Background blur on full frame vs crop

[kirsty_smith]

<p>Hi, I have a question about image apperance with a full frame body versus a 1.6 crop body.<br>

I have been using a Canon 20D for several years and I do alot of macro photography with the 100mm F2.8 macro lens (this becomes a 160mm magnification on the 1.6 body). I love the out of focus background effect that I get with this focal length in my macro pictures on the 20D body. <br>

My question is will I still get the same level of background blur if I start to use the 100mm lens on a full frame body(5D markii) as compared to the 1.6 crop body? or would I have a reduction in background blur as I would expect if I compared images taken with a separate 160mm lens (more blur) to ones taken with a 100mm lens (less blur)?<br>

My feeling is that a 20D image is essentially just a cropped version of the full frame sensor image, and that the level of image blur is dictated only by the lens itself.....so changing to a full frame body (with the same lens) would not make a difference to this effect. <br>

Or is my thinking all wrong?<br>

Thanks for any help</p>

<p>Kirsty</p>

[john_macpherson]

<blockquote>

<p>My feeling is that a 20D image is essentially just a cropped version of the full frame sensor image, and that the level of image blur is dictated only by the lens itself.....so changing to a full frame body (with the same lens) would not make a difference to this effect.</p>

 

</blockquote>

<p>Your thinking is right.</p>

<p>However if you change your working distance from the subject (to keep the subject size constant) the background blur will change due to the different focus distances between the 100mm and the apparent 160mm.</p>

[kirsty_smith]

<p>Hmmmm, I see that makes sense. I wonder how this actually translates to the pictures at the end of the day. Does anyone have experience of using the Canon 100mm macro lens on a full frame and a 1.6 crop body? Do you notice much difference in your images or have any preferences for one sensor over the other with this type of close-up work?<br>

Thanks</p>

[ed_v.]

<p>I don't do macrophotography, nor do I have a full frame camera (mine is a 40D). But, this is an interesting topic and I'm still learning about it myself. Due to optical physics, background blur is affected by camera-to-subject distance. The closer the sensor is to the subject, the narrower the depth of field and the blurrier the background . So, with a full frame sensor the background would blur more since you've got to move in closer to the subject.</p>

[tdigi]

<p>From what I understand Ed V is correct. I have used the 100 macro on FF and APS-C and to get the same shot one would need to be closer creating a more shallow depth of field. This could be good or bad since shooting at macro distances the depth of field is already very shallow. </p>

[mendel_leisk]

<p>Just to flog it:</p>

<p>Comparing to a full-frame camera: to achieve the same angle of view on a crop-factor camera, you need to use a shorter focal length.</p>

<p>The difference is directly related to the crop factor, ie: a 50mm focal length on full-frame corresponds to 50/1.6mm (31.25mm, if it were available) focal length on a 1.6 cropped sensor on the typical Canon crop-body.</p>

<p>And it follows, since shorter focal length lens have greater depth of focus, a shot with any angle of view taken with a crop-factor camera will have greater depth of focus than a similar angle of view shot taken with a full frame camera.</p>

[bobatkins]

<p>Smaller format = more depth of field = less background blur.</p>

<p>That's the simple explanation. The more complex answer can be found at http://www.bobatkins.com/photography/technical/bokeh.html.</p>

<p>DOF and background blur aren't quite the same thing and they are not governed by the same optical parameters, but in general the larger the format, the faster the lens and the longer the focal length, the more the distant background (i.e. that backround well outside the DOF) will blur.</p>

[nathangardner]

<p>full frame cameras take in the outside edges of the image circle projected to the back of the camera that the aps-c sensor misses, therefore creating greater background blur. The sharpest part of the image is in the center of the circle and the outer edges produce the most blur.</p>

[kirsty_smith]

<p>So I would get more background blur with a larger sensor (because the lens has to be closer to the subject)...... but regarding just the focal length effect.... would switching to a full frame body from a 1.6 crop body with the same 100mm lens cause the same reduction in background blur (not talking about DOF) as switching to a shorter focal length lens on the same body?<br>

As the effective focal length of my 100mm is 160mm on the crop body, would I need to use a 160mm lens on the FF body to get the same background blur? .....<br>

Basically I'm just concerned that if I go out and buy a full frame body, my 100mm macro shots just won't show the same subject isolation capability, and that to get the same kind of background blur I will have to go and buy a 180mm macro lens, which I cannot afford!<br>

Thanks for all your responses.</p>

 

[craig_meddaugh]

<p>When you switch to full frame, your field of view is going to get wider, increasing the probability of capturing something distracting in the background. You'll be able to compensate somewhat by being more careful in your composition, but I frankly don't feel that 100mm is long enough for effective subject isolation on a 1.6 body and prefer to do my macro work with far longer lenses when possible. I suspect that you might feel the same. However, Tamron and Sigma both make excellent 180mm macros that are quite affordable. </p>

[tom_mann1]

<p>Bob Atkins is truly an expert on this subject and has written numerous articles on the topic. Below are links to some of his articles as well as other discussions of DOF, blur, sensor size, etc.: </p>

<p>http://www.luminous-landscape.com/tutorials/understanding-series/dof.shtml<br>

http://www.luminous-landscape.com/tutorials/dof2.shtml<br>

http://www.bobatkins.com/photography/technical/<br>

http://www.bobatkins.com/photography/technical/bokeh.html<br>

http://www.bobatkins.com/photography/technical/digitaldof.html</p>

<p>http://www.naturescapes.net/docs/index.php/category-photographic-technique/57-the-mathematics-of-depth-of-field-part-two-crop-factor-magnification-and-the-13-myth</p>

<p>In addition, it seems that this question is asked every couple of weeks on photo.net. A quick search will turn up many threads which ask essentially the same question, e.g.:<br>

http://www.photo.net/nikon-camera-forum/00WZBp ( May 30, 2010 )</p>

<p>However, I suggest you start with the above articles (more or less arranged from simple to difficult), not the more casual threads.</p>

<p>HTH,</p>

<p>Tom M.</p>

[nathangardner]

<p>I think you'll get even more background blur by switching to full frame, but keep in mind that since the APS-C sensor is smaller, it makes your 1X lifesize macro like a 1.6X lifesize. While 1X lifesize is still great, it will be less than you're used to. Yes you can move closer with the FF, but the minimum focusing distance will still be the same; and at that distance the FF will take in more of the subject than the APS-C, making it look not quite as big in the frame as the APS-C.</p>

[scott_ferris]

<p>kirsty,</p>

<p>As you said, if you want to get exactly the same image from your ff as your crop then just keep subject distance the same and you are good to crop, the images, backgrounds, blur etc will be identical. You have the option of getting different effects with narrower DOF if you re-frame but if you want exactly what you have you can do that too.</p>

[jim_krupnik]

<p>The Hasselblad site offers a good tutorial with plenty of illustrations describing the sensor size vs DOF issue. In a practical sense, an identical scene can be recorded on a FF 35 mm camera, an APS-C camera, a 6x4.5 medium format camera, and a 6x7 medium format camera by using a lens with the appropriate coverage for each format. For the example above, say a 50 mm, 35 mm, 80 mm, and a 110 mm lens will capture about the same image area in each camera. If shallow DOF is important though, smaller image formats require faster apertures than larger image formats. In this case, if the FF 35 mm camera took a shot at f/2.8, the APS-C camera would need a 35 mm f/2.0 lens to match it in both image area, and DOF, while the 6x4.5 camera with an 80 mm lens could do it at f/4, and the 6x7 camera with the 110 mm lens only needs f/5.6 to match the EE 50 f/2.8 shot for area and DOF.</p>

<p>That explains why fast lenses are such important offerings for crop camera manufacturers. Modern sensors can deal with a lens sporting a max f/4 aperture, but image for image, f/4 on a crop camera can only deliver the shallow DOF of an f/5.6 lens on a FF camera. Likewise, that explains why lenses for MF cameras are usually f/4 wide open, and an f/2.8 MF lens is considered super fast. In MF sizes, f/2.8 can deliver razor thin DOF that would require one or two stops more to match on a FF 35 mm camera. At f/4, a MF camera can deliver shallow DOF that suits most needs, and is easy to build without compromise and high expense.</p>

<p>FF 35 mm is the goal for many, but as sensor tech improves, it improves at all levels, and just as it was in the film days, the pendulum is swinging back to the point where FF meant medium format. IQ between FF 35, and APS-C will end up pretty close, and lens choice can make up for DOF differences, but the sheer image real estate offered by a 6x6 or 6x7 MF camera with the same sensor technology will run away with the show.</p>

[daniel flather]

<p>If it's bokeh you want, buy the EF 200mm f2 L IS USM.</p>

<p> </p>

[mjferron]

<p>Tough call as DOF is affected by many different variables. APS in general has more DOF because you'll need to shoot the APS with a 24mm lens to get the same field of view with a full frame using a 35mm lens. Wider lenses have more DOF.</p>

<p>Put a 100 macro on your 20D and you get to stand back further than you would with full frame. That will give you more DOF. The closer you are to the subject the less DOF you have. I've found no matter what camera I'm using finding sufficient DOF is problem when shooting macros. The 4/3 cameras have a bit of an advantage with their increased DOF due to the smaller sensor. I find with todays fine digital cameras stepping back a bit and cropping some will increase that DOF and still let you make a fair sized quality print.</p>

[joe_c5]

<blockquote>

<p>would switching to a full frame body from a 1.6 crop body with the same 100mm lens cause the same reduction in background blur (not talking about DOF) as switching to a shorter focal length lens on the same body?</p>

</blockquote>

<p>For starters the full frame body should increase background blur rather than decreasing it, unless you were already at maximum magnification on the crop body. At true macro working distances, not particularly, since the depth of field will depend more on the magnification than the focal length. The full frame body should decrease the depth of field, whereas the shorter focal length lens will barely change the depth of field as long as the magnification stays the same. At longer distances, a 100mm f/2.8 lens on a full frame body would look similar to a 62mm f/1.8 lens on a crop body.</p>

<p>By the way, I have never heard of anybody trying to decrease depth of field for macro photography. Normally the trick seems to be getting much of the subject in focus at all. Sometimes people stitch together multiple focus-bracketed images just to get a larger depth of field.</p>

<p>To your specific point about background blur versus depth of field, your best bet is to have the background farther away from the subject. At macro working distances the background should blur <em>very </em>quickly with increasing distances.</p>

<blockquote>

<p>Basically I'm just concerned that if I go out and buy a full frame body, my 100mm macro shots just won't show the same subject isolation capability, and that to get the same kind of background blur I will have to go and buy a 180mm macro lens</p>

</blockquote>

<p>The reverse is true, that the background isolation will nearly always be better or at least equal on the full frame body, even with the same lens.</p>

<p>And finally, if you cannot afford a 180mm macro lens, I recommend against buying a full frame camera body without a very specific reason. I speak from experience, since I bought a Canon 5D with only a general reason and can no longer particularly afford a 180mm macro lens.</p>

[sarah_fox]

<p>As others have said, larger format => shallower DoF for any given field of view. This and other differences between full frame and crop-format discussed here...</p>

<p><a href="http://www.graphic-fusion.com/fullframe.htm">http://www.graphic-fusion.com/fullframe.htm</a></p>

 

[john_bolton2]

<p>FF has deeper DOF than crop with same lens and same distance to subject. However, considering you'll need to move in even much closer to your subject with FF for same apparent subject size (FOV), the DOF will be more shallow.</p>

[kirsty_smith]

<p>Well, I can see that this is a very complex issue!, but I think I can conclude especially from what Scott and John have said that changing from a crop sensor to a full frame sensor (with the same 100mm lens, aperture and working distance, ) would not effect the image other than to capture a wider view on the FF sensor. The image is identical on the sensor apart from the fact that the crop body shows less of it. I could actually crop away the access on the FF image and get an identical result to the crop image........so background blur would not decrease in the same way as if I shot with a 180mm lens and then switched to a 100mm lens on the same body due to focal length and lens magnification change.<br>

In response to Joe.C's comment, I am not specifically looking to get less DOF in my images, I just like the great background blur and therefore subject isolation that you get with longer focal length macro lenses so was only concerned that switching to a FF body would effectively render my 100mm lens as a 60mm, but I think this is not the case, the magnification of the lens has not changed only the crop of the image. ..........In addition, the reason I wanted to get the FF body was because the superb increase in image quaility and iso capability would take my macro photography to another level and allow me much more versatility in getting great hand held macro shots even in lower light. Craig also mentioned that you can get good and significantly cheaper longer focal length macro lenses from Sigma, which could be a good option with the FF body, if I decide to also get a longer lens.<br>

Thanks for all your resposnses and to Bob, Tom and Sarah for the articles. I think I need to do some serious reading on background blur and DOF!</p>

 

[joe_c5]

<blockquote>

<p>In addition, the reason I wanted to get the FF body was because the superb increase in image quaility and iso capability would take my macro photography to another level and allow me much more versatility in getting great hand held macro shots even in lower light.</p>

</blockquote>

<p>This is similar to the reasons I bought a full frame camera, other than the macro. What I discovered was that, for a given depth of field, the handheld low light performance was nearly identical to that of a crop camera. Most if not all of the extra dynamic range was in the highlights instead of the shadows.</p>

<p>I also found that the increased vignetting on full frame at large apertures took back much of the extra light gathered even if I had no issues with the lower depth of field on the full frame camera. Some types of lens aberration were also worse at the corners. Essentially the center of the image was better with the full frame camera, but the corners were arguably worse. With EF-S lenses the crop camera would have the same effects and the full frame would show more benefits, but you are not using the EF-S 60mm macro.</p>

<p>All I am really suggesting is to keep in mind that a full frame camera can be a trade-off rather than being categorically superior. Yes, you can always crop the full frame image to get back to where you before, but even that adds an extra step.</p>

[ty_mickan]

<p>a 100mm lens will have the same properties, regardless of what camera it is mounted on. as explained above though, if you move back to acheive a similar composition with the 1/2 sensor, then the boke will differ.</p>

[photom]

<p>Not sure if this would help but:</p>

<p>Say you are shooting a bug from 3.7 ft. away with the 100 macro at f11. The calculated DOF is about 1.9 in. and the frame diagonal of the image is 1 ft. 0in.</p>

<p>If you want the same shot (diagonal frame size) on FF, you will need to move in to 2.32 ft. and the new DOF will be - IF you used the same aperture of f11 - would 1.1 in.</p>

<p>The above is the simple answer because it compares the same aperture. DOF is quite a bit different. But, if you increase the aperture on the FF to f16, the DOF increases to 1.6 in.</p>

[mendel_leisk]

<blockquote>

<p>I think I need to do some serious reading on background blur and DOF!</p>

</blockquote>

<p>Not really. All you really need to do is re-read some of the above postings, mine included. Lemme try again:</p>

<p>It takes a wider lens to achieve the same field of view on a crop-factor camera. Wider lens have greater depth of focus.</p>

[kirsty_smith]

<p>

<p >

<p >

<p >Joe, about your comments about the full frame sensor and how using a FF is not, at the end of the day necessarily going to give you that much extra dynamic range. I was surprised at this given that the ISO capabilities are so much better on the FF compared to the crop...my understanding is you can get noise free images up to 800ASA ?...but I understand vignetting is a problem with the FF. If I end up having to crop back the FF image to get as good an image as on the crop body there is no justification for spending the extra 1000 for the 5D markii</p>

<p >Essentially the issue here is that I have a 20D body and a 100mm 2.8 canon macro lens. I get great macro shots with this lens and love it but I really want to change the body...the 20D is really outdated now and is only an 8 MP camera so I can't print images very large. Its time for an upgrade. I want to get the best combination of equipment for macro photography. Does anyone have an advice, or recommendations?</p>

<p >I can just about afford the Canon 5Dmark ii and a 150mm sigma 2.8 lens. Or alternatively I can just get a new crop body (which may be a better choice given Joe C's comments) in which case I would be looking at the 50D versus the 7D.....Ultimately I want a good camera body, I will still use my 100mm, and then possibly get a longer macro as well.</p>

<p >Cheers</p>

</p>

</p>

</p>