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peak4
11th June 2011, 09:13 PM
Well I thought I'd nip out and try my newly home made lens focus tester in view of the two recent posts regarding 50-200mm problems.
Since I knew mine was working fine with the EC-20, it seemed a good opportunity to have a play.
I'd already posted a few shots from Sri Lanka on another thread to prove it was a reasonably capable combination.

I went out to a local nature reserve the other evening to have a look at some orchids and tried a few insect photos whilst I was there with the 50-200mm & Ring Flash.
I completely failed to get any in focus at all and assumed it was down to me being an idiot.

First, The Lens Focus Tester (based on the commercial LensAlign one)
The methodology is fairly simple.
Using Bubble levels on both the camera tripod and in the tester, set everything up level.
Sight through the viewfinder and point the camera in the right direction. Replace lens cap.
Set the height and angle of the test target using the red dot laser to the centre of the lens cap.
Finely set the camera's centre focus point to the centre of the target.
http://e-group.uk.net/gallery/data/1213/lens_tester.jpg (http://e-group.uk.net/gallery/showphoto.php/photo/35142)

Test 1 just the lens without any converters
http://e-group.uk.net/gallery/data/1213/50-200mm_test.JPG (http://e-group.uk.net/gallery/showphoto.php/photo/35140) http://e-group.uk.net/gallery/data/1213/50-200mm_test_crop.JPG (http://e-group.uk.net/gallery/showphoto.php/photo/35141)

Conclusion; its a mile out, front-focusing severely.
I repeated the test several times, with and without both converters, and got front focus each time.

70-300mm, 40-150mm and 14-150mm PanaLeica were all OK.
Bigma Front Focus a little bit.
90-250mm also Front Focuses, which is really annoying to say the least. :mad:

The E-3 is only just back from a checkup in Portugal, where the shutter was replaced under warranty; even though it was over 2 years old, so that should be fine.

I now need to re do the tests again with the same lens and different bodies and then return it to Oly when I've got to the bottom of what's going on. It's not that long since it was repaired when it started to part company with itself in the middle.

birdboy
11th June 2011, 09:48 PM
Bill I feel partly responsible for your problem sorry mate:confused:. So what's changed since Sri Lanka? Is anything in focus? Do you remember knocking the combination? I've studied and studied my pictures to try and pin point the time when things deterioted and it points towards the camera falling over on the collapsed tripod.

It seems Oly support are going to be busy.

There is nothing more frustrating (other than black light) in having expensive equipment and it not performing. Good luck in finding and fixing your focus.

John

peak4
12th June 2011, 07:31 PM
The good new is that the 90-250mm isn't too bad on a variety of bodies, oddly worst with most Front Focus on the recently serviced E-3 and best on a Panasonic L10.

The 50-200mm however looks like it is after a holiday in Portugal again.
I had to make a longer ruler for the gizmo to work out where the point of sharpest focus was. :(
The Front Focus amounts to about 10cm in 4m


On the E-3
http://e-group.uk.net/gallery/data/1213/E-3_50-200_at_200.JPG (http://e-group.uk.net/gallery/showphoto.php/photo/35174) http://e-group.uk.net/gallery/data/1213/E-3_50-200_at_200_Crop.JPG (http://e-group.uk.net/gallery/showphoto.php/photo/35175)

On the E-420
http://e-group.uk.net/gallery/data/1213/E-420_50-200_at_200.jpg (http://e-group.uk.net/gallery/showphoto.php/photo/35176) http://e-group.uk.net/gallery/data/1213/E-420_50-200_at_200_Crop.JPG (http://e-group.uk.net/gallery/showphoto.php/photo/35177)

The E-1 was similar, but actually more accurate.

I guess I'll live with the 90-250mm and tune it in on my E-620 & E-5.
It seems that different bodies pick different focus distances repeatably with different lenses, and different Teleconverters have varying but repeatable effects on different lens/body combinations.
I'm beginning to understand why Olympus have introduced the focus fine tuning, but wonder of 20 combinations is sufficient.

The 2x teleconverter front focus effect was equally pronounced on the 300mm F2.8
Olympus in Japan commented that the converters caused an effect on the focus point. It was fine on its own and reasonable with an EC-14, but well out with the EC-20.
Unfortunately they could only set the lens up for one of the three scenarios.
I'll let you know how it performs when it returns from Japan.

The really bizarre thing is that it Back Focussed hugely with a 112mm front UV filter fitted. Olympus again acknowledged it, but were not able to adjust the lens accordingly.

Can anyone offer an explanation as to why a front filter should effect the focus point?
(I tried both a Tokina and a B+W filter; they both had the same effect. The rear filter was fitted for all tests)
With other lenses, you can attach filters or even close up lenses without effecting the focus point too severely.

Having just typed this last paragraph, I probably should repeat the 50-200mm tests without the front filter fitted to that as well.
In the case however, it used to focus fine, as was evident from the Bee Eater photo in the other thread.

Daveart
13th June 2011, 10:25 AM
Hi Bill one explanation could be, if you did physics at school is light diffraction as in the image I have uploaded, no matter how good the glass is made their are imperfection no matter how much you polish the glass surface there will be fine grooves on each of the surfaces which will deflect light to the angle depended on how coarse or fine these grooves are as to how much the light moves from its original path, then there is the imperfections within the glass ie molecules within the structure which also moves light from its path.
Which would increase or decrease the distance, and as your lenses is constructed to counteract this and because your lens magnifies the object so it magnifies the error of the glass in the filter.

Dave

peak4
13th June 2011, 08:32 PM
Cheers Dave, Seems odd that it only effects the 300mm though.

And it gets odder:confused:

I was just about the parcel up the 50-200mm, but thought I'd take a couple of "normal" photos to include with it, rather than just test shots.

Try as I might, I couldn't get it to front focus in the garden tonight; on rulers, fences, tables, hedges etc.

Previously either in sunlight, or artificial, on several bodies, it focused short.

A couple from this evening, OK they're not perfect by any means, but it wasn't very bright sunlight; yesterday, the whole flower was OOF.

E-3 Bee
http://e-group.uk.net/gallery/data/1213/small_Bee-2_P6139979.JPG (http://e-group.uk.net/gallery/showphoto.php/photo/35313)

E-5 Bee
http://e-group.uk.net/gallery/data/1213/small_Bee-3_E5137780.JPG (http://e-group.uk.net/gallery/showphoto.php/photo/35314)

So being satisfied all seems to have cured itself, on a temporary basis at least, I tried the AP test box just out of curiosity.
http://e-group.uk.net/gallery/data/1213/AP_Test_Box.JPG (http://e-group.uk.net/gallery/showphoto.php/photo/35322)
Somewhere between 4 1/2 and 5 front focus I think.
Back out with the bubble wrap :(

Daveart
13th June 2011, 09:14 PM
Hi I can see what you mean in the images you show, the greater the magnification a lens has like telephoto primes lenses and telephoto zoom lenses, the greater it magnifies the error in the ground glass in the filter, the same would be with macro lenses. And because a large telephoto lens like the the depth of field is so narrow, which would exaggerate the error.

This is a problem the manufacturers have when they design a lens, canon and nikon user find there lens a far less accurate than Olympus lenses, because a lot of there lenses come from film camera lenses.

Sorry that you are having problems with your lenses, hope you get them sorted out ok.

All the best Dave