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More Lhires III mods

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Alun_H's picture
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More Lhires III mods

 Been busy again tinkering with my Lhires III,this time automating the micrometer arm (grating angle actuator) and the focusing of the collimator lens. For the micrometer I used a JMI motofocus unit off my C9.25 attached to the lhires using two right angle brackets. Drive belt was taken from an old printer,cut a length and used araldite and heat shrink tubing to rejoin the ends. Didn't bother with gears as such,the belt grips the motor shaft and micrometer due to small teeth on belt. Motor is operated either manually with handheld control box,or connects to PC via a Shoestring Astronomy FCUSB box.

 For the focusing of the collimator lens I made a replacement cover so as to mount a Skywatcher focus motor. Cover is locked in place using original screw and is held by metal clip at other end. Using same belt,again cut to desired length and rejoined with glue and heat shrink,just looped over barrel of the collimator lens and over the shaft on motor (wrapped in hook side of velcro) and using enough tension to allow rotation but not too much to cause tilt in lens. Again PC control is via a Hitecastro focus control box.  Both systems work well and along with the automated calibration/flat lamp I don't need to touch the spectroscope at all whilst in operation and also allows me to work remotely when it's too cold :)

      Regards

        Alun

       

       

      

     

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Ingenious...

Well done Alun, that's a neat mod. 

Is there much weight added or vibration? 

Regards Tony

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A little..

Thank you Tony, there is a little bit of weight added,depends on size of motors, and the box to cover the motor is made from foam card so no weight there :)  As far as vibration is concerned I haven't witnessed any as such. I do know there is a very slight shift within the collimating lens when using motor but that can be sorted by adjustment of the original lock screws (found this out after my posting the info above).  I always thought I had focus on neon lines sharp when I set it up manually,but it's surprising how much sharper the lines get when I  can just nudge the rotation,certainly makes a difference.

     Regards  Alun

       

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Alun,

Alun,

Excellent work well done.

I would like to do the same conversion for the collimating lens on my Lhires.

What belt would you recommend and from where ?

Regards,

Jack

Essex UK

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Jack

 Hello Jack,

 Thank you.

 I got my belt out of an old printer I'd broken up, being a large loop of the stuff I just cut it to the length I wanted then re-joined the ends using Araldite and heat shrink tube.  I should think these guys will have what you are looking for though

  https://www.robotshop.com/uk/gears-belts-pulleys-tracks-sprockets-chains...

 An update:- A couple of findings,the motor and belts work as planned. No need for gear wheels on neither the collimator nor the micrometer spindle. No fear of belt slipping off the collimator due to lip on the end and both focus motors and micrometer have rubber tap washers on the ends to stop belt slipping off. I am planning on changing the Skywatcher focus motor as it is a bit on the  bulky side and now the Lhires will not go back into its supplied case, because of this I am looking at purchasing a much smaller JMI focus motor so as that the box covering the motor now can be done away with. I did state in my last message that there was some shift when operating the focus motor but realised afterwards that there is the same amount of shift when operated manually and also the lock screws need to be adjusted just loose enough to allow the collimator to turn but enough pressure to stop it tilting toward the motor. Same again with the belt, there is hardly any pressure against the collimator and motor, just enough to allow belt to keep contact without slipping . 

   Regards

     Alun

  

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Alun,

Alun,

Thanks for the link and further info.

Shame that motor is a bit bulky, I assume you don't have it permanently set up in an observatory.

Wouldn't a bigger case be a cheaper option than another motor and having to replace what works ?

I see there are a few options from RVO to consider;

https://www.rothervalleyoptics.co.uk/jmi-motofocus-for-celestron-c8-.html

Please can you post a picture showing how and where the motor is attached / bolted to the Lhires.

How many holes did you have to drill ?

This is a worthwhile modification.

Thanks for your efforts.

Jack

Essex UK

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Jack

Jack,

 I have an observatory but don't leave the Lhires attached to scope as at times I may use the Alpy or stick a camera on the scope to image :)

 The motor focus you linked to is much the same as the one I used to operate the grating adjustment,but the one I have ordered to replace the collimator motor is much smaller...

   https://www.rothervalleyoptics.co.uk/jmi-motofocus-for-skywatcher-pro-re...

  I am hoping I can modify the cog wheel covers by removing the large one and still use the top part to cover slot for belt again hoping to do away with the large box I have at the moment. Okay using the bulky motors but they do add extra weight to the unit. 

 Lhires was not harmed in any way during these modifications, no extra holes needed and all can be reverted to original. New replacement door/cover made from a bit of ply made long enough to attach the motor bracket (simply a length of ali bent to 90* angle) Bolt holes countersunk on reverse of cover so as not to foul body of Lhires. For latching down I just copied the original idea and moved it to the far end of the cover (only place it can go to clear belt). Also note the yellow velcro (hook side) on the motor cog, helps to grip the belt. (ignore the standoff nuts holding the bracket,they are all I had in the required size!) 

  Regards

       Alun

        

        

      

    

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Alun,

Alun,

Thank you for further information.

Looking at the link its difficult to see how the JMI would work without some modification, there appears to be no shaft correct ?

Is there one similar to the Skywatcher ? which appears to bolt straight on to the Lhires body.

Regards,

Jack

Essex UK

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Should work

 Jack,

   The motor has a shaft which is obviously a lot smaller than the Skywatcher motor,I am thinking the shaft's length will be near on the width of the belt so I will use the cover as a stop to keep the belt in place or failing that I will make a sleeve to slide over the shaft so as to make it longer. The motor itself will be easier to attach to the custom cover due to the bolts being at the rear of the unit (aiding stability of motor) 

              

  Another alternative to the Skywatcher from JMI is just as bulky and same price as all the JMI motor focusers (£185) is pictured below, but not sure if the width between mounting bracket forks will clear the belt so will possibly need modification with a file. Just to note the Skywatcher focus motor is only £45 - £50 if the bulkiness of the mod isn't a concern.

         

   Best Regards

       Alun

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Alun,

Alun,

RVO say Skywatcher or JMI will do the job.

Its not a question of money, but what works.

Bulkiness should not be a problem, I use a film changing bag to keep the unit light tight which should also accommodate the motor.

I suggest a slotted bracket would be good if the belt needs adjustment.

This is a great improvement.

Thanks for your efforts,

Jack

Essex UK 

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Good Luck

 Jack,

    You are welcome and I wish you good luck with your modification :)

 I agree the slotted bracket would be a better choice, and your mentioning it has made me come to realise that the motor I have planned to use hasn't got that luxury!  Oh well,more head scratching (avoiding the splinters) when the motor arrives :)

   Best Regards

       Alun

 

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Alun,

Alun,

Which motor have you ordered ?

And why can't you use a slotted bracket ?

From your posts I am minded to go with the Skywatcher, any reason not to ?

Regards,

Jack

Essex UK

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Jack

 Jack,

   It is the small one pictured in my last posting. I will get round it,just means I'll have to modify the bracket on the motor.If I cannot get it to fit satisfactorily then I'll attach it to my 6" refractor and keep the Skywatcher on the Lhires

   Only being bulky other than that it works I have no problem with it at all. In fact if the box covering the motor were to be reduced to just  cover the cog and slot to stop light and dust then I believe most of the bulk will be lost. The motor works with the HitechAstro focus controller for PC control. I recommend it for the job :)

  Best Regards

     Alun

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Alan,

Alan,

Thanks for clarifying I will order the Skywatcher.

Which is the smaller of the two, top or bottom picture ?

How long is the belt ?

Regards,

Jack

Essex UK

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Belt

 Jack,

 The belt diameter is roughly 3 inches in diameter depends on the thickness of the material you use to make the replacement door/cover. I found it easy to work out the diameter when all the bits where attached to the Lhires,then used length of string to wrap round collimator body and cog of motor. Have attached another photo showing the size of the teeth on the belt (these are small,don't need them too large) and the bits and pieces before assembly. As I described in my opening post the belt was originally in an Epson printer. Being a large loop I just cut it open and then just cut suitable lengths off to use for both the micrometer shaft and this mod,to close the loop I used Araldite and heat shrink tube.

     

     

      

Just to clarify the motor I have on order is the one I've added the text to a few posts back.

   Best Regards

       Alun

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Alun,

Alun,

Thanks for your advices. and pictures.

Today I installed the Skywatcher motor to the Lhires.

I have yet to get a suitable drive belt.

What is the yellow attachment on the motor shaft ?  

Regards,

Jack

Essex UK

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Jack

Jack,

  Looking good, I was going to ask how you intend to cover the hole but then remembered you use the black bag to cover the whole Lhires. Hopefully you'll find a belt to fit soon, as I stated earlier the Robot shop should have something suitable. The yellow is just a strip of velcro (hook side) stuck to the spindle just to give the belt a bit more purchase.

   Regards

     Alun

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Alun,
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Jack

 Jack,

    That belt looks ideal for the job. To join my belt I made sure that each end was in the middle of a tooth to ensure ample area to bond, slid a length of heat shrink tube on belt then used Araldite rapid (sets in 5mins) to glue the joint. Held the belt in place until glue held but was still slightly tacky then slid tubing in place over joint and added heat to shrink ensuring a good strong bond :)

  Regards

   Alun

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Alun,

Alun,

I found a belt that fits from RS Components;

https://uk.rs-online.com/web/p/timing-belts/7785064/?sra=pstk

Saves cutting and gluing.

The belt around the lens keeps slipping, but sort of works, I will try some Velcro or o ring. 

Regards,

Jack

Essex UK

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Slipping

 Jack

  I had to adjust the white screws on the collimator body until the belt stopped slipping. In fact I took one of them out completely leaving just the one to add tension to the body. Other than that,and the velcro added to the motor shaft nothing has been stuck to the collimator body. One other point now that you have removed the cover/door I would be more inclined to block off the gaps  that have now been introduced around the lens body so as to stop dust getting to the grating itself. Got the idea from Paul Lukas (second photo down)..

    http://jazzistentialism.com/blog/?page_id=1397

    Regards

       Alun

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Alun,

Alun,

Thanks for the link, some good modifications.

I can put one cover back on once I have got the belt gripping properly, will try putting o rings over the lens thread.

The Lhires is contained in a film changing bag which should keep dust and light out. 

A question, as I do not operate the spectrograph remotely is there any point in motorising the micrometer arm ?

Regards,

Jack

Essex UK 

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Alun,

Alun,

Which side did you remove the screw from the collimator body ?

Regards,

Jack

Essex UK

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No need to remove

 Jack

   Had a play with my setup last night and found that there was a slight play between the collimator body and its supporting frame so have now replaced the screw (was the one on the motor side) but have it screwed in just touching the collimator body to prevent unwanted tilt but at the same time not adding any force to tighten the turning of the body. All adjustment for tension on the collimator body is carried out by the screw on the opposite side.

 I motorized the micrometer shaft so that I didn't have to touch any of the kit during a session and I also run remotely so comes in handy. But the downside is the speed of the focus motor makes moving the grating from the Hb region to the Ha region painstakingly slow :(

  Regards

     Alun

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stability

Hi Alun,

Unwanted movement of components is a significant issue in spectrographs and the the tolerances are very small. (1/5 pixel (~1um) shifts are easily detectable.) The LHIRES design is particularly prone to these problems.  Have you checked by aiming the spectrograph in different directions (NSEW,Zenith) and watching the position of the lamp lines that your mod is not introducing any additional unwanted instability ?

Cheers

Robin

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Once focused

 Hi Robin,

    Yes I have checked in all directions and found no shift at all in the lines. There is a slight shift when using the motor to focus (much the same as if I were manually focusing) but this can be reduced as I stated earlier by adjusting the tension of the screw on the collimator body support opposite to the motor,once the unit is focused everything is stable.

   Regards

     Alun

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good news

That's good news. I see measurable flexure with my LHIRES even with everything done up tight. It was one of the early kit ones so perhaps I should take it all apart and rebuild it !

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Alun and Robin,

Alun and Robin,

Thanks for your advices.

I will take measurements as suggested.

A tear down sounds like a good idea which should sort any instability problems.

1. There is a problem with wavelength shift any idea what's causing this see attached.

2. The calibration lines are in focus at start and can go out of focus at the end of the session.

Both problems occur on and off, before motorising the collimator lens adjustment, I don't expect that to make any difference.

Has anyone else had these problems ? if so how did you overcome them ?

Regards,

Jack

Essex UK 

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Loose lens

 Jack

 Not had any problem in that respect regarding shifting/loosing focus of the neon lines but have read about the possibility of the collimating lens having a  loose fit within its cell. 

  Regards

   Alun

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Small Instabilities

Hi Jack,

I've seen both of what you describe.

I found that depending of the angle of the spectrograph due to gravity, then there can be small wavelength shifts. Nothing to cause a serious problem during normal observing, though on a run lasting over an hour might then the overall resolution could be slightly reduced. The tests I did were about 3 years ago and I'm not sure I've still got a copy. With the spectrograph off the telescope I took neon calibration images with the spectrograph on each side and vertical, to observe the most extreme effects. I then made careful measurements of the centres of the neon lines at the same position on each image.

It might be worth making sure all the screws in the body of the LHIRES III are tight, but I think small shifts are to be expected. There is more than one moving part and heavy cameras attached. Only a minute flexure will cause a small shift in wavelength. That is one reason why fibre fed spectrographs can be more stable, though using optical fibres introduces a different set of problems.

I also see shifts in focus with temperature. So on a cold night if I start with the neon lines in perfect focus then often they won't be in perfect focus at the end of the run. This is again something I live with. The flat fields will be slightly compromised, but if I refocus then that would also compromise the flat fields. Of course as long as you retake the flats after each refocus then that is not a problem. This is the same behaviour as needing to refocus a telescope due to thermal contraction from falling temperatures.

Best wishes,

Andy

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other things to look for

Another area to look at is the grating holder. I noticed one of mine was much worse than the other. One of the holes in the metal plate that the brass rod ran though was slightly oval and the springs on both of them were rather weak and were probably not taking up all the play in some orientations. I put an extra turn on both of them which improved things. If you have the removable grating type holder, check there is no slack causing the grating to move. (It needs to be just tight enough to clamp the grating but not too tight otherwise you risk distorting the grating which shows up as astigmatism)

I have also heard tell of one case where the mirror came lose (It was stuck with double sided tape in the original kit, not sure if this applies to the factory built versions) Also check that the screws hold the mirror mounting (both the adjusting screw and the pivot) are done up tight too.

Also the position of the neon relative to the slit affects the position of the calibration lines so check it is centred over the slit and comes to the same place each time. 

If  your calibration lines move back and forth as you rotate the doublet check that the lens is seated correctly in its holder. (The original kit had two fibre washers, one either side of the lens. I removed one so the lens seats directly against the metal holder on one side, Similarly I removed the plastic foot from the micrometer so there is direct metal contact which stopped some cyclic movement in the lines as the micrometer was adjusted. 

All this relates to the early kit though and may have been improved in later versions.

Robin

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Thank you all for your input,

Thank you all for your input, lots to consider here.

Almost finished motorising the collimating lens, I wrapped a 3 mm wide strip of Velcro round the edge of the lens which grips the belt and works best at fastest rotation speed setting on the handset.

I will test the system and make any changes as necessary as per your suggestions.

Once complete, this should be a more user friendly set up and relatively cheap to convert.

Regards,

Jack

Essex UK 

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Alun,

Alun,

The collimating lens worked loose in my Lhires but is easy to fix.

I advise Lhires users to check just in case.

Regards,

Jack,

Essex UK

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An Update

  Received the JMI motor focuser from Rother Valley Optics this morning so got to work attaching it to the Lhires in place of the Skywatcher motor. Just a case of removing a cog and the attachment that goes on a focuser knob and adding a small cog wheel (donated once again from the printer I broke up) to the motor shaft, also had to make up a smaller diameter belt,luckily had just enough printer belt left to do this. Works a treat,not as bulky as the Skywatcher motor and is lighter,just need to add small cover over the cog so as to seal from light and stop dust getting in slot.

  Regards

    Alun

      

      

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Alun,

Alun,

That's a neat mod with the smaller motor.

Attached is a pic of my finished mod with the Skywatcher motor.

I tried it out on Sunday night and got double calibration lines l l (don't have a pic) when I took the drive belt off and focused manually it settled down to give single calibration lines l .

What's causing this to happen ?

Regards,

Jack

Essex UK

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Not sure

 Jack

 Not had this happen with either motor (Skywatcher or JMI) so not sure what has gone wrong to cause the double lines. Clutching a few straws here, seems there could be the possibility that distortion is somehow introduced between the collimator body and its support. How tight have you got the tension on the belt? Only need a small amount,just enough to allow belt to grip the collimator body and turn it but feels slack if you pinch belt either side of the cog. Have you used the white screws in the support to alleviate any possible side to side movement, lastly did you have to join the belt, if so have you watched the lines as the belt turns and noted where the join is (being as the belt will be slightly thicker in the region of the joint tension on collimator body will increase slightly).

  Hope you get it sorted!

    Regards

      Alun

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Alun,

Alun,

The belt is fairly taught to turn the collimator with a Velcro layer wrap around for grip.

The white screws are slackened off 1/2 turn or so from tight to prevent side movement.

The belt is not joined.

I have adjusted both again and will see how it works tonight, and will report back.

Regards,

Jack

Essex UK

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Alun,

Alun,

Attached last nights calibration frames taken around H alpha line.

Far right double line with belt on, collimator screws loose to allow belt to rotate lens, same far right single line with belt off, collimator screws tightened and focused.

Any thoughts as to why only 1 calibration line is double and what's causing this ?

Regards,

Jack

Essex UK

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Jack

 Jack,

    I cannot see your attachment,but still baffled as to what could be causing the doubling of the line. I have not seen the effect in my setup at all. The only thing I can think of once again is that the belt is too tight and placing the lens slightly out of line,maybe my using a much thinner belt places less pressure on the setup. Have you tried using a replacing the belt with a rubber band? Maybe the velcro round the collimator body is the problem (I have just placed belt round the body and have no slippage).

   Regards

      Alun

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Alun,

Alun,

I have uploaded the pics again.

Regards,

Jack

Essex UK

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Check screws

 Jack,

    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. 

   Regards

     Alun

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Alun,

Alun,

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.

Regards,

Jack

Essex UK

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Lines

Jack,

 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. 

  Regards

     Alun

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shift in wavelength

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)

See attached

Robin

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Alun and Robin,

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,

Jack

Essex UK

    

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Jack

Jack,

  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 :(   

   Regards

     Alun

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the double line

Hello Jack,

I think you will find the double line is not a fault and really is a close double

Robin

Alun_H's picture
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Joined: 05/03/2014 - 08:04
Agreed

 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.

 Regards

   Alun

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Alun and Robin,

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.

Regards,

Jack

Essex UK

Robin Leadbeater's picture
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Questions

Hello Jack,

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

Cheers

Robin