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Observation by James Screech: Lunt 50THa first light

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James Screech


James Screech


2017 Jun 10 - 11:44


2017 Jun 10 - 16:15


The Sun

  • Lunt 50THa
  • ASI120MM
  • AVX

Gain 0, Exposure 1.8 ms



Target name



Lunt 50THa first light

About this image

Went a bought a Lunt 50THa from Widescreen Centre this morning, as the Sun was out (makes a change when you have a new toy to play with) tried imaging with my guide camera ASI120MM. Due to limited focus range I had to remove the 1.25" eyepiece holder from the diagonal and use a 7mm T2 extension to get focus, minor problem with Newtons rings. I tried for closeup detail with a SW 2x barlow and 2.5x powermate but could not get to focus with either. Does anyone know of a camera / barlow combination that will work with a Lunt 50?


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James Dawson
James Dawson, 2017 Jun 10 - 18:44 UTC

This is a really lovely first image. Is this a single exposure or a stack? Does the whole disc fit on the sensor of the 120MM.

I can't help with the Barlow / camera question but maybe try the forum or ask Lyn Smith to put the request in the next Solar Section newsletter.

Chris Hooker
Chris Hooker, 2017 Jun 11 - 07:14 UTC

Hi James,  This is an excellent result for a first image: well done!

Unfortunately I can't help with your Barlow issue: I have the opposite problem with my PST, namely it won't reach focus without a Barlow.

To deal with your Newton's rings, which aren't at all obtrusive, what you should try is flat-fielding the data. The illumination of these solar telescopes is often quite non-uniform, and your image has a rather bright centre which is probably due to that. You can capture a flat-field AVI with a piece of diffusing material over the front of the telescope. Materials like tracing paper or greaseproof paper generally make the field too dim; I use a piece of textured plastic cut from an A4 document sleeve which seems to work pretty well. It's best to aim the telescope at the centre of the Sun while acquiring the data. There is a Create Flat-field option in Registax (under the Flat/Dark/Reference tab at the top) which simply stacks all the frames, then you can save the result and use it when processing your solar data.

Good luck.