Can someone explain about the focusing

[John.B]

With a prime, say an f/1.4 50mm, When you look through the viewfinder at a subject and turn the focus ring the subject will go in and out of focus but not change size. With a zoom, turning the focus ring has the same effect, but turning the zoom ring on a lens like my 28mm-300mm Tamron change the focal length of the lens up or down within that range. The subject gets larger or smaller but the focus stays the same.

Picking nits here, but the focus only stays the same as a zoom lens changes focal length for parfocal lenses like Canon's 70-200mm f/2.8 IS or Nikon's older 80-200mm F/4. Most zooms today will need to have their focus touched up after changing focal length.

 

[AlaskaMoose]

OK here we go, in this example I will use this lens: Lumix 20mm f1.7 Lens.

It is a prime lens so fixed focus, so let us only talk of primes only.

In terms of auto focusing how does it work if I manually keep the aperture at f/1.7 so shallow depth of field, more light etc. Now it is fixed focus so if I have the aperture fully open can I only have a subject in focus up close, or is focusing different to focal length etc.

If I put it this was, I have the camera on end of table and a flower in front of lens with aperture at f1.7 it has nice bokeh etc. Then I choose to move flower further back but aperture at f1.7 will it be able to focus on the flower or not? If I was using this lens would it be shutter speed that I control and leave the camera to change aperture to keep subject in focus at different distances.

Please help I'm confusing myself lol, and without camera/lens to test I can't work it out through experimenting

Do people shoot shutter priority over aperture or do they set it to manual and control both

a. A 20mm lens is wide enough to allow for more DOF than lets say a 50mm lens set at the same aperture. Lets say that you are taking a photo of a person's face from perhaps 20 feet of distance with a 100mm lens set at f/1.7. While the subject may be in focus, it's very possible for both the foreground and the background to be out of focus or blurred. But switch your camera to aperture priority (Av on Canon), and then change the aperture from f/1.7 to f/8, and now more of the foreground and a lot of the background will be in focus. All you have done is to increase the area in focus (but don't forget that the wider the lens the more of the subject in focus).

b. For a landscape where you want to show both the foreground and background in focus (using your lens), instead of setting the lens aperture to f/1.7, try something like f/11 to f/22 or so. You may have to increase ISO and even use a tripod, but the higher the aperture number, the more of the subject that will be in focus.

c. Lest say that you move away from the subject with the 20mm lens still set to f/1.7. In this case, you still have the same DOF as before, except that more of the foreground (the distance from your camera to the point where the DOF begins) will be blurred, but the DOF will remain the same (the flower will still be in focus). In other words, if you want to show more of the foreground and background that is outside of the lens DOF, just close the lens aperture (turn the lens aperture (with the camera controls) to a higher "f" number. But again, don't forget that the widest the lens the more DOF.

d. When you want to control how much of the subject you want in focus, use aperture priority (Av), and the camera chooses the best shutter speed possible. But in some instances, you may have to increase ISO to prevent blur.

e. In cases where you want to increase blur, switch the camera to shutter priority (Tv on Canon). The camera then chooses the best lens aperture possible. This mode is good for taking photos of moving subjects. For example, a person walking across you field of view, and you want to show the person's legs and arms in a blur (moving), or perhaps when you want to show a stream of water looking sort of milky. In this case, you may have to decrease ISO and also shutter speed. Also, you can do the same by using ND filters. The filters block some of the light, which in turn creates a condition similar to shooting in low light.

f. While your 20mm lens may not be ideal for portraits, a lot of photographers use them. All depends on what you want to achieve. For example, a Canadian professional photographer I know of, takes wonderful images of his children playing indoors (in a small room) with wide-angle and fisheye lenses. His photos not only show the main subject in focus, but also the room. Again, all depends on what you want to achieve. On this one (taken around 12mm), the dog's nose was perhaps 10" from the glass:

A DOF calculator:
http://www.dofmaster.com/dofjs.html

And wide lens portraits:
http://www.photographic.com/issue-4-people-photography/0909_WIDE/

 

[G.T.]

a. A 20mm lens is wide enough to allow for more DOF than lets say a 50mm lens set at the same aperture. Lets say that you are taking a photo of a person's face from perhaps 20 feet of distance with a 100mm lens set at f/1.7. While the subject may be in focus, it's very possible for both the foreground and the background to be out of focus or blurred. But switch your camera to aperture priority (Av on Canon), and then change the aperture from f/1.7 to f/8, and now more of the foreground and a lot of the background will be in focus. All you have done is to increase the area in focus (but don't forget that the wider the lens the more of the subject in focus).

b. For a landscape where you want to show both the foreground and background in focus (using your lens), instead of setting the lens aperture to f/1.7, try something like f/11 to f/22 or so. You may have to increase ISO and even use a tripod, but the higher the aperture number, the more of the subject that will be in focus.

c. Lest say that you move away from the subject with the 20mm lens still set to f/1.7. In this case, you still have the same DOF as before, except that more of the foreground (the distance from your camera to the point where the DOF begins) will be blurred, but the DOF will remain the same (the flower will still be in focus). In other words, if you want to show more of the foreground and background that is outside of the lens DOF, just close the lens aperture (turn the lens aperture (with the camera controls) to a higher "f" number. But again, don't forget that the widest the lens the more DOF.

d. When you want to control how much of the subject you want in focus, use aperture priority (Av), and the camera chooses the best shutter speed possible. But in some instances, you may have to increase ISO to prevent blur.

e. In cases where you want to increase blur, switch the camera to shutter priority (Tv on Canon). The camera then chooses the best lens aperture possible. This mode is good for taking photos of moving subjects. For example, a person walking across you field of view, and you want to show the person's legs and arms in a blur (moving), or perhaps when you want to show a stream of water looking sort of milky. In this case, you may have to decrease ISO and also shutter speed. Also, you can do the same by using ND filters. The filters block some of the light, which in turn creates a condition similar to shooting in low light.

f. While your 20mm lens may not be ideal for portraits, a lot of photographers use them. All depends on what you want to achieve. For example, a Canadian professional photographer I know of, takes wonderful images of his children playing indoors (in a small room) with wide-angle and fisheye lenses. His photos not only show the main subject in focus, but also the room. Again, all depends on what you want to achieve. On this one (taken around 12mm), the dog's nose was perhaps 10" from the glass:

Thanks with all comments before it started to make sense, your comment was a good summarizer. I suppose I forget things in front of the subject will be out of focus too, so I kinda thought with a fixed aperture it would be fixed focus but know now the focal plane moves regardless.

 

[El Cabong]

Worth Mentioning

20mm on a 4/3 sensor is equivalent to 40mm full frame, i.e. not exactly a wide angle. 45-55mm would be more ideal for portraits on 4/3 cameras, however. Olympus makes a 50mm f/2 lens for the old 4/3 mount (requires an adapter for the GF1 and other u2/3 cameras) that is supposedly very sharp, and has macro (1:1) capabilities.

 

[John.B]

Also worth mentioning...

Also worth mentioning is that lenses with really short focal lengths (say, 10mm-16mm) will tend to exaggerate feature distance, which isn't necessarily what you want in a portrait; i.e. someone with a largish nose doesn't want it to look even larger.

Basically this works the opposite of the way that telephoto lenses (say, >=200mm) have a tendency toward compressing features; i.e. trees in the distance will tend look as through they are closer together than they really are.

The rub is that the effects of these focal lengths are independent of crop factor; because crop factor only changes the field of view but not perspective. 15mm is 15mm, whether on a full frame or a micro four thirds camera. This is why webcams on a MacBook or P&S shots from close range (e.g. arm's length) make people appear to have bulbous shaped faces.

This is why people argue (correctly) that you can't just do the crop factor math to say a 85mm f/1.2 "is like a 135mm on a crop sensor camera", because only the angle of view is similar.

So even with a 4/3 sensor with a 2x crop factor, be careful how close you get to your subject with that 20mm pancake lens.

 

[Phrasikleia]

This is why people argue (correctly) that you can't just do the crop factor math to say a 85mm f/1.2 "is like a 135mm on a crop sensor camera", because only the angle of view is similar.

Yes, but you will adjust your positioning relative to the subject to get the right framing, so the perspective will change as well. So it's pretty accurate to state equivalencies like the one you mentioned.

 

[G.T.]

Well i've been reading on the adapter e.g. something like this http://cgi.ebay.com/_W0QQcmdZViewItemQQitemZ350201470018

And there is not electric link so aperture can't be controlled, it says it is default to wide open would this be the case and would it still be worth getting on so I can use my canon lens.

To me I would think shooting with aperture wide is best with gf1 to reduce iso and have fast shutter speed. The lens max aperture is f/3.5 so its not too bad if it was stuck on that only, is it? I suppose it depends if I want everything in focus and if I did like with landscape I'd be using the pancake. If I was to take a portrait I would want to zoom in so would use the lens but also want a good DoF to isolate person so aperture being stuck wide isn't too bad.

When I have more money I could get another micro 4/3rds lens with similar range but I'd have more control and won't need the adapter.

Any thoughts/suggestions.

 

[John.B]

Yes, but you will adjust your positioning relative to the subject to get the right framing, so the perspective will change as well. So it's pretty accurate to state equivalencies like the one you mentioned.

If you put a 135mm lens on a full frame and an 85mm lens on a crop sensor and took side by side portrait shots, the framing in the viewfinder would be similar but the picture from the 135mm on the full frame would have more compression.

 

[Phrasikleia]

If you put a 135mm lens on a full frame and an 85mm lens on a crop sensor and took side by side portrait shots, the framing in the viewfinder would be similar but the picture from the 135mm on the full frame would have more compression.

No. You would have the exact same perspective. The only thing that governs "compression"/perspective is your distance from the subect. If the distance is identical, the perspective is identical.

 

[Edge100]

If you put a 135mm lens on a full frame and an 85mm lens on a crop sensor and took side by side portrait shots, the framing in the viewfinder would be similar but the picture from the 135mm on the full frame would have more compression.

Agreed. An intuitive way of looking at it, I think, is to consider what happens with an 85mm lens on both bodies. On a FF body, you get the classic H&S portrait length of 85mm. On a 1.6x body, you get 136mm. That is, you get the angle of view comparable to an 85mm lens on a FF body. BUT, to get the same shot with the same lens on the 1.6x vs. the FF, you've had to move back.

This is why "zooming with your feet" doesn't work as advertised (i.e. it's not the same as zooming). Yes, you change the framing of the subject, but you also change perspective, since that is determined by distance from the subject, NOT focal length. So having a 35mm prime and moving twice as close to the subject does not produce an identical photograph as using 70mm on your 70-200 zoom. The angle of view is the same, but perspective is completely different.

 

[Phrasikleia]

Agreed. An intuitive way of looking at it, I think, is to consider what happens with an 85mm lens on both bodies. On a FF body, you get the classic H&S portrait length of 85mm. On a 1.6x body, you get 136mm. That is, you get the angle of view comparable to an 85mm lens on a FF body. BUT, to get the same shot with the same lens on the 1.6x vs. the FF, you've had to move back.

This is why "zooming with your feet" doesn't work as advertised (i.e. it's not the same as zooming). Yes, you change the framing of the subject, but you also change perspective, since that is determined by distance from the subject, NOT focal length. So having a 35mm prime and moving twice as close to the subject does not produce an identical photograph as using 70mm on your 70-200 zoom. The angle of view is the same, but perspective is completely different.

What are you agreeing with? His scenario has the two photographers standing side-by-side with the same exact framing. They are using two different focal lengths, but on different sensors, so the field-of-view is identical, the distance from the subject is identical, and the compression/perspective is identical.

 

[John.B]

No. You would have the exact same perspective. The only thing that governs "compression"/perspective is your distance from the subect. If the distance is identical, the perspective is identical.

No, lens perspective at any given focal length is completely independent of crop factor. The crop sensor narrows the field of view, but it can't alter the physics of the lens itself.

Try this for yourself.

Make a print of an extreme close up of an object from a 7D and 10-22mm at 10mm and compare it to a same sized print taken from a 5D and 16-35mm at 16mm. The print from the 10mm lens will look "deeper" and more bulbous shaped than the print taken from the 16mm, even though inherently you might think they should be the same. The closer the working distance, the more pronounced the effect.

Likewise, if you take the 5D and a 100-400mm and make a print of a distant stand of trees at 320mm and then make the same print from a 7D at 200mm, the compression from the 5D print at 320mm will be noticeably more pronounced than the 7D at 200mm.

 

[Phrasikleia]

No, lens perspective at any given focal length is completely independent of crop factor. The crop sensor narrows the field of view, but it can't alter the physics of the lens itself.

Try this for yourself.

Make a print of an extreme close up of an object from a 7D and 10-22mm at 10mm and compare it to a same sized print taken from a 5D and 16-35mm at 16mm. The print from the 10mm lens will look "deeper" and more bulbous shaped than the print taken from the 16mm, even though inherently you might think they should be the same. The closer the working distance, the more pronounced the effect.

Likewise, if you take the 5D and a 100-400mm and make a print of a distant stand of trees at 320mm and then make the same print from a 7D at 200mm, the compression from 5D print at 320mm will be noticeably more pronounced than the 7D at 200mm.

Either you're not understanding me or you're not understanding perspective. You even said yourself here "the closer the working distance, the more pronounced the effect." If we're talking about the same working distance--the same distance between camera and subject--it doesn't matter what focal length you're using; the compression/perspective will be the same. The focal length and sensor combination will determine the field of view, but will have zero effect on perspective. Zero. Zip. Zilch. All that matters with perspective is your working distance.

 

[John.B]

What are you agreeing with? His scenario has the two photographers standing side-by-side with the same exact framing. They are using two different focal lengths, but on different sensors, so the field-of-view is identical, the distance from the subject is identical, and the compression/perspective is identical.

The only thing that's not identical is the compression/perspective.

That's the same reason why the 70-200mm zooms rock for portraits, you can emphasize or de-emphasize facial features (to get greater or lesser relief) as necessary just by changing the focal length and subject distance to get the same subject framing but different compression effects. Its also the same reason that many wedding and event photographers -- who may not be able to zoom with their feet -- carry both crop sensor and full frame cameras.

 

[Phrasikleia]

The only thing that's not identical is the compression/perspective.

That's the same reason why the 70-200mm zooms rock for portraits, you can emphasize or de-emphasize facial features (to get greater or lesser relief) as necessary just by changing the focal length and subject distance to get the same subject framing but different compression effects. Its also the same reason that many wedding and event photographers -- who may not be able to zoom with their feet -- carry both crop sensor and full frame cameras.

Good grief. All that matters is distance. That's where you get the perspective. If you use a long focal length, you'll stand further away to get the right framing. What matters is that you're far away from the subject. You could stand far away and use a wide focal length and get the same perspective; you could then crop the image in post to get the same framing.

 

[toxic]

So then is a 105 on a film 35 is good for portraiture because it places the camera at a distance which yields best perspective for a shoulder-up framing? 135 moves it farther away and a 50 moves it closer, right?

correct.

or more accurately, the focal length choice for portraiture is a combination of flattering perspective and working distance. you want the model to look good, but you don't want to be so close that it's uncomfortable or so far that it's difficult to communicate or move the lights.

 

[John.B]

Either you're not understanding me or you're not understanding perspective. You even said yourself here "the closer the working distance, the more pronounced the effect." If we're talking about the same working distance--the same distance between camera and subject--it doesn't matter what focal length you're using; the compression/perspective will be the same. The focal length and sensor combination will determine the field of view, but will have zero effect on perspective. Zero. Zip. Zilch. All that matters with perspective is your working distance.

I don't know a better way to show you. I had a link saved that explained this clearly with some great example photos but I don't seem to have it on this computer.

Borrow a 5D (or whatever) and a 100-400mm zoom, grab your 7D (or whatever) and try it out for yourself. Get the subjects the same size in the viewfinder and verify whether or not the backgrounds are different or the same.

BTW, apologies to the OP for completely derailing his thread.

 

[gnd]

Phrasikleia is totally correct. Perspective is only determined by the distance between the subject and the camera. Whatever field of view you get with whatever lens just determines what "crop" of the whole scene you take a photo of, but perspective is independent of the lens.

But if you want to frame your subject within the same boundaries using different lenses you'll have to change your subject-to-camera distance and thus change perspective.
For example:
- if you want a head shot with a 135mm lens on a FF body, you'll have to stand 10m away (for example),
- if you want a head shot with a 85mm lens on a FF body, you'll have to stand 6m away,
- if you want a head shot with a 135mm lens on a APS-C body, you'll have to stand 15m away,
- if you want a head shot with a 85mm lens on a APS-C body, you'll have to stand 10m away

All of these will make your subject be framed by the same boundaries.

 

[Phrasikleia]

I don't know a better way to show you. I had a link saved that explained this clearly with some great example photos but I don't seem to have it on this computer.

Borrow a 5D (or whatever) and a 100-400mm zoom, grab your 7D (or whatever) and try it out for yourself. Get the subjects the same size in the viewfinder and verify whether or not the backgrounds are different or the same.

I have a 5D2 in addition to the 7D. I suggest you borrow whichever you're missing because you seem to be confused, and I'm not sure where your confusion lies.

Phrasikleia is totally correct. Perspective is only determined by the distance between the subject and the camera. Whatever field of view you get with whatever lens just determines what "crop" of the whole scene you take a photo of, but perspective is independent of the lens.

But if you want to frame your subject within the same boundaries using different lenses you'll have to change your subject-to-camera distance and thus change perspective.
For example:
- if you want a head shot with a 135mm lens on a FF body, you'll have to stand 10m away (for example),
- if you want a head shot with a 85mm lens on a FF body, you'll have to stand 6m away,
- if you want a head shot with a 135mm lens on a APS-C body, you'll have to stand 15m away,
- if you want a head shot with a 85mm lens on a APS-C body, you'll have to stand 10m away

All of these will make your subject be framed by the same boundaries.

Thank you.

By the way John.B, this may be the link you had in mind:

http://photography-on-the.net/forum/showthread.php?t=672913

 

[John.B]

...
But if you want to frame your subject within the same boundaries using different lenses you'll have to change your subject-to-camera distance and thus change perspective.
For example:
- if you want a head shot with a 135mm lens on a FF body, you'll have to stand 10m away (for example),
...
- if you want a head shot with a 85mm lens on a APS-C body, you'll have to stand 10m away

All of these will make your subject be framed by the same boundaries.

I don't disagree. Yes, subject framing will essentially be the same. But that wasn't the point.

The head shot with a 135mm lens on a FF body will look "flatter" or "more compressed" (WRT front to back features) vs. the 85mm lens on a APS-C body.

Every wedding, event, and portrait photographer knows this (or should). The best use it to their advantage.

By the way John.B, this may be the link you had in mind:

http://photography-on-the.net/forum/showthread.php?t=672913

No, but that isn't bad, nor is this (esp. the pics of the yellow abstract sculpture).

What I'm looking for has aspen trees shot at different focal lengths and at different subject differences.

 

[gnd]

The head shot with a 135mm lens on a FF body will look "flatter" or "more compressed" (WRT front to back features) vs. the 85mm lens on a APS-C body.

No, because the distance between the subject and the camera will be the same in both cases, there won't be any perspective difference. This means the head shots will not look "more flat" or "more compressed" on one camera as opposed to the other.

 

[El Cabong]

Phrasikleia et al:

John.B:

 

[ChrisA]

I don't disagree. Yes, subject framing will essentially be the same. But that wasn't the point.

The head shot with a 135mm lens on a FF body will look "flatter" or "more compressed" (WRT front to back features) vs. the 85mm lens on a APS-C body.

Every wedding, event, and portrait photographer knows this (or should). The best use it to their advantage.

No. Perspective is controlled by subject to camera distance ONLY. Not by the lens used. Try taking the same portraint shot from different distances using the same fixed 50mm lens then crop them all so they are framed identically.

What does change in the above FF vs. APS-C example is depth of field. At the same distance and framming the camera with the larger sensor wil have less depth of field but of cource this can be controlled with the f-stop.

You don't even need a camera to see how perspective changes with distance, close one eye note the difference in appearent size of a close and distance object then move backward and note the relative sizes again.

 

[Grasher]

BTW, apologies to the OP for completely derailing his thread.

OP - are you still following along?

 

[G.T.]

OP - are you still following along?

I am actually all very interesting.

Though one of my questions has been unanswered, if someone could give their opinion thanks.

Well i've been reading on the adapter e.g. something like this http://cgi.ebay.com/_W0QQcmdZViewItemQQitemZ350201470018

And there is not electric link so aperture can't be controlled, it says it is default to wide open would this be the case and would it still be worth getting on so I can use my canon lens.

To me I would think shooting with aperture wide is best with gf1 to reduce iso and have fast shutter speed. The lens max aperture is f/3.5 so its not too bad if it was stuck on that only, is it? I suppose it depends if I want everything in focus and if I did like with landscape I'd be using the pancake. If I was to take a portrait I would want to zoom in so would use the lens but also want a good DoF to isolate person so aperture being stuck wide isn't too bad.

When I have more money I could get another micro 4/3rds lens with similar range but I'd have more control and won't need the adapter.

Any thoughts/suggestions.

Also if the 20mm pancake on gf1 is equivalent to 40mm, would my 28-80mm be equivalent to 56-160mm

I'm looking to purchase this 2day http://www.thedigitalcamerashop.co.uk/product_details.php?id=4284 tell me what u think. Can anyone find it any cheaper for the UK with that lens or had any experience with this site?