9 May 2018 at 8:46 pm #579453
I think the problem lies in the collimator body being loose in its support frame,having a bit of play between the threads the body is being pulled toward the motor side of the instrument and in doing so the line is being pushed towards the edge of the achromatic lens. Hopefully adjustment of the collimator screws will be enough to alleviate the tilt with just enough tension to allow rotation but at the same time keeping the collimator body square to the grating/camera sensor.
Alun12 May 2018 at 7:04 pm #579465
I have checked the collimator mounting screws all good, but the double line is still present.
I will adjust the collimator lens screws as tight as possible, so that it just rotates and see if that cures it.
Essex UK12 May 2018 at 11:46 pm #579469
Have been looking at the images of your neon lines again and something is puzzling me. They are obviously taken with the same camera but why are they different in that in one image there are three bright lines (plus fainter lines) but in second image only two are visible. Also I’ve noticed along with the doubling effect on the right hand line the fainter line next to it to the right again is still a single line,if doubling effect was caused by the collimating lens being pulled to one side then this line too would be distorted.
Alun13 May 2018 at 1:49 am #579470
The spacing of the lines is different in the two images and there are several extra weak lines in the one with the close double. There has been a big wavelength shift to the left of about half a field between the two images and we are looking at a different part of the spectrum. (The line on the right in the first spectrum corresponds to the line on the left in the second spectrum. The doubled line is outside the right hand edge of the field in the first spectrum)
Robin14 May 2018 at 6:26 pm #579478
Alun and Robin,
That’s because I adjusted the micrometer hence the shift in wavelength.
I will repeat this without touching the micrometer an post pics.
I spent Sunday morning fiddling with it adjusting the collimator lens screws but the double line is still there.
When I took the belt off and went back 30 min later it had reverted to a single line !
Thanks for your inputs,
Essex UK14 May 2018 at 7:17 pm #579480
I would honestly stop using the modification at this stage before there is any damage done to your Lhires,there is something obviously wrong whilst using the belt and it is twisting the collimator lens support housing somehow. Maybe the threading of the lens housing is different on the newer models of Lhires,possibly a much finer pitch than the original design I don’t know, but if that is the case then the belt mod could be pulling the thread out of the other hence the doubling (distortion) of the lines. Worse case scenario is that the collimator body ends up cross threading 🙁
Alun14 May 2018 at 11:10 pm #579482
I think you will find the double line is not a fault and really is a close double
Robin15 May 2018 at 11:56 am #579488
I agree with Robin in that after replacing the 2400 grating back into my Lhires that the line is indeed a close double. Whilst using the unit with the 1200 grating the line looks to be a single which is why I was puzzled to what was going on.
Alun23 May 2018 at 11:26 am #579521
Alun and Robin,
Thank you for your advices.
I have not had a clear night to re test !
I don’t think that cross treading is an issue, the tension on the belt is not much at all, so far not a problem. BUT you never know, when I had the collimator lens housing out, I could see no evidence of cross threading.
Robin 2 questions;
1. I removed one fibre washer in the collimating lens housing – as you stated in a previous post – but the lens was loose in the housing, I put the fibre washer back. So, how did you overcome the loose fitting of the lens inside the housing without replacing the fibre washer ? Perhaps your Lhires is different to mine ?
2. I do not recall seeing this double calibration line until I motorised the Lhires !
So, if the double line is real, can it be used as a valid calibration line ?
I will be at the AAVSO meeting.
Essex UK23 May 2018 at 12:18 pm #579522
It is over years ago since I built my LHIRES but just checked and I see I actually just moved both washers to the same side. Take care to tighten the screws evenly and not to tighten too much as it brings the lens into direct contact with the metal holder. I would only do it if you are seeing significant shifts in the lines backwards and forwards as the lens is rotated. Presumably the problem in my case was uneven thickness of the washers. I did it to prove what was going on. It worked so I left it rather than trying different washers.
I suppose you could use the double line for calibration if you can identify the wavelengths. You could check Richard Walker’s Atlas to see if they are identified
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