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Sunday HA and a bit of modding

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Well as I intended getting the Lunt mod out today I thought it would be a good idea to make it into a double stack Luntmonster. I don't have an adaptor plate for my scope, and don't intend paying £150 for one, so I made an adaptor plate out of an old aluminium camping plate and some toilet seat fixings. Cost for total project...........£0.00


IMG_3148 by allcart2, on Flickr

The whole scope. This is the smaller 120mm XLT, as the plate wouldn't fit the C6.


IMG_3150 by allcart2, on Flickr

Now I have to say, that with a 60mm Ha filter on a 1200+ focal length scope, the image is a bit dimmer than normal and the sweetspot relatively small, however it does fit within the frame of the DMK41. Although we had great blue skies today the image on the screen was very unstable, quite wiggly infact. Anywhoo, heres a sample of my first light with the double stacked Lunt mod.

First some prom pics.


prom 7-7-2013 by allcart2, on Flickr

Marching proms. DMK31


Marching proms 7-7-2013 by allcart2, on Flickr

Inverted DMK41


Invert proms 7-7-2013 DMK41 by allcart2, on Flickr

6 pane mosaic of AR1785 with the DMK31


AR1785 mosaic 7-7-2013 by allcart2, on Flickr

Active region with the DMK41


AR1785 DMK41-120 DS by allcart2, on Flickr

Last One. I'll post this because I actually caught a small flare.


AR1785 DMK31 by allcart2, on Flickr

Thats all folks.

Edited by allcart
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Nice set of pics Allan. If anything the 'sweetspot' should be bigger with a long focal length. The DS unit is designed for a scope with FL=400mm, so using it on a 1200mm scope will be like using a 3x barlow. The F/number of your scope will go up to F/20 (60mm object, 1200mm FL), so that should be okay for the Etalon.

The real advantage of this setup is that you don't have to use a barlow and the possibility of internal reflections, producing banding should be minimised.


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You may be right Robin. I will have to compare next time I use the 120mm mod. There is still a lot of reflections or ghost images to deal with. I have counted 1 true sun and 3 ghosts suns, and they make getting a band free image quite hard. The other problem is uneven illunination across the frame. Although I tried to be meticulous in the optical alignment of the 2 scopes, one side of the frame is always brighter than the other. It makes mosaics that much harder.

Edited by allcart
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My Lunt has a slight bias to the lower right, although it mounts upside down, so I suppose this is upper left. It is not so noticeable for single stack, but put the double stack on and it is very obvious. By moving the DS round in its holder, I can minimise it, but never get rid of it. For full disc shots, I have to have the sun in the lower right hand side of the frame and trim both Etalons plus the position of the front Etalon to minimise the tuning hot spots.

When using a 1.5x Barlow I usually have to detune slightly to get an field that is even enough to produce a mosaic.


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Oh I have a theory about Etalons, especially the pressure tuner. I suspect they have a very small tilt put in at manufacture, if they didn't then as an Etalon is a reflective type filter when double stacked multiple out of band reflections would occur. By introducing a slight tilt then these will be avoided. I suspect it is this small tilt that produces an offset in the sweetspot, otherwise I think I should be at the centre for a pressure tuned Etalon.


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Thanks Amra. :smiley:

Robin, I was thinking it was the optical alignment of the camera sensor. By rotating the camera and drawtube I can control the hotspot with the single stack, but the DS is a whole new ballgame. Its like having overlapping circles of light and the overlap is allways brighter and more on band. Lots of fiddling needed to produce an even image.

I think I'll put the DS filter on a scope on its own to see how it works as a single etalon. It might help me to understand the tilt tuning better.

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