Crop sensors and lens focal length effects

[clayne]

It's not just about cropping and how that affects composition. DOF is inherently different if you shift the distance to "match" the equivalent angle of view.

[isoterica]

Originally Posted by sevo

As a matter of fact, crop sensors are an advantage for tele-centric subject matter as they extend every lens by factor 1.5. Canon are still producing a dedicated pro crop body, as their sports photography customers request it.

You are right in the telephoto department, I was thinking more of shooting an entire baseball field wide angle in which case it wouldn't be so wide. Either way, crop sensor camera's can have an advantage as far as getting in closer.

[Dwig]

Originally Posted by Merkin

...Suppose I was using a 28mm lens on a Fuji X-Pro 1, which has a 1.5x crop factor. This makes the lens equivalent to a 42mm normal lens on a 35mm camera. Let us now suppose that I took an up close portrait of someone. Would the portrait turn out to look like a wide-faced slightly bug-eyed portrait like shooting with a 28mm lens on a 35mm camera would, or would it turn out looking like an up close portrait shot with a 42mm lens on a 35mm camera? Conversely, If I were using a 50mm lens (75mm equivalent) with a crop sensor camera, would I get a full frame 50 equivalent level of foreshortening or a full frame 75mm equivalent level of foreshortening? ...!

Your confusion comes from thinking that focal length, in and of itself, has an impact on the perspective rendered (foreshortening, ...). This is totally false.

The only thing that affects perspective is relative distances from the camera to the subject, the foreground object(s), and the background. In your portrait example, the only thing affecting the perspective is the camera to subject distance. The format (sensor/film size) and the lens focal length have no impact.

The only effect of focal length is the field of view on a given format. If you shoot a portrait from, say, 8 feet (subject to lens distance) it doesn't matter if you use a 50mm lens on 4/3 (2x crop factor) or FF. If you crop both to the same field of view the perspective will be identical. In fact you could use a 12mm lens on either camera shooting from the same 8ft distance and cropping to a matching field of view will yield exactly the same perspective.

[clayne]

Originally Posted by Dwig

The only effect of focal length is the field of view on a given format. If you shoot a portrait from, say, 8 feet (subject to lens distance) it doesn't matter if you use a 50mm lens on 4/3 (2x crop factor) or FF. If you crop both to the same field of view the perspective will be identical. In fact you could use a 12mm lens on either camera shooting from the same 8ft distance and cropping to a matching field of view will yield exactly the same perspective.

Yes, but what you're describing is really cropping of the FF-side to match the already cropped crop-sensor output. At the same distance this would yield the same perspective - but in no way would it be natively 50mm. And even if one tries to play mathematical games to emulate the same perspective as 50mm, uncropped, they will not get around the change in DOF.

[Merkin]

Originally Posted by clayne

Yes, but what you're describing is really cropping of the FF-side to match the already cropped crop-sensor output. At the same distance this would yield the same perspective - but in no way would it be natively 50mm. And even if one tries to play mathematical games to emulate the same perspective as 50mm, uncropped, they will not get around the change in DOF.

I'm not concerned about DOF. If anything, greater depth of field is good for the way I shoot. I only wanted to make sure that I could get flattering portraits.

[clayne]

Originally Posted by Merkin

I'm not concerned about DOF. If anything, greater depth of field is good for the way I shoot. I only wanted to make sure that I could get flattering portraits.

Define "the way you shoot." I could understand you if you were talking something like street photography, but traditionally greater DOF doesn't necessarily go hand in hand with flattering portraits.

[Merkin]

Originally Posted by clayne

Define "the way you shoot." I could understand you if you were talking something like street photography, but traditionally greater DOF doesn't necessarily go hand in hand with flattering portraits.

I don't like razor thin DOF in my portraits. I shoot most of my portraits at f4 or 5.6. I don't shoot in a studio, so I like a little context.

[Dwig]

Originally Posted by clayne

Y...but in no way would it be natively 50mm. ...

To think that there is some concept as being "natively 50mm" is rather nonsensical. Obviously you are narrowly considering 35mm FF some magic format and all others second-class entities.

My discussion targeted the OP's questions about perspective. DOF is a horse of a different color. With lenses yielding matching fields of view and when shooting the same scene from the same position there will always be more DOF at any one f/stop the smaller the format. 4x5 yields more DOF than 8x10, 6x7 yields more than 4x5, 35mmFF has more than 6x7, ... . This is nothing new that's been brought on by the so called "crop sensor" digital formats. It's been a fact of life in the photo world since the development of photography.

[sevo]

Originally Posted by clayne

but in no way would it be natively 50mm.

There is no such thing as a "native" focal length.

Originally Posted by clayne

And even if one tries to play mathematical games to emulate the same perspective as 50mm, uncropped, they will not get around the change in DOF.

The difference in DOF merely is a difference in aperture - stop down in proportion to the format increase, and there is no difference. This also implies that smaller format lenses with the same DOF and angle of view will be proportionally faster.

If any, the real difference is diffraction in relation to DOF - with growing film/sensor size, the margin for enlargement at a aperture delivering identical DOF decreases. Past some point rather smaller than 4x5" we are already inherently diffraction limited - people requiring large prints can only benefit from increasingly larger film/sensor formats if DOF is no or a manageable issue (subjects near infinity as well as those where the focal plane can be appropriately placed with camera movements) or low DOF is desired/acceptable.

[clayne]

Cmon guys, subject distance. This entire conversation is revolving around keeping the same perspective as a "full-frame" shot vs cropped. You cannot have the same perspective with the same DOF, using the same lens on a body that crops vs one that doesn't. One simply has to move to keep the same perspective (from the point of the cropped sensor, not the full frame) and with that, DOF changes as a factor of focal distance. Inherently the crop sensor will have greater DOF for the same perspective as a FF shot with the same lens because the crop sensor version of the shot would have required moving away from the subject.

[Dwig]

Originally Posted by clayne

...One simply has to move to keep the same perspective ...

Very, very wrong!

If you move you change perspective, period, whether you change formats, change lenses, neither, or both.

[clayne]

You are absolutely correct on that and bad choice of wording on my part. What I really meant was "framing" but that of course does not take into account the actual change of perspective or angle of view as a result.

But beyond all that basically the only possible thing that can ever be equaled is cropping the FF shot to the same as the cropped sensor shot. No combination of vectors can be entirely controlled to equal the same results be that AOV, DOF, whatever.

Crop sensors are a great way to handicap good lenses.

[Dwig]

Originally Posted by clayne

Y...
Crop sensors are a great way to handicap good lenses.

True only to a degree and not at all unless you replace "good lenses" with "good lenses designed for some larger format".

Even FF/FX sensors handicap good lenses when those lenses are designed for larger format (e.g. Hasselblad H series lenses, Leica S series lenses, ...)