Thursday, May 15, 2008

Who needs a lens anyway?

Yes, I did buy a Canon 20D recently. It had a few issues... Firstly, I noticed the viewfinder did not register focus no matter how I dialed the diopter adjustment. During a conversation with the seller (who was great to deal with despite the issues!) he mentioned swapping out a custom split-prism focusing screen for the standard Canon one in order to sell the camera - he had scratched the custom screen back when he installed it originally. Hmmm, I thought. What if it had not been re-installed correctly? Well, I dug up an install guide and in the process found out all about split prism focusing screens. Then I checked - sure enough the screen was clearly not seated properly. I took it out, and found that the little copper shim that spaces it out for good focus was pretty mangled. I did a bit of back and forth with the seller, who did offer to pay for a replacement part. In the end though what we agreed to is that he would send me the split prism screen ($75 to buy) which did not need the shim. I flattened the shim enough for use in the meantime with the help of some wondeful Knipex parallel jaw pliers. Then, to finish this part of the story, the split prism screen came in the mail and I installed it. Yes, it has a scratch - but I still prefer it to the standard screen. It is invaluable for manual focusing - which itself is invaluable sometimes.

The second "issue" was all the bad, out of focus photos I was taking. Thought it was something wrong with the actual camera at first but by looking over all my photos I found a pattern: images were extremely soft at anything below F6.3, and only pretty sharp by F8. This was especially marked at 35mm, the maximum zoom. The lens in question is a Sigma EX HSM DG 17-38mm - a pretty decent lens according to reviews. I never wanted it in the first place - it is a bit limited in zoom plus I wanted a lens designed for APS-C cameras to take advantage of the smaller size and lighter weight. The Tamron 18-50 F2.8 is really what I want, and later the Sigma 50-150mm F2.8 - but also some other things - I may be leaning towards a Sigma 18-200mm OS since one lens is all I will be able to afford for quite some time...
But this is really all an aside.

Back to the Sigma. I borrowed a friend's Rebel with kit lens and performed a series of tests swapping lenses to be totally sure that the problem was my Sigma 17-35. - Yes it was, most definitively.

I tried to open the lens and find an adjustment - but did not want to get into it very far because a) I didn't want to damage something I needed to sell in order to buy something else :) and b) the further you get into a lens for adjustments the more you have to replace each time you take a test shot. This gets very tiring....!
There was nowhere online where anyone had adjusted this lens - that I could find, anyway. I found what looked like a good screw to turn but it did not appear to do anything.

Finally, on looking it up, I saw the Sigma repair service center did offer free estimates so I have mailed it off to them to at least assess the damage!

And this is why you have the following images. Taken with a Canon pinhole camera! I was interested to read in one of CaptureOne's ads about someone who used one of their digital backs to make a (very expensive) pinhole camera. They went to quite some trouble to do it also - buying a special camera body etc. Well, I went to no trouble at all for these. I took a scrap of aluminum foil and blacked one side with magic marker. This did not work very well - and you can see the reflections quite clearly! I will next try some Roscoe cinefoil that I have - it is just the right stuff for this app. I taped the scrap of foil over the lens hole, taking care to keep the edges down to stop any light from entering - and pricked a hole in the center with a common pin.

As for the results - here they are! Most of these are taken using flash and at high iso because I was capturing a moving subject:) Maybe later I will try some more serious composing when I setup using the cinefoil.


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