Certified Professional Photographer Exam question

<p>The following sample question appeared on the Certified Professional Photographers Exam.</p>

<p>"If focusing on the same subject at the same distance, what will happen to the image size if a 300mm lens is used on a 35mm camera compared to a 300mm lens on a medium format camera?"</p>

<p>a) The image size will be slightly larger<br>

b) The image size with the medium-format will be larger<br>

c) There will be no difference in the image size<br>

d) The image size with the 35mm will be smaller."</p>

<p>The answer was "C".</p>

<p>I thought that the image size on a 35mm would be smaller (answer D) since the 35mm negative is smaller than a MF negative. Isn't this the same situation between a 35mm (full frame) image, and one created on an APS-C sensor on a DX digital camera? The image, in terms of what has been captured, will be larger on the 35mm full frame than on the camera with the 1.5 crop factor.</p>

<p>I must be mis-understanding the question since I find it hard to believe that the Certified Professional Photographer sample test would be wrong.</p>

<p>The key point is that 'image size' is something that happens at the film plane. With a 300mm lens, it projects the same image size, irrespective of what kind of film or sensor is there.</p>

<p>The trick in the question is that they're expecting candidates to reason as you did. "Well, I have to enlarge the 35mm 8x to get an 8 x 10 print, but I only have to enlarge the 120 negative 4x. So the 35mm image is twice as big." Uh-uh. Image size is what happens at the back of the camera. </p>

<p>Hi Graham,<br /> Sounds like someone has been eating too many Rice Crispies. <br /> The focal length is irrelevant on the M/F camera, as the image will always be larger depending on the format i.e. 6 x 4.5 to 6x9 or whatever. The image size is directly related to the area of film exposed, and that will always be greater on M/F.</p>

<p>Cheers,<br /> Adrian.</p>

<p>If "image size" means magnification, then C is true. The "image" itself (projection on film/sensor) is different if the lenses are dedicated to 35mm/MF, but that did not seem to be the question.</p>

<p>And "crop factor" is a pretty good description, because the projected image is "cropped" by the smaller sensor, but the magnification itself is the same. If the subject distance and focal length is the same, the larger format gets in a larger angle-of-view, i.e., simply more of the scene.</p>

<p>That is one badly asked question. They not saying if it's the <em>same</em> 300mm lens used on each format body. There are 300mm lenses made for each format that <em>do not project the same size image circle</em>. The size of an element <em>in</em> (common to) both images will remain the same, but the image size may very well change, depending on whether or not it's the same 300mm lens. </p>

<p>Seems badly worded as Matt says, but it's deliberate, referring to the size of the image of the subject that is focused on, not the size of the image circle.</p>

 

<p>I agree, the question is vague and can be interpreted multiple ways. The use of the word "subject" is what clued me in to its intent (meaning the size of the subject as projected by the two 300mm lenses), but it's not as clear as it should be.</p>

<p>To be correct, the question should have said the "projected image size", or "projected image magnification".</p>

<p>Thanks for your comments. I knew that I had to be misunderstanding the question. I do agree that it is somewhat misleading, but perhaps they intended it that way to make sure that person taking the test truly understands how focal lengths operate in different formats.</p>

<p>The second part of your text touches digital cameras and digital sensor that could have different pixel density, and thus some DSLR cameras could provide image magnification in the picture file, that is not visible in the viewfinder. </p>

<p>Yes a 300mm is the same on FX and DX cameras, but they produce magnified image in the file in crop sensor denser pixel cameras, approximately magnified by the value of the crop factor.</p>

<p>Thus use of a 300mm lens provides magnification in the picture file on DX camera, equivalent to the 300x1.5 = 450 mm longer lens.</p>

<p>Even if the same lens does not project any greater magnification on the sensor surfface, more dense image scanning, denser image resolution, in fact provides already magnification or greater reach inside the picture file, not visible in the camera optics or viewfinder. </p>

<p>This is the major benefit that crop factor cameras also provide magnificaation in the resultant digital file, providing pictures like much more expensive longer lenses on FX cameras.</p>

<p>Luckily the test question was only about film cameras, so the test was simple. <br>

It would be interesting to know what other tricky questions were there ?</p>

<p>Does anybody know who this PPCC is?? I've never heard of it before. Kind of a laugh, really, I think so anyway. A professional photographer is judged by his/her book and his/her ability to effectively work with people more than anything else.<br>

What do the PPCC offer, some kind of badge to wear? <em>"Hey Guys, I am a Certified Professional Photographer, step aside!"</em></p>

<p>I don't see anything misleading or vague about it. Image size is image size. Image circle is something else entirely. It couldn't be anything but answer C.<br>

Image size = S<br>

Focal length = F<br>

Angle subtended by the subject at the camera-subject distance = u<br>

Then S = 2*F*tan(u/2)<br>

This is a universal formula, irrespective of the format or sensor that S is projected onto.<br>

The question made it absolutely clear that F and u are not changed between the MF and 35mm cameras.<br>

So S cannot change.</p>

<p>Graham, you must really have been having an off-day when you arrived at this conclusion:</p>

<blockquote>

<p>Isn't this the same situation between a 35mm (full frame) image, and one created on an APS-C sensor on a DX digital camera? The image, in terms of what has been captured, will be larger on the 35mm full frame than on the camera with the 1.5 crop factor.</p>

</blockquote>

<p>...because even if you make the common mistake of scaling by the format size (instead of seeing that it is irrelevant), you have done the scaling backwards!</p>

<p>Adrian,</p>

<blockquote>

<p>Sounds like someone has been eating too many Rice Crispies. <br /> The focal length is irrelevant on the M/F camera, as the image will always be larger depending on the format i.e. 6 x 4.5 to 6x9 or whatever. The image size is directly related to the area of film exposed, and that will always be greater on M/F.</p>

</blockquote>

<p>If you seriously interpreted the question in that literal, completely uncontextual way, then...wow. I mean, did you really think that the question they were asking was "Is medium format film larger in size than 35mm film?"?! There was an obvious context to the form of words that you bizarrely missed. When someone asks you "How do you do?", do you reply "How do I do what?"! Maybe you were joking...I hope so.</p>

<p>Sorry to be harsh, guys, but I am bemused by this whole thing.</p>

 

<p>To me, it looks like a typical multiple-choice question. Enough information for you to get the right answer, with enough distraction put in to make you think about it, or even second-guess yourself.</p>

<p>I recall learning the basics about optics in High School Physics class (A long time ago, in a galaxy far away...). Wikipedia has a good explanation, and the <a href="http://en.wikipedia.org/wiki/Magnification#Calculating_the_magnification_of_optical_systems">mathematical formulae</a>. Note that the size of the sensor/film/whatever is not part of the equation!</p>

<p>Also, if you use "Test Taking 101" techniques for elimination of distracting answers, "C" was the only definitive answer. Both "B" and "D" are saying the same thing, so they can easily be discounted, and "A" could be easily construed as ambiguous <em>(Which </em>image is larger?). Which leaves us with "C".</p>

<p>Of course, 'tis better to know and understand the answer!</p>

 

<blockquote>

<p>I don't see anything misleading or vague about it.</p>

</blockquote>

<p>Neither do I.</p>

<p>OK, so they could have been eating CoCo pops, </p>

<p>seriously anyone who puts up that sort of a question has problems, their is a little bit more to Photography than arguing about inane questions that will not make the slightest jot of difference to anyone's portfolio.</p>

Inane?<br>Perhaps. But a reflection of how often people ask about focal lengths on different formats here and elsewhere.

<p>YEP !</p>

<p>I guess I will never be certified. I have zero experience as a professional utilizing 35mm equipment and I have never run a comparison test with, or between, any equipment -just because- in my life. Darn. Another club I won't be a member of.</p>

<p>Ironic isn't it that models show professional status through the work- even the U.S. government goes by tear sheets- yet the purveyors of this exam evaluate photographers based on math questions. </p>

<p>There's nothing even slightly ambiguous about the question.</p>

<p>Image size is a function of lens focal length and nothing else.</p>

<p>Take a photo of a subject on an 8x10 film, then cut out a 24mmx36mm section of that film. The subject detail on that piece will be exactly the same as it was on the full 8x10 sheet, right?</p>

<p>- Leigh</p>

 

<i>"Image size is a function of lens focal length and nothing else."</i><br><br>Uhm... <i>and</i> conjugate distances.<br>;-)

<p>Dear Adrian and Dennis:<br>

Many individuals on photo.net, and perhaps the public at large, hear the term "professional photographer", and in their minds they may visualize wedding photographers, perhaps commercial, photo journalistic, fashion, event or travel photographers. However, there is an entire segment of professional photographer which carry titles such as of technical, industrial, scientific, medical, forensic, and yes, museum photographer.</p>

<p>These jobs are real, well paying and are often full time, staff positions in science, industry, government and medical fields. There are many specialized freelancers as well.</p>

<p>These fields lack the glamor and attention of the commonly thought of "professional photographers" and require a level of technical competency far beyond simply possessing a "good book"</p>

<p>And Dr. Butler is quite correct.</p>

 

<p>Hi Louis,<br>

So "S" cannot change, but it will if you plonk a digital back on the camera, could be anything from a few megapixels to a lot of megapixels.<br>

Hey please don't preach, I have the greatest of respect for all the disciplines that Photography has to offer and I myself am always looking to implement new techniques that extend beyond the <strong>accepted parameters</strong> that we sometimes get brainwashed with.</p>

<p>Everything else being equal, the image in the 35mm viewfinder will be larger than the image in the MF viewfinder. The field of view of a 300mm lens on a 6x7 camera is about equal to the field of view of a 150mm lens on a 35mm camera.</p>

<blockquote>

<p>Take a photo of a subject on an 8x10 film, then cut out a 24mmx36mm section of that film. The subject detail on that piece will be exactly the same as it was on the full 8x10 sheet, right?</p>

</blockquote>

<p>Exactly. The lens doesn't know how big the film is and it couldn't care less as it's going to project an image the size it wants to.</p>

<blockquote>

<p>Everything else being equal, the image in the 35mm viewfinder will be larger than the image in the MF viewfinder.</p>

</blockquote>

<p>The viewfinder image is totally irrelevant to the question, which is about the photographic image, i.e. the image on the film or sensor.</p>

<p>You can make the viewfinder image any size you wish. It's a separate optical system.</p>

<p>- Leigh</p>