Help ! How would you test a new lens ?

Davidoff

Hello everyone. I just bought a Nikon 80-200 f/2.8 second hand from someone and I'm trying to determine if I should keep it or give it back. I've been shooting for about an hour at 2.8, various focal lengths, but how can I be sure it's a good sample and focusing properly ? Any help will be greatly appreciated !:clap

Wil Davis

In the absence of a test-target, you might use a sheet of newspaper (broadsheet, classified ads, lots of small print) pinned to a wall.

Set up the camera and lens on a tripod on the other side of the room.

Take care to get the plane of the camera image parallel to the sheet of newspaper.

Take lots of pictures at various apertures and focal length settings, trying to keep the EV constant.

Try to fill the frame with the newspaper image.

Use the lowest possible ISO setting (least noise) and examine the results closely from the centre of the image right out to the edge.

HTH -
- Wil

Art Scott

lens align ......could probaly set something up using a ruler and printed target of some sort......surely there is a DIY version somewhere.............

Davidoff

Art Scott wrote:

lens align ......could probaly set something up using a ruler and printed target of some sort......surely there is a DIY version somewhere.............

Okay, I'm printing this right now:
http://focustestchart.com/focus21.pdf

Davidoff

I've been shooting with it and my conclusion is this:

I knew it would be softer at 200mm, but it really really is a bit soft. It could be focusing problems, but I don't think it is because the images are so much sharper at 170mm for example, always at 2.8 . At 200mm, even f/4 is pretty weak. Should I keep it and use it like I would use an 80-170mm or should it go back because it's softer at 200mm ? How do I distinguish softness from camera focusing issues ? Here are 2 examples, 100% crops:

Focusing on the center of the frame, f/2.8, 135mm and in my opinion, great



Here, all the settings are the same but the focal lenght is 200mm:

ziggy53

Be sure to test the lens at typical shooting distances. Many lenses are not their best at closest focus distance and I normally test at no less than twice minimum focus distance for critical sharpness.

True macro 1:1 lenses are the exception and those I test right down to minimum focus distance.

Davidoff

Well, I sent it back. Thanks everyone.

dlscott56

In case you're interested for future tests there's another focus chart to be found here

ziggy53

Davidoff wrote:

Well, I sent it back. Thanks everyone.

Sorry it didn't work out but better you tested and found out. :cry

Davidoff

Absolutely ziggy, better right now than after buying it. Thanks scott, that's a great testing tool

PhotosbyKW

FYIW- I use a Bible, since it is the book in my house with the smallest print. Smallest print means top-to-bottom lines are closer spaced. I then take it and prop it up at 45 degree angle, and put a small pencil mark to underline a word in the MIDDLE of the page. I then stage camera on tripod at low ISO and max. aperature. I adjust camera/pod so that they are on horizontal axis to the word and use that word as my target. I compose the shot, and focus. Then I lock the lens focus, and use the timer to take the shot to illiminate any movement from me. This way, only the primary focus point will be in best focus, and I can easilly tell if the lens is focusing forward or rearward of "perfect".

FYI- the new 24-105L IS needed a little adjustment, since the next line down (being closer to camera) was in slightly better focus- but that is just being nit-picky, as in all reality, prior to this- my eyes could not pick up any difference in this small deviation- as I had done an 11x14 print of the same page when stood straight upright, and it was still really crisp.

I bring this up because I used to be overly concerned with noise that I'd fuss over on the monitor, until I started doing a few large prints, and could barely see it on the finished product.

Just throwing that out there...

KAW.

Ekaj

I don't understand how you based your decision on that photo...

That would not be the way I test a lens at all.

edit- I agree with the poster above me for testing focus