Defective 16mm/2.8 AIS Fishe Eye - Repairable?

<p>Over at dpreview in the Nikon lens forum I showed my comparison between my 16mm/2.8 AIS and 16/3.5 AI fish eyes on my D300 (DX sensor) and found that the 16/2.8 had a great center, but quite terrible borders and corners (on all sides) wide open compared to the f/3.5 (which was fantastic). It mostly clears up by f/8, but it still is not quite as good as the f/3.5. According to all reports (like from Bjorn Rorslett) the f/2.8 should have BETTER corner sharpness than the f/3.5 version. <br /> So, it appears I have a defective lens on my hands and I have a couple of repair-related questions:<br /> (1) Could there be some kind of mis-alignment in the lens elements that could cause this?<br /> (2) Is this kind of optical problem potentially repairable?<br /> (3) If it is repairable, where would the best repair place to send the lens be?<br /> <br /> I've looked through the lens as best I can and there is nothing obviously wrong, although I can see that at the very edge of one of the last elements there seems to be some sort of a small imperfection that doesn't seem to be in the light path (it's at the very edge of the lens where it mounts to the assembly and is only visible if viewed very obliquely from the side at the rear).<br /> <br /> Thanks -<br /> <br /> John<br>

Attached is a sample of border crops taken at wide-open through f/22 with the 16/2.8 on the left and the 16/3.5 on the right. Wide open through f/5.6 the border is substantially worse than the f/3.5 on my DX body - It is probably much much worse on a FX body.</p><div></div>

<p>It's been decades since I last had a 16mm f/2.8, so this is just a guess:<br>

Do you have a filter bayonetted onto the rear of your 16mm f/2.8? From all I've heard, the filter is necessary for the lens to operate properly. I heard the lens won't focus at infinity if there is no filter attached. I'm not sure if sharpness is affected too.</p>

<p>Yes, the rear filter is attached and the lens was tested at infinity using Live view on my D300 for achieving critical focus. Last night I cleaned the filter and inspected everything, but it still has the same problem.<br>

I may go out today and test it on something up close with and without the filter to see if it makes any difference at all.<br>

Thanks for the reply - John</p>

<p>John, mine is tack sharp to the edge. I think you have a bad apple. I'd send it directly to Nikon to have them take a stab at it. They'll have all the alignment equipment.</p>

<p>Well, I bought it from the local pro-shop here in Seattle with the aim of trying out using a full-frame fisheye on my DX camera as a way to get a very small and compact wide angle lens (once the distortion is corrected out). So far that has gone well. I only noticed how bad the corners were when I compared it to a 16/3.5 AI fisheye which I unexpectedly picked up from the local CL.<br>

I had planned to sell whichever one I liked the least - in this case the 16/2.8 due to the ghosting when pointed into the sun even if it had great corners. So I don't really want to put any more money into it (got it for $450), but I also don't want to sell it to someone else who will inherit this problem (bad Karma). So the way I see it I can send it in to Nikon and see what they want to repair/adjust it (if they can at all) and take the hit on the repair or trade it in on some gear back at the store that I originally bought it from OR sell it at a much reduced price with full disclosure.<br>

John</p>

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<p>trying out using a full-frame fisheye on my DX camera as a way to get a very small and compact wide angle lens (once the distortion is corrected out).</p>

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<p>The "de-fish" process involves stretching the pixels by a great deal around the edges. Make sure that you study the final result carefully and you are happy with it. To get the super wide result, I by far prefer getting a 10-24 type lens instead of de-fishing.</p>

<p>As far as your 16mm/f2.8 AI-S fisheye goes, I am afraid that the only way is to ship it to a qualified repair service and let them check it out. E.g., Nikon USA repair provides free repair estimates. Should you decline repair, you only need to pay for return shipping.</p>

<p>Your 16/2.8 is not performing as expected. Probably an element has worked loose or is out of alignment. The f/3.5 appears to be OK.</p>

<p>On an FX camera I much prefer the 16/3.5, it is amazingly sharp, and on the D3X in particular the images are superb. It tolerates shooting into the sun with ease. Perhaps the f/2.8 beats it in the extreme corners, but the other qualities of the f/3.5 makes this the obvious choice. The drawback is that CPU-modification of the f/3.5 is much more difficult than with the f/2.8.<br>

I kept my f/2.8 for use in an underwater housing where it functions well partly because the lens focuses much closer than the older f/3.5 (and removing the rear filter makes it go even closer).</p>

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<p>The "de-fish" process involves stretching the pixels by a great deal around the edges. Make sure that you study the final result carefully and you are happy with it. To get the super wide result, I by far prefer getting a 10-24 type lens instead of de-fishing.</p>

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<p>Actually, when a full-FX-frame fisheye is used on a DX body not that much de-fishing is needed and the result can be quite OK - I've already done it for a couple of "production" shots at Thanksgiving dinner this past week and I very much like the results. Is it distortion free? No, but I got the wide shot with the on-board flash and everyone in the picture looked pretty good (not all distorted).<br>

For a compact lens that can give a pretty wide (~20mm FOV on FX) I'm pretty happy.<br>

See my thankgiving dinner shots at www.hinkey.zenfolio.com - pick out the 16mm/3.5 AI lens shots on my D300 (Oh OK, the group shot was de-fished just a bit).<br>

- John</p>

<p>John, as long as you are happy with the result; that is the only thing that matters.</p>

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<p>Your 16/2.8 is not performing as expected. Probably an element has worked loose or is out of alignment. The f/3.5 appears to be OK.</p>

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<p>Thanks for the confirmation Bjorn! I think I'll send it in to a Nikon service center and see what they want to adjust/repair the lens (if possible).<br>

- John</p>