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November-December 2006 and up to July 2012

Baader C ERF (Cool Energy Rejection Filter) experiment and more recent developments

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Equipment 2006

I have a 70mm diameter Baader Planetarium CERF mounted in a cell made by Ambermile Astro (Arthur Edwards) and two adapters.

Using the PST etalon removed from the PST with the Boa constrictor tool (after removing the rubber cover and the locking screw so the adjusting ring is removable), I have a telescope that can be setup three ways.

A 40mm aperture Hydrogen alpha scope without the PST etalon (as it was before)


A double stacked 40mm aperture Hydrogen alpha scope

A 67mm aperture Hydrogen alpha scope

The assembly is done with adapters made by Ambermile threaded onto the PST etalon as in the photo below. The left hand one is the 2" focusser adapter that has been made before and the right hand one fits the etalon, is 54mm long and has a 1 1/4" fitting to take the Coronado BF10 diagonal. The assembly is too short for best results. It needs 200mm from the knurled ring to the image plane of the CCD to emulate the PST optics. (corrected when I started using the Lunt B1200 blocking filter)

I have recently added a DMK 31AF03 camera to my equipment which has increased the frame rate from 5fps (Toucam SC3 and Pro b/w) to 30fps (less in practice, probably 10), and the resolution from 640x480 to 1024x768. The IC Capture software also allows more control of the exposure and dynamic range.


Results to date 24/11/06

I have been able to confirm that the ED80 will reach focus easily with the PST etalon, with and without a Barlow lens.

The etalon does give H alpha images in both arrangements and is easy to optimise. I have not been able to make comparitive images to test the resolution, mainly because of rain, cloud and gales, but I will post results as soon as I can.

Using the PST etalon and 67mm CERF seems to give quite a bright image at the eyepiece. I don't think I will be looking longer than I need to set up for imaging. The sun is so low at the moment it is difficult to get comparison shots but I am planning to do this as I am able.

The contrast was not so good as the SM40 but there was a small improvement in resolution.

I felt that the ED80 and 67mm aperture was very promising so I decided to try a longer focal length low quality scope. The quality was not important as the application is monochromatic.

The first image is using the ED80 and SM40/BF10 with a x2 Barlow lens (1200mm focal length), the one below it is using the 67mm C ERF and the 1000mm Helios and PST etalon/BF10. I prefer the 1000mm image.


Results to date 10/2007

I have been pleased with results of the 70mm C ERF (67mm aperture mounted) and the secondhand 120mm Helios f 1000mm achromat, particularly with prominences. I started doing animations of these. Then I decided to try improving the resolution with a larger aperture filter on this low quality scope. I am now using a 110mm C ERF that mounted gives an aperture of 105mm. There is a marked improvement in resolution. It all needs more testing and improving. It will help to have some more solar activity to focus on.

110mm Baader C ERF on Helios 120mm

In 2008 after some discussions on the UKAI solar equipment forum I cut 50mm off the tube to get the etalon into the best postion in relation to the focal point of the objective. That is to match the position of the etalon in the PST. This has improved the contrast and made better images of the solar surface. It still has a sweet spot problem but by fiddling about this can be minimised.


I have now found an ED100 secondhand, which I can use with the white light filter (Baader Astrosolar and Continuum filters). I have bought (Nov 2008) a Lunt Ca K B600 module to use with both the ED80 and ED100. For full disk images I use the ED80 with an Atik x0.5 reducer. Very easy to use and good results.


Having bought a Lunt 75mm Ha filter with B1200 blocking filter (October 2009), I am experimenting with the ED100 and ED80 to see if this will be a better setup than the modified PST. It will be less susceptible to sweet spot problems and may have better surface contrast. I hope to get a better setup for full disc images as my Coronado BF10 blocking filter has developed rust over nearly the whole surface after about 4 years use.

ED100 and LS75

LS75 on ED100


After discussing ERFs with Jean Pierre from the CN solar forum ( jpb30), I have mounted the 110mm ERF(September 2010) within the tube of the 120mm scope so that I am now using the full aperture and have improved the resolution from105mm aperture. I am considering whether to upgrade to a 150mm scope using the same idea.

Jean Pierre also uses a PST etalon with a Lunt B1200 blocking filter. I tried this without succes but will do some more trials.
The Lunt 75 filter does not provide such good resolution but has a more even field except perhaps when using the focal reducer for full disk shots on the ED80.
The Coronado BF10 rust problem put my modified PST out of use for a while as it got so bad and neither Meade USA or UK were interested in repairing it. After looking at the forum about ITF components I realised that the rusted part is only to make the BF10 safe for visual use, so I removed it and now have a functioning (imaging only) blocking filter with increased shutter speed of the camera.

I found a second hand Celestron 150mm and put the ERF-110mm in the tube at the apropriate place, untilted (which seems to be OK). The Lunt B1200 works slightly better than the Coronado BF10 without the ITF (better contrast, despite less light passing) so that has become a 1200mm+ solar scope. It needed 6.5cm cut off the tube to reach focus with the PST assembly added. The B1200 fits the PST etalon assembly at the 200mm position needed to get f10 at the PST etalon collimating lenses.  Ongoing experiments with this and the LS75 which is very good at medium magnifications.

Celstron 150mm
Celestron 150mm with internal 110mm C ERF, PST etalon and Lunt B1200 blocking filter