Ugly Hedgehog - Photography Forum
Home Active Topics Newest Pictures Search Login Register ☰
Main Photography Discussion
Are you familiar with crop factor times aperture?
Page <<first <prev 4 of 8 next> last>>
Jun 5, 2017 17:15:25   #
Photocraig
 
Gene51 wrote:
There is a lot of word salad in that video.

DoF does change even if you use two lenses that provide the same field of view on both sensors, as I wrote in my first post on this thread. But not the amount of light. However, if you look at any DoF chart, something is at play. The same focal length on both cameras at the same distance will show the crop camera as having LESS depth of field compared to the full frame. The smaller circle of confusion on the smaller sensor camera will reveal out of focus more readily than the full frame, which makes sense, since you have to magnify the image from the crop sensor 50% more to get to the same size print. Depth of field will also change on a given print size as you move further away from the print - giving the impression that there is greater depth of field, regardless of what camera took the picture.
There is a lot of word salad in that video. br br... (show quote)


Thanks, Gene. I was waiting for the use of "circles of confusion" to be used in defining depth of field. DOF is a confusing term. There IS ONLY ONE PLANE OF FOCUS in any scene. The best definitions of Depth of Field use the words, "the field of APPARENT focus." Aperture, larger or smaller, defines the effect on items in those parallel planes closer to and further from the camera from the focus plane. That out of focus blurry look is what is described by the "circles of confusion." And predictably they are sized in proportion to the size of the aperture. And their registration onto the sensor is similarly less detectable when they are small, thus deep DOF, and larger if the aperture and circles are large yielding shallow DOF and Bokeh which look like circles appearing, usually, in the background.

There is a real relationship to how such phenomena project onto different sized focal plane areas. That is where the "crop factor" discussions arise. Most good DOF tables factor the format into the calculations.

C

Reply
Jun 5, 2017 17:33:45   #
Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)
 
Photocraig wrote:
Thanks, Gene. I was waiting for the use of "circles of confusion" to be used in defining depth of field. DOF is a confusing term. There IS ONLY ONE PLANE OF FOCUS in any scene. The best definitions of Depth of Field use the words, "the field of APPARENT focus." Aperture, larger or smaller, defines the effect on items in those parallel planes closer to and further from the camera from the focus plane. That out of focus blurry look is what is described by the "circles of confusion." And predictably they are sized in proportion to the size of the aperture. And their registration onto the sensor is similarly less detectable when they are small, thus deep DOF, and larger if the aperture and circles are large yielding shallow DOF and Bokeh which look like circles appearing, usually, in the background.

There is a real relationship to how such phenomena project onto different sized focal plane areas. That is where the "crop factor" discussions arise. Most good DOF tables factor the format into the calculations.

C
Thanks, Gene. I was waiting for the use of "c... (show quote)


You are 100% correct. Except for when you bring Scheimpflug into the discussion. When you tilt the front element of a lens, the "plane" of focus becomes a "wedge" or "cone" shaped field, and the aperture serves to widen the angle of the cone. The small part of the cone starts at the sensor, and the wider part goes off into the distance, at an angle that can include the ground plane as one of it's sides, and this is how the illusion of greater depth of field is possible with a tilt/shift lens. But this is a really really simplistic explanation.

Reply
Jun 5, 2017 17:34:35   #
Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)
 
windshoppe wrote:
A very informative resource. Thanks for the link.


It's not if you have been following this thread. Fake info not supported by fact or science.

Reply
 
 
Jun 5, 2017 17:43:11   #
Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)
 
SteveR wrote:
The only thing that will affect aperture is adding a teleconverter. If you use a 1.4x converter, multiply your aperture by 1.4. If you use a 2.0x converter you would need to multiply your aperture by 2.0. The significance of this is that, depending upon the lens, AF may cease to function.


But aperture has three main functions - controlling the amount of light getting through the lens to the sensor, and controlling the depth of field, and ultimately diminishing overall sharpness when diffraction starts to limit sharpness. Smaller aperture = greater depth of field and less light.

If you use a 1.4X TC, you add one stop of exposure, and using a 2X TC requires 2 stops extra exposure.

What does change, and it has already been mentioned and shown in Cambridge in Color DoF page - is that if you use the same composition a 100mm lens on a crop camera at F5.6 will have the same DoF as a 150mm lens on a full frame camera at F8.4 give or take.

But you are correct - using a crop sensor camera and a full frame lens will provide the same amount of light compared to the same lens on a full frame camera.

Reply
Jun 5, 2017 17:49:16   #
Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)
 
Rab-Eye wrote:
Ken Rockwell says to shoot in P mode (which is entirely up to him), but he calls it Professional Mode, not program. That's wrong, and a beginner will be led astray by it. I disagree with him on many other things, but I acknowledge that most of them are subjective. The example I offered here is objective. I also acknowledge that I find his reviews useful in some cases, especially when he identifies less expensive equipment that will serve most users just as well as the more expensive versions. Oh, this reminds me of another objective error: his assertion that the best Nikon flash is the SB-400 (I might have the model number wrong), but it is a very small flash that sits very low on the hot shoe and is more likely to produce harsh shadows and red eye than other flashes, although it can be bounced off a ceiling. He calls it the best because it is the smallest and lightest. He should call it his favorite because it is small and light, not claim that it is a better product.

Anyway, this is my two cents and your mileage may vary.
Ken Rockwell says to shoot in P mode (which is ent... (show quote)


My favorite quote from the KR website:

"I continue to do this site all by myself for fun — probably the last remaining 1990's for-fun website that hasn't sold out to other interests. Even though it has become popular, presumably because so many people find it helpful, it is still run just for fun. I am this site's only author. I have no one to proofread, spell check or fact check for me, so there will always be errors and omissions. Apparently the world finds my opinions very useful, but remember, they are the opinions of one man. I have a big sense of humor, and do this site to entertain you (and myself), as well as to inform and to educate. I occasionally weave fiction and satire into my stories to keep them interesting. I love a good hoax. Read The Museum of Hoaxes, or see their site. A hoax, like some of the things I do on this website, is done as a goof simply for the heck of it by overactive minds as a practical joke."

http://www.kenrockwell.com/about.htm

And there is the reason why people who know better don't waste time going there. The Internet is a good place to find reliably good information and advice, but unfortunately, for many, they can find lots of "fake info" that poses as good advice as well.

Reply
Jun 5, 2017 17:50:28   #
Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)
 
imagemeister wrote:
The notion of having a factor for multiplying the aperture has to do with "for equivalent full frame DOF for equivalent fields of view" and has NOTHING to do with light gathering or exposure - which everyone seems to fail to mention when they talk about aperture factoring ! They assume that everyone knows this



Reply
Jun 5, 2017 17:52:14   #
Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)
 
phlash46 wrote:
The crop factor affects DOF. The DOF is the equivalent of 8.4 on a full frame camera, but, the light gathering is still 5.6.


But only if you move forward with the same focal length to get the same composition. Shorter distance = shallower DoF so you have to stop the lens down to get comparable DoF.

Reply
 
 
Jun 5, 2017 17:52:25   #
hrblaine
 
When I was shooting dance with 35mm back in the '60s, I didn't have access to all this DOF info but I quickly learned that if I wanted everything in focus, I should use a more closed aperture (f8, f11 etc.). If I wanted to concentrate on one person and blur the rest, I should open the lens more (f2,f2.8 etc.). I would sometimes push Tri X to 800 but with concert dance, f8 was nearly impossible so willy nilly, I concentrated on one person or perhaps two or a small, tight group. I stopped shooting dance in the '80s so digital with it's impossibly high ISO never came into play.

Reply
Jun 5, 2017 17:56:58   #
Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)
 
mineart wrote:
Crop factor doesn't impact the amount of light, it impacts the way the bokeh will be. An f1.7 25mm APS-C lens still grabs fast light, but it will deliver bokeh as if it is f1.7 x1.5 crop or as if you were shooting with an f2.55 apeture.


Bokeh is a function of lens design, difference in distance between subject and backgroung (for background bokeh) and how far you are from your subject (image magnification). Crop factor in of itself has zero to do with bokeh, other than making you use shorter focal length lenses and/or putting more distance between yourself and the subject. Out of focus background is not bokeh. - Bokeh quality is the quality of the out of focus areas. Good bokeh does not show sharp edges, and highlights are usually circular and without fringing. Sensor size has nothing to do with that.

Reply
Jun 5, 2017 18:43:11   #
hrblaine
 
I like to read Rockwell, not so much for info as for the entertainment value. To say that he is opinionated is to understate his hubris. And while I don't always agree with him, I freely admit that he knows more about photography than I do. I come here for information but sometimes the subject is so complex (or is made so complex) than I have no idea if the poster is correct. Best I can hope for is that several people agree which then gives me more confidence in the original post.

Reply
Jun 5, 2017 19:05:10   #
Brucej67 Loc: Cary, NC
 
Absolutely, you know what you are talking about and those lenses don't come cheap.

Gene51 wrote:
Bokeh is a function of lens design, difference in distance between subject and backgroung (for background bokeh) and how far you are from your subject (image magnification). Crop factor in of itself has zero to do with bokeh, other than making you use shorter focal length lenses and/or putting more distance between yourself and the subject. Out of focus background is not bokeh. - Bokeh quality is the quality of the out of focus areas. Good bokeh does not show sharp edges, and highlights are usually circular and without fringing. Sensor size has nothing to do with that.
Bokeh is a function of lens design, difference in ... (show quote)

Reply
 
 
Jun 5, 2017 19:36:36   #
Rab-Eye Loc: Indiana
 
Gene51 wrote:
My favorite quote from the KR website:

"I continue to do this site all by myself for fun — probably the last remaining 1990's for-fun website that hasn't sold out to other interests. Even though it has become popular, presumably because so many people find it helpful, it is still run just for fun. I am this site's only author. I have no one to proofread, spell check or fact check for me, so there will always be errors and omissions. Apparently the world finds my opinions very useful, but remember, they are the opinions of one man. I have a big sense of humor, and do this site to entertain you (and myself), as well as to inform and to educate. I occasionally weave fiction and satire into my stories to keep them interesting. I love a good hoax. Read The Museum of Hoaxes, or see their site. A hoax, like some of the things I do on this website, is done as a goof simply for the heck of it by overactive minds as a practical joke."

http://www.kenrockwell.com/about.htm

And there is the reason why people who know better don't waste time going there. The Internet is a good place to find reliably good information and advice, but unfortunately, for many, they can find lots of "fake info" that poses as good advice as well.
My favorite quote from the KR website: br br i &... (show quote)


I have absolutely no doubt that he is being truthful when he says nobody is proofreading his writing for him. The guy is a professional photographer who spells focusing "focussing." Hukt on faniks werkd fer mi!

Reply
Jun 5, 2017 19:37:58   #
Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)
 
Rab-Eye wrote:
I have absolutely no doubt that he is being truthful when he says nobody is proofreading his writing for him. The guy is a professional photographer who spells focusing "focussing." Hukt on faniks werkd fer mi!



Reply
Jun 5, 2017 19:40:44   #
Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)
 
hrblaine wrote:
I like to read Rockwell, not so much for info as for the entertainment value. To say that he is opinionated is to understate his hubris. And while I don't always agree with him, I freely admit that he knows more about photography than I do. I come here for information but sometimes the subject is so complex (or is made so complex) than I have no idea if the poster is correct. Best I can hope for is that several people agree which then gives me more confidence in the original post.


I try, as often as possible, to clearly present opinion as my own, but state facts with at least one or two verifiable and reputable sources. It keeps me honest (old academic habit I suppose) and others not confused.

Reply
Jun 5, 2017 21:06:24   #
rmalarz Loc: Tempe, Arizona
 
Neither the focal length or the aperture are changed by using a full or crop sensor. The only thing that changes is the amount of the projected image circle that is utilized by the crop sensor. This makes it appear as if the lens is a longer focal length lens than if used on a full frame sensor. The amount of difference depends on the dimensions of the sensor.
--Bob

Rab-Eye wrote:
I had never heard of this before. If accurate, it means my FX 70-300 f/4.5-5.6 zoom is an f/8.4 at 300mm. This led me to investigate the Nikon DX 70-300, which I have now rejected for several reasons, including but not exclusively because of its plastic mounting ring.

I assume that not only focal length but aperture as well must be multiplied by the crop factor is accurate because Nikon itself is the source of the information. Still, it's odd to me that it is virtually never mentioned; in my own experience it has never been referenced except by this Nikon video. Have I been living under a rock, or is this news to you as well?
I had never heard of this before. If accurate, it ... (show quote)

Reply
Page <<first <prev 4 of 8 next> last>>
If you want to reply, then register here. Registration is free and your account is created instantly, so you can post right away.
Main Photography Discussion
Home | Latest Digest | Back to Top | All Sections
Contact us | Privacy policy | Terms of use | DMCA
UglyHedgehog.com - Forum
Copyright 2011-2024 Ugly Hedgehog, Inc.