Can Pentax make A Decent Lens? Ricoh have not fixed QC issues...

Started May 18, 2014 | Discussions thread
rgibbons Regular Member • Posts: 348
Re: Please use better experiment protocol

Trevor, Maybe you have a bad lens (I had one from Pentax that was poorly decentered, the replacement was good); Or maybe your testing could use refinement. But either way, you have some people that are trying to help you (and a few that aren't), and you seem to be arguing too much with those that are trying to help.

Trevor G wrote:

Except that you are wrong, very wrong.

Fo the first time ever I used a DOF Calculator.
Depth of field Near limit 42.8 m

No Trevor, you misunderstand the DOF calculators, The old formulas were meant to show what is acceptably in focus, for a print on the wall, viewed from a "normal" viewing distance. As the print size, and viewing distance change, the acceptable DOF changes. The calculator you used doesn't seem to have an input for these variables, and the result of 42.8m is NOT meant to be used for pixel peeping.

Trevor G wrote:

The subject is far enough that hot air turbulence can fuzz out minute details.

But it wasn't happening in this case. It's Autumn here.

Optics has been my main hobby for 40 years, I spend a lot of time with my telescope, trying to get maximum magnification. Air turbulence ("seeing" distortions) exist all year round, Hot or cold, night and day, It is almost always a problem and a the limiting factor, the building will not have equal turbulence on both sides. You might reduce this variable in your experiment by rotating the camera 180 degrees (take a picture upside down), and see if the left side of the building stays sharper.

The softer side of your photo of the building also has trees causing additional diffraction around some of the more blurry sections. The bricks far from the trees are better test targets (and yes, the bricks on the left do appear to be sharper).

For your Mixer board photo (I like the model, I spend time on one every Sunday), when I look at the left and right sides at maximum magnification for many minutes, I can't say one side is sharper than the other; rather it appears that the right side comes into focus a few rows of knobs higher than the left side, (either the board is not perfectly square with the camera, or the lens doesn't focus at the same distance for right and left side). But for my purposes, I'd say the lens is good enough that I'd use it, rather than return it and get someone else's problems when the Pentax service center sends back a rebuilt lens that was only tested for center focus.

I'm not sure why you can accept that 19 of 20 Pentax lenses are bad, but not accept that 4 of 4 bodies might have trouble, (they are statistically the same results as far as margin of error for the sample sizes).

I like optics problems, and just wanted to offer a possibility to the question of your original post. I've read the entire thread thus far, I'm not a Pentax Fanboy. I applaud the effort and testing you have done thus far to prove your idea; however, even good science benefits from peer reviews.

Hope you get to the root cause, and an acceptable solution for your pictures.

Russ G.

-- hide signature --

wish list: more time to take pictures

 rgibbons's gear list:rgibbons's gear list
Pentax K-3
Post (hide subjects) Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow