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09-03-2011, 03:38 PM   #1
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Had some time one my hands, so..........

I got to playing around with my film camera and K-x, I just wanted to figure out what everyone was talking about when it comes to a "cropped" sensor. I took my M 50mm 1:1.4 lens (my favorite after all these years) and put it on my ME Super and looked through the view finder aimed at one spot, I then put the same lens on my K-x and looked at the same spot.
WOW! NOW I UNDERSTAND!
I know this subject may be redundant but now I know how to explain to others who ask me what I mean by "cropped" sensor, on the ME Super it was more wide angle compared to my K-x. On my K-x it seemed like it was a 75mm lens which to me would probably be good for portrait work, I don't have any money and won't have any money for a while to go out and invest in one of those fancy fast 80mm primes so..........I am thinking maybe, just maybe this lens will fill that niche until I can afford one.
Whadya all think on that? this 50mm is one that I have had over the last thirty years and has taken many nice shots and Iearned all I know from this little lens, it is in near mint condition and I can take some awesome shots with it if I put my mind to it.
Thanks for any input.

09-03-2011, 06:03 PM   #2
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Most all 50mm lenses are quite capable as optics go - so many people made them so all that practice paid off
And yes, for portraiture it's close enough to the good-old-days 80-100mm range, plenty of nice background blur even at f/4 or so. You'll find plenty of uses for it!
09-03-2011, 06:28 PM   #3
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My poor attempts at portraiture. The lens was the A50/1.4, a couple were with the A28/2.8.

Mar 13, 2011 - a set on Flickr

Jul 10, 2011 - a set on Flickr
09-03-2011, 08:00 PM   #4
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Yes, a 50/1.4 on an APS-C cam like your Kr, is roughly like a 75/2 on a 135/FF cam like your ME Super. When you get a fancy 85/2 later, on APS-C it will be roughly like a 135/2.8 on your ME. These focal lengths and apertures are fine for much portraiture. And IMHO 50/1.4 is much more interesting on an APS-C dSLR than on a 135/FF SLR. That's probably one reason I have 50 Fifty's. (Plus, they're cheap, and great, and cheap.)

The crop-sensor effect is pretty pronounced, eh? My first sub-mini camera was an Olympus Pen-FT half-frame (135/HF) SLR, whose viewfinder was vertical (portrait mode), not horizontal (landscape mode) we're used to. It was like using a full-frame SLR whose frame had been CHOPPED IN HALF!! Turn your Kr on its side and that's exactly what you see through its VF.

09-03-2011, 08:54 PM   #5
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QuoteOriginally posted by BirdDude007 Quote
I got to playing around with my film camera and K-x, I just wanted to figure out what everyone was talking about when it comes to a "cropped" sensor. I took my M 50mm 1:1.4 lens (my favorite after all these years) and put it on my ME Super and looked through the view finder aimed at one spot, I then put the same lens on my K-x and looked at the same spot.
WOW! NOW I UNDERSTAND!
I know this subject may be redundant but now I know how to explain to others who ask me what I mean by "cropped" sensor, on the ME Super it was more wide angle compared to my K-x. On my K-x it seemed like it was a 75mm lens which to me would probably be good for portrait work...
Did you also notice that there wasn't any magnification? The field of view changed, but you got no added magnification by putting the 50 on the K-r.
09-03-2011, 10:41 PM   #6
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QuoteOriginally posted by RioRico Quote
a 50/1.4 on an APS-C cam like your Kr, is roughly like a 75/2 on a 135/FF cam like your ME Super
But the lens will still transmit the same amount of light as a f/1.4 lens will - meaning the shutter speeds will be the same whether you are on 35mm or Digital APS-C format. The smaller format on the digital cameras gives a slight increase to DOF, and larger formats assuming all things remain equal tend to diminish it.
09-03-2011, 10:51 PM   #7
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QuoteOriginally posted by Digitalis Quote
But the lens will still transmit the same amount of light as a f/1.4 lens will - meaning the shutter speeds will be the same whether you are on 35mm or Digital APS-C format. The smaller format on the digital cameras gives a slight increase to DOF, and larger formats assuming all things remain equal tend to diminish it.
Yes, I should have qualified the statement -- it refers to DOF and FOV, nor exposure.
09-04-2011, 01:58 AM   #8
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QuoteOriginally posted by RioRico Quote
Yes, I should have qualified the statement -- it refers to DOF and FOV, nor exposure.
It pays to be careful, there have been quite a few misinformed users on the forums that-shall-not-be-named that have said that a full frame sensor by virtue of its greater area receives more light from the lens and smaller APS-C sensors that have a smaller area receive less light. Which is weapons grade BS - the intensity of light falling on the sensor is governed by one thing - the size of the aperture* an f/2.8 lens is always f/2.8

*barring any flaws in light transmission or changes in the flange distance between the sensor/film and the optical centre of the lens.


Last edited by Digitalis; 09-04-2011 at 02:18 AM.
09-04-2011, 02:17 AM   #9
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It is very wrong to say that a 50mm lens on a cropped sensor becomes a 75mm lens. The lens does not transform optically just because you put it on another camera. ONLY thing that changes are that the edges are cropped. It means that sensor will receive the same amount of light and aperture will remain the same and there is no change in DOF. You can't even say the FOV becomes narrower in degrees, because perspective remains the same. So the only thing that changes is that you lose edges, the lens does not change optically.
09-04-2011, 02:31 AM   #10
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QuoteOriginally posted by Jüri Quote
ONLY thing that changes are that the edges are cropped.
there isn't any cropping going on here - cropping is what a photographer does to a photograph after it is taken. APS-C is is simply a different format, to use the term "cropping" is misleading.

QuoteOriginally posted by Jüri Quote
It means that sensor will receive the same amount of light and aperture will remain the same and there is no change in DOF.
you are right about the exposure part, a 50mm f/1.7 lens will behave identically for all 35mm pentax cameras. But bear in mind at a focus distance of 1m using a 50mm lens on 35mm camera to obtain the same framing with the same lens on APS-C, you will have to stand 1.5X further away from your subject and it is a known fact that the longer the focus distance gets, the deeper DOF will become.
09-04-2011, 04:22 AM   #11
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QuoteOriginally posted by Digitalis Quote
there isn't any cropping going on here - cropping is what a photographer does to a photograph after it is taken. APS-C is is simply a different format, to use the term "cropping" is misleading.



you are right about the exposure part, a 50mm f/1.7 lens will behave identically for all 35mm pentax cameras. But bear in mind at a focus distance of 1m using a 50mm lens on 35mm camera to obtain the same framing with the same lens on APS-C, you will have to stand 1.5X further away from your subject and it is a known fact that the longer the focus distance gets, the deeper DOF will become.
I think it depends on how you look at it. I prefer to look at the "crop factor" like this: full frame lens always projects exactly the same image, but APS-C sensor only uses the centre part of it, thus "cropping" the rest. Of course you may consider that the photographer frames the scence differently on different cameras, but it just makes it more difficult to understand.

So to answer the inquiry of original poster, full frame 50mm lens does not replace a 75mm APS-C lens one to one. When both are compared on a Pentax dSLR, the latter will give narrower prespective. I'm not sure about DOF, because the longer focal length, the narrower the DOF is, but on the other hand lenses designed to project smaller images also have smaller lens elements, so less out of focus blur.
09-04-2011, 04:47 AM   #12
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QuoteOriginally posted by RioRico Quote
Yes, a 50/1.4 on an APS-C cam like your Kr, is roughly like a 75/2 on a 135/FF cam like your ME Super. When you get a fancy 85/2 later, on APS-C it will be roughly like a 135/2.8 on your ME. These focal lengths and apertures are fine for much portraiture. And IMHO 50/1.4 is much more interesting on an APS-C dSLR than on a 135/FF SLR. That's probably one reason I have 50 Fifty's. (Plus, they're cheap, and great, and cheap.)

The crop-sensor effect is pretty pronounced, eh? My first sub-mini camera was an Olympus Pen-FT half-frame (135/HF) SLR, whose viewfinder was vertical (portrait mode), not horizontal (landscape mode) we're used to. It was like using a full-frame SLR whose frame had been CHOPPED IN HALF!! Turn your Kr on its side and that's exactly what you see through its VF.
I understand what you are saying, but I was only playing with an old full frame lens and I got the opposite effect, on the K-x it had about 1/3 more reach ie-aprox 75mm(about 25mm more) over the full frame camera, I really noticed the difference using a full frame zoom - on the ME it was 70~210, but on the KX it was more like100~300mm.
Are you talking more about the actual lenses that are made for digital cameras?, such as the kit lenses for example? I guess i have a little more research to do with my kit lenses.

Last edited by BirdDude007; 09-04-2011 at 05:55 AM.
09-04-2011, 06:01 AM   #13
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To me, all this talk of "crop factors" is a waste of time. It's just tech jargon that you don't really need to know since with an SLR, pretty much what you see is what you get. Forget about the crop factor and think more about composition and exposure. Your pics will never improve thinking about crop factors!
09-04-2011, 06:20 AM   #14
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QuoteOriginally posted by Jüri Quote

So to answer the inquiry of original poster, full frame 50mm lens does not replace a 75mm APS-C lens one to one. When both are compared on a Pentax dSLR, the latter will give narrower prespective. .
I disagree with you on this after doing a small bitof research with my kit lens, I found it actually does the exact same thing when i put it on my old film camera, the only thing differently that it does is some vignetting, that of which is expected with a lens designed for APSC sensors(there is no need to make these lenses so that they are covering a larger sensor)
This is one of the reasons I like buying lenses designed for full frame cameras, ya they take a little bit of re figuring but they are fun to use and I can use them on my old cameras and maybe one day if the planets are lined up correctly they will come out with a full frame camera (I say that crossing my fingers)

In a nutshell I noticed that no matter which lenses I try out between my cameras they all have the same effect, on the old camera they seem zoomed out, and on the digital (smaller sensor)camera they are all zoomed in 1/3rd more.
I feel that the amount of light coming through the aperture is the same on either camera but their may be some differences in the depth of field from camera to camera but that will require some further research which I will submit my findings at a later date.
Yes I do believe in the "cropped" factor because for example~ say Hypothetically I have a full frame Pentax (I WISH) and put the 50mm lense on it then I get a larger image but at 50mm, then I take a shot with it on my K-x that has a 2/3rd size sensor compared with the full frame, and upload the identical images in to photoshop layers next to each other, you will see the "crop" example I am talking about, the smaller sensor image will basically look like it was just a crop out of the full frame image.
With digital imaging these days I am impressed at the difference between digital and film.
On the other hand you can also figure in the resolution factor, it makes sense to me that a 12 megapixel APSC sensor has the same resolution as an 18 megapixel full frame sensor, Resolution is respective to physical size of the sensors. So in closing I would say that an actual 2/3rds crop from an 18 MP full frame image would actually produce the same size image as if it was taken with a 12 MP APSC sensor.
Am I wrong here? Thoughts.......Anybody?
09-04-2011, 06:28 AM   #15
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QuoteOriginally posted by billtin59 Quote
To me, all this talk of "crop factors" is a waste of time. It's just tech jargon that you don't really need to know since with an SLR, pretty much what you see is what you get. Forget about the crop factor and think more about composition and exposure. Your pics will never improve thinking about crop factors!
Ya I am with you on that, but I was just actually thinking about it and wanted to investigate and see just what it is all about and basically for fun and for a learning experience, things like this intrigue me. As for general all around shooting I really don't think about things like this, it's all about getting the shot when it comes down to it, and an all reality there is no need to worry about crop factor.
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