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11-23-2008, 04:21 PM   #31
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QuoteOriginally posted by offertonhatter Quote
On compacts they will say in the blurb 38-380 (35mm equiv) but in reality the lens as a 5.7mm-57mm lens (my fuji S5000). The blurb has just confused the issue a bit, due to consumers still thinking in 35mm terms, whereas photographers who are used to various film types in the past, know about certain lengths and what they will be on differing formats. D
Talking about a 5.7-57mm lens is pointless, it doesn't tell me anything useful at all. I don't care what the lens is, I want to know the fov. Saying it's 38-380mm equivalent on the other hand is a useful and useable statement, because I can compare it directly to my APS-C lenses

11-23-2008, 04:36 PM   #32
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Yes, but a 5.7-57mm is what is says, it is not a 38-380mm.

The fov will be as a 5.7-57mm, but the EFFECTIVE fov will be 38-380mm.

This is where the confusion comes in. When a manufacturer states the effective fov, consumers think it is a 38-380mm lens, when clearly it is not.

Also, you say it will compare with your APS-C, it won't, the 38-380mm in 35mm terms, so if you took that into account, then in APS-C terms it would be 57-570mm taking into account the 1.5 crop over 35mm. But of course it is'nt, it is a 5.7-57mm and taking the crop it has an effective fov of 38-380. You would have to get a 25.1-251 lens to get the equiv FOV on APS-C (to get the 38-380mm equiv on APS-C)

The important word is effective before fov. The fov will not change on a lens, but the effective fov will. they are two different things.

Confused? I am
11-23-2008, 05:11 PM   #33
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QuoteOriginally posted by Marc Sabatella Quote
.... One is that, as I mentioned before, high ISO capabilities have really diminished (although of course not eliminated) the need for the same kinds of speed needed for film.
There are things not related to ISO that can be improved by a wide aperture lens.
Consider that your 40mm/f2.8 lets in one quarter the light of a 50/1.4, half the light of a 43/1.9 (more or less).
I'd bet when you are forced to use ISO 1600 because of lighting conditions, your focusing, be it manual or automatic, could really use the extra light.
11-23-2008, 05:23 PM   #34
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QuoteOriginally posted by Wheatfield Quote
There are things not related to ISO that can be improved by a wide aperture lens.
True, and that's why I said the need was reduced but not eliminated. Getting super shallow DOF is one obvious case, and for that, I'm happy to also have my A50/1.7. However:

QuoteQuote:
Consider that your 40mm/f2.8 lets in one quarter the light of a 50/1.4, half the light of a 43/1.9 (more or less).
I'd bet when you are forced to use ISO 1600 because of lighting conditions, your focusing, be it manual or automatic, could really use the extra light.
Not really an issue in manual focus, since the focus screen itself "eats" light and doesn't really show any increase in brightness (or decrease in DOF) at apertures larger than f/2.8. Easiest way to do this is do a DOF preview at f/2.8 on a faster lens - really very little change in the viewfinder at all from wide open to f/2.8.

As for autofocusing, yes, I suppose in theory, more light could mean faster focusing. But given that the DA40/2.8 is already generally acknowledged to be about the fastest focusing lens Pentax has ever made, it's hard for me to get worked up about how faster it might focus if it had a larger maximum aperture. And actually, the increased mass of the extra glass required for f/2 or whatever might actually counteract this.

11-23-2008, 05:34 PM   #35
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QuoteOriginally posted by offertonhatter Quote
Also, you say it will compare with your APS-C, it won't,
When I compare with my DSLR, I will compare the p&s 35mm equivalent , 38-380, with my DSLR's 35mm equivalent, 24-450mm (16-45mm and 55-300mm lenses). That is a useful and easily understood comparison. Trying to compare 5.7-57mm on a p&s with 16-300mm on a DSLR is not helpful.
11-23-2008, 05:35 PM   #36
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QuoteOriginally posted by Sean Nelson Quote
I don't have a problem with someone saying "this lens has a field of view that's equivalent to a 75mm lens on a full frame 35mm camera". That's an accurate description. But saying that a 50mm lens somehow becomes 75mm (with no other qualification) is very, very misleading.
QuoteOriginally posted by audiobomber Quote
I think that's needlessly picky. We all understand that the lens remains the same and the FOV changes.
Maybe you and I do, but there are a lot of people who don't. How many times have you seen the following types of questions on these forums:

When I use a 50mm lens do I set SR for 50mm or 75mm?

When I calculate depth of field do I use 50mm or 75mm?

When my EXIF information says 75mm, was it really at 50mm?

Do I have to divide my flash guide number by 1.5 with my Pentax DSLR?

...and on and on. Confusion over focal length vs. field of view are the single leading cause of questions on the forums I visit.
11-23-2008, 05:41 PM   #37
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QuoteOriginally posted by Sean Nelson Quote
Maybe you and I do, but there are a lot of people who don't.
That's true, but newbies are confused about many, many things which they have to learn if they wan't to learn about photography. Crop factor is just another thing on the list.
11-23-2008, 05:54 PM   #38
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One almost funny thing is that a lot of people buying DSLRs have no concept of focal length to begin with, and instead of accepting 28-35mm as "normal" they're told that it's "equivalent" to a focal length in a format they've never used in the first place.

11-23-2008, 07:22 PM   #39
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QuoteOriginally posted by Marc Sabatella Quote
True, and that's why I said the need was reduced but not eliminated. Getting super shallow DOF is one obvious case, and for that, I'm happy to also have my A50/1.7. However:



Not really an issue in manual focus, since the focus screen itself "eats" light and doesn't really show any increase in brightness (or decrease in DOF) at apertures larger than f/2.8. Easiest way to do this is do a DOF preview at f/2.8 on a faster lens - really very little change in the viewfinder at all from wide open to f/2.8.

As for autofocusing, yes, I suppose in theory, more light could mean faster focusing. But given that the DA40/2.8 is already generally acknowledged to be about the fastest focusing lens Pentax has ever made, it's hard for me to get worked up about how faster it might focus if it had a larger maximum aperture. And actually, the increased mass of the extra glass required for f/2 or whatever might actually counteract this.
In theory, that two stops of light might be the difference between successful autofocus and hunting. I've been in situations where an f/4 zoom won't AF, an F2.8 will, after hunting for a while, and an f/1.8 lens works just fine.
Speed isn't the issue, securing focus is.
I don't know what you are talking about regarding the focusing screen eating light. I can certainly tell, and appreciate, the extra brightness when I have a faster lens on when compared to a slower one, both in light conditions where a higher ISO is required to secure a reasonable shutter speed, and when in the studio working under modeling lights.
11-23-2008, 10:49 PM   #40
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QuoteOriginally posted by Wheatfield Quote
In theory, that two stops of light might be the difference between successful autofocus and hunting. I've been in situations where an f/4 zoom won't AF, an F2.8 will, after hunting for a while, and an f/1.8 lens works just fine.
Maybe so in theory, but the DA40/2.8 doesn't really hunt in low light, either. Perhaps it's high contrast wide open makes it able to do better than other faster lenses.

QuoteQuote:
I don't know what you are talking about regarding the focusing screen eating light. I can certainly tell, and appreciate, the extra brightness when I have a faster lens on when compared to a slower one, both in light conditions where a higher ISO is required to secure a reasonable shutter speed, and when in the studio working under modeling lights.
Try the exact experiment I suggested: mount an f/1.4 lens, set it to f/2, and watch the viewfinder while you do an optical DOF preview. You'll see virtually no change in DOF, and only a small change in brightness. At f/2.8, you'll still see only slight change in both. Only at apertures smaller than f/2.8 will you see DOF increasing and viewfinder darkening as expected. That's because the viewfinder is basically showing you f/2.8 or so, even with faster lenses. I'm not saying there isn't *some* difference in viewfinder brightness between f/2.8 and f/1.4, but it isn't the "four times more light" you'd expect. Nowhere the same difference as between f/2.8 and f/5.6.
11-23-2008, 11:12 PM   #41
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I wouldn't call a 60mm (equiv.) f2.8 lens "fast", either.

It's not that I gush over "ooo, I get 1.5x the focal length for the same price!"

In fact, it's quite the opposite. I could spend about $400 US on the DA Limited 21mm...only to find out that its not even as wide as my Rikenon 28mm.

"But, Lithos," I hear you say, "that's what it is! That's the angle of view a 21mm is on digital! How can you be annoyed at that?"

Ah, but you see...if this was on a 35mm camera, the 21mm would be dramatically wide. Or, if you like the FOV of a 21mm on APS-C, you could have a 31mm lens on 35mm, which could be cheaper (or in the case of the 31mm Limited, would have a faster aperture), and easier to manufacture.

I can't think of what I've gained with the cropped sensor. I can only think of what I've lost. Sorry. I can't drink the Flavor-Aid.

Not to mention the noise benefits from larger sensels, etc.

"But," someone said, "you should stop comparing the APS-C digital bodies to the 35mm bodies, just because they use the same lens mount and are about the same size..."

Au contraire, I say, that's exactly why I compare the two. We're using the same lens mount, with similar sized bodies...how hard would it be to put a 35mm sensor in the K20D's body?
11-24-2008, 12:16 AM   #42
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I consider my 31 and 40 lenses as my 50mm replacement. My 50 is a medium telephoto lens for me.

Ben
11-24-2008, 07:49 AM   #43
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QuoteOriginally posted by rparmar Quote
People talk of 50mm as normal on film, when the reality is 43mm. This number is not arbitrary, but based on the diagonal of the frame size. However, most of us are quite willing to accept a range of focal lengths as being "normal", not getting too hung up on a precise measure. Using the same logic, and given that the difference between 24mm and 28mm is distinct but not excessive, I consider both to being the "normal" range. Any wider than 24mm I'd call "wide-angle", but you'd have to get a lot wider than that to satisfy aficionados of such fields of view.
The fact that the diagonal is 43mm is not up for debate, but where is this technical definition of "normal"? I hear it bandied about and it's even shown up in photography books, but is there any real technical/engineering backing behind the claim? What makes a lens with a focal length equal to the diagonal of the film the "perfect normal"? Where's the real definition?

Do optical engineers refer to it as "perfect normal"?

Just honestly curious here since I can't find it myself...
11-24-2008, 08:54 AM   #44
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55mm focal length (physical) will provide you with the perspective of human vision at any distance or field of view.

this is why more and more i have been wanting a full frame camera and enjoy using my film camera once in awhile

this is also why i want a MF camera even more, because with a 50-55mm lens, when you bring the camera up to your eye, you get zero perspective distortion, or, magnification as one could say and a HUGE field of view, to capture the world as i see it.

if you are looking at a bottle 5 feet away, when you bring up your 55mm equiped camera (ANY camera) the bottle will still look as if it is 5 feet away.


when you start increasing the focal length (physical), when you look at that bottle through the viewfinder you will feel as if the bottle is closer to you than 5 feet


when you start decreasing the focal length, when you look through the view finder you will feel as if there is a greater distance between you and the bottle than 5 feet.


again.. ON ANY SIZED SENSOR/FILM whatever


==================

field of view, is a different beast all together.

a 5-10mm lens on a point and shoot gives you similar FIELDS OF VIEW, but it most definetly does not give you the same sense of perspective that you would have gotten otherwise. When using a point and shoot, you always feel like you are not in the shot, because even though you are standing 5 feet away from your subject, it feels like you are like 50 feet away,

you are shooting someones face on a point and shoot, who's face is more than than the size of the LCD screen, yet they fit on the LCD screen entirely, with their shoulders, and the drunken stranger to the side....



if field of view is all you care about, then none of this should matter to you

if genuine optical magnification and shrinkage is important to you, and subsequently, how you approach photography, then you will see the faults of smaller sensors.

Last edited by Gooshin; 11-24-2008 at 09:14 AM.
11-24-2008, 10:27 AM   #45
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QuoteOriginally posted by Gooshin Quote
55mm focal length (physical) will provide you with the perspective of human vision at any distance or field of view.
Well, as long as we're digressing into ongoing debates:

Focal length has nothing whatsoever to do with perspective. Perspective is a function of the position of the photographer relative to the subject and nothing else.

QuoteQuote:
if you are looking at a bottle 5 feet away, when you bring up your 55mm equiped camera (ANY camera) the bottle will still look as if it is 5 feet away.
You can put any lens on any camera and the bottle will still look as if it is 5 feet away as far as perspective is concerned: the relative sizes of the bottle compared to its surroundings, the vanishing points formed by converging parallel lines, etc - none of this changes one bit. Of course, if the size of the bottle in the viewfinder is bigger or smaller than it looks to the unaided eye, it might look closer or further away, but this is not constant with focal length: it's also a function of viewfinder size/magnification.

QuoteQuote:
if genuine optical magnification and shrinkage is important to you, and subsequently, how you approach photography, then you will see the faults of smaller sensors.
I have no idea what "genuine optical magnification and shrinkage" means, but I defy you to tell the difference between a picture taken with a P&S digital versus a mdeium format film camera if the focal lengths and apertures are set to create the same field FOV and DOF.
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