Crikey, the Sun!

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Gordon Ewen
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Crikey, the Sun!

Post by Gordon Ewen »

Well, after weeks of dire weather I have had 2 mornings in a row of clear air and the sun in the sky. It's been so long since I did any solar imaging I thought I might have forgotten how to do it. Fortunately, I hadn't.
Here are a couple of images from today; both with the double stacked LS152. Full disc is 2 panes with 0.6x reducer and ASI174MM camera, and the other was with ASI290MM at f6.
Still experimenting with finding the optimal tuning. To date I start with the pressure tuners fully 'relaxed' and tune one to get the histogram to a low point - at this point the image is quite dark. I then wind in the second tuner until I have something that looks..................... contrasty. This is basically what the Lunt data sheet advises for a DS unit. Today, having got to that point, I then adjusted the tuners by winding them in and out a few mm to see what happened. I believe I found an optimal tuning but I would add that there seems to be a bit of tolerance either side of optimal where the image doesn't seem to change much at all. Be interesting to hear other DS users experiences of tuning.
Gordon
Attachments
AR2565.jpg
082724 IMPPG edit.jpg
Sun 2 pane.jpg


Lunt 152 DSII Ha scope, Orion Optics 12" ODK, C9.25
Skywatcher EQ8 x 2
Lunt 1 1/4" Herschel Wedge, 2x,3x Barlow, 5x Powermate, Baader Ca filter and solar film.
https://www.flickr.com/photos/74614447@N02/
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Re: Crikey, the Sun!

Post by Derek Klepp »

Cheers Gordon .Yes the second does seem to have differing illumination but at least you are getting some good results with the DS.


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Re: Crikey, the Sun!

Post by Ewan »

Some lovely fine detail caught in those on a fantastic day in the sun.


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Re: Crikey, the Sun!

Post by Gordon Ewen »

Thanks for the comments. The uneven illumination is an interesting issue . The second picture was taken on Wednesday and I noticed it was uneven and tried a flat to reduce it but it made it worse ( i get this occasionally). The pictures I shot yesterday didn't show the uneven illumination at all. I believe, in part at least, it is determined by how well tuned the system is; I spent some time yesterday trying to optimise the 2 tuner settings. The Lunt 152 definitely has a sweet spot and just where that sits on the chip might contribute also, which is consistent with the effect being least when Barlows are employed.
Happy to hear any other thoughts from the forum.
Gordon


Lunt 152 DSII Ha scope, Orion Optics 12" ODK, C9.25
Skywatcher EQ8 x 2
Lunt 1 1/4" Herschel Wedge, 2x,3x Barlow, 5x Powermate, Baader Ca filter and solar film.
https://www.flickr.com/photos/74614447@N02/
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Re: Crikey, the Sun!

Post by Valtori »

Hi Gordon,

Beautiful shots!!

Val


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Re: Crikey, the Sun!

Post by Montana »

Wow! these are quite stunning :bow :bow :bow

DS is a dark art :)

Alexandra


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Re: Crikey, the Sun!

Post by OTangen »

Hallo Gordon!

My experience is with a DS Lunt100 but the principle should be the same. My procedure is like this:
When I feel it is a long time (weeks) since I tuned the filters for optimal performance, I remove the DS unit and tune the SS to best contrast of filaments and other surface details. I start with the pressure tuner almost out and go inward. Then I remount the DS unit and tune to maximum brightness. Then comes the tricky part. I too experience a bit of unevenness across the image. I therefore tune the filters, particularly the DS unit a bit, just half a turn or so to obtain the flattest possible field. I do this by looking at an area well away from the edge of the sun, where there inherently is some gradual darkness towards the edge.
I usually do mosaic images of the whole disk using a 2.5x Powermate and my Grasshopper3 PG camera and I sometimes have problems getting the composite image flat. This happens when I do not succeed in tuning the filters for maximum flatness. An example of this is:

http://www.knuttangen.no/astro/index.ph ... 154653_utc

Where you clearly can see the stitching. I try to reduce the effect by using the lasso tool in photoshop and either darken or lighten the area.

An example where I think I have succeeded with the tuning is here:

http://www.knuttangen.no/astro/index.ph ... 071816_utc

I hope this might be of some help to you. Please tell me if there are parts of my explanation which might not be clear.

Best regards
Oivind Tangen
60N 10E


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Re: Crikey, the Sun!

Post by Gordon Ewen »

Val, Alexandra, Oivind, thanks for your comments.
Oivind, it is a good point to remove the DS unit occasionally as it means that the tuning of the first tuner can be optimised and also it is a reminder of the difference between single and double stack. Your 'lassooed' image is amazingly flat for such a mosaic, well done.
Regards
Gordon


Lunt 152 DSII Ha scope, Orion Optics 12" ODK, C9.25
Skywatcher EQ8 x 2
Lunt 1 1/4" Herschel Wedge, 2x,3x Barlow, 5x Powermate, Baader Ca filter and solar film.
https://www.flickr.com/photos/74614447@N02/
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Re: Crikey, the Sun!

Post by pedro »

Very nice images Gordon, I'm glad you finally had a solar fix


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Re: Crikey, the Sun!

Post by Carbon60 »

Nice images, Gordon.

Tuning DS filters can be really tricky. Removing the front and optimising for the internal is a good option, which I've used when getting a good image seems particularly difficult. I've also found that rotating the front filter relative to the scope sometimes helps overcome uneven illumination (maybe depending on the time of day and how the tilting filter is 'pulled by gravity' as we rotate under the Sun, if you see what I mean). It might also be due to a bit of 'sloppiness' in the optical train that affects the alignment of some element or other. As Alexandra says, it's a bit of a 'black art' and requires a lot of tweaking.

Stu.


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