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11-21-2007, 07:02 AM   #1
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Portrait Lens Alternative?

Folks:

After reviewing several threads about portrait lenses and what length is best, it seems many users like something in the 85 mm area. This agreement seems to be backed up by obvious price spike on 85 mm glass on the auction sites.

I understand the reasons why a longer lens like 85mm is used for portraits, but considering the 1.5x change introduced by non full frame sensors, it seems that 85 is really 128 mm and much longer than what portrait shooters really want.

My question is this: Pentax made a 55mm 1.8 SMC Takumar lens that (I think) rivals any of the fast 50s in image quality and contrast. Figuring in the smaller sensor, the 55mm should shoot like a 82mm lens on a full frame 35.

The 55 mm relatively cheap on ebay, perhaps because it's an "oddball" length. It's a nice lens and is just a few mm short of the magic 85mm that many target for portraits figuring 1.5x. Is there some other quality that makes "real" 85s preferable over a low cost alternative like the Takumar SMC 55mm 1.8 for portrait work?

Thanks,

germar

12-13-2007, 10:13 PM   #2
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It's a concept that's often misunderstood. The reason 85+ is chosen is because of perspective and depth of field for human subject. the smaller digital sensor simply perform a "crop", it does not change the perspective & DOF at all. Hope that helps.
12-14-2007, 03:35 AM   #3
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I am actually finding my Tamron 90mm quite a nice longer portait lens
12-14-2007, 05:49 AM   #4
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Perspective depends only on the distance to the subject.

The angle of view of a 55mm on a 1.5 crop camera is the same as that of an 85mm on a "full frame" camera.

Therefore, you will be at the same distance with either kit.

Ergo, the perspective will be the same.

Or is there something I misunderstood ?

12-14-2007, 06:21 AM   #5
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QuoteOriginally posted by RBellavance Quote
Perspective depends only on the distance to the subject.

So are you saying that if I take a photo with a 16mm lens and a 200mm lens, both 4 feet from a subject, that the perspective will be the same? I don't think so.
12-14-2007, 07:32 AM   #6
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It's somewhat counterintuitive, but it's true:

Perspective distortion (photography) - Wikipedia, the free encyclopedia
12-14-2007, 01:31 PM   #7
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I'm glad this came up. The confusion that swirls around focal lengths on different formats seems to have gotten worse since most of us (and I include myself, as well as many manufacturers) have stopped using the term "equivalent angle of view", and defaulted to the easier to understand, but less accurate "equivalent focal length". As was mentioned previously, angle of view is just a part of what makes a particular focal length 'look' the way it does.

As a sidebar, I just looked at the exif data for a portrait shoot I did of my friend Paula last month. Using the DA 50-200 all of the head and shoulders shots were done at focal lengths between 80mm and 115mm, averaging just shy 100mm.
12-14-2007, 03:26 PM   #8
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QuoteOriginally posted by RBellavance Quote
Perspective depends only on the distance to the subject.

The angle of view of a 55mm on a 1.5 crop camera is the same as that of an 85mm on a "full frame" camera.

Therefore, you will be at the same distance with either kit.

Ergo, the perspective will be the same.

Or is there something I misunderstood ?
You are pretty close.

As someone has stated, perspective is a function of image to lens distance. What people forget is that when they look in a view finder, to get the same image size (in the view finder) with a shorter lens, then they move in closer. it is that movement that alters perspective. If, on the otherhand, you shoot both a 55 (with ASP-C sensor) and 85 (on film) from the same distance and print the images on the same size paper, they will be identical in terms of size and perspective.

You can also take a telephoto and a wide angle, shoot something from the same distance and then enlarge and crop the wide angle shot to show the same field of view and again the perspective will tbe the same (it is just that that moch crop and enlargement produces a really bad image,

12-14-2007, 07:07 PM   #9
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Matt, this link as well serves to support everyone explaining that/how perspective is only a function of distance from the subject and nothing else:
Perspective: Optical: Glossary: Learn: Digital Photography Review

This link above states that if the 16mm and 200mm lenses were in the same position and you cropped the picture taken with the 16mm so the subject is the same size as the subject taken with the 200mm lens, they would be the same perspective. ... that is what this page says, and shows, too.
12-14-2007, 08:27 PM   #10
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QuoteOriginally posted by germar Quote
Folks:

After reviewing several threads about portrait lenses and what length is best, it seems many users like something in the 85 mm area. This agreement seems to be backed up by obvious price spike on 85 mm glass on the auction sites.

I understand the reasons why a longer lens like 85mm is used for portraits, but considering the 1.5x change introduced by non full frame sensors, it seems that 85 is really 128 mm and much longer than what portrait shooters really want.

My question is this: Pentax made a 55mm 1.8 SMC Takumar lens that (I think) rivals any of the fast 50s in image quality and contrast. Figuring in the smaller sensor, the 55mm should shoot like a 82mm lens on a full frame 35.

The 55 mm relatively cheap on ebay, perhaps because it's an "oddball" length. It's a nice lens and is just a few mm short of the magic 85mm that many target for portraits figuring 1.5x. Is there some other quality that makes "real" 85s preferable over a low cost alternative like the Takumar SMC 55mm 1.8 for portrait work?

Thanks,

germar
Why not the DA 50 1.4 Lens. It is awesome for portraits. Medium telephoto, fast, sharp and compact.

Ben
12-14-2007, 09:22 PM   #11
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QuoteOriginally posted by benjikan Quote
Why not the DA 50 1.4 Lens. It is awesome for portraits. Medium telephoto, fast, sharp and compact.

Ben
You're going to start another uproar.....
12-15-2007, 01:29 AM   #12
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QuoteOriginally posted by Matt Miller Quote
So are you saying that if I take a photo with a 16mm lens and a 200mm lens, both 4 feet from a subject, that the perspective will be the same? I don't think so.
As long as both lenses are rectilinear (the 16 is not a fisheye), the perspective will be exactly the same. Even in the fisheye, the perspective is the same, it is just camouflaged by the distortions introduced by the lens design.
12-15-2007, 02:19 AM   #13
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Interresting reading here, very usefull, thanx for the info and links guys...
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