dsjtecserv

Lives in United States Northern, VA, United States
Works as a Technical Director
Joined on Jan 21, 2005

Comments

Total: 17, showing: 1 – 17
In reply to:

dr8: then what do you call the visual effect that is seen, for example, at a televised baseball game when using a long telephoto lens (800+) looking past the pitcher toward the batter, the batter is the same size or larger than the pitcher? The far objects - like spectators in the stands- appear closer while closer objects don't change apparent size very much. If you were to walk on the field with a 24mm lens and position near the pitcher to get him the same size in the field of view as with the long telephoto, the batter would look far away and much smaller than the pitcher. Apparent distances do indeed compress with a telephoto lens. I suppose you can call it perspective compression, but it is still an effect that is affected by the lens.

Yes, BBQue is correct. The proportion of near and far object changes with your relative distance, and the difference in size will DECREASE the FURTHER away you view them. If you walk up close, the opposite happens: the near object will appear progressively larger than the further object, the closer you are to the near one. That is a real thing, but it is not a function of the lens in any fashion, but is simply a result of where you view things from; it is the same whether there is even a camera and lens involved at all. And, BTW, I don't know where you got this "zoom with your feet gives the same visual effect" but it is not something I said.

Link | Posted on Jun 20, 2018 at 20:23 UTC
In reply to:

dr8: then what do you call the visual effect that is seen, for example, at a televised baseball game when using a long telephoto lens (800+) looking past the pitcher toward the batter, the batter is the same size or larger than the pitcher? The far objects - like spectators in the stands- appear closer while closer objects don't change apparent size very much. If you were to walk on the field with a 24mm lens and position near the pitcher to get him the same size in the field of view as with the long telephoto, the batter would look far away and much smaller than the pitcher. Apparent distances do indeed compress with a telephoto lens. I suppose you can call it perspective compression, but it is still an effect that is affected by the lens.

The further away the vantage point, the closer in size distant objects will appear. In the case of the pitcher and batter, assuming they are about the same actual height, the batter will come closer and closer to appearing the same height as the pitcher the further away they are viewed. But the batter can never appear larger than the pitcher, as you correctly note. That is an inherent property of the viewing distance, not the lens, though. If you simply view the same scene, without any camera or lens, you'll see the same thing.

The link goes to a pciture of a golfer, not baseball. My first impression is that it is a composite. The ship, the golfer, and the crowd are not illuminated by the sun at the same angle.

Link | Posted on May 30, 2018 at 23:34 UTC
In reply to:

MrBrightSide: As usual with these "everything you know is wrong" videos, the dude completely misses the real point of his little demo. The purpose of changing focal lengths is to change the size of your subject in relation to the background. If you want more background—like with an environmental portrait, use a shorter lens. If you want less background so that viewers concentrate on your subject, use a longer lens.

I'd actually suggest that knowing about what factors affect the characteristics of your image, and being able to use them, would potentially be very useful to one's photography. But of course, one has to be interested in using them!

Understanding that shooting position alone determines perspective relationships reminds you to consciously choose where to shoot from to produce the desired perspective, and then separately choose the focal length that produces the framing you want.

Link | Posted on May 25, 2018 at 02:45 UTC
In reply to:

(unknown member): Ugh.. this is so stupid. "Lens compression does not exists, but the distance and perspective compression does exists".

Paint me black and white, but the lens is pretty darn crucial in creating the perspective and dictating the distance you about to take the shot. Hence it is totally valid to call it lens compression, or perspective compression, or distance compression, or just plain old compression.

What is neglegted here, is the DOF that is also crucial part of this whole equation. As you may observe from the video, the 24mm shot cropped hell out of it, will not produce the same DOF as long tele shot. In fact, the apeture you would need for that 24mm lens to produce it, is probably physically impossible.

So the lens and its specifications are crucial factor of the end result.

Ultimately, it is the lenses focal length, crop factor, aperture, and the shooting distances that dictate the end result. Hence, I am totally fine with "lens compression".

Right, that is certainly your choice, though you might alternatively choose to show the player in a wider context. In either case, the perspective would be the same. The point is that the decision about the perspective you want is separate from the decision about the framing. You use your choice of shooting position to determine perspective, and your choice of focal length to determine framing. Neither dictates the other.

Link | Posted on May 25, 2018 at 02:31 UTC
In reply to:

CekariYH: So, what would a be the right words to replace "lens compression"?
Lens perspective background distance distortion (LPBDD)? :-)

I am saying that the size and position relationships among objects is determined by viewing position, and exists independent of whether anyone takes a picture of it and views that picture from some distance. That is what we call perspective (it doesn't need the additional word "compression" or, for that matter, "distortion; its just "perspective".) That is all the article is referring to, and that is really all that is under discussion here.

The way that the image is viewed (including the viewing distance to the print) further influences the impression given by the image. But the perspective relationships that are the inseparable result of the original position of the camera relative to the scene are indelibly recorded at the time of capture. And that is what is being discussed here.

Link | Posted on May 25, 2018 at 00:28 UTC
In reply to:

CekariYH: So, what would a be the right words to replace "lens compression"?
Lens perspective background distance distortion (LPBDD)? :-)

dan pv, actually the phenomenon does exist, physically. The relative sizes of objects when viewed from a certain location exist and can be readily observed, without the making an image or without the use of a camera or lens. You are familiar with two things of similar actual size appearing be the same size when view from a distance, while one will look larger than the other view viewed closer that the other? That's just perspective, and it is no less real than anything else you can observe or take a picture of.

It also has nothing to do width angle of view. When you view the world your angle of view is not limited as it would be with a camera. And yet you can observe those perspective relationships, and they don't change even if you look through a toilet paper tube! Similarly, the perspective that is inherent in your shooting position is faithfully recorded by your camera, regardless of the focal length you use or the angle of view it produces.

Link | Posted on May 24, 2018 at 21:46 UTC
In reply to:

(unknown member): Ugh.. this is so stupid. "Lens compression does not exists, but the distance and perspective compression does exists".

Paint me black and white, but the lens is pretty darn crucial in creating the perspective and dictating the distance you about to take the shot. Hence it is totally valid to call it lens compression, or perspective compression, or distance compression, or just plain old compression.

What is neglegted here, is the DOF that is also crucial part of this whole equation. As you may observe from the video, the 24mm shot cropped hell out of it, will not produce the same DOF as long tele shot. In fact, the apeture you would need for that 24mm lens to produce it, is probably physically impossible.

So the lens and its specifications are crucial factor of the end result.

Ultimately, it is the lenses focal length, crop factor, aperture, and the shooting distances that dictate the end result. Hence, I am totally fine with "lens compression".

You are correct that shooting position, focal length, and other factors also influence other characteristics such as depth of field, but those are not topics of this discussion.

Link | Posted on May 24, 2018 at 21:33 UTC
In reply to:

(unknown member): Ugh.. this is so stupid. "Lens compression does not exists, but the distance and perspective compression does exists".

Paint me black and white, but the lens is pretty darn crucial in creating the perspective and dictating the distance you about to take the shot. Hence it is totally valid to call it lens compression, or perspective compression, or distance compression, or just plain old compression.

What is neglegted here, is the DOF that is also crucial part of this whole equation. As you may observe from the video, the 24mm shot cropped hell out of it, will not produce the same DOF as long tele shot. In fact, the apeture you would need for that 24mm lens to produce it, is probably physically impossible.

So the lens and its specifications are crucial factor of the end result.

Ultimately, it is the lenses focal length, crop factor, aperture, and the shooting distances that dictate the end result. Hence, I am totally fine with "lens compression".

>>Yes, you can achieve the same compression by putting a wide angle and crop the hell out of the result, but (HERE IS THE POINT, READ CAREFULLY) it will not look anything like taking it with a tele lens and using the whole image plane.

With respect to perspective, which is the topic of the discussion, it will look exactly the same, as demonstrated. No one is suggesting that one actually make narrow-angle pictures by cropping wide-angle images. But the exercise demonstrates indisputably that the focal length of the lens has nothing to do with the compression (or the opposite effect); it is entirely due to the viewing location relative to the subject(s).

Shooting position and focal length have different and discrete effects on the impression given by an image. One choose one's shooting position to determine perspective (or accepts the perspective from the available shooting position) and then selects the focal length to produce the desired magnification and framing.

Link | Posted on May 24, 2018 at 21:33 UTC
In reply to:

dr8: then what do you call the visual effect that is seen, for example, at a televised baseball game when using a long telephoto lens (800+) looking past the pitcher toward the batter, the batter is the same size or larger than the pitcher? The far objects - like spectators in the stands- appear closer while closer objects don't change apparent size very much. If you were to walk on the field with a 24mm lens and position near the pitcher to get him the same size in the field of view as with the long telephoto, the batter would look far away and much smaller than the pitcher. Apparent distances do indeed compress with a telephoto lens. I suppose you can call it perspective compression, but it is still an effect that is affected by the lens.

dr8, it is simply called perspective. The lens itself cause not cause the effect you describe. The compression you describe is the result of viewing the pitcher and batter from a long distance away. In fact there doesn't need to be a camera lens involved at all. If you simply look at that scene, with your eyes, you can see those same size relationships. The only contribution of the long lens is to allow you to magnify a certain part of the scene so that it is framed as you desire. The compression was already there, and is there regardless of the lens used. Simply put: viewing location determines perspective; lens focal length determines framing.

Link | Posted on May 24, 2018 at 21:17 UTC
In reply to:

Steve Balcombe: Mounting a ball head upside-down looks like a great idea until you try it, then you realise it has one MASSIVE flaw. As with any panning clamp, It only works with the horizon dead-centre of the frame. I guess it's better to have the ability than not have it, but a levelling base together with a ball head mounted the right way up is a much better solution.

That's a point I frequently make to users of simple nodal slides, and you have the same problem with a leveling base. It isn't so much a defect as it is incomplete. A vertical arm and upper rail are needed to allow for adjusting the other axis - pitch - around the no parallax point.

I have used an Acratech ballhead inverted for years, without such limitations. The ballhead serves as both base rotator and leveling base, so I don't have to carry around those extra devices.

Link | Posted on Apr 28, 2017 at 13:07 UTC
In reply to:

Joesiv: Doesn't the moon rotate around the earth? seems like a strange heading for the story. Perhaps, "p900 shows the moon moving across the sky..." Would be more accurate, and probably less exciting (to match the video)

The movement you see in the video is due to the earth's rotation (hence the story heading). The moon's rotation around the earth is much less significant (it takes 28 days compared to a little more than one day to come around); and by itself would be hard to discern in such a short video.

Link | Posted on Jun 30, 2015 at 13:18 UTC
On article What is equivalence and why should I care? (2512 comments in total)
In reply to:

mosc: I would like this article to cover autofocus. Metering systems don't cover the entire area of the sensor (yet) but they do use the lens for their gathering so the intensity of the light is particularly important. Autofocus systems can struggle with not enough light (higher f-stop) OR shallow depth of field (lower f-stop) so it's messy to talk about but the smaller formats have the equivalence advantage over most focal lengths of brighter lenses for easier focusing. The 24mm equivalent on the RX100m3 for example is f1.8 which is a lot of light for the contrast metering points to focus with, compared to the equivalent f4.7 on FF. I guess in some ways this is obvious since smaller sensors are able to focus while gathering so much less light but it is a point if your choice is FF f4.7 or 1" f1.8 that the lens would have an easier time focusing the f1.8.

Gentlemen, focusing is done with the lens wide open. It doesn't matter what f-number will be used once the aperture is stopped down and the picture taken. If the lenses on either format have the same maximum aperture, they will both have the same light intensity to work with when auto-focusing. The equivalent f-number across formats thus has no relevance to auto-focusing.

Link | Posted on Jul 7, 2014 at 14:01 UTC
In reply to:

GradyBeachum: A reminder to EVERYONE, you DO NOT OWN the software you use, unless you wrote it or purchased the intellectual assets of the company that created it or live under the delusion that you are the center of everything.

If you don't like the subscription model to lease the license, go somewhere else.

But under a perpetual licensing arrangement, which is how Adobe software was previously sold, you DO own a license which permits you to use that software in perpetuity. That license is an asset that can be transferred, bought and sold. The rental model, which is the only one Adobe now offers, affords you none of that -- you only use the software as long as you keep paying for it, and you have no equity in the license. That's an unavoidable, fundamental difference, and it cannot be glossed over.

Link | Posted on Sep 6, 2013 at 18:24 UTC
On article Service lets you order prints of any Facebook photo (114 comments in total)
In reply to:

Indio888: To repeat from earlier: No. I'm not happy that photos I upload, which are my copyrighted IP, are being exploited by some unauthorized service so they can compete with me and sell prints. I sell prints myself and a third party does NOT have my permission to do so.

If this company was selling coffee mugs with Disney characters on them, you better believe they would be sued into oblivion.

This urban myth won't die. You didn't not sign away your rights to your photos under the FB TOS. You only granted a license to allow them to display the photos in connection with the service -- which is necessary if you you want your pictures to be visible on a Facebook page. That does NOT permit Facebook or any other agency to sell your photos or convert them for other purposes. The Instagram ploy of a couple months ago attempted to do just that, and it was quickly buried in user outrage. it is likely that this latest FB gambit will see the same reaction.

Link | Posted on Apr 2, 2013 at 20:00 UTC

As Karl and szedman point out, this analysis is incorrect. The previous TOS was similar to that of other photo sharing sites and does not grant a license for the host to do anything not connected with the job of displaying the pictures, as necessary to provide the hosting service. The new TOS would go well beyond that to permit commercial use of the photos without compensation or notice to the artist -- that is, clearly usage beyond that which is necessary to simply provide the hosting service. That's different, and it justifiably has caused considerable concern.

Link | Posted on Dec 18, 2012 at 18:49 UTC as 25th comment
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