Given the cost, is double stacking worth it for someone who primarily does electronic imaging?

[AJamesB]

Staring to mull over tucking money away for an eventual external doublestack for my lunt100. From what I've read, it makes a sizeable difference for those that do visual imaging, but I was wondering if there is any advantage to someone who primarily does 90% imaging, and only about 10% visual? Are cameras all ready able to see most of what doublestacking would bring out, or does it make a noteable difference when imaging? And if so, would it be a difference commensurate with the cost of purchasing it?

Thank in advance to anyone that can chime in with their experience.

[Montana]

I mainly do imaging with a little visual. Once I got a double stack unit for my Solarscope I have never gone back to single stack. The view through the camera is just as beautiful as the visual. There is no longer the double limb effect, the spicules take on a 3D fluffiness, prominences and surface can suddenly be imaged in the same shot. Active region plage becomes brighter and more exciting. However, it is more difficult to see spots in the cores of active regions (lower bandwidth so seeing higher in chromosphere - can no longer see photosphere leakage) and perhaps fainter proms are more difficult to image due to reduced brightness. However, the benefits are far outweighed.

Once double stack, you can never go back.

Alexandra

[Bob Yoesle]

Ditto to what Alexandra has stated - with the caveat that if your single stack etalon allows significant background glow, faint prominences might be unaffected, if not even more visible, due to the suppression of this scattered light (i.e. poor transparency). This is especially true with front mounted etalons.

Here's what's going on with single (left) vs. double (right) stacking:

double stacking normalized.jpg (131.69 KiB) Viewed 619 times

Left - single stacked chromosphere + photosphere. Right - double stacked "pure" chromosphere. Outside of +/- 0.65 A of the Ha CWL, parasitic continuum from the photosphere leaks from the "tails" of the filter system and reduces chromospheric disc contrast. Also note that the reduced "bandpass" from double stacking is almost completely irrelevant. Prominences are largely unaffected, except by the overall reduced filter peak transmission. The reduced peak transmision is the product of the individual etalon transmissions, i.e. for 80% etalons 0.80 x 0.80 = 0.64, or a 20% reduction in overall transmission.

On the other hand, scattered background light is generally exacerbated with internally double stacked etalons. A circular polarizer between the etalons can be used to greatly reduce this scattered light and reflections between etalons, but at the cost of reduced (again) overall transmission. The best choice with an internal etalon is to double stack with a front (objective tilt-mounted) etalon with a slightly higher CWL than would otherwise be normal.

[AJamesB]

Awesome info, thanks all! I guess I'll start saving:)

[EGRAY_OBSERVATORY]

Indeed, I have been using a Double-stack on my Lunt 60mm Ha scope for some time now and the contrast is quite considerable for both visual and
imaging purposes. The only drawback with having to tune both the Etelon in the primary-scope and the Etelon in the Double-stack, is that it takes
some practice as well as a little extra struggling to reach up to the Double Stacks' tuning-wheel, but a small amount of patience - should solve any issues.

I can't vouch for any pressure-tuned Ha scope though, but also accurate focusing which will be different when changing eye-pieces for a camera and is a must.

I now use a large LCD screen (remote from the PC) to make any scope-pointing, fine-tuning and focusing adjustments - which does save much time and getting better results, even though my first images on this website can do with a little more work and processing to get the best of...

[marktownley]

Simple answer yes.