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01-11-2013, 06:58 AM   #1
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Portrait lenses... does Crop Factor matter?

The reason I ask this is that I've seen that 85-90mm is a great target range for portrait lenses... even back before digital, this was the way to go.

Then I've seen that you should never ever do a closeup with a 50mm lens because of the distortion to the subject.

However, with APS-C's 1.5x crop factor, a 50mm is a 75mm (not too far off from 85-90).

Likewise, my Rokinon 85mm is actually a 127.5mm, well past the target range. But it and other 85mm lenses are considered the bee's knees for portraits (and they do look good). My DA*55mm is closest at 82.5mm as well.

So while reading an article about how the crop factor works (essentially capturing the center of the incoming image onto the sensor, thus effectively magnifying it optically vs. digitally) it started me wondering if the 1.5x crop factor should be well, "factored" in when deciding which lens to use, or does the effective 35mm focal length matter in this scenarios?

Since all the "ancient wisdom" still says grab an ~85mm for portraits does that apply no matter what the crop factor?

01-11-2013, 07:24 AM   #2
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QuoteOriginally posted by klkitchens Quote
Then I've seen that you should never ever do a closeup with a 50mm lens because of the distortion to the subject.
The question is, how close are you to the subject to get the framing you want? Perspective distortion becomes noticeable when you get too close. So, yes, this is a case where "crop factor" really does need to be taken into account. The classic FLs for portraiture range from 85 to 135 -- on full 135 format. That translates to about 55 to 90 on our Pentax DSLRs. So your 85 is still in that range, suitable for tightly-framed closeups. Of course you need not restrict yourself to those FLs. Sometimes perspective distortion can be used to good effect. And longer FLs have their own look, too, and can really help dealing with busy backgrounds.
01-11-2013, 07:49 AM   #3
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You still get distortion with a 50mm lens if you plan the shot poorly. All the "crop factor" is doing is using the center of the lens, which is still 50mm. It is better to use longer lenses for great portraits, but the working distance can become a problem. If you have the room, do use as long of a lens as you can. However, with a little planning, you should be able to take great pictures with a 50mm lens. For example, make sure all body parts are on the same plane - don't angle the person you are taking a picture of. No protruding arms, etc. I find noses aren't a problem at 50mm.
01-11-2013, 07:52 AM   #4
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Working distance matters, due to crop factor. A 50mm lens on FF at 6 feet may show distortion, but on APSC you have to step back a few feet to get the same frame. The increased distance reduces the effect of distortion on the subject.

01-11-2013, 08:00 AM   #5
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Um, I remember reading that the DA* 55mm was pretty much made for portraits. I guess the only way to tell if your lens has too much distortion for your liking is to take some test shots and see if its noticeable. You can also remove distortion in post, to some extent (and at a cost).
01-11-2013, 08:03 AM   #6
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First of all, crop factor doesn't turn your lens into another. Pentax 55mm doesn't become 82.5mm on APS. It is still 55mm, it just have the field of view equivalent to 82.5mm. Nothing more.
As for distortions, you really shouldn't worry, as the Pentax 55mm is basically distortion-free.
01-11-2013, 08:49 AM   #7
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Yes, you should take the crop factor into account when choosing a portrait lens. The "ancient wisdom" should be updated to say "grab an ~85mm-equivalent for portraits". It is something of a cardinal sin here to say "my Rokinon 85mm is actually a 127.5mm", but it is okay to say "my Rokinon 85mm is effectively a 127.5mm."

It is true that the crop factor doesn't change the properties of the lens, but it sure as heck changes the properties of the image, which is really what matters. And the resulting field-of-view or angle-of-view is pretty much what determines the working distance to the subject. Which, in turn, is the only thing that affects the perspective distortion. So personally I am not offended when someone says one lens is something else on APS-C, but it causes confusion for novices.

There is nothing wrong with using a longer lens, which can provide additional subject isolation, by putting less of the background into the picture. But then you need to step farther back from your subject to fit it into the frame, and you may have a practical limit to space in a studio or indoors. And you need to stabilize the camera better. Another potential problem is that as you move farther away from your intended subject, whatever does fit in the frame which is behind your subject, becomes closer to the back of your subject, compared to the distance between the camera and your subject, which actually makes the background more in focus. So you have to weigh the isolation of the field-of-view, vs. the intended out of focus effect. It all depends on the working distances all around your subject.

Anyhow, your Rokinon 85 mm should produce some awesome portraits if you have the room. And yes, some people do like to use old 50 mm lenses for portraits on APS-C, even if it is a little shorter in focal length than the typical rule of thumb.
01-11-2013, 09:56 AM   #8
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QuoteOriginally posted by Tanzer Quote
It is true that the crop factor doesn't change the properties of the lens, but it sure as heck changes the properties of the image, which is really what matters. And the resulting field-of-view or angle-of-view is pretty much what determines the working distance to the subject. Which, in turn, is the only thing that affects the perspective distortion.
I agree, perspective distortion is the concern, and distance to subject is the determinant. I have heard looser translations of "portrait length", i.e. 70-135mm, which qualifies a 50mm and 85mm on APS-C. Of course you can go beyond these focal lengths, this is just a guideline to give a slight amount of telephoto compression, because mild compression of perspective is considered flattering in portraiture.

Note that the FA 50mm f1.4 is actually 52mm, and on APS-C is 78mm.

01-11-2013, 10:11 AM   #9
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Just look at the past to see the present. The classical portrait focal length on a 6x7 medium format camera is about 165mm and on an 4x5 camera around 240mm. Just think of the 1.5 crop as a smaller format than FF and it fits the pattern.

Last edited by tuco; 01-11-2013 at 10:18 AM.
01-11-2013, 02:25 PM   #10
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QuoteOriginally posted by audiobomber Quote
Note that the FA 50mm f1.4 is actually 52mm, and on APS-C is 78mm.
Really? What about other Pentax 50mm lenses?
01-11-2013, 02:44 PM   #11
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QuoteOriginally posted by klkitchens Quote
The reason I ask this is that I've seen that 85-90mm is a great target range for portrait lenses... even back before digital, this was the way to go.

Then I've seen that you should never ever do a closeup with a 50mm lens because of the distortion to the subject.

However, with APS-C's 1.5x crop factor, a 50mm is a 75mm (not too far off from 85-90).
No, your 50mm lens is a 50mm lens, regardless of sensor size.

QuoteQuote:
Likewise, my Rokinon 85mm is actually a 127.5mm, well past the target range. But it and other 85mm lenses are considered the bee's knees for portraits (and they do look good). My DA*55mm is closest at 82.5mm as well.
No, your 85mm is actually 85mm, and your 55mm is actually 55mm, regardless of sensor size.

Focal length is a physical property of the lens. What changes is the angle of view.

The distortion you speak of is the result of camera to subject distance. The closer you are to the subject, the greater the distortion will be.

Any lens can be used for a portrait. The choice of lens depends in part on what type of portrait you take. A wide angle is fine for a full-body portrait, not so great for a head & shoulders portrait (unless your goal for the portrait includes the distortion for artistic purposes).

Cameras and lenses are just tools. Use the right tool for the job.
01-11-2013, 03:06 PM   #12
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QuoteOriginally posted by klkitchens Quote
Since all the "ancient wisdom" still says grab an ~85mm for portraits does that apply no matter what the crop factor?
No, it does not, at least if you phrase it that way, since 'a 85mm' suggests that the perspective distortion at a given framing is all you care about. In that case, you should find yourself an 57mm lens on APS-C (Helios 44 comes to mind).

Now, perspective distortion is not all that matters in portrait photography, so a particular lens might be a good choice for different reasons (bokeh, skin tones, etc.). Also, I disagree with the premise that there is a single subject distance that is equally beneficial for all faces. I would agree in the case of the model in this series (they don't show 85, but somewhere between the 70 and the 100 is the sweet spot for my taste) but not all faces are created equal. Rounder faces often benefit from wider lenses, faces with more hawkish features might benefit from longer ones. That's if you want to make them look good. Otherwise, just the reverse.
01-11-2013, 03:20 PM   #13
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The crop factor in this case means a lens described as being perfect for portraiture on full frame would be considered (by me, anyways) as too long on a crop camera.

As others have noted, a nifty fifty (or 55) on a crop camera is ideal--and economical.

I have the DA 70mm Limited - it's also pretty darn good for portraits.
01-11-2013, 03:42 PM   #14
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QuoteOriginally posted by Apapukas Quote
First of all, crop factor doesn't turn your lens into another. Pentax 55mm doesn't become 82.5mm on APS. It is still 55mm, it just have the field of view equivalent to 82.5mm. Nothing more.
As for distortions, you really shouldn't worry, as the Pentax 55mm is basically distortion-free.
The OP is talking about"distortion" due to the impact of perspective and not lens distortion.
01-11-2013, 03:54 PM   #15
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This whole. Discussion is a lot of BS (sorry for the strong language). The fact is that portrait lens discussions usually revolve around a few salient points. What is the shooting distance you have, since shooting distance determines the focal length. While an 85 might be great for portraits, consider a head and shoulders shot, the subject height is likely 30cm. Image height, assuming vertical format is 2.4 cm on APS-c. Since image height is subject height x focal length / distance, to use an 85mm lens results in the following

2.4 / (8.5 x30) = 1/ distance ,

To distance = 106 cm it about 50 inches, not too bad, but now what if you want full body, you are talking about a subject height of 150cm minimum to a shooting distance of about 5.3 meters or 16 feet. Do you have this space?

This is the start, shoot the focal length that fits your space.

Then you get into the subject of Bokeh and background.

If you want great bokeh you need a long lens, why, because the biggest element of bokeh is blurred , simple background, you achieve this because a long lens is better to keep the backgouund size larger, as a result you get big, in identifyable blobs of color, not confusing little dots.

Sort lenses create confusing bokeh.



Personallyninlove 135 mm for portraits even on a ,APS c sensor. But you need space
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