Thursday, May 24, 2012

First light with new solar imaging setup!

This is a report from the 'first light' session with my new high resolution solar imaging setup!

During the bright summer months here in Denmark I stop work on deep sky or planetary imaging and switch to solar. I do H-alpha imaging with a Skynyx 2-2M camera, i.e. the 'lucky cam' technique with thousands of images.

In the past years I have been on a trend towards ever higher resolution. It started with increasing my focal length to get better sampling on a Coronado SM60 setup. Next, I increased the aperture to 100mm by acquiring a Daystar rear-mounted filter (back-to-back comparison with Coronado is here). This year I purchased a second hand 152mm F=900mm achromatic refractor to use with the Daystar. Normally (and safest!) a Daystar is used with a front mounted energy rejection filter (ERF), but on the Daystar Yahoo forum I heard that this could be replaced by a high quality UV/IR filter that is mounted internally. ERF's are VERY expensive for large apertures so this trick was really what inspired me to try working at six inches.

The scope is a Chinese made achromat mounted on a Takahashi EM-200 equatorial mount. The scope mechanical quality is very good for the price level and I have heard that the optics also are good - especially when the light will be filtered and a tele-extender is used with a small chip camera. Super-duper APO's with super-duper H-alpha filters are really a joke! I had made special adapters so that a Baader 2" UV/IR rejection filter could be placed just after the focuser. This is the highest quality filter and nothing less must be used for this kind of application out of safety concerns. The filter is mounted in a way so that it is not carrying any weight. This is important since a very long imaging train causing lots of torque is used. After some T2 spacer tubes I have a Baader TZ4 tele-extender, then comes the Daystar Quantum SE H-alpha filter. The spacer tubes places the TZ4 at the optimal position relative to the telescope focal plane while ensuring that the 3" Crayford focusser is not extended at all - thus minimizing problems with a sagging drawtube. After the Daystar comes a lightweight helical focusser from Borg and then the Skynyx 2-2M camera. The helical focusser enables me to only move the camera and not the entire long, huge and heavy imaging assembly. Everything is screwed securely together (no draw tubes or clamping rings) to minimize sagging. To achieve this is a true nightmare in adapters! Check out the photos of this setup below.

6" solar imaging setup on Takahashi EM200 mount. Note that dew cap is fully retracted to avoid possible tube currents.

Details of the assembly for high resolution solar imaging
After fiddling with all the spacer tubes and adapters in the imaging assembly I had time to try a few shots. I took two 90 second sequences consisting of ~1500 images of active region 11484. First the Daystar was at 6563.8Å and then I set it to the H-alpha wavelength of 6562.8Å. Images below are stacks of the 60 best images followed by some wavelet sharpening:
AR11484 @ 6563.8Å. Total length of this complex is ~120 arcsec.

AR11484 @ 6562.8Å a few minutes later.

I did not bother to remove traces of Newton rings. The images were taken two hours past midday over a low black roof, so the seeing should not have been to good. Finally, I have not checked the scope collimation after it arrived. Still, I estimate the resolution to be around 1 arcsecond - not bad for a first try. I can't wait to play more with this setup over the summer. Let's hope for clear weather during the Venus transit on June 6th!!


  1. Hi Mikael,

    So with the TZ4 you'll now be at about f24. Do you plan to stop down to try it at the rec. f30 to see if you can get more contrast ?


    1. Hi Andy - no, I'll leave it at f24. If you look at fig. 12 in the Quantum SE white paper from Daystar ( it is evident that the penalty for doing so is very minor - nothing that I could measure. Maybe the bandwidth increases from 0.50 to just ~0.52Å. The extra aperture is more important since it increases possible resolution and helps keep the exposure times short. -Mikael