Nailing focus... *focus test 11/9*

[boBQuincy]

Although the perspective in the sample images did change it was due to the distance to the subject changing in order to keep the image size consistent. If the camera position was kept constant the perspective would be the same for different lenses, although the image size of the subject would change.

This is a common misconception about lenses because it appears to be so from the way we typically use short and long lenses. Once the facts are known it can change the way we use our lenses to match our pre-visualization of the scene.

A really good article on lens choice and perspective:
http://luminous-landscape.com/essays/changing-perspective.shtml



From http://www.cambridgeincolour.com/tutorials/camera-lenses.htm

"Many will say that focal length also determines the perspective of an image, but strictly speaking, perspective only changes with one's location relative to their subject. If one tries to fill the frame with the same subjects using both a wide angle and telephoto lens, then perspective does indeed change, because one is forced to move closer or further from their subject. "

 

[photo_chick]

Back to basics here, the lens focal length has nothing to do with perspective. Only the distance from the subject can change that. Obviously we change distance from a portrait subject according to the focal length but it still is not an effect of the lens.

I get what you're saying. If you're framing the exact same shot with a 28mm, a 50mm and a 100mm you'll see the how the image changes. Yes, the distance to subject changes but that wouldn't change if you didn't change focal length. So from that point of view focal length has everything to do with it because the different focal length changes your field of view and if you want to frame exactly the same shot then you do have to move.

 

[Marlton Mom]

~Marlton Mom

PS, All this is very thought provoking so thanks to all who are posting. I also am having a problem with "mushy focus/resolution" and I'm beginning to think that it's because the lens (and camera focusing system) just can't perform to the sharpness I desire because it is out of it's peak resolution/focusing zone.

I am well aware of all the focusing options on the Nikon D90 and I thought I could get the focus I want using AFS single point (the crossed center focus point) for relatively static subjects. It seems to not want to get sharp for me especially if the subject is far away. When the subject is closer, sharp focus is a 50/50 proposition. The apertures are from F8 to F11 so depth of field doesn't really come into play as a limiting factor.

This happens with all of my lenses BTW (18-105, 35mm and 55 -200).

I'm at my wits end working the focus to death and I'm starting to wonder now if I need to make the jump to a full frame camera and ditch the DX format.

 

[ukcatfan]

wbeem,

I understand what you are talking about, but your examples do it zero justice. The guy looks much healthier and normal in the 50mm shot. He looks almost overweight in the 200mm shot and has bigger ears in it. The 50mm is also a much more properly exposed shot. Sorry, but you fail to make the case for 200mm with it.

The woman is more dramatic, but come on, who takes a shot like that with a 24mm? Nobody with a clue does! Then she is standing at a different angle, which makes the comparison pointless.

Again, not trying to argue your point, just pointing out that your examples are not good.

 

[theduck619]

Although the perspective in the sample images did change it was due to the distance to the subject changing in order to keep the image size consistent. If the camera position was kept constant the perspective would be the same for different lenses, although the image size of the subject would change.

This is a common misconception about lenses because it appears to be so from the way we typically use short and long lenses. Once the facts are known it can change the way we use our lenses to match our pre-visualization of the scene.

A really good article on lens choice and perspective:
http://luminous-landscape.com/essays/changing-perspective.shtml


From http://www.cambridgeincolour.com/tutorials/camera-lenses.htm

"Many will say that focal length also determines the perspective of an image, but strictly speaking, perspective only changes with one's location relative to their subject. If one tries to fill the frame with the same subjects using both a wide angle and telephoto lens, then perspective does indeed change, because one is forced to move closer or further from their subject. "

Thank you for the links!

 

[mchhp]

One focus point is key, and you want that on the subject's closest eye, However, don't leave it in the center. Move it around to get the composition you want.

Something else that may happen is having your focus set to Continuous instead of Single mode. At least, that's something I have on my Nikon. I presume there's a comparable setting on your Canon. Basically, you want to set your focus with a half-press of the shutter and lock it. That happens on Single mode. A continuous mode would keep searching for something else to use as its focus point, despite what you want.

As for portraits, use something longer than a 50mm lens. It distorts facial features, pushes hairlines back, and other nastiness you probably don't want. I prefer 200mm when possible, but even 85mm is a good minimum.

Thank you for your response. I do have it set to single focus mode.

 

[wbeem]

wbeem,

I understand what you are talking about, but your examples do it zero justice. The guy looks much healthier and normal in the 50mm shot. He looks almost overweight in the 200mm shot and has bigger ears in it. The 50mm is also a much more properly exposed shot. Sorry, but you fail to make the case for 200mm with it.

The woman is more dramatic, but come on, who takes a shot like that with a 24mm? Nobody with a clue does! Then she is standing at a different angle, which makes the comparison pointless.

Again, not trying to argue your point, just pointing out that your examples are not good.

The "guy" is Pete Collins with NAPP. That photo was taken by his co-worker, RC Concepcion, to demonstrate this point. I've seen Pete, and he looks like the guy in the 200mm shot, not the 50mm shot.

It's interesting that you have an opinion on which image you prefer, but I haven't failed at anything here.

That said, you keep taking your portraits with whatever lens you want. My point was to offer some information about the effects of focal length and lens distortion. If you choose to ignore it, that's your prerogative.

 

[ukcatfan]

The "guy" is Pete Collins with NAPP. That photo was taken by his co-worker, RC Concepcion, to demonstrate this point. I've seen Pete, and he looks like the guy in the 200mm shot, not the 50mm shot.

It's interesting that you have an opinion on which image you prefer, but I haven't failed at anything here.

That said, you keep taking your portraits with whatever lens you want. My point was to offer some information about the effects of focal length and lens distortion. If you choose to ignore it, that's your prerogative.

Why in the world would it matter who it is??? It could be the Queen of England and it wouldn't matter. The 50mm shot looks better. Game, Set, Match! BTW, the vast majority of people want to look the "best" in a shot, not what is the most "accurate" representation. How many fashion photographers have you ever heard of that go for "accurate" over "attractive"?

And why exactly are you attacking me here anyway??? To quote myself "I understand what you are talking about". These are just bad examples. The guy is a bad shot and looks better at 50mm regardless of how "accurate" it is and the 24mm of the woman is unrealistic because only clueless people would do that. Stop being so aggressive!

 

[boBQuincy]

Back to the original subject, nailing focus, someone who works with many cameras and lenses has some interesting things to say on the subject. The short version is that all cameras and lenses have a tolerance. If the camera and the lens are both at the edge of tolerance in the same direction it will be difficult to get sharp focus at f/1.4 even though both the lens and camera are within specification.

http://www.lensrentals.com/blog/2011/10/notes-on-lens-and-camera-variation

http://www.lensrentals.com/blog/2011/10/the-limits-of-variation

My Rebel Xsi was front-focusing and it was obvious with a 50 mm f/1.8 (not quite as obvious with the 18-55 but still soft). Canon adjusted the camera and it is much better.

 

[ukcatfan]

Back to the original subject

 

[wbeem]

Why in the world would it matter who it is??? It could be the Queen of England and it wouldn't matter. The 50mm shot looks better.

The reason that piece of information matters is because I've seen him with my own eyes and I can tell you which one looks like the person you would see if you saw him with your own eyes. Perhaps you could try a similar test with someone you know to see what results you get.

Game, Set, Match!

How childish of you.

BTW, the vast majority of people want to look the "best" in a shot, not what is the most "accurate" representation. How many fashion photographers have you ever heard of that go for "accurate" over "attractive"?

The reason fashion and other photographers use longer focal lengths is because it produces a better looking image; more flattering to the subject.

And why exactly are you attacking me here anyway???

I haven't attacked you. I've disagreed with you, and done so without exclamation marks or sports metaphors.

Stop being so aggressive!

Right.

 

[ukcatfan]

The reason that piece of information matters is because I've seen him with my own eyes and I can tell you which one looks like the person you would see if you saw him with your own eyes. Perhaps you could try a similar test with someone you know to see what results you get.



How childish of you.






The reason fashion and other photographers use longer focal lengths is because it produces a better looking image; more flattering to the subject.




I haven't attacked you. I've disagreed with you, and done so without exclamation marks or sports metaphors.



Right.

You are something else. I never disagreed with your position. I only pointed out that your " visual aides" were bad. BTW, your tone of writing comes off arrogant and rude. Try calling them "examples" instead of "visual aides" for one. You come off as a know it all. Then name dropping. That screams arrogance. If you don't get it then well...

 

[wbeem]

You are something else. I never disagreed with your position. I only pointed out that your " visual aides" were bad. BTW, your tone of writing comes off arrogant and rude. Try calling them "examples" instead of "visual aides" for one. You come off as a know it all. Then name dropping. That screams arrogance. If you don't get it then well...

It's been nice chatting with you.

 

[ukcatfan]

It's been nice chatting with you.

Now I remember why your name looked familiar. I remember your history here now. I am literally cracking up right now. You won't even get the respect of a response from me again.

 

[mom2rtk]

Now I remember why your name looked familiar. I remember your history here now. I am literally cracking up right now. You won't even get the respect of a response from me again.

I wondered how long before someone else remembered that too.

I found it amusing that his first piece of advice was to tell the gymnast photographer in another thread to challenge the rules about no flash.

Then a somewhat confrontational interaction here.

Yeah, I can't believe that issue from a while back hasn't repeated itself for others.

 

[wbeem]

I wondered how long before someone else remembered that too.

I found it amusing that his first piece of advice was to tell the gymnast photographer in another thread to challenge the rules about no flash.

Then a somewhat confrontational interaction here.

Yeah, I can't believe that issue from a while back hasn't repeated itself for others.

You know, you can accept the world as it is or you can try to do something about it. As I pointed out in my example on the gymnast thread, a friend of mine had the same issue and she found a way to make a change. I merely suggested that possibility may work in the scenario presented here.

Having just re-read this thread, I honestly don't see that I was confrontational here. I presented my thoughts and some images that demonstrated a point that I raised. Apparently, that was considered aggressive.

As for the issue from a while back, it did repeat itself a few weeks after my incident. I'd be happy to point it out on that person's blog post about it, but I'm afraid I may be accused of "name dropping" again. So I'll withhold unless someone requests it.

I came here to participate and share, not upset folks.

 

[ukcatfan]

You know, you can accept the world as it is or you can try to do something about it. As I pointed out in my example on the gymnast thread, a friend of mine had the same issue and she found a way to make a change. I merely suggested that possibility may work in the scenario presented here.

Having just re-read this thread, I honestly don't see that I was confrontational here. I presented my thoughts and some images that demonstrated a point that I raised. Apparently, that was considered aggressive.

As for the issue from a while back, it did repeat itself a few weeks after my incident. I'd be happy to point it out on that person's blog post about it, but I'm afraid I may be accused of "name dropping" again. So I'll withhold unless someone requests it.

I came here to participate and share, not upset folks.

I might not be speaking for everyone here, but I don't think you are welcome here. Seriously.

 

[mchhp]

Back to the original subject, nailing focus, someone who works with many cameras and lenses has some interesting things to say on the subject. The short version is that all cameras and lenses have a tolerance. If the camera and the lens are both at the edge of tolerance in the same direction it will be difficult to get sharp focus at f/1.4 even though both the lens and camera are within specification.

http://www.lensrentals.com/blog/2011/10/notes-on-lens-and-camera-variation

http://www.lensrentals.com/blog/2011/10/the-limits-of-variation

My Rebel Xsi was front-focusing and it was obvious with a 50 mm f/1.8 (not quite as obvious with the 18-55 but still soft). Canon adjusted the camera and it is much better.

first off, oh my.

although, I think the information regarding focal length and how it give different prespectives is interesting.... It really has nothing to do with my issue, nor the question asked. I think focal length came up because I am truely natorious for getting too close to my subjects anyway (then with a f stop so wide, it gives me very little wiggle room for movement).

So, when I have a moment (been working night shift, and of course got stuck working the one saturdya when the time changes and I have to work 13 hours instead of 12... btw that toally blows), I am going to try to retest the camera and lens with the focus test. If I feel like both lens are either front focusing or back focusing, then I cans send my camera to canon for an adjustment? or do i send it all, or how does that work? has anyone done this who could advise.

 

[photo_chick]

If you have done the focus test and you really feel like it's the camera and not you, send it in. Once in a while you do get one that's a bit wonky. Call 1-800-OK-CANON and they'll get you started.

 

[boBQuincy]

first off, oh my.
...snip...
I am going to try to retest the camera and lens with the focus test. If I feel like both lens are either front focusing or back focusing, then I cans send my camera to canon for an adjustment? or do i send it all, or how does that work? has anyone done this who could advise.

From reading the LensRentals article it appears this can be a slippery slope. A lens/camera combination that tests poorly at close distance can be better (or worse) at far distance. Mine was front focused close up and at a distance, manually tweaking the focus after autofocus resulted in an improvement in all cases. The lens(es) worked well on my other Canons so I was pretty sure this camera was out of adjustment. Canon noted that if the adjustment did not work then I should send the camera and lens in together, something I did not want to do since none of my other cameras had this issue.
I attached some small jpgs of the focus tests to my email to Canon and they seemed convinced that there was a problem.

If you can test the lens and camera against someone else's it would help to verify where the problem is.