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Forum: Pentax Camera and Field Accessories
05-05-2014, 04:47 PM
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Welcome to the Pentax forums!
As noted above, there is no "back focus" when using manual focus lenses, though there are possible difficulties with using them on most dSLR cameras. The problems can be summarized as follows:- Problems determining focus point due to focus screen design (poor precision)*
- Poor calibration of focusing screen to focal plane
The first point is a fact of life with the stock focusing screen and any lens faster than about f/4. The second is hard to detect and correct if the first has not been rectified. :D
You can fall back on the AF system for focus confirm, but the precision (actually finding the true focus point twice in a row) is not much better with faster lenses than the stock focus screen. Sorry :( An aftermarket focus screen is often a good solution. I have been using the KatzEye screen with Optibrite on my K10D since 2008 and can strongly recommend that product. I am currently trying out the Type-S screen from focusingscreen.com on my new K-3. I am happy so far, but sort of miss the solid confirmation of the split image. Time will tell.
There are some negatives to an aftermarket screen however. They include:- Poor quality/service from some vendors (I have good experience with both KatzEye and focusingscreen.com)
- May be significantly less bright than stock screen
- Loss of spot metering with screens having center split-image focus aide
- Focus aides generally only work well with faster lenses
My opinion is that the negatives are worth dealing with if a person is going to do much manual focus at all. This would include any subjects where critical focus is essential.
Steve
* The problem is present across brands and not limited to Pentax.
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