I think you misunderstand; the only way someone is going to find the 'flaw' due to a single 'dot' is if they look at the image with at 1:1 and know exactly where to look (such as masking with a different lens) and even then they might not spot a difference. Your talking about something (if i understand your description) that is smaller than a speck of dust. It is possible (though unlikely) that such a flaw could catch a ray of light and create a streak but it would have to actually be a fairly deep defect (such as a nick in the element) which I doubt from your description.
Believe me as someone who obsessed over new equipment I've been down this path of fret more than once. The optical defect of decentered lens is far greater.
Please ignore what I wrote if the mark you are talking about is significantly larger than 2 or 3 specks of dust.
Guys, if you had both the systems, will you go for this lens over a regular 85/1.8?
Well that's a tough one - this lens is better than most 85f1.8 (I presume you are talking about nikon or canon); but it is also a 150mm lens with regards to shooting distance so it is a bit difficult to compare. Having look at a lot of images on the web (not the best source for comment) this lens is incredibly good with regards to image quality but it also has a perspective that I find in many cases a bit annoying for 'street' stuff - so if your happy with a 70-200f4 lens (with most of your pictures closer to 200) then this is the lens to love; but if you really want to shoot with an 85f1.8 (on a ff camera) then there will definitely be an adjustment.
(I'm making an assumption that you are talking about an 85f1.8 on a FF and not aps-c).
Just want to thank all who gave me advice on my decison on whether to exchange my Olympus 75mm f/1.8 or keep it. The 30 day return period is over and I decided to keep the lens. I could find no traces in my images created by the tiny 'flaw' I could see looking in the lens. I am so pleased with the results I am getting from this lens that I simply would not risk getting a replacement that looks perfect, burt is decentered or not as contrasty or sharp. It is the best lens I have owned. Thanks again for the help.
Hi there, I just got my new 75mm lens and of course took a whole lot of "test" pics. The sharpness is incredible but only upto f/8. After that the images become unbelievably blurred, actually images taken with 70-300 are much sharper. Is this "normal" and my expectations are too high? Of course to return the lens to B&H shouldn't be a problem if I want to forfeit the shipping costs and quite a high customs duty. I feel I am trapped...
The first example is f/5.6, the 2nd one is f/16:
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>The sharpness is incredible but only upto f/8
Don't use f/16