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12-14-2014, 12:07 PM   #1
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K30 question about "crop sensor" and 1.5x crop

First of all I am a noob. I got my camera 2 years ago.

I got a 35mm fantastic plastic lens.

I'm thinking about getting the 50mm plastic fantastic lens.

I know with the K30 it's got the 1.5x crop from the sensor not being full frame. So... does that mean... my 35mm lens acts more like a 52.5mm lens? And will the 50mm lens act more like a 75mm?

I'm a little confused about how 1.5x crop sensor affects my focal lengths. So does this mean my 35mm lens is actually better for portrait photography for my K30?

12-14-2014, 12:16 PM   #2
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It is correct but, since pentax doesn't have a full frame, you don't need to worry about conversion.
12-14-2014, 12:19 PM   #3
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Yes, that is how they act. If you are looking at old film photos and the caption says 50mm the view is really. Close to the view you see with your 35/2.4.
12-14-2014, 12:24 PM   #4
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QuoteOriginally posted by flaviopetrone Quote
It is correct but, since pentax doesn't have a full frame, you don't need to worry about conversion.
Film cameras are full frame. :-)

"Crop factor" does not affect focal length only angle of view. :-)

Ronnie

12-14-2014, 12:27 PM   #5
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QuoteOriginally posted by ronnies Quote
Film cameras are full frame. :-)

Ronnie
That's true!
I was talking about digital cameras only.
12-14-2014, 12:27 PM   #6
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A 35mm lens is always going to be a 35mm lens. Same thing for a 50mm or any other focal length. Its not the lens, its the camera - or rather the sensor, and the view it is able to capture. If the lens puts an image on a 8 1/2 x 11 sheet of paper, and then you slide a 3x5 index card in its place, the index card is going to capture less of the image. It is going to capture the view of what a longer lens would have captured. Same thing here. No need to worry about the crop factor.

12-14-2014, 12:36 PM   #7
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QuoteOriginally posted by mellowyeahlow Quote
I know with the K30 it's got the 1.5x crop from the sensor not being full frame. So... does that mean... my 35mm lens acts more like a 52.5mm lens? And will the 50mm lens act more like a 75mm? I'm a little confused about how 1.5x crop sensor affects my focal lengths. So does this mean my 35mm lens is actually better for portrait photography for my K30?
Unless you regularly shoot with a FF camera or have extensive and residual experience with 35mm film cameras it is really best to just ignore the whole "crop sensor" thing. If all you have used is the k-30 then a 35mm looks like a 35mm lens, and a 50mm lens looks like a 50mm lens. If you put your lens on a FF camera the view will look strange because you are not used to that angle of view.

The only time I find the crop sensor conversion thing to be of any use to me is when I read an old book or get told to use a "portrait" focal length that is a hold over from film days. With FF "portrait" was roughly 85mm, so on your camera that would be 55mm. In practice anything from 50 to 105mm can and has been used for portraits. Portraits being roughly defined, since full body would not be the same as a head shot. So 50mm on your k-30 would be a good portrait length.
12-14-2014, 12:45 PM   #8
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QuoteOriginally posted by mellowyeahlow Quote
*snip*

I'm a little confused about how 1.5x crop sensor affects my focal lengths. So does this mean my 35mm lens is actually better for portrait photography for my K30?
Welcome to the wonderful world of equivalence and related threads!
It's quite a complicated matter... especially if you consider DoF, sensor size, print size etc.

You can find quite a wealth of information on this topic on the internet, but actually a large part of it is indeed misinformation...
I'd suggest the article on equivalence on Dpreview as a starting point... just ignore the comment section...

12-14-2014, 12:56 PM   #9
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QuoteOriginally posted by mellowyeahlow Quote
First of all I am a noob. I got my camera 2 years ago.

I got a 35mm fantastic plastic lens.

I'm thinking about getting the 50mm plastic fantastic lens.

I know with the K30 it's got the 1.5x crop from the sensor not being full frame. So... does that mean... my 35mm lens acts more like a 52.5mm lens? And will the 50mm lens act more like a 75mm?

I'm a little confused about how 1.5x crop sensor affects my focal lengths. So does this mean my 35mm lens is actually better for portrait photography for my K30?

This thread is going to get long... but here goes.

Focal length is the focal length. It is the measure of how many mm it is from your sensor to the front element. That does not change regardless of sensor size.

Each lens projects a circle of light into the camera. Light enters the front and exits the back...in circular shape.

A full frame captures a physically larger area of that circle of light and a crop sensor captures physically less area of that circle.

You do not gain or lose zoom with a crop sensor. What does change is your FIELD OF VIEW or ANGLE of VIEW.

When you look through the view finder the same lens will show either more or less of the scene you are shooting based on sensor size. With a crop sensor camera it 'crops' the image before it is ever recorded in the camera.

In order to compensate for this people use different lens focal lengths to get to what is considered 'standard' field of views. So a 35mm lens on a 1.5 crop sensor will show you a scene equivalent to a 52.5mm lens when compared to the "standard size" sensor.

So in short with one lens on two bodies... you will have two different angles of view. The only difference is in what you are seeing around the edges of the frame.

Why 35mm sensors are considered standard I don't know. I guess it's just history because that's the size of a standard 35mm film slide.
12-14-2014, 01:01 PM   #10
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Hmmm... that brings me another question then.
Angle of views..... alter how a subject looks. Which is the reason why people say 50mm is the ideal for portrait shots.
So... does this mean.... if I slap on a 35mm on my K30... it would give me the ideal angle of view for portraits?

Sorry guys. I didn't realize what a loaded question this would be lol.
12-14-2014, 01:01 PM   #11
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To be technical, the focal length does not change - the edges just get cut off! This means the field of view of the final photo is different. Focal length is a property of the lens, and is independent of the camera that you put the lens on.
Crop sensor is basically like taking a film photo and cutting off a part of the edges.
One more thing that is often confusing - focal length is a lens property. This means that 35mm made for film, or 35mm made for crop sensor, will give you the same field of view on a crop sensor camera. Which will be similar to a 52mm on a film camera.
But ignore equivalence. It is only important if you already know exactly what 35mm or 50mm looks like on film cameras, and then you want to imagine what 35mm looks like on crop sensor. If you start out on crop sensor, you can just ignore the whole issue.

What you really need to know is that 35mm is not very wide angle on crop sensor cameras. It is "normal". Above 35mm is telephoto, and wider is wide angle. On 35mm film/full frame, 35mm is already wide angle, and 50mm is normal (and above 50mm is telephoto)

QuoteOriginally posted by mellowyeahlow Quote
Angle of views..... alter how a subject looks. Which is the reason why people say 50mm is the ideal for portrait shots. So... does this mean.... if I slap on a 35mm on my K30... it would give me the ideal angle of view for portraits?
Mmh, I wouldn't quite agree with that. I assume we are talking about face only portraits, closeups where maybe the shoulders can be seen, but not much more of the body. For such photos, 35mm is way too wide on film, but it is too wide on crop as well. 50mm is barely okay for portraits on full frame (usually 85mm-135mm is portraiture focal length on film), but it is much more acceptable on crop sensor (on crop sensor, 55mm-85mm is for portraits. DA* 55mm f1.4 is practically made for portraiture, great lens but pricy). The reason for this are minimal focus distance, aperture, distortion, and the perspective when you fill the frame with a person. DA 35mm f2.4 for example, on Pentax crop sensor cameras, will make a face look a little rounder. But it is okay for full body photos, or group photos. Some people use it for portraits, but its not my first choice. DA 50mm f1.8 is much better for that purpose, because it has different field of view, focal length, and aperture. If you want perfection, you want to look at even more telephoto, with fast aperture. And a tripod, lights, makeup artists, etc. This is why photography gets pricy!

Last edited by Na Horuk; 12-14-2014 at 01:09 PM.
12-14-2014, 01:22 PM   #12
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QuoteOriginally posted by mellowyeahlow Quote
Hmmm... that brings me another question then.
Angle of views..... alter how a subject looks. Which is the reason why people say 50mm is the ideal for portrait shots.
So... does this mean.... if I slap on a 35mm on my K30... it would give me the ideal angle of view for portraits?

Sorry guys. I didn't realize what a loaded question this would be lol.
Distance from subject alters perspective
That's why close-up portraits taken from a cellphone look terrible (long noses, "alien" faces etc.), because you are forced to take them very near your subject in order to be able to fill the frame with the face.

You could take a perfectly fine portrait with a rectilinear 24mm from the distance a 50mm would fill the frame, and then crop.
You'll lose a bootload of pixels thus IQ (that's why you generally use a 50-100mm for portraits), but the proportions of the face would be the same.
12-14-2014, 01:41 PM   #13
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QuoteOriginally posted by jatrax Quote
Unless you regularly shoot with a FF camera or have extensive and residual experience with 35mm film cameras it is really best to just ignore the whole "crop sensor" thing.
Exactly.
12-14-2014, 01:44 PM   #14
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Confusing?A 50mm is a 50mm,some of the edges of the photo are cropped off by the smaller sensor.It is the angle of the lens that most effects perspective,wide angle lenses have more distortion so they don't make good portrait lenses not the distance from the subject.The physical properties of the lens don't change with distance from the subject it just magnifies them.A 50mm can be a good portrait lens but most prefer the 70-85mm range for less distortion,more working distance from the subject,and shallow depth of field.
12-14-2014, 01:52 PM   #15
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QuoteOriginally posted by bschriver11 Quote
Confusing?A 50mm is a 50mm,some of the edges of the photo are cropped off by the smaller sensor.
Correct.

QuoteOriginally posted by bschriver11 Quote
It is the angle of the lens that most effects perspective,wide angle lenses have more distortion so they don't make good portrait lenses not the distance from the subject.
I'm afraid that's wrong. If you trace perspective lines from the P.o.V. to the subject, they will have different angles depending on the distance of the observer.
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