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Forum: Troubleshooting and Beginner Help 02-09-2010, 12:28 AM  
OOF problems; don't know what to do anymore.
Posted By ma318
Replies: 15
Views: 4,271
--------from dofmaster faq------

What is the meaning of circle of confusion?

Circle of confusion is difficult to explain in non-technical terms. You shouldn't worry about it if you're just beginning to learn about depth of field. The circles of confusion listed on this page are reasonable values that you can use to get reasonable estimates of depth of field.

Note that the circle of confusion is subjective. Thus, some people use 0.025 mm as the circle of confusion for 35mm format, while others will use 0.030 mm. There isn't a "correct" value. The values of circle of confusion on this website are calculated using, approximately, the circle of confusion that Canon uses for calculating the depth of field tables for their lenses (Canon Camera Museum - Len Details).

See Anthony Collins' article "Aperture and Depth of Field - how it works" for a somewhat technical explanation of circle of confusion.


Depth of Field FAQ

Circles of Confusion for Digital Cameras
Forum: Pentax SLR Lens Discussion 07-28-2009, 02:04 PM  
DA 16-45 repair
Posted By ma318
Replies: 17
Views: 14,076
The focusing ring on my DA 16-45 was stuck so I took the lens apart to determine the cause of the problem. I was able to determine one of the internal plastic parts had couple of pieces broken off it and was jamming the focusing ring. I sent Pentax Canada, located at Mississauga, Ontario, an email last night (service@pentaxcanada.ca) asking them whether they sell parts for my lens. This morning I got a reply from a Pentax parts technician indicating that they do sell parts for it. I sent him an email this morning with the description and photo of the part. In about 4 hours later, he replied to me with the part number and cost. I then called him with the number he sent me and placed the order for the part this afternoon. $9.50 for the replacement part and $10 for shipping which I think is reasonable. I am very impressed with the service offered by Pentax Parts Service in Canada! This is the first time I had to deal with Pentax Service Canada and so far they have shown to be very responsive to even a little guy like me.

Photo#1 shows what the lens looked like after it was taken apart.
Photo#2 shows the pieces that were broken off
Photo#3 & #4 show where the pieces were broken from

(I bought this lens from e(vil)bay as part of a camera set but the seller did not indicate a problem with this lens. He ended up refunding some money to account for it.)
Forum: Pentax SLR Lens Discussion 07-30-2009, 10:15 AM  
DA 16-45 repair
Posted By ma318
Replies: 17
Views: 14,076
I already had the lens put back together when I placed the order for the replacement part. The focus ring works now but it could still jam when the lens is focused at infinity and tilted upward. I could "un-jam" it by pushing the front of the lens forward. I will take better pictures of the repair process when I take the lens apart again to install the new part. The first time taking it apart was slow-going and difficult for me. I think the second time around should be a lot easier. Of course if you take your lens apart, you do it at your own risk. I would not recommend it if you are not good at using small tools or have not taken stuff apart before. It also requires a lot of patience and good eyesight to put it back together as some of the screws and spring contacts are very small.

I could not find any information on how to take the front element housing of the DA 16-45 apart. With older lens, I read you would first use a tool to rotate the front engraved ring to get it off. I found by trial and error that the front engraved ring is just a piece of nylon ring glued to the front element housing. I used a tiny jewelry screw driver and tweeter to slowly pry and lift it off. Once off, you would see two holes on the front element housing and you would use these two holes as anchoring points to rotate the front element housing off. I made a tool using stuff that I already had in the house to do this. I found that I had to use a heat gun (or hair dryer if you don’t have a heat gun) to heat the front part up a little before I could get it to rotate. Once the front element housing is off, you would have to start at the rear of the lens and unscrew petty much every screw off, one group of screws at a time, to dismantle the lens. I use a tiny jewelry screw driver from my watch repair kit. It is important to have a good and tough screw driver otherwise you may have trouble unscrewing the tiny screws.

Wherever possible, I also used masking tape and a pen to make alignment marks on pieces that fit together before I dismantle them so I know how far to tighten them later or how to orientate them for re-assembly. I also used masking tape to tape up each group of screws and related parts. I wrote on the tape identifying where they come from to make it easier to re-assemble everything together later.


(I suspect the lens must have been dropped with the front hitting something in order for the plastic pieces inside to break off like that. I doubt you would get this problem with normal usage.)

photo #1: the tool I put together to unscrew the front element (small vise, parts from a clamp, 2 jewelry screw drivers)
photo #2: how I use the tool (note: I taped a piece of paper on the lens to somewhat protect it. I think this is the most hazardous part of the repair process. Any slippage here could cause scratches on the lens.)
photo #3: how the front looks like with the front element rotated off
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