I currenlty own a 70D and a T3i with a bunch of EF-s lenses.
My question is wether to upgrade to a couple of L lenses or upgrade to a full frame camera. Ideally I love to have a Mark III but a 6D is more realistic.
My budget is about $3500
I do real estate photography with some portrait side gigs on the side, no weddings or big projects.
Will it make sense to keep my 70D with some prime lenses for portrait photograpy? or go full frame
is there much of a difference if i used a 70-200 2.8L lens on a 70D then a 6D?
your help and expertise is greatly appreciated.
Unless you want to get into really high end real estate photography, I'd suggest you stick with your 70D for now and start gradually changing your lens line-up, with a goal to build a system that will eventually allow you to add a full frame camera to use alongside the crop sensor camera. There are advantages and limitations with both sensor formats.
I use both crop sensor and full frame cameras (a pair of 7D and a 5DII in my case, right now). I prefer the crop camera for sports/action and anything requiring longer telephoto lenses. And I like the full frame for landscape, architecture, portraiture and sometimes for macro work.
One of the reasons I choose the full frame for portraiture is control over depth of field. Now, DoF is governed by lens focal length, working distance and lens aperture.... it doesn't actually change due to different sensor formats. However, in order to frame a subject the same way with a full frame camera, it's either necessary to use a longer focal length or move closer to the subject, or a little of both. Changing either distance or focal length will tend to render shallower depth of field.
Conversely, full frame cameras can use smaller apertures before diffraction becomes an issue, so a FF also has some advantage for macro work or for landscape/architecture where great DoF is often wanted.
In generaly, there's a bit less lens selection for FF, though it's still quite extensive in the Canon system. This is because a FF camera can only use EF lenses, while your crop sensor 70D and my 7Ds can use both EF-S/crop-only and EF/full-frame-capable lenses. Also in general lenses for FF cameras will be larger, heavier and more expensive. It's most noticeable with telephotos, of course, but to some extent is true even with wide angle.
IMO, on 70D a 70-200mm is a bit long for a lot of portraiture work. My most prefered lenses for portraits with a crop sensor camera are 50/1.4, 85/1.8 and 24-70/2.8. On full frame, my most frequently used portrait lenses are 85/1.8, 135/2, 70-200/4 and 70-200/2.8. Sure, there are times that wider and longer lenses can be useful for certain types of portraits. But these are what I use most often and feel are the most basic or "traditional" focal lengths for the purpose. Short telephotos generally render the most ideal perspective for portraits. Also, I mostly shoot candid portraits, not posed. Because that often means working with less than desirable backgrounds, I prefer larger aperture lenses that allow me the option to blur down distractions behind (and sometimes in front of) the subject. If shooting in studio or more posed at a planned location, with more control over the background and other elements, it would be different and large aperture lenses would be less necessary.
Real estate photography work often calls for a wide angle and a lot of depth of field. With your crop camera, the EF-S 10-18mm you've got probably sees a lot of use. If you were shooting full frame, you'd probably want EF 16-35/2.8 or EF 16-35/4... or EF 11-24/2.8 (but that would use up most of your budget and not leave room to buy a camera to use it on). Tilt shift lenses such as the TS-E 17/4 and TS-E 24/3.5 II are also top choices for architectural photography. Compare size, weight and prices. Also, if you use filters a lot, some require larger (16-35/2.8 II uses 82mm) and the TS-E 17/4 and EF 11-24/2.8 both have stongly convex front elements that won't allow standard screw-in filters to be used at all.
There aren't many truly wide lenses for crop cameras that are also FF compatible. The EF 11-24/2.8 is one of very few. The EF 14/2.8 II is another. So, to use the crop camera for wide angle shots, you'll probably want to keep at least one or two EF-S/crop only lenses. The EF-S 10-22mm is an older lens than the EF-S 10-18mm, but is a little better built and with more edge-to-edge image sharpness... it's one of the best ultrawides made by anyone... but costs about 2X as much.
If it were me, I'd prefer the Canon EF-S 17-55/2.8 IS USM over the Sigma 17-70... but once again this is a "crop only" lens. For dual format purpose, one of the 16-35mm or the EF 17-40/4 might replace it better and be able to serve on both camera formats. I use a little longer 24-70 and 28-135 as my "walk around" or mid-range zooms.
6D is a nice camera and, compared to 70D, would be desirable for very large prints or for low light/high ISO shooting situations. That's because full frame images need less magnification for enlargement and use bigger pixel sites that capture more fine detail, both of which allow for bigger prints. Not that you'd notice much difference with 13x19 or smaller prints. And certainly you wouldn't be able to tell any difference at Internet resolutions if a lot of your stuff ends up on websites. Because the FF camera's 20MP sensor is so much less crowded than the 20MP crop sensor, there is less heat and less cross talk, making for cleaning or less noise in very high ISO images. The difference would be most noticealbe at ISO 1600 and above.
The 70D has a more sophisticated and versatile AF system, except that the 6D's can still manage to focus in one or two stops lower light (center point only). 70D has 19-point AF that's similar to original 7D, active matrix focus screen, and zone focus in addition to the all points/auto and single point/manual focus patterns offered by all Canon DSLRs. The 6D only offers the last to focus patterns, doesn't have zone, and it has a fixed (but interchangeable with a few types) focus screen.
70D's active matrix focus screen makes possible the camera's "grid on demand" feature that can be turned on or off via the menu, and which can be quite handy when shooting architecture inside or out. With 6D you can get similar grid in the viewfinder, but to do so would need need to swap out with a separately sold, accessory "D" type focus screen.
In 70D all nineteen AF points are the more sensitive dual axis/cross type, with the center one enhanced for f2.8 and faster lenses. 6D's eleven AF points have only one dual axis/cross type... the center point... while all the others are single axis type. Either camera's AF system is probably more than adequate for what you say you shoot primarily. If you were shooting sports/action/wildlife/birds, the 70D's AF system would likely be more ideal, though... so I'd rate it as more versatile. The 6D's would be a better choice for low light work, though.
70D also has articulated LCD screen and built-in flash, while 6D has neither of those features.
The 70D and 6D share batteries, chargers, memory and have mostly similar control layouts, always nice when using two different cameras interchangeably for various purposes.
So, if it were me, I'd probably keep shooting with the 70D and work on lens upgrades first, then add the FF camera later. But that's just me. Your needs might be different and call for another approach.
My stock answer is usually, get the best lens you can. Better than the camera most of the time. However sometimes a better camera is the way to go. Your requirements should determine that. A big deal is made over FF and APS-S sensor cameras. In truth all cameras are full frame. You get what you see in the view finder for the most part.
All the explaination that Alan Myers opined is right on. But I would like to submit a better way of thinking about the subject. Actually why photographers got stuck with lens millimeters as a measurement is questionable. It really describes little.
The better way is Angle of View. Once this is known, nothing else matters.
To eliminate all the confusion, perhaps it is time to stop thinking of lenses in terms of millimeters and instead identify lenses in terms of their angles-of-view. Angle-of-view (AOV) is a constant. An 84° AOV will always identify the lens as a wide-angle. On a DSLR containing a 5D Mk III (FF) this would translate into a 24mm lens, while on a 1D Mk IV (1.3x) it would be closer to an 18mm lens. There will be subtle differences between each of the resulting images based on the sensor size, but the angle-of-view will always appear the same.
IMHO, the best there is (combo) for a portrait camera is a FF with the EF 70-200mm f2.8 lens. Again this lens' AOV and its large aperture make a truly fine lens for this use. It is becoming the standard in professional portrait photography. If you want to couple that lens with the 6D, that is the cat's meow.
With the exception of the EF 50mm f1.8, none of your current lenses will work on a 6D. The brutal truth is the lenses you have are not all that great. Especially if you are considering and/or comparing them with a EF 70-200mm f2.8 As others have said the 70-200mm is a little short on the AOV for a 1.6x crop body. Using that concept you would need to find a 50-150mm lens. Sigma used to make that lens and you can find them on the used market from time to time. They were/are great lenses for crop bodies.
For WA you need to find a lens in the 75 to 100 degree range AOV. For a crop that is 12mm to 17mm. In FF that is 20mm to 24mm. Roughly! AOV is the same no matter what body the lens is used on.
I added one L lens, when using a 40D, then added a 7D, then added more L lenses and a second 7D, before adding older 5D and then 1D Mark II N cameras. (The 5D is "full" 35mm frame; the 1D II N has the in-between APS-H sensor.) My newest cameras, however, are a pair of the 7D Mark II, so "full" frame is, for me, not an "up-grade," but an option. I have generally avoided EF-S lenses, the most notable exception being my very useful, and notably low-distortion, EF-S 10-22mm. Overall, I have prioritized good lenses.
I also have the option of using the Nikon D700, which is "full" 35mm frame, roughly equivalent to a 5D Mark II, and two or three of my Nikon lenses are about L-equivalent, but still, my 7D Mark II cameras are my newest, so there is more to life than a larger sensor. It depends upon ones needs and desires.
Serious portrait shooting would be a valid reason to acquire a "full" 35mm frame camera, particularly if one wishes to create images with a shallow depth of field. I do shoot quite serious images of people, but it is because they were assault victims, and forensic/evidentiary images are created with much depth of field, starting in the range of f/8 to f/11. Portraitists, unless shooting a group, will normally want a shallow depth of field, and at a given aperture, a "full" 35mm-frame camera will have a shallower depth of field.
"Serious portrait shooting would be a valid reason to acquire a "full" 35mm frame camera, particularly if one wishes to create images with a shallow depth of field."
You don't understand AOV? If the AOV is the same, so will the DOF be. The body is immaterial.
There will be subtle differences between each of the resulting images based on the sensor size, but the AOV and DOF will always appear the same.
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