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[OM] 35-80/2.8: Distortion at 35mm

Subject: [OM] 35-80/2.8: Distortion at 35mm
From: "Olaf Greve" <olaf_greve@xxxxxxxxxxx>
Date: Wed, 30 May 2001 08:36:10 -0000
Hi,

Good, it seems we've got some discussion going on this topic. Here's a bit more input from me:

[C.H.Ling]

Testing at 5m is not enough, at least you should test it at infinity
too. Pop photo also test lenses at closest distance, in most case the
distortion is much higher.

Hmmm, the closest distance test should be possible, but the infinity one might be a bit more complicated, i.e. it may be a bit difficult to find something like a brick wall that's big enough to fill the full frame when using the lens @35mm at the infinity setting...

Do these two settings really influence the distortion heavily? If so, our tests may be void again. Oh well, as mentioned previously, for me the most interesting part of these tests is to have an indication of how badly the distortion shows; I guess I'll be satisfied with a less-than-perfect test...:/


[Joel Wilcox]

I agree. I don't expect to find something different from Gary's results. I'm just interested in how those results may affect my photography and what I may wish to do about it.

Exactly, that's my idea too.

Olaf, I shot at f8, rather than f5.6, sorry.

From what I've understood from Erwin, the aperture used shouldn't have any
effect on the distortion. I chose f5.6 because that is the biggest aperture setting which all lenses that I tested have in common :)

I shot at approximately 4-5 m.

That should be fine. I can measure the distance I more or less shot at, but I estimate it to be some 5m.

I painstakingly tried to get the camera square to the wall. This may seem a little comical. [...] Was there an easier way to do this?

Hmmm, good question, as I was 5m away from the wall, I didn't go out of my way to get the camera 100 0n parallel to the wall, but rather I was satisfied with getting it pretty parallel to the wall. I did give this some attention, but I didn't use such a method... No idea if there are easier reliable methods :)

Using an adapter, I mounted my spirit level on a Bogen QR plate and leveled the tripod. I noticed that I got a different reading when I put the spirit level in the shoe of my OM-4. So I have to assume that the shoe is not perfectly parallel to the base of the camera. I checked my other bodies and only a OM-2S that John H. CLA'ed in the last couple of years is really level. So if you use a spirit level in the shoe, you might want to ascertain where level really is with your camera.

The Manfrotto tripod I used has 4 levels incorporated in it. Out of these 4, 3 of them are featured in the head, and these are the ones I used for leveling the camera. I cannot be 100ertain that the camera itself was absolutely level then, but as this is a $400-$500 tripod, I guess (hope) I came close enough. Actually I'm glad I could borrow this tripod for this test, as my own tripod is a simple lightweight video tripod (with weight being the keyfactor for selecting it), which only has one simple level in it.

A funny thing to notice, BTW, is that when looking through the viewfinder all lines seem to be nicely straight, and I couldn't detect any distortion with any of the lenses this way. Nonetheless, I'm positive the distortion will show up in the end results. Does anyone know why this appears to be the case, or was I perhaps drunk in such a way that the bent lines appeared straight to me ?!? ;)

[Gary Reese]

Hopefully there would be space in an OM Book to show what kind of
distortion a statement like "pronounded barrel" etc. really means.

That's certainly an interesting idea! If anyone wants to use my images for the book, please let me know and I shall grant permission to do so. Actually, I would have loved to contribute something to the book, but unfortunately I can't seem to find the time to do so...:( I hope the progress is going well though, and perhaps in the future I might be able to contribute to the book...

[George S]

correct. Even the ads and specifications for Zeiss optics mention that "distortion has been reduced" or "distortion has been minimised". It (distortion) - at some level WILL be there....how noticeable... well... that's the $64,000 question...

Indeed, and that's exactly the reason why I'd like to see how badly the distortion influences the end results :)

[Erwin Voogt]

For me, the idea was to see if I should avoid the 35-80/2.8
at its 35mm setting for critical pictures,

!!! Funny, we are talking here about a $1000 lens...

Yes we are. And to draw an analogy: would you want to use a $200,000 Ferrari in city traffic and traffic jams? IOW: no matter how expensive something may be, it may have its "flaws" (or at least disadvantages) under certain circumstances. So, even though it sucks that such flaws/disadvantages exist, it's best to learn to live with it, and if an easy workaround (like using the 35/2.8 Shift which I already happen to have where the lenses are concerned) can be had, why not use it for the critical work around 35mm? Now, since I do live in the centre of a city, my sole reason for not having a Ferrari is my bicycle workaround of course ;)))

I did make some brick wall pictures with the Tokina ATX. They look very good and you can use this $200 lens for critical pictures... ;-> In about a month I will get a new computer, so I will be able to scan slides again.

Yes, it should be good to see these results too. Did you actually also test the lens around 40mm and at the 70mm setting? If not, would you please do this too, so we can see if the lens has little distortion at these focal length settings too?

Cheers!
Olafo

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