Technical: Reducing reflections in the optical train

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Technical: Reducing reflections in the optical train

Post by Merlin66 » Tue Apr 17, 2012 9:48 am

Alexandra:....I seem to have a reflection that appears to some extent on all of them. My question to the imaging pro's is, can I do anything about it to remove it or stop it? or am I just being fussy.
Solarscope SF100 / 2x Barlow DMK41


What you have here is a reflection from the overexposed full disk coming off the barlow - the brightening mid frame... What can be done about it - easy peasy really, when you are imaging in this configuration what you need to do is set your etalon tuning for the run, fire off your pics as usual, then when done move to mid solar disk, defocus outward, and then back off on the exposure till your frame goes darkish grey and you can see the brightening of the central patch (that pesky reflection!) - then record this as an avi usual length as usual - you have just shot the basis for a flat frame. Then in stacking software of your choice load in as a flat frame; I can tell you how to do this in avistack if you need, but dont know how this works in autostakkert.

May take a bit of playing around to get the level for the flat correct, but the principles of the method are there...

...these reflections occur on my images when I use Barlows like the 3x TV and the 2.4x TAL (not as bad).
Maybe it depends on your Barlow.
Normally I use a Barlow-element, screwed onto the IR-Cut filter in the nosepiece of my DMK. Try that and you might not notice any reflections anymore.

Had the same reflection problem when I used a Barlow. Found most of it went away when I placed flocking material in in the 1 1/4" - C adapter tube on the camera. Though the inside of the adapter tube is threaded, if you look down it at a bright light source you can see a very bright specular reflection. I think you'll find most, if not all of that bright spot will disappear after lining the camera adapter tube.

Before flocking 1 1/4" - C adapter using a 2x shorty Barlow:


After flocking 1 1/4" - C adapter using same 2x shorty Barlow:

"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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