Lunt LS80 Mini Review/SMII 90DS comparison
Posted 21 January 2013 - 12:59 AM
I did get about an hour or so of clear skies this morning to try out my new LS80THa PT (single stack), with a B1800. My initial impressions are very positive with regards to build quality, with probably the stock Crayford focuser being the weakest part. It took quite a bit of tightening to get it so it would support itself and the Lunt zoom eyepiece. But once adjusted, it performed fairly well and I think was easier to operate that the SMII's helical.
At 560mm, the solar disk takes up about 1/2 or so of the field of view with the eyepiece on the longest FL setting. The full disk almost fits on the chip of my e2v Flea 3 (1/1.8"). There's plenty of room horizontally, but just not quite enough vertically, so at natvie focal length, I'll need to do a 2-panel mosaic for a full disk.
Details were good all around the disk with the surface detail not as defined as with the SMII, but not unexpected with a SS vs. DS. There does seem to be what I would term as "backscatter", but I honestly can't remember whether the DSII exhibited the same thing. No reflections or kidney beaning with viewing on axis, but you could see the etalon's center spot when you moved your eye off axis. Again, not unexpected and I've seen similar issues with the SMII.
The tuning of the LS80 is more subtle than with the SMII. Where with the SMII's internal etalon, you can make fairly large moves with both the internal and external etalons, the pressure tuner takes more turning to affect the on-band tuning. I haven't decided if this is a good or a bad thing, or just a different thing.
I'm looking forward to spending more time with the scope and still debating about the purchase of the DSII double stack module. I've been reading mixed reviews of performance of the stacked PT modules vs an external etalon.
Also, just a small kudos to the Mini-Tower mount that I borrowed from my club. I'm continually impressed by the simplicity and yet accuracy of this mount. Not wanting to deal with the cold and wind today, I set up in the hours next to an open window. Even without a positive GPS lock (just used the previous sessions's settings) and not quite exact leveling, the mount managed to place the sun almost dead center in the FOV and keep it there. For grab and go goto, this thing can't be beat.
Posted 21 January 2013 - 08:51 AM
For me, what I like is that for about the same view as the Solar Max II 90DS it is half the weight and bulk, the disk is near perfect, there is no banding, there is no sweet spot (i.e., it is bigger than the sun), you can sweep the DS filter above and below H-alpha easily, and you can always remove the DSII and use it SS.
The down side is the presence of reflections and what you call backscatter. You can minimize the reflections by attaching the DSII to the main filter correctly (if you just tighten it casually, they won't be parallel). If you do that, there are no reflections when the sun is centered, and when the sun is off-center there is a circular or arc-like glow, in which case you put the area of interest in the center of the eyepiece (e.g., a prominence).
But even with an ideal setup, there is a greater reddish background in the DSII than in the SS. It does not interfere with seeing prominences, but it is there (i.e., the dimmer disk makes it easier to see prominences but the background removes the advantage).
Posted 21 January 2013 - 09:39 AM
Are they easy enough to change out that if I wanted better prom detail I could take the DSII out? Or is it something that once it's in place, you don't want to go fussing with?
Posted 21 January 2013 - 01:14 PM
When you put it back in, you just have to be sure to align it optimally. I would say it takes me less than 120 seconds to remove it and about the same to put it back in. Most of that time is deciding where to put it so I won't drop it (but same goes for the binoviewer, etc.).
The redder background is unacceptable for some people, there may be variation among units (but mine was not special and was not matched in any way), and some feel more comfortable taking it apart in the field than others. On the whole, I am extremely happy but others have sold theirs.
I always use mine with a binoviewer, at 20x, 60x, 80x, and 140x if seeing is great. I could use 100-110x, but I don't happen to have that combo. For average seeing, I find 80x to be the max useful.
Posted 21 January 2013 - 07:44 PM
Now I'd just like to get out and use the dang thing without needing an hour to defrost afterwards. Viewing out an open window of a heated house plays hell with seeing
Posted 22 January 2013 - 08:24 AM
I've had good luck at times viewing through the window while waiting for the temp to warm up outside; at times could not tell the difference. It's worth a try.
Posted 22 January 2013 - 10:47 AM
Posted 22 January 2013 - 12:42 PM
I guess that I was not clear enough in describing what I wanted to say; I meant viewing through a CLOSED window.
Again, if the seeing outside is bad, it's not going to help, but if the seeing is good, you can maybe get good results by not allowing the inside heat to escape and ruin the seeing.
Posted 22 January 2013 - 04:03 PM