan off trials. Here are DropBox links to them.

https://www.dropbox.com/s/auogcinqvz1ng7z/IMG_2448.MOV?dl=0
https://www.dropbox.com/s/wch3ty1di4mrwiq/IMG_2449.MOV?dl=0

Can you advise whether this sounds normal. There also seems to be a "high" setting which cuts in from time to time.

Interestingly I had wondered whether I could produce an image by leaving the fan off and imaging at -10C, when the ambient temperature was 5C. However, even though I had ticked "fan off" and the power consumption was nowhere near 100%, the fan would come on for a few seconds every now and then so that made any imaging infeasible.

I am concerned that if the fan is defective, by the time I receive the foam, then run trials and show that it doesn't help and then you send a replacement fan another 3 or 4 months will go by. I am not sure how well air fright is operating these days with the pandemic.

Please advise.

Thanks Niall

 

Doug,

When did you switch to improved material?

I have 16200 and was suspecting fan vibration issue (discussed in another thread). Is it possible that you send me some replacement?

 

Hello all. I am so so so so so so so so glad I stumbled across this thread.

I’ve been dealing with similar issues for about 18 months now. I am using an STX-16803, Astrodon Gen2 LRGB filters, and I have a PlaneWave CDK12.5 mounted an MX+. PW support has been assisting me for the past 6 months.

I recently purchased the Hotech Advanced CT Laser Collimator (love it,) and got collimation down to 0.7” per CCDI. PlaneWave support is also pleased with collimation results, having run my star field images through their analysis software.

Just for giggles, and after reading this thread, I dialed down the fan to 30% the other night and my AO-X guided image eccentricity (per Pix) dropped from 0.8 to 0.3.

Sweet.

So is there a path to also obtaining some replacement foam? Should I open a separate support ticket? Thanks!!


Note my STX-16803 serial # is X18020009.

 

Here are the detailed results of my trails for completeness:

Red Filter Fan On vs Fan Off

Red Filter Eccentricity Fan On vs Fan Off

Red Filter FWHM Fan On vs Fan Off

Luminance Filter Fan On vs Fan Off

Luminance Filter Eccentricity Fan On vs Fan Off

Luminance Filter FWHM Fan On vs Fan Off


No Filter (in SII slot) Fan On vs Fan Off
No Filter (in SII slot) Filter Eccentricity Fan On vs Fan Off

No Filter (in SII slot) Filter FWHM Fan On vs Fan Off

 

Results of Star Roundness Trials after replacement of the Fan

Firstly a comparison of the noise made by each of the fans when cooling:
This is a movie of the original fan in operation:
https://www.dropbox.com/s/dytoss7aiqmwxar/IMG_2448.MOV?dl=0
This is the sound made by the new fan. In my judgement there is a large difference in the amount of noise produced by the fans and the new fan is much quieter:
https://www.dropbox.com/s/0cw3fystgouzy4b/IMG_2698.MOV?dl=0

Firstly this was the auto guiding performance: Satisfactory


Star Roundness Trial 1: New Fan ON





Star Roundness Trial 1: New Fan ON....repeat