Ha solar vignetting

[Dawson]

Using a 50mm Lunt, B600 blocking filter and ZWO585MC, in fact with any camera, is the vignetting at the edge of the FoV caused primarily by the blocking filter? Even when the Sun is positioned in the centre of the FoV, equidistant from the vignetting, there is an even illumination of the disc, even when the seeing is perfect and there are no clouds. Again, is this in part due to the B600 blocking filter? Would the B1200 improve this? I’m hoping a video uploads but I’ve been fighting with the website from my phone for half an hour so now lost the will to try other options 🙂

Thanks.

[Callum Potter]

Hi James,

I don’t have direct experience as I have a B600 on my Lunt 60 – but the B600 is recommended for visual use, and the B1200 for imaging.

Quite an expensive upgrade as an experiment…

Hopefully someone will be able to advise better.

Callum

[Ron Morley]

Hi James, I have a 50mm Lunt with B600 which I use for solar imaging. It is a bit fiddly to use but not that bad. Lunt did advise that the LS50 was more for visual while the LS60 was best for imaging – but much more expensive. My initial problem was Newton Ring type banding with my Altair GPCAM2 130 Mono. This was reduced by using a tilt adapter. But there was still some uneven lighting across the solar disk. Nearly all problems disappeared when I put my large Altair 24M on the small Lunt. It looked ungainly but there were no rings, vignetting or uneven light that couldn’t be controlled. No need for a tilt adapter. I have a new ZWO ASI585MC but haven’t tried it on the Lunt. As you will have found the LS50 helical focuser and etalon adjuster are not fine adjustment controls – mine is on a camera tripod which is a bit wobbly – but practice makes adjustment manageable. I’ve noted with the larger chip on the 24M (it’s one of the models that uses the IMX571) that there seems to be better areas than others to position the solar image. Again trial and error. But I’m delighted with the LS50, the B600 and the images it produces. I’ve used a 5x Powermate too (with the 130) – which looked ridiculous on the scope – but it focused – and produced respectable edge prominence images. Ron

[Dawson]

Thanks both.

The Lunt website talks about the issue, but gives conflicting advice on a solution. At one point says the B600 is fine for imaging with the 50mm Lunt, but then in the next paragraph suggests one should go to the next blocking filter up for imaging. I’ll email them, as they have been helpful in the past. It also sounds like tilt may be an issue, so something else to explore and MUCH cheaper to rectify!

Thanks.

James

[Dawson]

I’ve had a useful email conversation with a technical person at Lunt. This is a summary of their suggestions which I have yet to try asI’ve not had time nor a clear day! It has a new blue filter in which I replcaed before the April 2024 total solar eclipse.

Now, may I ask with the double stack removed, do you also experience such views? It is certainly true that a double stack can really make your image extra special but if not tuned correctly, can also consistently be at odds with the primary etalon.

What I might recommend here, might seem like a step backwards. When I test double stack units, for the LS50THa or otherwise, I of course start with my scope in single stack mode. I tune and adjust until I am at the best point, and then I introduce the double stack. From there, I make sure my double stack is at rest (that is, no tilt introduced through the tuning wheel) and begin to tune from there. There are times when double stacks need a little something else. If I was testing your LS50THa, with this LS50c, the first thing I might do is go through the entire range on the LS50c that is attached and find my absolute best view while tuning that (after having tuned the primary without the double stack attached). If my field is much like your picture, my next thing I do, is to attempt to retune the primary etalon. At times, a little adjustment on the primary can really go a long way to making the double stack image what I would like it to be. From there, I would lastly try rotation of the double stack unit itself. This may seem the most precarious, but of course you have multiple threads securing it, and you wont need to during any more rotation than the initial 360 degrees, as anything past the first complete turn will put you at the same physical position in terms of lens tilt, but with just less thread to hold the filter onto the telescope.

Very often, customers who are experiencing a lack in quality views with their double stacks will find some relief between these suggestions.

Lastly, I am uncertain how old your telescope may be- but have you checked the BG (Blue glass) optic in your blocking filter as of late? This would be the blue glass element found under the nose tube that is introduced into your focuser. It should be perfectly clear, and without occlusion. Some of our older scopes have an uncoated version of the BG, while the new ones have a coated version. In either case, it should be 100% clear.

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