Lunt 60 SS/DS or Lunt 80 SS/DS?

[Robson87]

OK, me too I really love double stack systems, so I've decided to go that way with my Lunt 60.

At the end I've purchased 2 used Solarmax 60 front etalons, one it's type I and the other is type II.

I'll try both the front etalons (and also the triple stack) and decide which is better.

Thank you very much Calavera, very interesting thread!!

Now I have 2 more questions
- What does it consist of the modification of the BF?
- How did you have attached the Solarmax etalon to the Lunt?

[Calavera]

Hi Roberto,

the blocking filter unit was modified with another blue-glas and a tiltable blocking filter frame (therefore is that little silver lever you can see in one of the pics).

The changed blue-glas gives a brighter view which is very usefull if using the scope as doublestack system with a second etalon in the front (which has another red-front-ERF too). In single stack the blocking filter is just usable after the mod but a little bit too bright for my taste.

The tilting of the blocking filter itself allows to bring reflexes by the blocking filter out of the field of view (what didn´t helps for refelxes between the etalons!).

All the filters are fixed by special made adapter-rings.

All the mods and the adapter rings too were made by Wolfgang Lille a very well known specialist for solar viewing - check out his website at: http://www.sonnenfernrohr.de - a very nice guy!

cs
Chris

[george9]

Hi Bill,

Objective mounted (in front of objective) etalons have largest possible sweet spot. So, any 90mm and up refractor equipped with SM90 Coronado front mounted etalon will have significantly better uniformity of sun disk than Lunt 80THa with internally mounted etalon. Not say that 90mm aperture have greater resolution and allows to push magnification more than 80mm aperture.

If both LS80THa and SM90 have the same band wide, I would go with SM90. Second SM90 costs only a little more than DSII unit for LS80THa. But front mounted DS SM90 is far superior (sweet spot and uniformity wise) than LS80THa + DSII unit.

I can add that I never saw such a contrast SS telescope as my former Coronado SM90 + BF30 combo.


Valery.

I understand that in theory, a front-mounted filter should have a larger sweet spot than an internal one due to the angles involved. But in practice, I am finding that the sweet spot on my LS80 SS is significantly bigger than the sun and my LS80 DSII is a little bigger than the sun. And both are perfectly even.

My pre-Meade 60mm Coronado DS, on the other hand, has significant banding (worst when binoviewed), so you have to pick which part of the sun you want to look at. Whether that is due to the etalons or the blocking filter, I am not sure.

George

[Valery]

My pre-Meade 60mm Coronado DS, on the other hand, has significant banding (worst when binoviewed), so you have to pick which part of the sun you want to look at. Whether that is due to the etalons or the blocking filter, I am not sure.
George

All depends. Some DS etalons are - the secondary production which do not corresponds to the requirements as to main etalons.
They typically require much larger tilt to come to the CWL Ha. This cause sweet spot banding.

I have had very similar Lunt LS35F - it is very narrow, but require a lot of tilt. So, the sun is not completely in H-a.


If the etalons are right, then all what I have said is true.


Valery.

[george9]

What I have found is that the single most important factor is the variation between units of the same model and maker. So a good sample of model X is better than a bad sample of model Y no matter what the two cost. It is unsettling to know that you are taking a chance on any filter you buy, especially given their expense. This goes for any maker. I think my LS80 is very good, but I saw a not-so-good sample at NEAF. Also a not-so-good LS100 and LS152; and a spectacular LS152. And varying PSTs. And I've seen a Coronado 90mm that looked great for 30 minutes, and then lost all contrast as it heated up in the sun. I've seen Coronado banding and low contrast (as Valery notes, it depends on how they are made). On the other hand, someone I trust sold his SolarScope because his Meade Coronado worked better. And DayStar varies in contrast and homogeneity, too.

The second factor is whether you are willing to take the time to optimize your filter. E.g., I made a copper shim to optimize the tilt between my LS80 and its DSII and did a lot of experiments on it. (Although now with the anti-reflection filter and brighter blocking filter, the tilt does not seem to matter so much.)

The good news is that what is available today is unbelievable compared to pre-2000 and pre-1980. In the older days, you had to be an engineer and make your own prominence filter. Then (pre-2000) DayStar amazed everyone, although by today's standards, they were very inhomogeneous and low contrast. Compared to pre-2000, every scope offered for purchase today works well. Compared to perfection, they vary a lot.

George

[Robson87]

So, I have news.

I thought that spending money now on a Lunt 80 and then on a DSII (which is hard to find second hand, and however not so cheap), it's too much money for me.

So I have seen an offer and I have decided to buy 2 front Solarmax 60 (one is type I and the other is type II) and a BF 15.
I'll try both the etalons to double stack my Lunt 60, then I'll sell the other etalon with its BF 15.

And I can start saving for a Lunt 100

And thank you for all your posts, your experiences are really useful!!

[Robson87]

After one month and a half I've reached my final setup.

I've found a great offer and I've bought 2 Solarmax 60 front etalons, 1 type I and 1 type II.
I've tried both in double stack on my Lunt 60 and I've tried also the triple stack.

These are the 4 configurations:


And the 2 different front etalons:


Both the Solarmax 60 etalons are great for double stack the Lunt 60, even if the type I is easier and faster to use because is has not to be tilted such as the type II (type I is already tilted and it's not tiltable). And it's also smaller and lighter then type II.

The image is very very good with both the etalons, both present a clear but not disturbing banding, but the ghost image of my type II is closer to the Sun then that one in my type I, so in my type I it's easier to put the ghost image away from the field of view.

With the double stack, there is less light so the maximum magnification is reduced, but the contrast is beautifully increased!

In the triple stack mode, the maximum magnification is even more reduced and the contrast is quite more improved over the double stack (not such an improvement like from single to double stack), but I really had to stay low with the magnification because otherwise the image was too dar,k and in this way it starts to be difficult to appreciate the increased contrast of the surface.

Prominences are still there in double stack (just a little bit less defined) and even in triple stack.

At the end I've sold the type II and I'm very happy with my Lunt 60 double stacked with the Solarmax 60 type I; that's my final setup:



Now I'm ready for the transit of Mercury