What is this abberation??
Posted 02 August 2005 - 04:12 PM
I'll try my best to describe this, but it is something I have never before seen in any binocular I've used (good, bad, or ugly).
When attempting to focus, it seems that this specimen would only focus sharply along a 1/4 AFOV vertical band, which migrated from left to right throughout the range of focus. Picture holding your finger vertically along the left side of the FOV (this is the in-focus portion of the image), then wipe your finger toward the right while keeping it vertical. This is how the focus abberation behaves.
Has anyone ever seen this before? What defect would this indicate (besides sloppy QC, and "you get what you pay for")? Explanations only please - if I wish to read posts which bash Chinese manufacturing, there are already numerous threads in which this abounds.
Thanks in advance.
Posted 02 August 2005 - 04:56 PM
Posted 02 August 2005 - 05:09 PM
Warped objective, funky prism, goofy eyepiece, something aint right.
Definitely doesn't sound normal though!
Posted 02 August 2005 - 06:19 PM
The binocs are already on their way back to the vendor, with a refund on the way - no hassle.
The reason I chose the refund over replacement was due in part to the time it would take to replace the defective unit (it took 3 weeks just to recieve this one), and also due in part to some obvious shortcomings I also discovered.
Some of the problems I noted with my specimen (aside from the optical abberation) were a sloppy focuser with a lot of play, a very soft IPD adjustment which I suspect would only become more loose over time, and what looked to be undersized prisms - the upper edges of both exit pupils were cut off very noticeably. There was also a HUGE amount of pincushion distortion, I thought I had developped walleye vision for awhile.
For the money, I wasn't expecting much - but I was expecting something a bit better than this. I would have loved to put that wide FOV to use during the Perseids this month and for sweeping up Saggitarius before it completely disappears, but it looks like I'll be shopping around for awhile yet.
Oh well, shopping can be fun too...
Posted 03 August 2005 - 12:52 AM
<<Some of the problems I noted with my specimen (aside from the optical abberation) were a sloppy focuser with a lot of play, a very soft IPD adjustment which I suspect would only become more loose over time, and what looked to be undersized prisms - the upper edges of both exit pupils were cut off very noticeably.>>
It seems to me that the first cause could be too tilted prisms and maybe also prism strain (with as a result no round exit pupils + uneven focus in the FOV and aberrations). Moreover, a sloppy focusing mechanism definitely increases the focusing problems.
Posted 03 August 2005 - 01:11 AM
Sorry to hear of your problems. I have to agree with the previous poster--it appears that there is something quite incorrect with the prism system. Possibly even some obstruction (some thing that came loose and lodged?). Best you sent them back.
I purchased a set a few months ago. I was pleased with the unit for the cost, and it's a light grab-and-go for me with a pleasing FOV. Your unit was definitely defective. Again, sorry to hear of your frustrations.
Posted 03 August 2005 - 07:25 AM
Posted 03 August 2005 - 12:09 PM
I've decided to create a makeshift illustration to show what I was seeing, maybe this will help it become more clear. I should add that this was a problem with the left barrel only - the right barrel seemed to be fine.
In the diagram below, RED represents a completely out of focus and unuseable image, and WHITE represents a clearly sharp and focused portion of the image which looked fine. As the focus was moved from outside of focus, through focus, to inside focus, the clear and sharp vertical "band" of image migrated horizontally across the FOV. Hopefully my illustration makes this more clear.
Posted 03 August 2005 - 12:36 PM
Posted 03 August 2005 - 12:53 PM
Could be one of the prisms has an improper angle cut to one surface and is changing the focal length in one plane only.
Any guess is just a guess. it's obviously a bad piece of equipment.