PDA

View Full Version : newbie question


iCe
10-04-2003, 09:09 PM
This is something I noticed on some of my photos. Say there's a vertical object on both sides of a photo. For this example let's pretend there is a tall building at the left side of the photo and a lamp post at the right side of the photo. The thing is the building seems to slant toward the middle, and so do the lamp posts. It's almost like they are trying to form a circle!

Why is that?

mu23
10-05-2003, 08:49 PM
Distortion due to the curvature of the lens? I never noticed until I realized I was submitting pictures that were out of level/plumb. Now I notice anything along those lines. My first batch of pictures would make an alien visitor think there were no levels on the entire planet. I have gotten into the habit of pulling back when framing a picture that has tall parallel vertical lines near the edges. I have also come to realize that there are very few utility poles, signs, etc, that stand up straight and try to observe which items in the picture come the closest to being plumb and/or level while I'm on site.

E.M. Bell
10-06-2003, 04:13 PM
Sounds like you are using a lens with a wider angle than 28mm, which can sometimes cause the "fisheye" effect. While that would be most in-acceptable in most cases, it could also lend itself to some of those artsy fartsy type shots we screeners love,, A little cropping in Photoshop will usually get rid of those curled up edges..

BTW, what kind of camera is this occuring on, and is it a "fixed" lens?? There are several companies that make a non distorting wide angle lens that you might want to look into. Our beloved co-grand poobah Mr. Starnes has a most groovy cannon 17mm that I have played with, but if I was gonna spend money on a lens, it would be a bigger, badder, tele... 300mm just dont cut it no more :twisted:

iCe
10-06-2003, 11:08 PM
I have the worst camera in the world, Fuji Finepix i40

but furtunately that problem is not always present, only sometimes I have noticed that

Guilford350
10-06-2003, 11:22 PM
Our beloved co-grand poobah Mr. Starnes has a most groovy cannon 17mm that I have played with, but if I was gonna spend money on a lens, it would be a bigger, badder, tele... 300mm just dont cut it no more :twisted:

Greedy, greedy... :D

Bob
10-08-2003, 01:45 PM
Actually, this "pincushion" effect will be visible with any lens of less than 50mm (35mm equivalent). It is more pronounced in the wider lenses, but the MAIN cause is the film plane ( in a digital camera this would be the CCD) is not parallel with the subject, and in fact is more properly referred to as parallax distortion. One can spend an inordinate amount of money getting rid of this problem, but the SIMPLEST way is to make sure the film plane, i.e. the back of the camera, is perfectly perpendicular to the base of the subject. In most cases this will be the ground, and in most cases that requires the camera be at the mid-point of the subject.
HOWEVER, in the case of buildings, lamp posts, or our favorite subject, those objects are too tall to get at the proper elevation. Then again, with a locomotive, etc., they are normally only around 15 feet tall, so a ladder would be adequate.
So, bottom line, when you're wanting to get "the shot" look around and see what is available to stand on. Anything that is sturdy enough to support you and your equipment when the action gets hot is fine. Then, BEFORE YOU SHOOT, look at the edges of the viewfinder and make sure the edges of your subject are as straight as you can get them, and when you get into your digital darkroom you can do some tweaking to straighten the sides.
Hope this is a help and not a bother.

iCe
10-08-2003, 10:05 PM
Hey Bob,

Thanks for the tips. I'll try that next time.

Will

Wmas1960
10-09-2003, 09:41 PM
Just started reading this thread and don't know if this has been mentioned yet. I notice this a lot when I am out shooting.

I use a Nikon D100 and my most frequently used lens is the 24-85mm AF-S G lens. I have noticed odd distortions when shooting with this lens. When you are close up and go too wide, and are shooting head on the engine or train will look like it is tipping back away from you. I have a picture taken from a station platform of a stack train coming through on the nearside track. I was soooooo close. I widened out and took a picture of a METRA F40C that was pulling in on the opposite track. I framed the shot between the cars of the stack train. The METRA locomotive looked fine at about 20 or so feet away from me but the stack cars looked like they were tipping backwards into the commuter train. As if they were going to topple over. Same would be with any subject that you are shooting straight on. They will tip back. As for items or objects to the side they will tip in. The stack train example was one where my vantage point was about 45 degrees to the subject. Thus the containers looked as though they were tipping in and back.

On the other end of the spectrum, at the 85mm end I begin to see noticable compression to the picture. This is noticable with trains where each car gets noticably shorter as the back of the picture magnifies closer and the image appears to flatten.

Because of these problems, I try to position my self, relative to my subject, so that I am using a focal length in the middle of the spectrum. Maybe around 35-65mm? That may mean getting back from the tracks a little more. Into a parking lot, field etc. If you get really close and widen out you may see the tipping problems. So, try to get a bit further away so you can frame in the center of your lenses zoom. If you are too far away and have to use the higher zooms then try getting a little closer. Iof course stay away from the tracks. Don't go on railroad property.)

I posted some time ago, relating to a thread on another site, Yahoo Groups, I think, where they were talking of a fellow railfan who was killed last winter by an AMTRAK train North of Chicago, I replied that you don't have to get dangerously close to get that good shot. In fact, my experiences have been that those extremely close shots are not that dramatic and desirable because of the distortion caused by the lenses. Also by getting back a little you can add some interest to your foreground and add some depth to your pictures. Frame a tree in the forground or a sign post. Maybe some trackside brush or weeds.

My other lens for this camera is the 80-200mm AF D Nikkor zoom lens. I don't find myself using it much with trains though. With that lens I can be quite a distance and get some OK shots. However, as mentioned before, you tend to get compression at the high end. The lens works pretty good though when you are shooting into a curve where you can shoot a little from the side or get the train in the turn, which will minimize some of the compression and increase the appearance of depth. It also works good where the engine might be coming right at you but the cars are still perpendicular to your line of sight. I have a shot taken at Highland Park, Illinois where it came out pretty good. The cars were in the curve but the engine was coming at me. I was at the far (opposite) end of the platform shooting down the tracks into a curve. The only thing was a commuter walking accross the tracks in front of me (maybe about 50' in front of me) looked as though he was going to get creamed by the train. Truth was the train was about 1/4 mile or more from the station. Get far away and zoom in down the tracks and you can get such effects. Or get closer to your foreground subject and you will get a different effect.

That is one of my favorite things about photography and using a good quality SLR rather than a point and shoot model camera. You can play with things and get a much better knowlege of how things work in relationship to eachother. You can work around such problems or even use them when appropriate to enhance your composition. Somtimes they can have a positive effect when used the right way.

Wmas1960
10-09-2003, 09:52 PM
"the SIMPLEST way is to make sure the film plane, i.e. the back of the camera, is perfectly perpendicular to the base of the subject."

You bring up a point that I thought of right before reading your post and after sending my previous one.

When I have been taking pictures from the commuter platforms, I have found some good results by getting back a little, if I can. Then stretching myself to make sure that I am as straight as I can be and, consciously, holding the camera up and tipping the lens down a little so that it is straight and level. Then I compose with the zoom. By doing this I am making sure that I am not pointing UP on the subject but straight AT my subject. Because of the sizes of the engines (Locomotives) and many of the cars it doesn't always make a big difference but it does often help. I find this helpful also because sometimes, when not on a platform, I might be where the tracks have been laid on a hill or built up road bed. Thus, often, I might actually be lower than the level of the tracks. That can make problems even worse for distortion as you have to point upwards to get your shot.

Bob
10-10-2003, 04:50 AM
This is a most interesting thread! Haven't enjoyed talking photo shop, pun intended, in a LONG time.
Has anyone ever played with a view camera??

tomh
10-10-2003, 01:58 PM
An uploaded example of the problem (rather than the annoying 4 flickering photos) would have helped this discussion.

Now I'm no artist, but I do remember back 40 years to my high school art classes and the concept of perspective, which is neither parallax or pincushion. But before getting into that, you ought to familiarize yourself with the vanishing point, which is
1. the appearance of a point on the horizon at which parallel lines converge
2. the point beyond which something disappears or ceases to exist

The last post above is starting to get to the heart of the matter, in that a view camera deals with this problem quite nicely. So does a PC (perspective correcting) lens on a 35mm SLR. These are also known as "shift" lenses because of the internal moving elements. As for finding one of these on a digital camera, good luck. If you were to make your own prints with an enlarger, you can also tilt the easel and correct the "leaning back" that you see.

Or are we really correcting it at all? Maybe what we are actually doing is introducing distortion to make us more comfortable with the image as viewed on the screen. The answer lies in whether or not we see the "leaning back" in real life. You tell me.

iCe
10-10-2003, 10:00 PM
http://www.railpictures.net/viewphoto.php?id=28497

Here you go, there's an example. The lamp-posts on the right bends left. And the building on the left is slightly leaning to the right.

I guess I should have provided an example from the beginning. But calling my avatar isn't that nice...Actually quite a few people here liked it and asked me to make some for them.

:x

Wmas1960
10-10-2003, 10:24 PM
I would agree. There is nothing wrong with your Avitar. In fact I like the idea. If I did have any complaint it might be the speed that it cycles. How do you do that and can the speed be adjusted to slow it down a little? Also, might be a lot to ask but can transitions (desolves) be put into that.

I don't recall your original post but I would also agree it would have been better to have the link that you posted on your original post.

As for the linked photo, I can see the tilting of the lights, a little, but don't really sense the building tilting. I don't think either is really that bad. My instinct of this would be that some such distortion is unavoidable due to the way lenses are. Especially with the Wide Angle/Telephoto Zooms. I am sure they have improved greatly since but when I bought my first 28-85 zoom for my Canon A-1 I remember all the talk of how bad the lenses were because the designs for Wide is so contrary to Tele, or something like that. The word was that you had to make certain compromises and that you couldn't expect perfection. You just need to look carefully at your lenses when you buy them and buy the ones that are best for your needs, or best that you can afford. Better lenses will cost more. Sometimes a lot more. Or you can buy a lot of single focal length lenses, ie. 50mm or 35mm or whatever. Those single FL lenses will be better but will cost in the inconvenience of constant changing and expense of more lenses.

I just recalled a comment in a previous post about creating a defect in the image to correct the distortion. By slanting the image during printing etc. I recall from Photography in College (Physics) that some lenses are intentionally designed with defects that are intended to counter or correct other defects. The result, is that I don't think you can expect a "Perfect" lens or image from that lens. You will often have to except some leser defect rather than the much larger flaw.

Curtis Wininger
10-10-2003, 10:44 PM
This may have already been stated in some way or another, but I hope it helps.

Telephoto lenses naturally have the effect of making objects at different distances from the camera look closer together. The distance between objects is less obvious. This is used in movies to make, say an actor who darts through traffic, look closer to the danger than he really is. Wide angles have the opposite effect. If that shot were taken with a normal or wide angle lens, it may not look as dramatic.

I hope that helped. That's the best example I can think of.

Guilford350
10-10-2003, 11:25 PM
OK, now I see what you guys are talking about. That photo tells alot. The light poles do bend to the left a little but the building, on the other hand, seems to be straight. Although a closer inspection reveals that it is ever so slightly bent to the right. Yes, I do have to agree with most of you here about the lens distortion theories.

Tomh, I don't find exactly what is so annoying about our avatars. They are only about 22KB so they shouldn't take too long to load, even if you're on a dial-up connection. The speeds can be adjusted and, yes, you can put different transitions in there (which I think would be pretty nice but it might make the file size larger, avatars can be no larger than 24KB).

This is an interesting topic, indeed. :D

tomh
10-12-2003, 01:46 AM
The suggestion about raising yourself up a little higher is the best way to reduce the appearance of "leaning". I have done this many times myself and it really helps. Your shot with the light poles is really quite nice, the angle of the posts is something expected, so it isn't a problem with this photo at all. This perspective thing is most noticeable with lenses if a certain focal length range, (I don't know exactly what that range is but the shorter the focal length, the more notecable it is.) It is found in all lenses no matter how much you pay for them, so I don't think higher cost equates to less apparent leaning.

I mentioned perspective correction (shift) lenses. I don't think I have ever seen a rail shot taken with one of these, though I would like to see some, as they would be very interesting. The aircraft photos I have seen taken with view cameras, which reduce the leaning greatly, have been outstanding.

The flickering avatar is to me an unnecessary distraction, that's all. I'm not suggesting they be restricted in any way. Actaully, they are clever-but distracting. The word avatar is not one I am familiar with, so I looked it up in several dictionaries, both in print and online. It is listed, usually under religion, as "A divine incarnation." Hardly a term I would apply to any of my train photos. Anyway, I'm not trying to put anyone on the spot with this avatar thing-you guys seem to like it, that's fine. Devine, in fact.

iCe
10-12-2003, 03:06 AM
devine incarnation?

Actually it's just something I made to make the forums more cheerful! :D