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Old May 15th, 2010, 02:23 PM   #1
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A lens is a lens

With all the threads about lens and the confusion over different formats, Mitch Gross gives a visual demonstration.

A Lens is a Lens is a Lens | CineTechnica
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Old May 16th, 2010, 06:14 AM   #2
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The first 44-seconds was enough counfusion to make me want to click the off button... :)
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Old May 17th, 2010, 10:38 AM   #3
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Badly titled. Badly scripted (assuming that it was scripted). I watched the 1st half & then gave up. He kind of defeated his own purpose by not really demonstrating what he thinks he is.
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Old May 17th, 2010, 12:12 PM   #4
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You really need to watch through to the end and it does make sense. Unfortunately, it's a highly compressed demonstration and there are one or two leaps that you need make along the way.

This is a first attempt to pin things down and I gather they are planing to make an improved version based on the feedback.
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Old May 17th, 2010, 01:09 PM   #5
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With my ex-college lecturer hat on, he made the mistake of trying to introduce too many new concepts, too quickly. Each individual experiment didn't have a conclusion, but linked to the next subject before the first was answered. The demonstrations worked fine, but he forgot to explain what we were actually meant to be doing!

The first section, where the left monitor showed a circular edge rather than the full frame image of the other didn't explain that the reason was the lens didn't expose the full sensor area. He mentioned 16mm and 2000 - but didn't explain at all what these signified. Some of us know, but there again, if he assumes we know things he can't be certain of, then at least some of the audience will be lost and give up.

Things like the impact of sensor size can be easily demonstrated with a small profile (elipsoidal) theatre spot. You use the divergence of the beam in the same way as a lens converges. So you have a frame shaped gobo in the spot, and then have a white card for it to land on (actually, a video projector works nearly as well) The angle of the emerging beam is fixed - this simulates the focal length acceptance angle of the video lens. If you have two white cards, one for say 2/3" sensor size, and another for 1/3" sensor, you can show the effect of sensor size v angle of view.

Once you have this done, you can move onto the next bit, which is distance v focal length and the resultant perspective changes. Best demo is of course the psuedo Hitchcock effect where subject size is maintained throughout a zoom by changing distance - with the size of the background changing.

Depth of field, again, is a separate topic area - in the video all these things merged together. Used on beginners, it's a failure I'm afraid. If you understand these things, it makes sense, BUT you already understand them, so it doesn't count.

I doubt there was a script - probably not even bullet point cue cards. A bit of a ramble, really.

What's for certain is that students would be lost within the first minutes. It looks good, just a tad confusing.
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Old May 17th, 2010, 06:04 PM   #6
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I don't think it's aimed at beginners, perhaps more those people who have problems working with different sensor/film gauges and consistently refer to an equivalent lens focal length, rather than the actual lens being used.
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Old May 17th, 2010, 11:03 PM   #7
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Quote:
Originally Posted by Tony Davies-Patrick View Post
The first 44-seconds was enough counfusion to make me want to click the off button... :)
I sat through it but I had the same urge at the same time.

Ironically in the blog entry the writer comments
Quote:
Originally Posted by Mitch Gross
...But often written explanations confuse as much as they explain
We now have proof that video explanations can be equally confusing. I think with Paul R Johnson's recommendations this could become a very informative video.

Brian Drysdale, I think this video actually demonstrates why referring to an equivalent lens focal length is a good thing to do as it helps with composition, which is the most important thing in any visual medium in my opinion.
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Old May 18th, 2010, 02:49 AM   #8
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The equivalent lens focal length is something you do when you're starting a new format, but it's something that actually using the new format and referring to the actual focal length you quickly no longer need. It's part of a learning process, but like support wheels on bicycle with practise you don't need them once you get used to a format.

However, if you just keep referring to the equivalent, you never learn the new format's angle of view for a particular focal length. It's the angle of view that's important.
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Old May 18th, 2010, 04:05 AM   #9
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I wonder if the real problem is like when you learn a new language, while you constantly convert from say, French, back to English to understand it, then re-translate back to French to reply, you'll never be fluent.

I was brought up on 35mm stills, so to me 28mm is wide, 300mm is pretty tele - but on my modern DSLR, I never even bothered to learn the new focal lengths, they're about the same as my old lenses, but have new numbers.

Perhaps the fault is in using an optics meaurement, as in focal length, rather than a more sensible angle of view. Angle of view would mean that sensor size and focal length would be less important. I suppose all you'd really need to know is that reducing sensor size effectively narrows angle of view and narrow angles of view mean smaller depth of field.
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Old May 18th, 2010, 04:19 AM   #10
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The old turreted broadcast TV studio camera lenses used to be referred to by their angles of view, rather than the focal lengths. This is something that carried over the zooms for the pre 2/3" cameras - a 50 degree to 5 degree for example.

Of course this doesn't supply information for optical calculations, but it give the information that a director requires.
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Old May 18th, 2010, 03:22 PM   #11
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Originally Posted by Brian Drysdale View Post
You really need to watch through to the end and it does make sense.
Sorry, but I think that kind of proves my point. You shouldn't have to sit all the way through to the end before you "get" it. That almost guarantees that you won't sit through to the end.

If he's trying to build from one principal to the next, he needs to start with principal 1, explain it, then move onto #2.

And I just turned it off when he claimed to be trying to demonstrate how focal length and sensor size determine the area of view, and instead he moved the camera. So he really showed how moving the camera changes the composition.

He needs to organize his notes point by point and create a simple, logical flow.

Honestly, Ansel Adams explained this quite beautifully in his book "The Camera". I'd refer people there first.
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Old May 18th, 2010, 04:31 PM   #12
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The reaction to this video blog does seem to cover quite a wide range. What it isn't and I gather it's not intended to is give a full explanation, it's an extremely condensed demonstration of a particular aspect, so reading a book is a far better way to go into the subject in depth. A few minutes on video will never be the same as book.

I know Mitch has taken on board feedback from various sources, so I expect the comments made will used to refine the video.

Perhaps it does need more of a hook, but some films do require you to sit through to the end and some great films never explain even when you do get to the end. Although I don't think Mitch was intending to make one of those.
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Old May 18th, 2010, 06:16 PM   #13
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Good afternoon,

Well, after reading a few of the posts I went and watched the blog. Having grown up in the older film days, with large format cameras (, 5x7 4x5 & 2.25xx2.25) being able to change lenses and dealing with al the differences, the blog was clear enough for me to understand. I even used 8mm and 16 mm bolex flim cameras in the early 60's.

However, as a retired educator, IMO the presenter could certainly do a lot better job of it. It is apparent he is winging it as he is almost flipitant in presentation.

He needs to slow down the presentation,

the old, " tell em what ya gonna talk about, Tell Em, Tell em what ya told them" would be helpful. It would tie it off and conclude with the significant points he wanted to make.

for just tossing something together it wasn't so bad; now, if he was doing this professionally, well thats another story.
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Old May 18th, 2010, 10:23 PM   #14
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I'll let Mitch know about this thread. I'm sure he will appreciate the feedback. This is a confusing topic for sure and perhaps, as many of you have suggested, he could break it down into smaller sections.
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Old May 19th, 2010, 02:32 AM   #15
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I've mentioned it to Mitch yesterday on CML and he has been taking on board the comments.

Being a film person as well, the blog made total sense. I could sense what it was about from the opening images and the issue he was trying to address, because it does seem to be a recurring question.

The 2k mentioned in the blog being on the RED One, which is roughly the same size as standard 16mm, as against the full 4k sensor's S35mm. The 2k is a window within the large sensor. The RED can also use a 3k window, which has higher quality. The "k" being the number of horizontal Bayer pixels, not 2k RGB.
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