Here is a brief review/comparison of these two binoculars. Hope you find interesting to read
I've been a Lunt 10x50 FMC Magnesium owner for 5 years and their optical quality outperformed by far my previous Nikon Aculon 8x42 in every aspect. Sharpness in the center of Field Of View (FOV) is amazing, wide field of view, bright due to high transmission... However, these Lunts have one big flaw: They suffer from field curvature, that is, the stars remain in focus in 50-60% of the FOV and then they become progressively out of focus as they become closer to the edge of the FOV.
Personally this field curvature bothers me a lot and doesn't let me enjoy the views. So one of my priorities when choosing a binocular is to have Flat-Field. I bought a Kowa prominar BD XD 8x32 for casual observing 2 years ago as a compact bins for hiking and traveling. I was AMAZED by their optical performance. They are almost 100% flat field: The amount of blurring in the edge of FOV is almost zero and stars remain in perfect focus in (almost) the entire FOV. With 55° of AFOV these Kowas are not wide angle bins but I prefer by far to have "narrow" and well corrected FOV instead of having wide FOV and poor edge sharpness as some binocs have. So these Kowas became my second astro binoculars and I enjoy a lot looking though them night sky despite they are not very bright.
Then I read a lot of threads and reviews about the Fujinon 10x50 FMTR-SX. These bins have Field Flattener lenses in eyepieces so it is expected to have better field correction towards the edge of FOV. After 2 years thinking about buying a pair of Fujis (they cost 1100€ but you can find then at 900€) finally I aquired a pair last week.
I was looking for the non-rubber version but seems it is discontinued by 2021 so the only version available was the rubbered one. When they arrived I made a first quick test through my window looking some TV antennas and buildings during daylight. They have clear better FOV correction than the Lunts. The amount of edge blurring is almost zero!!!
But the real test will be under stars...
Next day I had the opportunity to test then under Bortle 4 sky and make a direct comparison between Fujis and Lunts.
Both bins are very well built and seems they will last longer than I will. Fujis are better built and the mechanics are a little bit stiff but ok. Only time will tell how the rubber armouring will age… (I will storage the fujis in a foamed transport box like a flying case)
*Whiteness of image:
Lunts show yellowish images during daylight and the Fujis have almost perfect neutral color correction.
*Field Of View:
I prefer to observe with the eyecups retracted for both Lunt and Fuji since in this configuration I set my IPD and rest eyepieces in my nose and can observe the entire FOV. Both bins state 6.5deg of FOV and 65º of AFOV. This seems to be true but initial impressions showed that Fujis seems to have apparently a slight wider AFOV.
I realized this is because with eyecups retracted I can see the entire of FOV with the Fujis but not with Lunts due to huge eyepiece diameter (I can see almost the entire fov with lunts, the difference is small). I was not expecting this since both bins have same eyepiece diameter and dimension but the Fujis work better with my face and nose anatomy (my nose is small and my IPD in Fujis is 64mm)
*Stray Light, internal reflections:
Lunts have some internal reflections and this can be seen when looking at the area near to M57 when the ghost image of Vega apperas. Fujis do not suffer from this. Lunar tests have to be done...
*FOV Edge Sharpness:
Here is where I wanted to come...
It is important to set properly IPD, and eye placement to be in the optical axis. Taking this into account let´s try to focus a bright star at the center of FOV and move it towards the edge of FOV…
Lunts have moderate to big amount of blurring towards the egde of FOV and stars get out of focus progressively. In the edge the stars appear as a radial tear drops (think this is coma). No matter how I set eye placement, tilting the binocs of moving them together with my head gives similar results. The stars can be focused in perfect points at the edge of fov if you refocus the binos, but leaving the center of fov unfocused.
In the case of Fujis... well, the field correction is improved significantly and the amount of blurring is soft. I could not tell in what % of FOV stars are blurred since the degradation increases towards the edge progressively. What´s more, the amount of edge blurring is not the same in all directions, I mean, there is more blurring in the upper part of the FOV edge (at 12 o'clock) for both eyepieces than at the bottom of the FOV (6 o'clock) where blurring is less. In fact, the stars at 6 o´clock barely are out of focus whereas they are clearly out of focus at 12 o´clock (but much less than Lunts) . This happens for both eyepieces as I mentioned above.
Have you experienced this?
If after observing through Fujis I take the Lunts to make quick comparison, the blurring is much more evident in every directions.
The differences between Fujis and Lunts are evident but not that much. I admire how Lunt did copy Fuji at 1/3 of the price and have an optical performance comparable to the Fuji´s...