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I'm somewhat new to birding and have a question about possible major defects on my spotting scope (see pictures). Kowa TSN-99a (2 Viewers)

nwoptics

New member
United States
I purchased a binocular last year and have recently purchased a spotting scope, the Kowa TSN-99a.

I did a lot of research into different scopes and this is what I settled on. I had read about lemons and cherries among optics. Tolerances in the manufacturing process. I was also curious how my scope would perform against other high end optics.

I took my scope into a store which sells optics and set up an optics chart and image resolution chart on a pillar in the store approximately 70m away. I compared the swarovski atx 115mm to my tsn-99. I used both the mono and binocular eyepieces on the atx.

I was in the store comparing them directly for about 30min and spent an hour in the store. I found that I was able to focus the kowa more accurately and more easily for extreme fine details. I saw more detail from the kowa than the swarovski. Both optics were outstanding but this really made me happy with my purchase. Not only is the kowa smaller and lighter but it outperformed the swarovski. I also set up a chart that is supposed to test chromatic aberration and didn't notice it at all from the kowa. Both optics performed excellent in regards to CA although the tsn-99a seemed to perform better.

Over the past few night I have been testing the tsn-99a against stars. I've been overfocusing and underfocusing on stars and they form perfect circles. However I notice when I focus on the brightest object in the night sky which I think might be venus I get a faint diffraction spike. It looks similar to the diffraction spike shown in the top photo in this thread:


I also noticed when I unfocused from what I think was venus I saw small blotches within the circle. At the time I thought they might be small imperfections on the lens. Today I tried shining a flashlight into the main objective lens to look for any imperfection. I see what appears to be hundreds of dried water droplets or splotches on the inner lens. They look like little specs of dust or what you might see if you let droplets of water dry on a mirror or let glass cleaner dry on a mirror, you can see them in the photos I attached to this post. The splotches were hard to capture through my phone's camera but I will attach the images to this post. This is concerning to me. I tried to wipe off the front lens and it seems these splotches are inside the scope. I don't know if this is normal or a manufacturing error. Keep in mind I had to rotate the flashlight around to specific angles for them to present themselves. If I look straight through I cannot see them.

I am not sure if this is normal given the price of this scope (4000 usd). I am left feeling extremely unsatisfied after seeing these imperfections.

Should the diffraction spike be acceptable or do you think I should contact Kowa or try to exchange for another tsn-99a? What about the splotches on the inner lens? I feel like I might return it. Maybe the scope wasn't sealed properly and moisture was trapped inside, or maybe there was a problem with the lens coating. During normal daytime use, and without shining a flashlight through the objective this scope performs great. However I wonder if I could have spent a fraction of the cost of this scope and achieved similar results under normal use.

I felt like I had a good optic after I tested it against the atx 115. I can see the potential of this scope. Even with the imperfections mine still performs well in low light and day use. It just doesn't seem like diffraction spikes should be present on an optic of this caliber, and after seeing the splotches with the flashlight I am feeling uneasy about it. I don't have a camera to digiscope with and my phone makes the stars appear to have many diffraction spikes which is inaccurate. I will be purchasing a camera in a few weeks and might post some photos when I can. Until then the thread I linked from starry nights is similar to the diffraction spike I see. I'm not sure if I got a defective optic. Hopefully someone more knowledgeable can help.
 

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Hola nwoptics! A warm welcome to Birdforum from all the staff and moderators (y)

You can check the specific Kowa scopes sub forum here:

or just post your own thread there and for sure somebody will reply to you :)
 
Hi nwoptics and a warm welcome to you from all the Staff and Moderators. LOL Fritz... we were working on that at the same time! I've moved your thread to the Kowa 'scope forum as they're better placed to be able to advise you.

I'm sure you will enjoy it here and I look forward to hearing your news.
 
The spike may be from the erecting lens, I see then when I use an erecting diagonal on my refractor, depends on the optical design if you’ll get one or not. The “dots” are intriguing, certainly shouldn’t be there, don’t look like dried moisture or coating issues, we worth asking Kowa.

Peter
 
Hi nwoptics,

The fact that you resolved more with your Kowa 99 than the Swarovski 115 means it is likely a replacement Kowa 99 may be worse optically.

The slight flare on Venus is acceptable and maybe from a prism edge.

Venus is not a point object and has considerable size in a 99mm scope.
Although it is bright.
The only common brighter thing is a street light or car headlamp.

The small spots may be outgassing of grease.
Although annoying they probably don't affect the view.

I suppose Kowa should clean the offending glass surface, but one has to hope the technician is excellent and the optical collimation, spacing, and refilling with inert gas is done properly.
If not, the quality may actually be worse after the trip to Kowa, so I would ask that a top technician does the job.

Regards,
B.
 
Very good advice from Binastro. From your description of the optical performance of your particular 99A, it seems like an exceptionally good sample worth holding onto. The prism line you describe is a problem only if it is severe enough to cause astigmatic spiking in best focus stars, and it sounds like yours doesn't. If it is bad, it can also be seen in defocused ring patterns as a double diffraction line cutting through the ring pattern.

The dirt spots are difficult to assess in the photos, but there needs to be quite a bit before it visibly affects the image quality, whereas even a minuscule amount of SA, astigmatism, coma etc. other optical defects make a marked difference.

- Kimmo
 
Very good advice from Binastro. From your description of the optical performance of your particular 99A, it seems like an exceptionally good sample worth holding onto. The prism line you describe is a problem only if it is severe enough to cause astigmatic spiking in best focus stars, and it sounds like yours doesn't. If it is bad, it can also be seen in defocused ring patterns as a double diffraction line cutting through the ring pattern.

The dirt spots are difficult to assess in the photos, but there needs to be quite a bit before it visibly affects the image quality, whereas even a minuscule amount of SA, astigmatism, coma etc. other optical defects make a marked difference.

- Kimmo
Hello Kimmo,

This was my concern with sending it in. I emailed Kowa with a description of the spots and I'm waiting to hear back from them. I love the scope it is just dissapointing to see the white spots. The optic still performs excellently.
 

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