Doing it wrong on digitalcamerareview.com

asdf · 03-29-2009, 11:46 PM

This guy has trouble focusing:

Pentax DA* 300mm f/4 Lens Review - Digital Camera Forums and Discussion

Pentax DA 17-70mm f/4 SDM Lens Review - Digital Camera Forums and Discussion

At least I got to use my boring center crops (DA 17-70, f/4 and f/5.6 at 70mm) to debunk his heap of fail.

octavmandru · 03-30-2009, 12:01 AM

in the first review for DA300, f4, the picture is shaken in my opinion.
I can clearly see that on the center crop

What do you think? (well, I already read your opinion...

)

asdf · 03-30-2009, 12:05 AM

Originally Posted by octavmandru

in the first review for DA300, f4, the picture is shaken in my opinion.
I can clearly see on the center crop
What do you think?

That was my impression, too.

EDIT: In fact, by f/16 he should be getting softer images because of diffraction.

asdf · 03-30-2009, 12:32 PM

Here's a 100% center crop of DA17-70 at 70mm and f/4 done by me (straight from raw, no unsharp mask):

Here's the digitalcamerareview.com 100% center crop at the same settings:

What's wrong with this David Rasnake?

*Wheatfield* · 03-30-2009, 02:56 PM

Originally Posted by asdf

Here's a 100% center crop of DA17-70 at 70mm and f/4 done by me (straight from raw, no unsharp mask):

Here's the digitalcamerareview.com 100% center crop at the same settings:

What's wrong with this David Rasnake?

Probably like most people on the internet, he doesn't know how to set up a test correctly, and doesn't know how to use the equipment he is testing.
From reading his blog it looks like he admits to introducing a parameter that has the potential to skew the results, but he is standing behind his flawed results as true.
One can't account for willful stupidity.

*ryno* · 03-30-2009, 05:57 PM

It's always possible that someone has a bad copy of a lens, or a malfunctioning camera, but people seem very quick to post problems. There was a long thread on "another" forum about how the 17-70 was soft at infinity at the tele end. I'm not much of a tester, but when I got mine last week, I wanted to make sure there were no problems. To make it easier, I set the camera to manual focus with the ring at infinity and did an aperture series. Like the other review, mine was soft at 70mm until f11. I retested today using auto focus, and f4 was slightly soft, but everything else was perfect. Almost like manual focus focused past infinity. Maybe the other review used manual focus too, but they posted the photos without checking things out. It's easy to bad mouth good equipment, and people tend to believe what they read.
Ryan

asdf · 03-30-2009, 06:24 PM

Originally Posted by Wheatfield

Probably like most people on the internet, he doesn't know how to set up a test correctly, and doesn't know how to use the equipment he is testing.
From reading his blog it looks like he admits to introducing a parameter that has the potential to skew the results, but he is standing behind his flawed results as true.
One can't account for willful stupidity.

Definitely.

asdf · 03-30-2009, 06:35 PM

Originally Posted by ryno

It's always possible that someone has a bad copy of a lens, or a malfunctioning camera, but people seem very quick to post problems. There was a long thread on "another" forum about how the 17-70 was soft at infinity at the tele end. I'm not much of a tester, but when I got mine last week, I wanted to make sure there were no problems. To make it easier, I set the camera to manual focus with the ring at infinity and did an aperture series. Like the other review, mine was soft at 70mm until f11. I retested today using auto focus, and f4 was slightly soft, but everything else was perfect. Almost like manual focus focused past infinity. Maybe the other review used manual focus too, but they posted the photos without checking things out. It's easy to bad mouth good equipment, and people tend to believe what they read.
Ryan

How exactly did you perform the test? With a collimator?

If it does focus past infinity, then it wouldn't be the first lens to do so. Here's a comment from the Canon EF 17-40 f/4L USM manual:

" To compensate for shifting of the infinity focus point that results from changes in temperature, you can rotate the distance scale slightly past the normal infinity focus mark.

* The infinity position at normal temperature is the point at which the vertical line of the [graphic] mark is aligned with the distance indicator on the distance scale.
* For accurate manual focusing on subjects at infinity distance, look through the viewfinder while rotating the focusing ring. "

BTW, the problem with the digitalcamerareview reviews was the reviewer. He couldn't manage to take a sharp shot with either the DA* 300 or the DA 17-70. Also, raw files are always relatively soft because of the way sensors (other than the foveon ones) are made.

Quicksand · 03-30-2009, 06:36 PM

Originally Posted by ryno

I'm not much of a tester, but when I got mine last week, I wanted to make sure there were no problems. To make it easier, I set the camera to manual focus with the ring at infinity and did an aperture series. Like the other review, mine was soft at 70mm until f11. I retested today using auto focus, and f4 was slightly soft, but everything else was perfect. Almost like manual focus focused past infinity.

The lenses I have where I can just slam it against the infinity-stop and get good results are in the minority, I think. In most cases they focus a touch past infinity, and I need to back off a bit to get the sharpest picture at wide apertures.

*ryno* · 03-30-2009, 08:33 PM

I've always had good luck using the infinity stop and hyper-focus with older MF lenses. This new one is much better with AF. That was how I planned on using it, so I'm very happy.
It wasn't a scientific test. One series in MF with the focus at the infinity stop, and one series in AF. The AF series was much sharper.
Ryan

*Jonson PL* · 03-30-2009, 10:28 PM

Thanks for the info

*Wheatfield* · 03-31-2009, 11:07 AM

Originally Posted by Quicksand

The lenses I have where I can just slam it against the infinity-stop and get good results are in the minority, I think. In most cases they focus a touch past infinity, and I need to back off a bit to get the sharpest picture at wide apertures.

Telephoto lenses in particular are generally designed to focus slightly past infinity to make up for lens barrel deformation when the lens gets warm.