The Lowspec spectrometer

[Thalestris24]

My measured R-value is 594 which seems quite low though my pixels are quite big (5.4um). The theoretical value with a 20um slit is 1906. Quite a big discrepancy? Wavelength range seems fairly close, theoretical: 3785 - 7215 (3430 A), so a little less than that in practice.

Louise

[Thalestris24]

Hi Paul

No worries! I guess it is that causing the shadows above? I thought I'd get away with ignoring it but it obviously affects the BASS chart. Reprinting the guide platform would be a bit of a pain. Would just enlarging the hole version a bit more be good enough? 

Any idea why my R value (above) is only 594 - not sure if the theoretical value (Simspec) takes into account the ccd properties?

Cheers

Louise

ps I had enlarged the openings with a file - I suppose not quite enough....

Edited January 6, 2020 by Thalestris24

[Merlin66]

Louise,

Yes, SimSpec considers the CCD properties....

I'll look at that wavelength labelling issue and get back to you.

The actual R value v's theory can vary due to numerous conditions. Also, remember, for a tilted slit plate the effective slit gap will be smaller than the physical - a 30 micron @15 deg tilt = 29 micron.

Edited January 6, 2020 by Merlin66

[Thalestris24]

3 minutes ago, Merlin66 said:

Louise,

Yes, SimSpec considers the CCD properties....

I'll look at that wavelength labelling issue and get back to you.

The actual R value v's theory can vary due to numerous conditions. 

Oh, ok. I'm still learning BASS... I did another reading on the same chart and it came out at 859 - maybe I'm not doing it properly!

Louise

[drjolo]

When I measured FWHM of different lines it also gave me some different results - for orange/red part I got R values from 1300 to almost 1700. You may double check if spectrum image is focused well, because it definitely affects FWHM. 

[Merlin66]

Louise,

The x10 in the X Axis.... I can only assume is due to an error in calibration settings - the wavelength entered  and the display setting i.e. entered as angstrom but it thinks it's nm and then displays as x10 angstrom.......

[Merlin66]

Lucas/ Louise,

The R value will always vary across the spectrum, even with perfect focus...always lower towards the blue.

 

[Thalestris24]

1 minute ago, Merlin66 said:

Lucas/ Louise,

The R value will always vary across the spectrum, even with perfect focus...always lower towards the blue.

 

Oh, ok. I just zoomed right in on what otherwise looks like a narrow peak on the full chart:

739 this time!

Louise

[Thalestris24]

7 minutes ago, Merlin66 said:

Louise,

The x10 in the X Axis.... I can only assume is due to an error in calibration settings - the wavelength entered  and the display setting i.e. entered as angstrom but it thinks it's nm and then displays as x10 angstrom.......

I'll do a new calibration when I can

Thanks

Louise

[Thalestris24]

A quick test of the 12V/40W cheap, Chinese DC to 220VAC inverter:

It works ok with a 12V battery and a neon - yay! You can see from the image of the board where I've sketched the position of the diodes which look like they give a DC output at B. 220V AC is between A and C. There is a 267V DC voltage between A and B - so care is needed! It doesn't look like a standard digital multimeter picks up the AC output which I suppose is high frequency - not a 50Hz sine wave! That means the inverter is really only good for things like lighting.  Also, one shouldn't assume the inverter isn't working if you do use just a multimeter to check it. There is an AC voltage between A and 1 which lights a neon. There is a higher AC voltage between A and 2 which lights a neon very brightly! It could be that the voltage between A and 1 is 110V AC. I'll try a starter bulb with a resistor between those to points . Just to mention, the inverter is 40mm square and 25mm high so only needs a small box to put it in - I need to try and seek one out... Anybody know a source of inexpensive small, plastic boxes? The price of ABS ones I've seen is a bit out of proportion to the size and value of the inverter!

Louise

 

[Paul Gerlach]

Wow! That looks great!
I think I'll order these as well. They are way smaller and smaller is better. Did you provide a link to the site? Have to look back in the thread.
Curious to see  how the starter will perform with this unit. Will this inverter produce an amount of heat that could be an issue (cooling vents in the box?

Small plastic box? 3D printer... hmmm 😉

Paul

[Thalestris24]

1 minute ago, Paul Gerlach said:

Wow! That looks great!
I think I'll order these as well. They are way smaller and smaller is better. Did you provide a link to the site? Have to look back in the thread.
Curious to see  how the starter will perform with this unit. Will this inverter produce an amount of heat that could be an issue (cooling vents in the box?

Small plastic box? 3D printer... hmmm 😉

Paul

You can get them very cheap off Ebay - as little as £1.50 from China. You can also get them without the diodes that provide the unwanted DC output (I think I'll clip off the diodes on my board). Unfortunately, despite my initial belief, there doesn't seem to be a 110V tapping after all . It doesn't really matter - just seems marginally safer at 110V (it could be very easy to pick up the bare board forgetting the 12V is connected.. Zap! Ouch! So really need a box for it). They are supposed to supply up to 40W - so at 220V that would be a current of about 0.2A.I don't know what the 12V side draws - not much with little load on the secondary side. But I think a starter only draws about 3-4mA, so less than 1W. I calculate a 22.5K resistor will allow up to 4mA to pass so that would dissipate 0.36W. I'm assuming a Sylvania 70W starter which has a non-reclosure voltage of 140V and running it at 130V. I'll try that in a minute It should be quite bright... Should be virtually no heating from the inverter board. 

I think that '150W' board you ordered is also quite small? It does have the advantage of different output tappings (as I've seen online)

Louise.

 

[Paul Gerlach]

Hopefully no to bright. I remember having used them a few year ago via mains and resistor and after a while a thin layer of metal was deposited in the inside of the bulb. Seriously lowering the intensity.
So the 150 W boards I ordered are probably less useful for this purpose? Or at least overkill?

[Thalestris24]

Here is Sylvania 70W starter and the neon:

It's not as bright as the neon to my old phone camera! But should be fine. I've no idea how long these bulbs last. The ones I just bought had a blackened inside out of the box. But they are pretty cheap - cost me £1.50 for 5. I suppose they are not meant to run continuously for any length of time. Every make/bulb is different. As I mentioned before, the non-reclosure voltage (Below that threshold the bulb shouldn't close it's contacts) for the Sylvania 70W starter bulbs is 140V so I calculated the resistor based on a more conservative 130V and 4mA. A problem is that the characteristics of the bulbs aren't defined for our purposes but I'm sure we can muddle through! Oh, I found yesterday that you can get starter bulbs for 125W systems and with a non-reclosure voltage > 150V. I might get some and try them, just for fun! But I really should get on and finish the Lowspec now and get it mounted and tested.

Louise

[Thalestris24]

Paul - have you received your 150W inverters yet? I think they are also small but, as you say, *overkill... I did clip off the diodes on my board but it looks like they are generally being sold without them on Ebay

Cheaper from China but quicker from UK  

Louise

ps a 1W inverter would do! But then you have to make your own.

 

Edited January 8, 2020 by Thalestris24

[Paul Gerlach]

2 hours ago, Thalestris24 said:

Paul - have you received your 150W inverters yet? I think they are also small but, as you say, *overkill... I did clip off the diodes on my board but it looks like they are generally being sold without them on Ebay

Cheaper from China but quicker from UK  

Louise

ps a 1W inverter would do! But then you have to make your own.

 

No, I've not received them yet. I do have received a small solenoid (5 volt) that I want to use to push the reflector above the slit.

[Merlin66]

Louise,

Any updates??

Ken

 

[Thalestris24]

8 minutes ago, Merlin66 said:

Louise,

Any updates??

Ken

 

Hiya

Not really. I reprinted the slit illuminator with Paul's new version. Also enlarged the hole in guide platform rather than printing the new version. Yet to test it. Have printed a small box for the 12V inverter. I'm waiting for some panel mounted 12V sockets and new soldering bit - hope they come tomorrow. That's about it, really.

Cheers

Louise

[Thalestris24]

I'm thinking ahead a little and wondering what my procedure would be for getting a particular star in position on the slit? I'd planned to use plate solving via a separate guide scope (Celestron Travel Scope 70) but I'm not totally convinced that will be accurate enough. However, I can't see another way of doing it. If I can identify the selected star in the fov of the Lowspec guide camera then I think could make any necessary fine adjustments via PHD2. I'm also wondering how I'll manage to keep the target star over the slit when my guiding is only +/- 4 arc secs on the AVX - it might be ok but I'm not sure how to convert arc secs to microns (I should know but my brain has gone to sleep!). The practicalities of using a slit spectrometer are still a bit unknown to me at the moment! I gather from Ken's book (ASA) using a flip mirror and aligning the slit in RA is the way to go. The latter is fine but a flip mirror won't work for me. So it looks like platesolving of easily identifiable stars is all I can do. At the moment my Travel Scope is fixed rigidly to the scope clamps. I'll need to be able to adjust it so that I can get its centre of fov to precisely align with that of the imaging scope (or near enough). I'll have to think about how best to do that - I suppose guide rings are probably the way forward.

Louise

[Merlin66]

Louise,

Softy, softly....

The flip mirror in the book was used to replace the reflective slit option, which is now much more available....

Yes, for convenience and repeatability I have the length of the slit gap sitting along the Dec axis, so any PA issues would cause drift up/ down the slit - easy processed later.

Think of the reflective slit plate as on on-axis guider... depending on your guide camera you should be able to view the whole of the available FOV around the slit. This allows you to use say PHD to nudge the target star onto the slit gap.

Acquisition - I can use a 60mm finder with a ol' DMK41 as an electronic finder using FireCapture to accurately position a target star such that it's visible in the slit plate. (I also use EQMod to GOTO the target initially...) Doesn't have to be 100% aligned to the centre of the slit plate - you can set an off centre Cross wire to compensate....

Yes, I occasionally revert to plate solving - using the eFinder FOV, just to confirm the target. Plate solving a slit guider image doesn't work.....due to the secondary reflection images from the slit plate - you may be luckier than me, but never worked successfully for me.

Summary:

An eFinder with/ without plate solve to identify the target

Align a cross wire overlay on the eFinder to drop the target onto the slit plate ( FireCapture has this ability)

Nudge the target star into/onto the slit gap (I use the spectroscope feature of PHD) - try to get the target star close to the centre of the slit height to minimise aberrations.

Start guiding......

 

[Thalestris24]

8 minutes ago, Merlin66 said:

Louise,

Softy, softly....

The flip mirror in the book was used to replace the reflective slit option, which is now much more available....

Yes, for convenience and repeatability I have the length of the slit gap sitting along the Dec axis, so any PA issues would cause drift up/ down the slit - easy processed later.

Think of the reflective slit plate as on on-axis guider... depending on your guide camera you should be able to view the whole of the available FOV around the slit. This allows you to use say PHD to nudge the target star onto the slit gap.

Acquisition - I can use a 60mm finder with a ol' DMK41 as an electronic finder using FireCapture to accurately position a target star such that it's visible in the slit plate. (I also use EQMod to GOTO the target initially...) Doesn't have to be 100% aligned to the centre of the slit plate - you can set an off centre Cross wire to compensate....

Yes, I occasionally revert to plate solving - using the eFinder FOV, just to confirm the target. Plate solving a slit guider image doesn't work.....due to the secondary reflection images from the slit plate - you may be luckier than me, but never worked successfully for me.

Summary:

An eFinder with/ without plate solve to identify the target

Align a cross wire overlay on the eFinder to drop the target onto the slit plate ( FireCapture has this ability)

Nudge the target star into/onto the slit gap (I use the spectroscope feature of PHD) - try to get the target star close to the centre of the slit height to minimise aberrations.

Start guiding......

 

Hi Ken

Along DEC rather than RA? I suppose that makes sense, and the AVX has a lot of DEC backlash. I've never used an oag before. Until I try, I won't know what's visible in the guide cam. My Travel Scope is 70mm x 400mm and that's what I'd use for plate solving - not the internal guide image. SharpCap has a 'reticule' option and supports plate solving. I'm not sure if the reticule is the same as Firecapture's overlay. I don't understand about setting an 'offset crosswire'. Plate solving is my only practical way of finding a target - I normally use it with SharpCap or APT, but it's only accurate up to a point. It won't necessarily get a star precisely in the centre of the fov but is always good enough for a DSO. I bought an Altair Astro GPCAM3 178m to use on the Travel Scope a couple of months ago. Not even properly tried it yet! It should give a smallish fov of ~1 deg x 0.70 deg at full fov though supports ROI. I'll need the plate solving in order to know what's visible in the Travelscope/178M fov. I've never really used an overlay before either - nor the PHD 2 slit overlay, obv. Lots to try out!

Thanks

Louise

[Merlin66]

Louise,

The FireCapture reticule can be adjusted in X-Y, to compensate for any misalignment.

In my case the eFinder FOV is 105 x 79 arc min and the visible slit plate 9.8 x 7.4 arc min ( C11 @ f10) - See attached CdC screen

The attached shows the typical PHD2 screen with slit overlay, slit positioned on target star and calibration/ guiding on target.

 

Ken

 

Edited January 11, 2020 by Merlin66

[Thalestris24]

Hi Ken

In my case, the slit takes up the width of the guide cam fov - think I posted an image some time ago. I'll have another look at it today. I don't think the SharpCap reticule is moveable, unfortunately but I'll double check that and maybe try Firecapture also. I have the bits to add slit illumination

Thanks

Louise

[Thalestris24]

Here is my PHD2 image of the slit with the overlay. The overlay won't extend to the actual length of the slit but I'm guessing that doesn't actually matter. This is a screen grab and illumination is restricted daylight.

I've not found it easy to adjust the guide mirror on the Lowspec. I might try and get some M3 thumbscrews rather than using the grub screws. On the other hand, the current setting seems to give quite good coverage? An astro FOV calculator gives the following results for the guide camera and lens:

Those figures would encompass M45! - so not sure how they apply to the relationship with the physical slit? Ovio don't specify the lengths of the slit but measuring with a ruler they are about 6mm. The sensor diagonal measurement is also ~6mm. I guess if I could adjust for the slit to be in the full diagonal then the whole slit would fit ok.

Louise

ps at the moment my slit position isn't stable. If I use the slit rotation mechanism to select a different slit, its position in the guide cam fov changes a lot, even if I return to the initial slit. I may have to do some work on the slit holder mechanism...

Edited January 11, 2020 by Thalestris24

[ejp1684]

Ken, could I ask what camera you use for guiding?

Thanks,

Eric.