LHires experience – and some issues…

[Mr Jack Martin]

I have spent a small fortune on my Lhires getting it upgraded and buying all 6 gratings. Now it suffers from light loss which I have been unable to solve as its enclosed in a film changing bag ! Bearing in mind other peoples issues, would it be possible for the BAA to organise a Lhires users weekend ? It would give users sufficient time to compare notes and maybe solve some issues.

Regards,

Jack 

Essex UK

[Andy Wilson]

Hi Steve,

I hear what you are saying, as you should not need to introduce a washer to get a good image. It will be interesting to hear how Kevin gets on.

I am a bit biaised as I started off with the cheaper L200 (by JTW) before upgrading to the Lhires III at about twice the price. These are both Littrow spectrographs with some similar design features. The quality of the guide image I was seeing through my Lhires, while not perfect, was far superior to my L200.

Example L200 guide image with obvious flaring and triple image of the star.

Example Lhires III guide image. Not perfect with a secondary image of the star, but overall better image quality.

To put this in context for anyone following this thread, in spectroscopy the purpose of the guide image is to allow you to locate your target star, position it on the slit and to keep it there. So while a good quality makes this job easier it is not strictly speaking essential. The Lhires III and L200 have a series of mirrors and lenses to relay and focus the guide image to a camera, and these can introduce various image aberrations. For example I was able to get some excellent spectra out of my L200 even though the guide image was not very good.

Cheers,

Andy

[Andy Wilson]

Hi Jack,

Sorry to hear you are having problems with your Lhires III. Do you mean light loss from the spectrograph, or light leakage into the spectrograph from outside?

Will you be coming to the Observers’ Workshop – Variable Stars, Photometry and Spectroscopy on 29th September? That is a good place to start as there may be other Lhires users present. I can try to find out if you are interested. I would not rule out an Lhires III weekend, but we would need enough interest to make it work, and people willing to organise it. Also a weekend event has much bigger costs due to the need for overnight accommodation.

Cheers,

Andy

[Kevin Gurney]

Hi all

I have now used my Lhires with the ‘engineered shim, guiding mod’ (aka washer for tilting the mirror). My guide image looks a bit more like Andy’s second image above – prior to that it looked a bit like the first… Its now much easier to guide. I use slit guiding in Prism.

I can vouch for the light leakage problem (ingress not exit). This isnt a problem I guess, unless you try and do some of the daylight solar experiments they suggest (that’s how I first discovered it). I have now used judicially applied electrical tape (reduced but not eliminated light entry entirley). There might be a problem if you had excessive glare from a laptop similar?

I also managed to get  something ‘out of the box’. But I am finding going past the mag 4.5(ish) barrier is not trivial… The SNR goes down appreciably, but I am hoping the easier guiding will help here.

I think the Lhires is an early design and was made as a kit. It has this feel about it, whereas the Alpy is built like a tank…

I would also be up for a weekend on this topic. I will be at the meeting on 29th.

Cheers

Kevin

[Mr Jack Martin]

Kevin and Andy,

I will be at the meeting on 29 Sep.

Jack

Essex UK

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