D300 problem - AF out with circular polarizer

03/29/2008 04:53:03 PM · #1

Has anybody with the D300 noted problem with autofocusing using tele (>100mm) lenses with circular polarizer? With wide angle polarizer=no problem. With my 300mm Nikon AF-S 1:4D lens using the same polarizer AF is useless (strong mis-focusing). With the Sigma 100mm f/2.8 macro lens the difference is more subtle but clearly AF is less accurate with the polarizer on.

Now what?

If you have ever used c. polarizer with a >100mm lens on a D300, please let me know if you had or had not problem. If you haven't, but you own a D300 and a >100mm lens and a matching circular polarizer, please take the time and test if the AF stays accurate. It might help you too, and certainly me (otherwise tomorrow I'll just go back to Best Buy, and ask for a replacement-->the camera is just 10 days old).

Message edited by author 2008-03-29 20:14:48.

Sigma 24-35mm f/2.0 DG HSM A

03/30/2008 01:33:41 AM · #2

Just to demonstrate, here are some test shots.
wide lens (Sigma 10-20mm) with polarizer

wide lens no polarizer

100mm 1) with 2)w/o polarizer 1)

300mm 1) with 2) w/o polarizer 1)

geoffb

03/30/2008 02:23:51 AM · #3

I had the same problem with a CPL on my 55-200mm lens. AF mis-focused badly at 200mm, but got better as I moved toward the wide end.

I never did find the solution. I just sort of stopped using the lens (it's not great). I think the problem might have to do with the fact that the lens has a widest aperture of f/5.6 at that focal length, so the AF simply cannot work. The only problem is, I couldn't seem to focus using MF either!

I hope you find a solution.

MelonMusketeer

Nikon D7000

Nikon MF 50mm f/1.4

03/30/2008 02:49:11 AM · #4

I had an inexpensive (cheap) cir pol that came with a used lens. It was so bad that I couldn't even manually focus correctly thru it. It may just be the polarizer that you have. I bought a Hoya Pro CPL and that solved the problem. I could see a marked difference in contrast and sharpness from the first shot with it.

dmadden

Canon EOS-40D

03/30/2008 02:52:39 AM · #5

Maybe light loss on the slower end of the lens has something to do with it. Try with a fast lens with a constant aperature, like a 70-200 f2.8 and see if it happens.

MelonMusketeer

Nikon D7000

Nikon MF 50mm f/1.4

03/30/2008 03:03:18 AM · #6

The problem that I had with the cheap one was that it was causing some kind of interference with the focusing screen. I think that it was something like Newtons lines when you look thru two window screens. The idea about light loss is a good theory too.

FireBird

03/30/2008 09:04:51 AM · #7

Originally posted by redpanda:

300mm 1) with 2) w/o polarizer 1) 2)

In this photo your withCP shot was taken at 1/50 of a second.

The second shot without, is at 1/200 of a second.

1/50 of a second is mighty slow for a 300mm lens. I suspect you're
showing 100 percent crops too. 1/50 of a second is a very slow
shutter speed for a 300 mm lens, unless you're using a tripod. So
I don't think on this example your autofocus failed. You just shook
during the exposure. 1/200 for the second is still just barely fast enough shutter for hand holding. 1/400 would be much better. Of course you'll have to select a higher ISO, or larger aperture to achieve the same exposure.

03/30/2008 09:28:15 AM · #8

Dude,

You guys are totally right! One test I haven't done, since I haven't experienced this problem with the D70 using the 300mm lens with a similarly priced polarizer. For some 'mystery' reasons that polarizer ($60 Hoya) disappeared (got lost) and the current polarizer is a $50 Sunpak. For the above reasons I haven't tried before to see if I got the same problem with the D70 (which I fortunately haven't sold). I have just done the test and I got the same bloody problem on that machine too!

Sorry folks, and SORRY D300 FOR EVER DOUBTING YOUR GREATNESS!!!!

Message edited by author 2008-03-30 09:30:03.

FireBird

03/30/2008 09:46:21 AM · #9

Originally posted by redpanda:

Now what?

I'm curious. When you use a CP with the 100mm Sigma macro, what are you making images of? I never use a CP with my macro lens. Doesn't mean you can't but I don't see the need. A macro lens has a longer focus throw range than most non-macro lenses. The focus problem could just be with trying to focus twice, exactly the same on a difficult target. Since your samples are crops, it would be interesting to see what the full frame looked like, and..... what type of focus did you have the camera set at? The D300 has a very complex AF system.

I see your 100mm tests are a little better performed. One at 1/2000 second and the other at 1/6400 second. You must have done these in broad daylight in a bright location. The shots at 300mm were 1/50 and
1/200. Nowhere near fast enough shutter speed to eliminate shake on a hand held shot with that length lens.

If you're using the 100 macro for regular snapshot and landscape photos I can see the need for a CP occasionally . For macro, I really can't see using one. In any event, with macro, I never use AF anyway. If you check my challenge entries and porfolio, any that are macro are manual focus. I use the 180mm version of the same lens.

Even though you used a fast shutter speed for the 100mm tests, if you hand held the shot, you presented the autofocus system two different targets, to which it may have slightly different solutions. If the crops you present are 100 precent, then I think you are tilting a windmills.

To properly test the AF you're going to have to place the camera on a tripod and make sure the AF sees exactly the same target, with, or without the CP. In other words you'll have to screw the CP off very carefully without moving the camera, or take the non-cp shot first and carefully screw the CP on. (probably the easiest route) Then you'll have to shoot in manual mode, using exactly the same aperture. (Which you are already doing) When you shoot with the CP you'll have to adjust shutter speed and/or ISO to achieve the same exposure, for comparison purposes.

Plus, you're going from a 6 megapixel camera to a 12 megapixel. If you're showing us 100 percent crops from a 12 mpx camera you're pushing lens technology to the limit. Plus, you're not using the manufacturers own lenses on the camera. And it does make a slight difference. When you're pixel peeping on a 12mpx camera it can make a big difference.

My suggestion:
Use a tripod to check your AF on the 100mm. Take two shots with no cp for every one with cp, this will give you a control. If the two without are different, there is probably something wrong with your test technique.

My prediction:
After you return this camera for another one, the problem will still be there.

In any event good luck. I'd love to be going through these teething problems right now. But financial constraints will keep me with my D200 for a couple more years or longer.

03/30/2008 10:24:18 AM · #10

Thanks for the long note.

Usually if I go for bugs I also use manual focusing with the macro lens, but here I wanted to test the AF.

You cannot convince me that some unwanted reflections on shiny creatures would not be reduced by using a polarizer, but I accept you might loose more with all the light blocked out by the polarizer.

The effects on AF I am talking about are harsh, and clear-cut. I could have spent more time with the verification but it would have just confirmed what I already had. The shots were taken at high ISO, wide aperture (motion blur is ruled out).

It seems, I better give a closer look to those higher-end polarizers.

Cheers,

GYorgy

Originally posted by fir3bird:

Originally posted by redpanda:

Now what?

I'm curious. When you use a CP with the 100mm Sigma macro, what are you making images of? I never use a CP with my macro lens. Doesn't mean you can't but I don't see the need. A macro lens has a longer focus throw range than most non-macro lenses. The focus problem could just be with trying to focus twice, exactly the same on a difficult target. Since your samples are crops, it would be interesting to see what the full frame looked like, and..... what type of focus did you have the camera set at? The D300 has a very complex AF system.

I see your 100mm tests are a little better performed. One at 1/2000 second and the other at 1/6400 second. You must have done these in broad daylight in a bright location. The shots at 300mm were 1/50 and
1/200. Nowhere near fast enough shutter speed to eliminate shake on a hand held shot with that length lens.

If you're using the 100 macro for regular snapshot and landscape photos I can see the need for a CP occasionally . For macro, I really can't see using one. In any event, with macro, I never use AF anyway. If you check my challenge entries and porfolio, any that are macro are manual focus. I use the 180mm version of the same lens.

Even though you used a fast shutter speed for the 100mm tests, if you hand held the shot, you presented the autofocus system two different targets, to which it may have slightly different solutions. If the crops you present are 100 precent, then I think you are tilting a windmills.

To properly test the AF you're going to have to place the camera on a tripod and make sure the AF sees exactly the same target, with, or without the CP. In other words you'll have to screw the CP off very carefully without moving the camera, or take the non-cp shot first and carefully screw the CP on. (probably the easiest route) Then you'll have to shoot in manual mode, using exactly the same aperture. (Which you are already doing) When you shoot with the CP you'll have to adjust shutter speed and/or ISO to achieve the same exposure, for comparison purposes.

Plus, you're going from a 6 megapixel camera to a 12 megapixel. If you're showing us 100 percent crops from a 12 mpx camera you're pushing lens technology to the limit. Plus, you're not using the manufacturers own lenses on the camera. And it does make a slight difference. When you're pixel peeping on a 12mpx camera it can make a big difference.

My suggestion:
Use a tripod to check your AF on the 100mm. Take two shots with no cp for every one with cp, this will give you a control. If the two without are different, there is probably something wrong with your test technique.

My prediction:
After you return this camera for another one, the problem will still be there.

In any event good luck. I'd love to be going through these teething problems right now. But financial constraints will keep me with my D200 for a couple more years or longer.

FireBird

03/30/2008 11:25:59 AM · #11

Originally posted by redpanda:

You cannot convince me that some unwanted reflections on shiny creatures would not be reduced by using a polarizer, but I accept you might loose more with all the light blocked out by the polarizer.

It would still be nice to know if your crops were 100 percent.