From what I have read, the FPL55 performs similar to FPL53 and there should be no difference in performance visually regarding the APM binos. I'm not sure if the actual glass being used for the 150 SD will be FPL55 when and if it becomes a reality.
I spoke to Markus at NEAF just over a week ago and he mentioned several things about the APM150 status.
So far, there are three ED models that have been shipped including mine. Possibly one other is sold, so I would guess that six ED versions are available.
The SD is on hold for now until the ED sales are enough to make the SD possible.
I forgot to ask about the 90 degree version, but it could also be on hold until the (10) 45 degree ED units are sold.
My experience with the 150 ED is that the longer focal length, higher resolution, and light gathering ability of the 150mm lens makes up for any small loss in performance between the two glass types.
In other words, it allows me to see what I want to see at a very sharp level of resolution.
For a lens system operating at F/5.5 the 120 is good on planets, but the 150 is clearly superior despite the glass type.
Very interesting info, Mike, thanks! I was hoping that they might have sold more than four units, but being as costly, and not too well known, I understand.
Nice that you got to speak to Marcus at NEAF. Any idea how many units he will have to sell before he can start assembling the 150 SD models? I'm hoping that I'm not waiting for something, (the SD), that will never happen!
You're probably right about the glass for the SD, I've noticed that plans and spec's, etc, sometimes seem to change a lot before final release of a model. I've wondered why they didn't just choose to use FPL 53 for the SD model in the first place.
I'm glad to hear that the ED unit is just what you need for your purpose. It sounds like a wonderful instrument. I'm a little surprised that aperture wins out over the better glass in the 120. With yours being so good with the FK 61 glass, I wonder if I'm setting my sights too high, and should just order the ED model. On the other hand I have to wonder just how good the SD might be with FPL 55 or similar glass.
If I can ever get a copy of the 150, I still want the SD, if i can get it, since it will be the only large astro instrument I have. I would like to be able to get the best planetary views, as well as other higher magnification use. I think the better glass might enhance higher magnification use quite a bit. I have enough dark skies and good seeing here that I think it would be worthwhile.
Hope I'm not missing the boat by waiting for the SD.
Still not sure whether I would order the 45 or the 90 right now. I've leaned toward the 90, but I use my 100 mm Lunt for a lot of terrestrial viewing, so may end up going for the 45.
Please excuse the long ramble, I'm just excited about the prospects of this new instrument!