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02-16-2010, 07:29 PM   #1
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For those with a DA 15mm who use Cokin P sized filters...

I'm sure this will only be of interest to a few people and not the majority of DA 15mm Limited users, however, it's here for anyone who uses Singh-Ray/HiTech/Cokin filters - or if anyone is thinking of getting the 15mm but is looking for a solution to the lens-hood.

Since I got the DA 15mm, I've been trying to figure out how best to use my Cokin P sized filters with this lens for Landscape shooting. The problem has been that with a 49mm filter alone, everything was fine, but the second I added the cokin P adapter ring to that filter, I started getting some vignetting at infinity focus all the way to f/11. The reason is that even with a 5.5mm filter ring, the cokin adapter stuck far enough out to catch the corners of the image area.

I've toyed with the idea of shaving down the filter hood so that when it's retracted, it would be flush with the end of the lens, thus allowing me to attach the adapter ring directly to the lens, but it seems kind of blasphemous. So I decided to play around a bit.

I took a really old & cheap 49mm kenko UV filter which employed an aluminum ring and removed the glass so the cokin adapter would sit further down, but this only had a marginal effect.

Don't underestimate just how tough the glass in those filters is. I felt like I was high-priest in a ritual sacrifice on the final blow which finally did it in. And one last tip....wrap the filter in a rag or something before bringing the scissor tips/screw-driver down on the glass; it prevent sharp particles from scattering around the kitchen .

Once the glass was out and the ring was cleaned, I grabbed the first sheet of sand-paper I could find and went to work. Admittedly, 220 grit was a slow process, but in retrospect, it delivered a smooth finish to the sanded surface and no debris clogged the inside threads, so it worked well enough.

And here's my word of caution:
Although the sanded surface is quite smooth after having at it for 30 minutes, the inside edge takes on quite a sharp edge. This isn't a problem if you're expecting it. It may be a problem after you wash the dust and use one of your wife's tea-towels to dry the filter ring thoroughly and accidentally cut through it. On the bright side, I'm sure she won't notice it until after the laundry is done

Admittedly, I took a little too much off the filter ring (this whole measure twice, cut 4 or 5 times thing is a bit beyond me ) but if you sand a filter ring down to 1/8th of an inch not including the threads that screw into the lens, this will almost completely eliminate the problem. Actually, if you go a bit further down than 1/8th, this will help prevent the filter ring from binding to the lens when you attach it to the cokin P adapter ring snugly first, so my error...was really a cunning compensation to prevent binding .

From what I've seen, at infinity focus at f/4, there's still some vignetting - most of which is natural to the lens itself. At f/5.6, there's some nominal vignetting only at the very extreme corners and by f/8, the problem is completely gone (I didn't test in between f/5.6 & f/8 yet).

If there's interest, I'll post some photos of the before and after.

Anyways, I hope this proves useful to at least one other person.

Cheers!


Last edited by Andrew Faires; 02-16-2010 at 10:55 PM.
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