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04-24-2014, 06:37 AM   #16
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Compression - Is the compression on a 50mm the same on an APS-C sensor as it is on a full frame sensor? Or, is it closer to what a 75mm lens would give you on a full frame? From the above, I believe the compression is the same regardless of the size of the sensor. Did I get that right?

04-24-2014, 08:06 AM   #17
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QuoteOriginally posted by Lowell Goudge Quote
It is all about understanding your format, not playing with little calculators
And that, ladies and gentlemen, is the quote of the month! Can we have a big round of applause for Lowell!!!




Steve

---------- Post added 04-24-14 at 08:11 AM ----------

QuoteOriginally posted by Spodeworld Quote
Compression - Is the compression on a 50mm the same on an APS-C sensor as it is on a full frame sensor? Or, is it closer to what a 75mm lens would give you on a full frame? From the above, I believe the compression is the same regardless of the size of the sensor. Did I get that right?
There is no such thing as "compression". The so-called tele-compression is simply perspective born of being further away from the subject. You can do the same thing by simply cropping an image from a wide angle lens. I have a set of comparison images somewhere (posted on this site about six years ago) that I will have to link to.

In case you are wondering, perspective* is the key to many, many things in photography.


Steve

* That being the position of the camera relative to the subject. There is no substitute for perspective and it can't be faked.
04-24-2014, 09:38 AM   #18
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Maybe I didn't ask correctly, or maybe I did and just don't realize that you answered my question. I've heard that using a 50mm on a full frame for an up close portrait tends to distort the nose and ears, not as bad a wider lens, but this is why I often hear recommendations to use a 85mm or more on a FF to avoid that. Is this distortion the same if the 50mm is used on a crop sensor? That is, is the distortion of the nose and ears would be the same for a 50mm on either a FF or crop sensor?

Thanks
04-24-2014, 09:48 AM   #19
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QuoteOriginally posted by Spodeworld Quote
Maybe I didn't ask correctly, or maybe I did and just don't realize that you answered my question. I've heard that using a 50mm on a full frame for an up close portrait tends to distort the nose and ears, not as bad a wider lens, but this is why I often hear recommendations to use a 85mm or more on a FF to avoid that. Is this distortion the same if the 50mm is used on a crop sensor? That is, is the distortion of the nose and ears would be the same for a 50mm on either a FF or crop sensor?

Thanks
I like 70mm on 24x17 and 85-105mm on 36x24. Being too close to your subject is what distorts the way the face looks. As long as you're far enough away a 50 should be fine, but you'll get a lot of the environment. If you get up close and personal with a 35mm you're going to have issues with either format. Better just go hog wild and use your 10mm fisheye so it looks campy.

04-24-2014, 09:48 AM   #20
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QuoteOriginally posted by Spodeworld Quote
I've heard that using a 50mm on a full frame for an up close portrait tends to distort the nose and ears,
Volumetric distortion ("duck face") is also simply perspective. It is not a factor of focal length per se.* It is what happens when you are close to the subject. Perspective (working distance) is everything. A 50mm lens on APS-C allows a working distance equivalent to 75mm on 35mm FF. As such the facial features will have the same relative sizes and locations. A portrait taken with the FA 77/1.8 (an accepted portrait lens at the time it debuted) on 35mm film will be fully equivalent to a photo taken from the same position with a Pentax DA 50/1.8 on APS-C.


Steve

* Many (most? all?) rectilinear wide angles suffer from a stretching of objects at the margins of the field of view. This is not the familiar wide-angle "duck face". That is an unfortunate side effect of providing straight lines and is not generally a problem with lenses longer than about 28mm.
04-24-2014, 10:01 AM   #21
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I've been trying to understand this for years and it still confuses me. The general rule seems to be that as the area of the sensor is halved, the depth of field is increased by one stop (and the effective aperture is reduced by one). I, however, thought this was a consequence of equivalent focal lengths, so that a true 50mm lens has the exact same depth of field on either full frame or crop, it is only the distance from the subject to create the same field of view that changes it. Is this not the case?
04-24-2014, 10:20 AM   #22
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OK. So it looks like the answer is the distortion would be the same, it's just that impact is lessened due to the greater working distance.
04-24-2014, 10:29 AM   #23
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QuoteOriginally posted by Spodeworld Quote
Maybe I didn't ask correctly, or maybe I did and just don't realize that you answered my question. I've heard that using a 50mm on a full frame for an up close portrait tends to distort the nose and ears, not as bad a wider lens, but this is why I often hear recommendations to use a 85mm or more on a FF to avoid that. Is this distortion the same if the 50mm is used on a crop sensor? That is, is the distortion of the nose and ears would be the same for a 50mm on either a FF or crop sensor?

Thanks
It is not compression or any other thing.

Go to my post. It is all about the relative magnification of different parts of the scene as a function of distance from the camera. A nose gets bigger, relative to the remainder of the face with a short lens, because magnification is the ratio if distance to focal length, and with a short focal length, and close up, the difference in distance between your nose and upper lip, for example, is significant with respect to the magnification of those two parts of your face.

04-24-2014, 10:31 AM   #24
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All sensor DOF arguments need to be prefaced with "to get the same field of view" to make any sense.
People are getting confused in assuming that the smaller sensor magically changes the depth of field with everything else remaining constant.

With everything else but sensor size equal, the image from an APSC sensor will simply be a crop of the identical FF image.
This assumes equal sensor density so the FF would have a 1.5x larger MP count (24mp APSC compared to 36mp FF for example) as otherwise stretching the same amount of pixels over the much larger sensor would lead to the image changing quality wise.

It would personally be well worth it to me to get that significant extra FOV at the same magnification (and larger viewfinder that comes with it).

EDIT: As far as portrait lenses go you can add the same "to get the same field of view" line for it to make sense. To get the same field of view with an 85mm as with a 50mm you stand back farther, and from that perspective change the near and far objects blend together more so the persons features don't stick out as much and appear to have more uniform focus.

Last edited by PPPPPP42; 04-24-2014 at 10:36 AM.
04-24-2014, 10:36 AM   #25
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QuoteOriginally posted by PPPPPP42 Quote
All sensor DOF arguments need to be prefaced with "to get the same field of view" to make any sense.
People are getting confused in assuming that the smaller sensor magically changes the depth of field with everything else remaining constant.

With everything else but sensor size equal, the image from an APSC sensor will simply be a crop of the identical FF image.
+1

For an equivalent field of view, an APS-C crop sensor camera has at least 1.5x MORE depth of field that a 35mm full frame camera would have - when the focus distance is significantly less then the hyperfocal distance (but the 35mm format needs a lens with 1.5x the focal length to give the same view).

Using the same lens on an APS-C crop sensor camera and a 35mm full frame body, the a APS-C crop sensor camera image has 1.5x LESS depth of field than the 35mm image would have (but they would be different images of course since the field of view would be different)

If you use the same lens on a APS-C crop sensor camera and a 35mm full frame body and crop the full frame 35mm image to give the same view as the APS-C crop image, the depth of field is IDENTICAL

If you use the same lens on a APS-C crop sensor camera and a 35mm full frame body, then shoot from different distances so that the view is the same, the APS-C crop sensor camera image will have 1.5x MORE DOF then the full frame image.

Close to the hyperfocal distance, the APS-C crop sensor camera has a much more than 1.5x the DOF of a 35mm full frame camera. The hyperfocal distance of a APS-C crop sensor camera is 1.5x less than that of a 35mm full frame camera when used with a lens giving the same field of view.
04-24-2014, 12:52 PM   #26
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Depth of field difference between FF & APSC

DOF calculators are invaluable for determining foreground and background focus, especially on complex shots with objects at multiple depths.

Of course to understand DOF properly one must understand FOV. That is the key advice to take away here.

If you've ever stuck your head under a large format view camera cloth and tried to focus, you'd understand. The best workaround is to buy a Ricoh GR, set snap focus to 3 metres and set aperture and shutter speed appropriately, and then always stand 3 metres from your subject.

See? Problem solved.
04-24-2014, 05:37 PM   #27
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QuoteOriginally posted by Spodeworld Quote
OK. So it looks like the answer is the distortion would be the same, it's just that impact is lessened due to the greater working distance.
You will not get unnatural looking facial features with a 50mm lens unless it is a 50mm macro lens and you are using it to look up somebody's nose. That might appear unnatural.


Steve

---------- Post added 04-24-14 at 05:43 PM ----------

QuoteOriginally posted by Aristophanes Quote
If you've ever stuck your head under a large format view camera cloth and tried to focus, you'd understand.
Absolutely. Work with a view camera for even a few minutes and be prepared for an epiphany.


Steve

---------- Post added 04-24-14 at 05:46 PM ----------

QuoteOriginally posted by jsherman999 Quote
If you use the same lens on a APS-C crop sensor camera and a 35mm full frame body and crop the full frame 35mm image to give the same view as the APS-C crop image, the depth of field is IDENTICAL
Now you've done it. I do need to find the photos where I did exactly that.


Steve
04-25-2014, 08:54 AM   #28
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There's no difference in DOF. A 50mm on an APS-C, on a FF or a medium format camera will produce exactly the same DOF IF and only IF all images were shot at the same distance and f/stop.
The DOF apps don't do this when you switch from one format to another. They are a bit deceiving because they adjust the distance required to maintain the same crop as you change from one sensor size to another. So since DOF is a product of focus distance, f/stop and focal length, AND the DOF apps are changing the focusing distance in their calculations, that is how any lens can appear to have more or less DOF merely by using a camera with a smaller or larger sensor.
04-25-2014, 09:42 AM   #29
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QuoteOriginally posted by FrankC Quote
There's no difference in DOF. A 50mm on an APS-C, on a FF or a medium format camera will produce exactly the same DOF IF and only IF all images were shot at the same distance and f/stop.
The DOF apps don't do this when you switch from one format to another. They are a bit deceiving because they adjust the distance required to maintain the same crop as you change from one sensor size to another. So since DOF is a product of focus distance, f/stop and focal length, AND the DOF apps are changing the focusing distance in their calculations, that is how any lens can appear to have more or less DOF merely by using a camera with a smaller or larger sensor.
Huh? I've never seen an online DOF calculator that automatically adjusts distance to subject, it's always presented as a user-set variable or as an unchanging constant, as it has to be for the calculator to be of any worth. It doesn;t automatically change in any one I've seen.




Last edited by jsherman999; 04-25-2014 at 09:48 AM.
04-25-2014, 10:02 AM   #30
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Guys really, if your DoF is that critical, shoot with your lens wide open up to ƒ16.. at various ƒ-stops and see what you get. If you're shooting wide open and your DoF isn't narrow enough you need a wider opening lens. If you check out the wider opening lens and it doesn't give you what you want, you need a bigger format. But before you buy that expensive 1.4 lens, depending on what you're looking at, you might want to try a 24 Mp 36x24 sensor with an ƒ2 lens as opposed to an APS-c with a 1.4. As has been noted many times, if that's your preferred shooting technique, the D600 or 6D system, may save you some money.

It's not really rocket science and experimentation is worth more than any formula, because you know at the end what the pictures will actually look like. There's lots of guys on the forum who have given this an objective look and said "I need a 35x24 to get what I want." There's nothing wrong with that. But base that on an examination of your images, not some formula.

I have some great images taken on 35mm film that I don't think I could duplicate on APS_c, I just don't get a chance to take that type of image much anymore.

Just my 2 cents worth.
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