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I have a 50mm Lunt with a double stacked etalon on the front (LS50FHa) and B600 diagonal, pressure tuned; currently using an ASI ZWO 174MM non-mini with IR cut filter. For the life of me I cannot get an evenly illuminated disc of the Sun on any chip. I’ve tried single stack, tilt adapter(s), different cameras. There is no sweet spot where there is even illumination. I feel as though the blocking filter is too narrow, else something else is amiss. It was a second hand scope and the details it reveals are amazing, but even illumination is impossible. Lunt talked me through various things to try, but nothing has solved it. Do you think the B1200 filter would fix it? Unfortunately I don’t know anyone with one to try. Else is it unlikely the blocking filter and time to just get a new solar scope and stop wasting my time and surges in blood pressure 🙂
Thanks.
James
I’ve not. Invariably this scope is set up outside so tracking is usually awful. I just feel there is somethign fundamentally wrong and I’d like to resolve it one way or another.
Thanks.
James
This is from today. The gradient in brightness is not a natural feature, it is artefact.
I know nothing about solar imaging but is it just me or is there less detail at the 5 o’clock position compared to the 11 o’clock? If so, could that be indicative of tilt?
Grant, thanks. It may be that tilt here is reducing evenness of focus, but no end of playing with tilt does nothing to the unevenness of illumination. It isn’t even as though there is predictable gradient across the FoV, it seems there are areas of the FoV which have minimal gradient but these areas are not big enough to take the whole disc of the Sun and I’m not using a Barlow. I’ve just been looking and the B1200 is over £1000. Looking at Chris Hookers images in Ha with his newly acquired Acuter Pheonic 40 solarscope (https://britastro.org/observations/observation.php?id=20250509_220342_3acfea1c341b631f) he has no gradient, and I’d suggest potentially even better contrast than I can achieve. I am having to stop myself just clicking buy now Rother Valley Optic’s website (£999).
James
I also saw Chris Hooker’s images and I did not stop myself clicking buy on the FLO website (same price). No regrets it’s a great scope. The sweet spot is comfortably bigger than the sun and the illumination is even without the need for any additional processing (flat frames or similar).
I know next to nothing about this, and can’t comment on the hardware, but looking at the even illumination on the Chris Hooker photo, I wonder what his raw image(s) looked like and if or how he processed them ?
When dealing with some solar eclipse photos a few years ago I used a “radial blur and subtraction technique” which gives a more even illumination and increases the contrast, that should solve the limb darkening.Chris Hooker emailed about something else and mentioned this. He strongly suggest I try some flats. I’ve found this video so will try some form of cereal bag flats later in the week; I probably won’t use a cereal bag, but something along those lines.
https://youtu.be/M7rSOXWQDZM?si=A6BESGiqf-UoXE5V
Thanks for the replies. I am feeling hopeful again.
James
I have an old Lunt LS60T telescope (tilt-tuned) and also two 5Omm Lunt aperture filters (tilt-tuned). These come from before 2010, the early days of Lunt.
The LS60T came with the B600 blocking filter and the 50mm filters with the B1200 filter.
I also was very concerned about the highly uneven illumination the Lunt 60mm gave both visually and in images, and did extensive tests, including pulling the filter units apart and using the blockers separately from the diagonals, in a straight-through configuration using an adaptor I made on my lathe (invalidating all warranties obviously).
My conclusions were:
1) The B1200 gave very much better results than the B600, with all other components being the same. It was chalk and cheese, the B600 just seemed to be a low-quality item.
2) The straight-through configuration was better than using a Lunt diagonal, and substituting a 2″ mirror diagonal from another manufacturer was better as well, though not as good as straight-through. When I pulled the Lunt diagonals apart I noticed how crudely and inaccurately made they were, components just glued with a rubbery substance to rough aluminium castings, the inside a total contrast to the polished outside finish!Since then I have taken all my images with the straight-through system I made incorporating the B1200 and a replacement IR block filter (the original Lunt IR block filters all crazed over after a few years; this is likely due to the dampness in my observatory). That said there is still an unevenness in my images from the Lunt that cannot be completely removed by any adjustment of components. Here’s a typical example. Not flat frames have been used.
Flat frames will (or should) correct Newton’s rings (which I get with certain cameras), but will not make the uneven filtration of Lunt systems even. In other words, even if you flattened the illumination, you would still see the uneven detail. The only H alpha telescopes I have experienced personally that do not suffer from such unevenness at all are the Solarscopes made in the Isle of Man (3 times the price of Lunt). However, I’ve been very impressed by images from users of the new Sky-Watcher Heliostar and Acuter scopes.
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Peter, I do relatively little processing on my images. I stack in AS3! using typically 1500 out of 2000 frames (8-bit, not 12 or 16). I process the resulting PNG files in Registax using wavelets 2, 3 & 4 and a slight gamma adjustment to brighten the darker areas: this is to enhance the prominences. I don’t do a histogram stretch because the gain and exposure time are set so that the maximum brightness in the sharpened images is at about 80%. On most days I will capture around 10 videos if the clouds permit, and I compare the resulting images to find the sharpest of them to post here.
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