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01-17-2021, 05:53 AM   #1
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Wondering what happens ...

Wondering what happens if you place a K 3 Lenses on a K 1 other then Making a 50 mm a true 50 mm ? Is there a real difference between a crop camera lens and a full frame lens ?

01-17-2021, 07:02 AM - 2 Likes   #2
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A 50mm lens is still a 50mm lens, but a lens designed for a crop sensor may not project an image circle large enough to fully cover that sensor e.g. vignetting in the corners/at the edges. Lenses tend to loose sharpness and have other optical issues when reaching the edge of the image circle. A lens designed for the full frame should provide reasonably good image quality to the edges. Regarding field of view, the crop sensor is covering a smaller area, which in simple terms will result in what is often described like a magnification of 1.5x, so your 50mm on a crop sensor will be like 75mm on full frame for the amount of area you see in the final image.

Last edited by clickclick; 01-17-2021 at 09:05 AM.
01-17-2021, 08:32 AM   #3
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QuoteOriginally posted by Richard B 13 Quote
Wondering what happens if you place a K 3 Lenses on a K 1 other then Making a 50 mm a true 50 mm ? Is there a real difference between a crop camera lens and a full frame lens ?
That depends greatly on the lens, focus distance, aperture, etc.

First the lenses focal length never changes. The angle of view is what gives the illusion of change. Imagine you had a scene in from of you, then you saw the same scene from the same spot but a wall with a large window was put between you and the scene. Your view would be truncated to a narrower angle. This is what happens to a full frame lens on crop. The reverse situation results in potentially black corners where the crop lens fails to have a wide enough image circle to fully cover the sensor.

Hereís a practical guide to how many lenses that are Crop by name/design work on a full frame: Full Frame Coverage of DA Lenses: Comprehensive Test - Gear Guides | PentaxForums.com
01-17-2021, 09:04 AM   #4
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Another thing you would see is less dof on the k1 at the same aperture

01-17-2021, 09:12 AM - 2 Likes   #5
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QuoteOriginally posted by Sidney Porter Quote
Another thing you would see is less dof on the k1 at the same aperture
This is a tricky one. Effective DOF might be a way to think of it. The DOF for a given aperture and focal length and distance to the subject will be the same regardless of format, but to have the same field of view (framing), you'll have to change the camera position, which is going to then impact your depth of field, since the distance to the subject and focus is now different.
01-17-2021, 09:37 AM - 1 Like   #6
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The only real difference is the image circle with the lens projects on the sensor. FF lenses make a larger circle or have to hold up edge quality further out. Thatís why there are often larger lenses.
The other way around: if you have a FF lens and swap out the FF body for a crop body (and leave everything else the same), the only difference will be that you just get the centre crop of the image. Everything else will be exactly the same.

Logic: a crop camera just records a smaller area of the image that comes through the lens.
01-17-2021, 10:09 AM - 1 Like   #7
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QuoteOriginally posted by clickclick Quote
This is a tricky one. Effective DOF might be a way to think of it. The DOF for a given aperture and focal length and distance to the subject will be the same regardless of format, but to have the same field of view (framing), you'll have to change the camera position, which is going to then impact your depth of field, since the distance to the subject and focus is now different.
thanks for adding that clarity
01-17-2021, 10:35 AM - 2 Likes   #8
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QuoteOriginally posted by clickclick Quote
This is a tricky one. Effective DOF might be a way to think of it. The DOF for a given aperture and focal length and distance to the subject will be the same regardless of format, but to have the same field of view (framing), you'll have to change the camera position, which is going to then impact your depth of field, since the distance to the subject and focus is now different.
Yes and changing your camera to subject distance is going to have change other aspects too. Perspective distortion changes too. The closer you are to your subject the more distorted the features such as nose are going to appear. Lens compression will also be affected so the closer you are to a subject the more the background will appear to move away from them.

When producing a print or viewing an image in full-screen, the crop format will have to be "enlarged" more, also reducing apparent DOF.

The best thing to do is ignore crop versus full frame comparisons and get used to the equipment you own.

01-17-2021, 11:42 AM   #9
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QuoteOriginally posted by Richard B 13 Quote
Wondering what happens if you place a K 3 Lenses on a K 1 other then Making a 50 mm a true 50 mm ? Is there a real difference between a crop camera lens and a full frame lens ?
K 3 Lens ???

do you mean a lens developed for the ASP-C sensor

you may want to look at this article

QuoteQuote:
Full Frame Coverage of DA Lenses: Comprehensive Test
Which DA lenses cover the full 24x36 mm frame?
By PF Staff in Gear Guides on Jan 7, 2019
Read more at: Full Frame Coverage of DA Lenses: Comprehensive Test - Gear Guides | PentaxForums.com
01-17-2021, 01:54 PM - 2 Likes   #10
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this is not an expert test or presentation, the photos are from hand and taken by accident when writing this text, there is a small frame shift because the camera is not static on a tripod, thanks for understanding,

settings on K1 (FF photo body) with F50 / 1.7 (FF lens) for both FF and APSC format are the same:

aperture: f1,7
shutter: 1/80
ISO: 100
lens: Pentax F 50/1,7
camera: Pentax K1


here I just tried on K1 + F50 / 1.7,
in the 1st case it is in FF mode
in the 2nd case it is in APSC (cropped) mode,
in the 3rd case it is in FF but truncated in PS to APSC mode

1.


2..


3.


at first it seems that the differences with the same lens on the APSC and the cropped FF mode do not exist, they do exist-in the last two photos pay attention to the background, you can see the difference in perspective, to get the same photo in the last image in APSC mode I had to move approx. 2 meters backwards so that the whole car would be in the frame as in FF mode
,at greater distances than this example of mine this difference in perspective is very noticeable, a direct difference with the same FF lenses on an FF camera or APSC camera with the same settings and the same focus point / same distance from the frame is obvious

one example FF with settings:
aperture: f4,5
shutter: 1/80
ISO: 100
lens: Pentax FA 80-320/4,5-5,6
in 35mm: 110mm
camera: Pentax K1



one example of APSC with settings:
aperture: f4,5
shutter: 1/80
ISO: 100
lens: Pentax FA 80-320/4,5-5,6
in 35mm: 110mm
camera: Pentax K1



a little more theory:

pictorial representation of the size of the sensors and their displays



an obvious difference in perspective on different formats with the same lens with respect to the crop factor and the same settings




I switched from APSC format to FF primarily because I really like the perspective provided by FF, ie I prefer DOF (depth of field) provided by FF system than APSC system (FF also has better iso / better dynamic range), but that is just my personal commitment in the desires I want to have with my photo equipment, those who always want high depth of field / large part of the frame or always the whole frame in focus and a very large focusing range with smaller size and overall lower weight will choose the APSC format
or some other smaller eg MFT m4 / 3 format

Last edited by mbukal; 01-17-2021 at 04:23 PM.
01-18-2021, 01:32 PM   #11
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These are good illustrations. They also show why many of us have both FF and APS-C, to get the wanted effects depending on subject matter and circumstances, as well as practical considerations. For me, if I had to choose one, it would be APS-C as I find it can provide the best compromise for all-around versatility. Quality differences have become much narrower these days.

---------- Post added 01-18-21 at 01:45 PM ----------

QuoteOriginally posted by Richard B 13 Quote
Wondering what happens if you place a K 3 Lenses on a K 1 other then Making a 50 mm a true 50 mm ? Is there a real difference between a crop camera lens and a full frame lens ?
As others have said, the main difference is the viewing angle or field of view (FOV).

In your statement here, however, regarding a "K-3" 50mm lens, meaning one designed for the K-3's APS-C size sensor, it would be unwise to mount this lens (the DA 50mm f/1.8) on a K-1, as the glass elements are sized and cut to match up with the smaller APS-C sensor. Therefore, coverage would be lacking for the larger FF sensor of the K-1, resulting in substantial darkening around the edges of images. But if using a 50mm lens designed for use with a FF camera like a 35mm film body or a FF DSLR like the K-1, it will be a bit larger than the DA 50mm yet fully usable on your K-3. Its elements being cut larger for FF use would not matter, as the outer edges are simply unused.

Last edited by mikesbike; 01-18-2021 at 01:48 PM.
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