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DPChallenge Forums >> Photography Discussion >> What focal length is this?
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09/02/2017 09:34:57 PM · #1
Ok.

Now it's time to learn focal lengths.

I know when I shoot a long lens, the background is compressed. When I shoot quite wide, you get the distortions. But what I haven't learned was to look at someone's else's photo and be able to figure out the type of lens/focal length they used, how far away and from what height they were shooting.

So I'm starting a thread to start dissecting photos. I'm hoping that other people might find it interesting and be as clueless as I am.

So I'm starting with two of Judi's photos:

Copyrighted_Image_Reuse_Prohibited_1037660.jpg

I assume this is a longer lens and that she's standing back quite a bit? Is the bokeh created by using a 70-200 lens at the longer length and zooming in? Or more at the 70mm level and a fast lens opened up quite a bit? Is there a way to tell the difference? Is there much of a difference between the two?

And with this one:

Copyrighted_Image_Reuse_Prohibited_1133207.jpg

You'd think it would have to be quite a wide lens, but the verticals are so straight. Is she back quite far and actually zoomed in more than you'd expect? Or is it wide and just had its perspective corrected? It seems like when you correct the perspective, things seem so much shorter and squatter, and that doesn't seem to be the case here.

Discuss -- and then if you have photos about which you're curious, post them here. Or if you have photos that will confuse/teach us, challenge us here.
09/02/2017 09:38:40 PM · #2
I think it might be more useful to post images of your own, where you know the specs, and ask people to explain how they figured it out (if they did) -- either way the info should be relevant.
09/02/2017 10:05:52 PM · #3
Originally posted by GeneralE:

I think it might be more useful to post images of your own, where you know the specs, and ask people to explain how they figured it out (if they did) -- either way the info should be relevant.


That will work if other people do it. I'm trying to learn how to reverse engineer. So I want to be able to look at something I don't already understand. If I knew the answer, I wouldn't have to ask. :D
09/02/2017 10:23:12 PM · #4
Both Judi's images were shot with a FF camera. The green one was shot with the 70-200mm at 104mm focal length, at f/4. The orange one was shot with a 17-40mm at 27mm focal length, at f/7.1.
09/02/2017 10:34:14 PM · #5
Wendy, here's something I want you to do, it will help you a lot with your visualizations.

1. Take your camera, lenses, and a tripod somewhere and set up a shot that has substance from foreground to background, like a pier or a city street or... whatever.
2. Set up and take a shot at 400mm, then zoom back to 100mm and shoot that.
3. Then, without moving the tripod or camera body at all, dismount the big lens and mount the 24-105mm and shoot the same scene at 24mm.
4. Finally, mount the 10-22mm and shoot the same scene at 10mm.

To keep it simple, I suggest shooting JPG, at the highest quality.

Now open all those images in photoshop. Start zooming in on the wider ones until the framing matches the 400mm shot. You will find that you can't tell the difference between the shots, except for the obvious difference that the heavily cropped images will be grainier/noisier.

The lesson you are learning here is that telephoto lenses do NOT "compress" perspective and that wide angle lenses do not "distort" anything except objects near the edge of the frame. And even that, incidentalyy, is not really a "distortion", it's just what happens when you project 3D objects onto a plane: the more oblique the projection, the more oblong the object becomes, just like shadows get stretched out when the sun is low in the sky.
09/02/2017 10:53:08 PM · #6
That may very well be the case, but you can't zoom in that close on the 10-22 effectively, so if you want that type of look, with things closer together as they go towards infinity, you grab the longer lens. You're changing lens to more easily get the part that you want.

So if I'm photographing a person in a walkway with arches down both sides, if I want those arches to be more spread out, I'll have the person closer to me and use a wide angle lens. If I want the arches to be closer together, I'll send them down the way a bit and use a longer lens.

So I'm curious what people choose when they're sitting particular photos and why.
09/03/2017 12:32:59 AM · #7
its all about Depth of field the longer the lens at full or near full apeture and at the extent of its zoom range will give this effect,I guess that if two photographers used the same make of digital one with FF and one crop. the same will apply. according to hoyle .
I use my 100mmm Macro on crop sensor and it works like Judies photo. A telephoto lens 200mm @ f 2;8 would do wha you want .

Message edited by author 2017-09-03 00:36:41.
09/03/2017 09:32:41 AM · #8
Ok...

Bear had me ready to scream last night.

I've done everything by instinct, and I new there were still things that were eluding me.

Bear's post helped, but I'm still holding my ground.

I had a set of shots that I knew would explain things, so here it goes:

Bear's right.

10-22mm
Copyrighted_Image_Reuse_Prohibited_1205033.jpg

100-400mm
Copyrighted_Image_Reuse_Prohibited_1205034.jpg

If I zoom in on the 10-22, it's about the same as the 100-400mm
Copyrighted_Image_Reuse_Prohibited_1205036.jpg

However, I still maintain that even thought the long lens doesn't compress, it still gives the feeling of a more compressed background. If you wanted to take a shot like this, I couldn't do it with a wide angle (I've tried), because the area would be too small to get any detail.

Copyrighted_Image_Reuse_Prohibited_1004424.jpg

And this one of Judi's, could you really do this with a long lens, even from very far back?

Copyrighted_Image_Reuse_Prohibited_1127833.jpg

And if you wanted to do something like this, it could only be done with a long lens, correct?

170210-full-moon-mn-0930_20560a48203962f3f32ed0d55ee27130.nbcnews-fp-1200-800.jpg

So it is definitely a help to realize that you are getting basically the same shot regardless of lens, now I just need to figure out how to quickly decide which lens is the best choice for what I'm trying to achieve. But it sounds like my options were a lot more open than I had realized.

(I was hesitant to post anything, because I'm sure this is incredibly obvious to others. But I'm starting to want to understand what, some of the time, I know instinctively. Yet I don't have it in my logical knowledge, simply gut instinct. I want to know now, not just feel or guess. But I'm feeling rather dumb in posting and asking. But what the heck. I'm going to keep going!)
09/03/2017 10:05:13 AM · #9
FWIW I tend to visualize ahead of time what I want and go from there in terms of lens choice. These days I often use the 50mm as my default lens for studio, and for walking around the 50mm and the warhorse 18-200. But often I don't have the *perfect* lens for a particular shot with me, so I make do with what I have. I like pushing the envelope and so it doesn't bother me to use lenses for the wrong purpose. For example my 300mm f.4 birding lens Copyrighted_Image_Reuse_Prohibited_996171.jpg for some pretty decent portraits even with a TC up Copyrighted_Image_Reuse_Prohibited_990525.jpg and same lens but without the TC Copyrighted_Image_Reuse_Prohibited_1035377.jpg

Message edited by author 2017-09-03 10:15:53.
09/03/2017 10:58:53 AM · #10
Under Bear's conditions one is not allowed to move the camera, but only to crop the image to get a matching framing. Ignoring loss of resolution, one can get the exact same frame regardless of focal length. It doesn't mean focal length is unimportant, because a wider lens allows one to move the camera and get closer to the scene, with a profound impact on the captured image.
09/03/2017 11:42:58 AM · #11
Originally posted by mitalapo:

Under Bear's conditions one is not allowed to move the camera, but only to crop the image to get a matching framing. Ignoring loss of resolution, one can get the exact same frame regardless of focal length. It doesn't mean focal length is unimportant, because a wider lens allows one to move the camera and get closer to the scene, with a profound impact on the captured image.


That's what I'm trying to figure out. How to make the profound impact with a wider lens. Like Susan's examples, I'm so used to creating with a long lens. When I use a shorter lens, I don't seem to be able to really emphasize the subject like some seem to do. They just turn out like a regular point and shoot snap.
09/03/2017 11:53:44 AM · #12
By the way, if you see a news article of a local amateur photographer killing her husband -- please ignore. No big deal.

(I'm watching a video on how to hypersync my einstein strobe. Jeff walks behind me and says: "he's shooting canon".)

gack!
09/03/2017 01:04:06 PM · #13
Wendy, for your last two examples consider this:

1. In the Judi balloon shot, no you CAN'T duplicate that with a longer lens because you'd have to move back to fit it all in the frame and the relationship of foreground to background would change.
2. Contrariwise, you CAN duplicate the moon shot with a shorter lens just by cropping, assuming you were standing in the exact place from which it was shot. Standing at any given spot, the relationship of foreground-to-background elements never changes regardless of which lens you are using. ALL that changes with a lens change is the angular projection that shows up on the sensor. Obviously, trying to crop that final image out of a 10mm WA frame would fail, simply because of resolution limits, but if that were a 600mm shot, say, and you tried to duplicate it with the 400mm, you could do so satisfactorily by cropping in post.

Regarding DOF, that's entirely controlled by aperture, not focal length. DOF is dependent on the physical diameter of the aperture; tiny holes give more DOF than big holes. Now, "f/stop", which is how we define our apertures, is a ratio between the diameter of the aperture and the focal length of the lens. For this reason, f/4 on a 50mm lens would be 12.5mm in diameter, while f/4 on a 400mm lens would be 100mm in diameter. Why is this so? Because light falls off with the square of the distance traveled, and the light has a lot further to go in a telephoto lens than it does in a wider-angle lens. So based on all the above, the 400mmn lens WOULD have the "same" DOF as the 50mm lens if you shot both of them with a 12.5mm aperture, which would mean shooting the 400mm at f/32.
09/03/2017 01:42:25 PM · #14
Originally posted by Bear_Music:

Wendy, for your last two examples consider this:
Regarding DOF, that's entirely controlled by aperture, not focal length. DOF is dependent on the physical diameter of the aperture; tiny holes give more DOF than big holes. Now, "f/stop", which is how we define our apertures, is a ratio between the diameter of the aperture and the focal length of the lens. For this reason, f/4 on a 50mm lens would be 12.5mm in diameter, while f/4 on a 400mm lens would be 100mm in diameter. Why is this so? Because light falls off with the square of the distance traveled, and the light has a lot further to go in a telephoto lens than it does in a wider-angle lens. So based on all the above, the 400mmn lens WOULD have the "same" DOF as the 50mm lens if you shot both of them with a 12.5mm aperture, which would mean shooting the 400mm at f/32.


I LOVE this! This is extremely helpful! It's the type of information I probably read when I was learning, but wouldn't make sense until you have context. (The other info has also been very helpful, but that was exciting. :)
09/03/2017 04:58:05 PM · #15
My talented friend, Wendy... You have over twice the ribbons that I do.

You have the MOST RIBBONS EVER on DPC!

I think you're doing things just fine. Don't confuse yourself with the facts! Ha!
09/03/2017 05:17:21 PM · #16
Originally posted by Lydia:

Don't confuse yourself with the facts!

My dad used to have a rather uncomplimentary phrase he used to describe some people which included this wording, but this is a time where I think the advice is indeed applicable. :-)

Message edited by author 2017-09-03 17:18:01.
09/03/2017 06:11:13 PM · #17
FWIW, I still don't know a dangling gerund from a misplaced participle. Sure I know they're grammatical things but the theory of them escaped me then and still does so now. However, that doesn't stop me from using them all the time, and I've made my living as a wordsmith. So I must be doing something right!

ETA: My talented friend, Wendy... You have over twice the ribbons that I do.

You have the MOST RIBBONS EVER on DPC!


Which is about twelvety billion times as many ribbons as I have and ever will have...so why are you tying yourself in knots over focal length again?

Message edited by author 2017-09-03 21:23:37.
09/03/2017 07:55:40 PM · #18
Copyrighted_Image_Reuse_Prohibited_833422.jpg

Hi Wendy. I've enjoyed reading this thread. FWIW I think it's your storytelling talent that wins for you. Technical talent is useful, but it's a tool.

I am not a photographer & my talent at storytelling is very small. I see abstracts everywhere, & I shoot just to find out what happens. I'd just rec'd that lens & was taking it for a walk. I thought you might find it interesting.

Keep posting these. I've been reading them without posting up to now.
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