Hi Everyone,
I just thought I would share the following experience with the Kowa 663s so that you can check in on some of these points, the next time you are considering a scope. This is by no means a review - I do not think I am qualified enough.
TLDR:
1. I will 100% recommend the K663 for its competitive resolution, colors, CA control, and build quality, and the Kowa company's support.
2. One caveat … I will do so ONLY after you have had a chance to look through it, and when you are absolutely sure you are comfortable looking through it.
I had a chance to check four objective copies and three 20-60X TE-9Z EPs from different sources. The difference between the best and worst performing among these objective-EP combos was no more than a block in the USAF chart. Because I have some doubts about my distance measurements, I would take my measurements ranging from ~116/65 to ~116/61 arc seconds with a grain of salt.
I spent some time star testing these under different conditions, with a good amount of advice from Joachim, Henry & David (thank you all!). If there’s one aberration they all shared, it is astigmatism. All K663 + TE-9Zs just couldn’t shake it off. One copy added slightly excess CA to the mix. One copy added slight coma. Another copy (a 1 year old demo from store) added both pinching and coma. I am still not sure of spherical aberrations so I would rather let an expert chime in when they get a chance. These conclusions were made by relating the realized star test result with the images posted by Henry Link and his descriptions on the subject in various scope/binocular reviews here.
My newb-ness with star tests means I am unable to conclude how severe these effects are relative to the rest of the scope landscape but the “worst” aberrated scope here (the in store demo) beat an ATS65 with their standard zoom and their Swaro wide-angle EP by at least a block in resolution, and an Opticron MM4/60 (perhaps an an apples to oranges comparison here given the objective diameter difference). I guess the ATS was a poor copy.
In addition to the aforementioned optical aberrations & resolution considerations, there were differences in focus wheel smoothness ("buttery smooth" to "stutter-y"), which further contributed to variations in the ease of focus. For terrestrial observations however, I thought one must be real astute to notice a significant difference in resolution across all these scopes when focused on target at reasonable zoom ranges. I agree this is not the same as conclusively saying the scopes are diffraction limited.
Now for the caveat mentioned in TLDR: Where the K663s continue to bother me a lot is in their available ER. I do not wear glasses, and I do not yet 100% believe in Kowa’s ER ~16-16.5mm specifications. My current measurements indicate the ER profile here is like a parabolic curve, started in the neighborhood of the listed ER specification around 20X, falling down rapidly to their lowest to about ~35X and recovering relatively slowly post. Specifically, around 20X and 60X, the scopes would perhaps meet the listed ER specification of ~16mm. By 25X, the ER appears to quickly drop by about 3-4mm, and around ~35X, the ER feels quite narrow for me at ~10-12mm. It then starts going up again slowly. So: I have some serious doubts about the listed 16-16.5mm ER specification here. When I am certain, I will update the thread.
With careful eye positioning, I am finding this ER pattern to not cause too much of an issue. However, if I do not get used to this within a year or so, I would be actively looking for another scope despite its competitive attributes.
I must acknowledge the help from David, Henry, Joachim and Paul Kardos during this process once again.
Cheers, and thank you all,
Kumar
I just thought I would share the following experience with the Kowa 663s so that you can check in on some of these points, the next time you are considering a scope. This is by no means a review - I do not think I am qualified enough.
TLDR:
1. I will 100% recommend the K663 for its competitive resolution, colors, CA control, and build quality, and the Kowa company's support.
2. One caveat … I will do so ONLY after you have had a chance to look through it, and when you are absolutely sure you are comfortable looking through it.
I had a chance to check four objective copies and three 20-60X TE-9Z EPs from different sources. The difference between the best and worst performing among these objective-EP combos was no more than a block in the USAF chart. Because I have some doubts about my distance measurements, I would take my measurements ranging from ~116/65 to ~116/61 arc seconds with a grain of salt.
I spent some time star testing these under different conditions, with a good amount of advice from Joachim, Henry & David (thank you all!). If there’s one aberration they all shared, it is astigmatism. All K663 + TE-9Zs just couldn’t shake it off. One copy added slightly excess CA to the mix. One copy added slight coma. Another copy (a 1 year old demo from store) added both pinching and coma. I am still not sure of spherical aberrations so I would rather let an expert chime in when they get a chance. These conclusions were made by relating the realized star test result with the images posted by Henry Link and his descriptions on the subject in various scope/binocular reviews here.
My newb-ness with star tests means I am unable to conclude how severe these effects are relative to the rest of the scope landscape but the “worst” aberrated scope here (the in store demo) beat an ATS65 with their standard zoom and their Swaro wide-angle EP by at least a block in resolution, and an Opticron MM4/60 (perhaps an an apples to oranges comparison here given the objective diameter difference). I guess the ATS was a poor copy.
In addition to the aforementioned optical aberrations & resolution considerations, there were differences in focus wheel smoothness ("buttery smooth" to "stutter-y"), which further contributed to variations in the ease of focus. For terrestrial observations however, I thought one must be real astute to notice a significant difference in resolution across all these scopes when focused on target at reasonable zoom ranges. I agree this is not the same as conclusively saying the scopes are diffraction limited.
Now for the caveat mentioned in TLDR: Where the K663s continue to bother me a lot is in their available ER. I do not wear glasses, and I do not yet 100% believe in Kowa’s ER ~16-16.5mm specifications. My current measurements indicate the ER profile here is like a parabolic curve, started in the neighborhood of the listed ER specification around 20X, falling down rapidly to their lowest to about ~35X and recovering relatively slowly post. Specifically, around 20X and 60X, the scopes would perhaps meet the listed ER specification of ~16mm. By 25X, the ER appears to quickly drop by about 3-4mm, and around ~35X, the ER feels quite narrow for me at ~10-12mm. It then starts going up again slowly. So: I have some serious doubts about the listed 16-16.5mm ER specification here. When I am certain, I will update the thread.
With careful eye positioning, I am finding this ER pattern to not cause too much of an issue. However, if I do not get used to this within a year or so, I would be actively looking for another scope despite its competitive attributes.
I must acknowledge the help from David, Henry, Joachim and Paul Kardos during this process once again.
Cheers, and thank you all,
Kumar
also that: please check in store if you can before you buy, and that the mechanical bits like focus wheel stutter appear to cause more significant differences in real life (at least with these copies) than their subtle optical aberrations, which mostly died out in 3-5 rings of defocus.
