Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
03-23-2010, 06:38 AM   #1
Inactive Account




Join Date: Mar 2009
Location: Coral Springs, FL
Photos: Gallery | Albums
Posts: 5,218
Lens Testing Technique

I want to run 3 of my Taks through some real testing on the KX to see what's really what:

50 1.4, 55 1.8 and 105 2.8. (Maybe the Mir 37 too.)

Right outside of my office, there's a beautiful, old, dead cypress tree stump that's backgrounded (is that a word?) by what we call waterfront property in South Florida. (It's actually just a huge hole someone dug so they could sell houses as higher priced waterfront property.) Anyway, this stump and smelly water have my name on them as the subject for my testing.

I'm going to use a tripod and 2-sec self-timer.

1) Since the EXIF data won't include the aperture, I guess I'm going to have to keep a written log, unless there's a way to add this info to the file after taking the shot. Is there? (Please don't yell at me for not reading the manual. Plus, I swear--I left it home today.)

2) I'm just going to shoot JPEG, but when I'm done with the series of F-stop tests for each lens, I guess I'll resize them into one large JPEG, with tags below each example, for posting here and your comments. Make sense?

3) Center-weighted metering because the stump will be center. (HAH!)

4) Any other advice? Like, I predict being about 7 or 8 feet back from the stump for the 50 and 55, so maybe I should do a series of tests like this for close-up.

I'm doing this not just to test lens characteristics, because I'm also discovering the funky metering characteristics of this old glass on DSLRs. There doesn't seem to be a one-size-fits-all EV fix, with some actual apertures working fine, and others giving me under. In addition, I was horrified at the quality of the first few shots I did with the 105 recently. Might just be dirty, or something very wrong with the lens.

Anyway, thanks for your input. I'll appreciate your comments when I get these posted here later.

03-23-2010, 07:00 AM   #2
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,312
I would consider doing 2 tests, one using a sjubect just to evaluate sharpness etc, the other for the sole purpose of evaluating exposure.

For the record, I attempt (although I am a little behind) to map the exposure of all my lenses on each body.


for the exposure test, select a uniformly lit uniformly colored surface , (paved road, sidewalk, block wall etc...)

set exposure compensation so that at F4 you have the peak of the histogram exactly in the middle.

then take a full series of tests shots over every aperture detent.

You can then, using the greyscale histogram in your photo editor measure the greyscale for the 10% center and corner areas of the frame. This will let you judge light fall off at the corers (vignetting) as well as exposure accuracy. Note that with neutral contrast in jpeg each 45 greyscale (between about 25 and 225) is one stop.
03-23-2010, 07:07 AM   #3
Ira
Inactive Account




Join Date: Mar 2009
Location: Coral Springs, FL
Photos: Gallery | Albums
Posts: 5,218
Original Poster
QuoteOriginally posted by Lowell Goudge Quote
I would consider doing 2 tests, one using a sjubect just to evaluate sharpness etc, the other for the sole purpose of evaluating exposure.

For the record, I attempt (although I am a little behind) to map the exposure of all my lenses on each body.


for the exposure test, select a uniformly lit uniformly colored surface , (paved road, sidewalk, block wall etc...)

set exposure compensation so that at F4 you have the peak of the histogram exactly in the middle.

then take a full series of tests shots over every aperture detent.

You can then, using the greyscale histogram in your photo editor measure the greyscale for the 10% center and corner areas of the frame. This will let you judge light fall off at the corers (vignetting) as well as exposure accuracy. Note that with neutral contrast in jpeg each 45 greyscale (between about 25 and 225) is one stop.
Okay, so for now, I'm just doing the general test. But since these manual lenses can meter so funky on DLRs anyway, is there really any point in doing formal exposure tests? Regardless of what I find, it's not like I'm going to repair or throw them out anyway.
03-23-2010, 09:50 AM   #4
Pentaxian
audiobomber's Avatar

Join Date: May 2008
Location: Sudbury, Ontario
Photos: Albums
Posts: 6,631
I've found that writing (print) is the best subject matter to check for resolution. Judging sharpness is tough with flowers, trees etc. Shoot a cereal box with some writing on it and you'll see clear differences in sharpness.

(Edited for clarity)


Last edited by audiobomber; 03-23-2010 at 01:13 PM. Reason: Edited for clarity
03-23-2010, 12:48 PM   #5
Ira
Inactive Account




Join Date: Mar 2009
Location: Coral Springs, FL
Photos: Gallery | Albums
Posts: 5,218
Original Poster
QuoteOriginally posted by audiobomber Quote
I've found that printing is the best way to check for resolution. Judging sharpness is tough with flowers, trees etc. Shoot a cereal box with some writing on it and you'll see clear differences in sharpness.
Makes sense--and it's a good thing I didn't already do it as planned:

A few tires washed up right onto my idyllic scene.
03-23-2010, 01:06 PM   #6
Pentaxian




Join Date: Apr 2008
Location: Central Ohio (formerly SF Bay Area)
Posts: 1,464
QuoteOriginally posted by Ira Quote
1) Since the EXIF data won't include the aperture, I guess I'm going to have to keep a written log, unless there's a way to add this info to the file after taking the shot. Is there? (Please don't yell at me for not reading the manual. Plus, I swear--I left it home today.)
Correct.

One way to do this -- which might be easier than keeping a separate log -- is to take a cue from the movie business and make yourself a "clapperboard."

Only it's not exactly a clapperboard, because it won't clap. Bring a blank notebook and a bold pen, and whenever you change your aperture setting, write it down on the notebook and take a picture of the page. That way your aperture data is interspersed right into your photostream and you can't lose it or fumble which info goes with which shots.

You can also write down other conditions that might not make it into EXIF, like your location, or how sunny it was, or what you intended to focus on.

And I'll clarify one more thing about what you said -- it's true you can't annotate shots with the actual aperture IN CAMERA (as far as I know), but you absolutely CAN add metadata notes into the jpg files on your PC using various photo editing packages. How you do it depends on which one you use. So after you're done, if you're feeling patient, you can sit down at the computer, transfer your manually recorded info to the photos, and then delete the extra "clapperboard" shots. I'm usually too lazy for this extra step, myself -- storage is cheap!

Last edited by Quicksand; 03-23-2010 at 01:13 PM.
03-23-2010, 02:28 PM   #7
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,312
QuoteOriginally posted by Ira Quote
Okay, so for now, I'm just doing the general test. But since these manual lenses can meter so funky on DLRs anyway, is there really any point in doing formal exposure tests? Regardless of what I find, it's not like I'm going to repair or throw them out anyway.
the point is, they don't have funky exposure, it is consistent (i.e. the lens will always do the same thing at any F stop) , and as long as you know how the lens performs it is quite useable.

Note that the performance also varries a lot depending on camera

from my experience the *istD meters very well with manual lenses (except that exposure compensation is needed on M42 lenses that don';t short the lens contacts, the K10D is the worst, and the K7 is in between.
03-23-2010, 03:16 PM   #8
Ira
Inactive Account




Join Date: Mar 2009
Location: Coral Springs, FL
Photos: Gallery | Albums
Posts: 5,218
Original Poster
QuoteOriginally posted by Lowell Goudge Quote
the point is, they don't have funky exposure, it is consistent (i.e. the lens will always do the same thing at any F stop) , and as long as you know how the lens performs it is quite useable.

Note that the performance also varries a lot depending on camera

from my experience the *istD meters very well with manual lenses (except that exposure compensation is needed on M42 lenses that don';t short the lens contacts, the K10D is the worst, and the K7 is in between.
I can see already that I have some major meter problems in M (forget Av) at two f stops on one of my lenses. I'll know for sure once I'm on a tripod and test with consistency, but in M mode, I don't need ANY compensation on the rest of the stops. It more or less nails it. Av is ALWAYS underexposed.

As another example, I can't get focus confirmation on any of my Taks on the kx when they're closed down all the way. F16, I'm cool, but forget F22. Just doesn't happen.

So I think funky things do happen meter wise with these lenses on a DSLR, regardless of the mechanical integrity of the lens.

I appreciate your expertise, but I don't see a logical mechanical reason why the metering takes a crap at 5.6 and 11 (for example), but not at all of the other stops.

Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
characteristics, comments, jpeg, k-mount, lens, pentax lens, series, slr lens, stump, tests, waterfront
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Focusing technique with fast manual lens Corvairfan Troubleshooting and Beginner Help 14 10-28-2010 09:09 PM
Orbs and flare..just a crappy lens or technique? Pictures attached. Raptorman Pentax SLR Lens Discussion 18 01-21-2010 10:57 PM
Please help beginner - new lens testing Lumic Troubleshooting and Beginner Help 8 01-10-2010 09:41 AM
Testing new lens slowpez Post Your Photos! 5 02-19-2009 03:16 PM
On Lens Testing (Or, Is This 50mm Lens Any Good?) carpents Pentax SLR Lens Discussion 18 06-21-2007 05:45 AM



All times are GMT -7. The time now is 09:43 PM. | See also: NikonForums.com, part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top