[everydaylife]

How much barrel distortion would be normal with a 30 mm lens. Would you say that these images have little to no distortion?
f2.8

[IMG][/IMG]

f4.5
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f5.6


Below was taken with a da15mm wide open. Just for comparison. Shouldn't the 30mm be better?
[IMG][/IMG]

[Digitalis]

If it is a prime, then yes, it should be better. Zoom lenses typically have some distortion at the extremes of their range with the middle of the lenses range being relatively free from it.

Though with the appropriate lens profile this kind of distortion can be corrected. FYI - the aperture has no effect on lens distortion.

[everydaylife]

If it is a prime, then yes, it should be better. Zoom lenses typically have some distortion at the extremes of their range with the middle of the lenses range being relatively free from it.

Thought with the appropriate lens profile this kind of distortion can be corrected. FYI - the aperture has no effect on lens distortion.

Thanks for the quick reply and thanks for confirming that the distortion does not change when stopped down.

The images were actually taken with the dp2 merrill bought 2 weeks ago which is reported to have little or no distortion.
Do you think that most of the distortion is because I did not have the camera perfectly parallel to the subject?

[SpecialK]

Do you think that most of the distortion is because I did not have the camera perfectly parallel to the subject?

Nope. Most lenses have distortion.

[everydaylife]

Nope. Most lenses have distortion.

Originally posted by everydaylife Quote
Do you think that most of the distortion is because I did not have the camera perfectly parallel to the subject?

When I asked the above I should have said the unevenness to the distortion. The da15 image has pretty much the same distortion in each corner whereas the other 30mm images are distorted more on one side than the other. Is that something I should be concerned about?

[Digitalis]

The da15 image has pretty much the same distortion in each corner whereas the other 30mm images are distorted more on one side than the other. Is that something I should be concerned about?

Distortion is unlikely to be affected by de-centering* - the fact that the distortion in your images is uneven purely because of a lack of parallelism.

* De-centering defects affect resolution and contrast, you would notice the effects on resolution well before it had any impact on general lens characteristics like distortion or vignetting.

[zapp]

There is also decentring distortion, but here we are looking at radial symmetric distortion which has much larger effect on images. The point of symmetry may not exactly fall in the middle of the frame, but from that point distortion is radial symmetric. Decentring distortion is caused by decentring of lens elements not by a decentering of the origin of radial symmetric distortion. A 30mm lens for a SLR camera will always experience much distortion by design. The smaller the focal length the more distortion can one expect from a lens. At the same time distortion is just one lens abberation. You can sacrifice distortion for sharpness in lens design that is the reason why larger aperture lenses often show much larger distortion than others.
So, yes you can assume a certain performance, but you have to check the particular lens to see how well it really performs. Distortion can be corrected in most image processing software packages, contrast and sharpness cannot be improved. At the end distortion may be the leseer evil. A simple 30mm wide angle zoom lens can distort more than a 15mm fixed focal length lens... although it should not in my opinion.

[tibbitts]

I don't know what your subject is in the case of the 30mm, but the first issue is to determine if whatever it is is precisely square.