Understanding Cropped & FF cameras

[Columbarius]

I’m struggling to decide whether to spend the money I earned from a little seasonal job (No I wasn’t Father Christmas!!) on a 6D or a 70D and some more glass.

As part of this process I’ve been trying to understand the true difference between cropped & full frame images.
My thinking to date is a follows.

Let’s say I want to take a shot of a car with the 70D and my trusty 24-105 f4 L lens. I stand at a distance from the car such that the image of the car exactly fills the viewfinder at 24mm & I take the shot. (Can we ignore for the purposes of this line of reasoning the quoted 98% viewfinder coverage). The image of the car should completely fill the sensor (all 20.2mp), but the outer edges of the image projected by the lens falling outside the sensor area will be “lost”.

If I swap the lens to the 6D and stand in exactly the same location and again shoot at 24mm the car will neither fill the viewfinder nor the sensor. The outer edges of the image “lost” in the previous example will be recorded. In other words the physical size of the car in the image on either sensor will be identical, but the one on the 70d will be recorded on more pixels.

However because of larger physical size of the 6D sensor (with the same number of pixels as the 70D), each pixel is larger, and can therefore capture more light giving better high ISO performance. In addition in the above example I could zoom in to 38mm and therefore fill the frame on the 6D in the same way as I had on the 70D and the image of the car will be recorded on exactly the same number of pixels as the shot at 24mm on the 70D.

Have I got this correct??? I'd appreciate your expert feedback.

[colin C]

Re: Understanding Cropped & FF cameras

Have I got this correct??? I'd appreciate your expert feedback.

You have it spot on.

In the days of film SLR's, the size on the negative was 36mm x 24mm and that equates to the current digital Full Frame. In the early days of digital, the larger the sensor, the more expensive to produce and the higher the failure rate. We are not talking just a few pounds between a 1.6 crop and a full frame, but hundreds. As manufacturing techniques improved, larger sensors became more cost effective and it needn't be restricted to just the high end pro cameras. There was also the secondary factor of processing the image and early full frame bodies were pretty much restricted to studio and landscape work, because they were slow to process the image. That gave rise to the 1Ds for studio and the 1D with a 1.3 crop for sports and wildlife. With the technology available at the time they couldn't achieve both with the same body. That has recently change with the introduction of the 1Dx.

To have a crop camera and see the final image as a given size print, or on a screen, it is magnified by a factor of 1.6 over the same image from a full frame camera. That has an "effect" of making your telephoto's more telephoto and your wide-angles less wide-angle by a factor of 1.6x. But, in your analogy above, if you use your current lenses wisely to fill the frame as you would have with your crop camera, you will have a considerably higher quality image over your crop body, all other things being equal. Or, take the same image, from the same position with the same lens and although it looks smaller, crop the image to what it would have been with your crop body and you have the same image of the same quality, again, assuming all other things are equal.

Generally, full frame gives you more options over a cropped body and there are often bonuses such as larger pixels with smaller gaps between them providing much better quality at higher ISO's.

Hope that helps.

[Columbarius]

Re: Understanding Cropped & FF cameras

Excellent, thanks Colin.

[Mightyquin]

Re: Understanding Cropped & FF cameras

Colin has summed it up well. Crop bodies were made to provide cameras at a certain price. If FF cameras were possible at low prices to begin with would we even have crop bodies now?

But then a crop body can be smaller/lighter as can crop sensor lenses, which provides a number of advantages, and FF lenses use the best area of IQ on a crop body.

I was mostly dismissive of crop bodies but now find myself leaning toward them for size advantages mostly - a huge body & lens can be very intimidating to some people.

[Nathaniel]

Re: Understanding Cropped & FF cameras

For the reasons mentioned above I prefer to use the crop camera (like the 650D,60D,70D,7D) for wild life photography esp BIF making use of the crop factor of 1.6, which gives a larger image. For everything else I prefer to use FF now that I have got a 6D. The experts amongst us might disagree with my rationale but this is exactly what I am doing. This is also one of the reasons I am now selling my Sigma wide angle lens as I prefer a wider lens for use with my FF, and I will eventually buy a wider lens starting either at 10mm or 12mm & going up to either 24mm, 30mm or 35mm.

[Cyberman]

Re: Understanding Cropped & FF cameras

So now you understand it fully you have unenviable task of choosing between 6D and 70D.
They are both good cameras.
I have the 70D and have been very pleased with, performs well in most tasks and gives good results.
A good friend of mine has the 6D and it does give excellent results and excels in very low light.

I think it comes down to how you want to spend your cash. You could go all out and get the 6D and blow a bigger chunk of your cash, or you could get the 70D and put some of the cash towards lenses or other equipment.
I have taken the path of getting the 70D and am starting to get good glass that is future proofed if I move to full frame later.

Of course you may decide to stay with a crop sensor as you know what your lenses can do and don't want to relearn all those characteristics.
Whatever you do, have fun deciding.

[DrJon]

Re: Understanding Cropped & FF cameras

If you don't need very whizzy Auto-Focus, high burst rates, ultimate ruggedness or are size-critical the 6D is almost certainly Canon's best camera (IMHO).

Differences between smaller and bigger sensors (sorry if a bit technical, but someone might be interested):

* Smaller sensors give less field of view at a certain focal length (they don't cover as much image area), or to look at it another way you need a shorter focal length lens to get the same field of view (FoV) from the same shooting position.

* Smaller sensors capture less light at the same f-stop than bigger sensors. If you shoot at f2.8 (say) all sensor sizes get the same light per unit area, and so will require the same exposure, but the bigger sensor captures more total light (due to larger area) and so should have less noise (depending on the sensor technology). Do note that improvements in sensors (by a bit) and processing of sensor data (by a lot) are now so good that the lower noise won't be noticeable in a lot of shots, so you get the extra Depth of Field (see the next item) more-or-less "for free" a lot of the time.

* Smaller sensors give greater depth of field for the same FoV and aperture. This is an effect of using a shorter focal length for the FoV. A lot of the time this is handy, e.g. you can shoot at f2.8 and get more in focus - HOWEVER see the next section for more on that.
Getting shallow depth of field can be harder, although careful focal length and subject distance selection can help.

* Smaller sensors suffer from diffraction effects causing noticeable softening of the image at wider apertures than bigger sensor cameras. So you might not want to shoot much below f16 on a FF camera or f11 on a 1.6x crop for best sharpness. If you want the best pixel-level sharpness (rather than full-image print) you need to knock a stop off each of those with modern pixel-counts (18-21MP). Combining this with the lower noise means you can always match the greater DoF of a smaller sensor with a bigger one at the same shutter speed and with the same noise (as long as it is in a similar technology) by reducing the aperture and raising the ISO according to the difference in sensor sizes.
A pixel-level diffraction table is here (although note is a gradual effect, so not a point you should stop at, just be aware the further below it you go the more the effect): http://www.the-digital-picture.com/R...ra-Review.aspx

* Smaller sensors tend to have smaller pixels, although noise is really down to sensor size rather than pixel size unless you are pixel-peeping or cropping big-time. (Pixel size is more of a noise issue on small non-backlit sensors, where the chip's wiring can eat into the image-capture area of the pixel.) As a rule more pixels is better, as it will improve overall image sharpness. However it can lead to big files, lower burst rates, etc., plus the sharpness difference is small except for the sharpest lenses. (For example the Canon 24-70 is sharper than the Nikon 24-70 but put the Nikon on a D800 and it will give a sharper image due to the extra pixels. A much less sharp lens would only show a very small improvement.)

* One other effect of the smaller pixels is you can see extra detail on images shot at the same focal length. This is most handy on telephoto lenses, where going longer can cost stupid amounts of money. While the crop factor on Canon sensors is 1.6x the crop sensors have less pixels than the FF cameras, so you get about 1.5x the pixels across an object using the same lens (hence 2.25x by area). If your target would be within the crop sensor area of the image with your longest lens then a FF sensor just adds more crap around the edge of the picture while giving less detail in the centre. However when I looked into this you don't get 1.5x the resolution as you're further into the limits of the lens performance, so a 20-30% improvement is more likely. Then again going from a 300/2.8 to a 400/2.8 costs over three grand, so a crop camera might look attractive to 300/2.8 owners. (BTW I do own a 300/2.8 and I decided the improvement isn't worth it, especially as the Canon extenders are available to also crop the image, but optically, and the crop sensor advantage is even less when they are used.)

* Dynamic Range really doesn't go with sensor size, except at higher ISOs. My little 1" sensor RX100 has more low-ISO Dynamic Range than anything Canon make (12.4 stops vs. 11.8 for a 1Dx and 12.1 for a 6D), several crop sensor cameras have 2x-4x the Dynamic range of any of the Canon cameras at low ISO (e.g. Nikon D5300, D7100; Pentax K3; Olympus E-M1 etc.) but Canon catches up at higher ISOs. IMHO you typically end up with about 10 stops in a photo that pops, so having a stop or two more is handy to fix exposure issues, improve shadows/highlights, 14 stops is nice but of more specialised uses. Meaning this is for information and I wouldn't worry about it unless you know it's an issue for you.
Dynamic range graphs, see DR tab in Measurements tab for effects over ISO range: http://www.dxomark.com/Cameras/Compa...___895_836_812

* Some smaller sensors have advantages over bigger sensors at this point in time, e.g. Phase Detect pixels for better live-view Auto-Focus. The 70D is the extreme example of this, offering live-view AF way ahead of any of the Canon FF cameras (at time of writing).

* Smaller sensors CAN mean smaller cameras and lenses and so either less to carry or you can carry more for the same weight. For example with my 5DmkII I would carry just the 24-105 or the 85/1.2 lens with either my RX100 or the 40/2.8 for walking around, as that's all the weight I want for a non photo-specific day. With my micro 4/3 camera I carry both 24-70 (equiv focal length allowing for FoV) f2.8 and 70-200 f2.8 lenses for a bit less total weight. After all the best camera is the one you have with you. Theoretically weight change with sensor crop factor is close to a square law. However a lot of lenses used on Canon/Nikon crop DSLRs are FF lenses so the weight saving is a lot less. (Panasonic 70-200 f2.8 lens is 360g, Canon 1490g, Canon don't do a crop equivalent to the 70-200 f2.8.) It can be fun to play at camerasize.com, e.g. http://camerasize.com/compact/#381.3...7,469.389,ha,t

* Manufacturers like to "up sell" people to more expensive models, so lower models can have less features to help encourage this (or just to justify the price of the high-end models). Since the top-end FF cameras are very expensive the sensibly priced ones do tend to have stuff missing. As a top-end crop sensor camera (from manufacturers who make both crop and FF) will always be de-featured compared to a FF camera (sensor size being the feature) there is a limit to what they can charge for one, so you can get better features in a crop camera for less money. The 7D is a classic example of this. As is the Pentax K3, which is quite a bargain - Pentax don't make FF cameras, but have to compete against the pricing of camera manufacturers who do (plus they have the best range of small lenses for APS crop cameras; micro 4/3 also have a great range of small lenses designed to take advantage of their crop size).

Okay, I need a coffee... I wonder if anyone got this far? I also wonder if I typo'd in any big errors, or just wrote the wrong thing in the first place anywhere... It does look okay on a re-read though, so any errors are maybe more my brain than my typing...

John

P.S. the Sigma 18-35mm f1.8 crop lens is probably the best thing to come along for Canon crop sensor users in a long time.

P.P.S. I'd answer your conundrum as...
70D plusses - best for video auto-focus or live-view auto-focus; smaller; if you already have EF-S lenses you can still use them; a bit better for long telephoto work with lenses you have, plus equivalent length lenses cost less, the 70-300 IS for example is a cheap and good way to go long on an APS camera.
6D plusses - better for everything else; wide-angle prime lenses are still wide-angle. A really good camera IMHO. Dual-pixel AF would make it a great one, but alas life is never that simple...

[Columbarius]

Re: Understanding Cropped & FF cameras

Thank you all for your feedback. DrJon - I hope you enjoyed the coffee. You probably need it after that long and comprehensive post.

Nat illustrates the issue I was really trying to get my head round

making use of the crop factor of 1.6, which gives a larger image

. The thing is it doesn't!

The image transmitted by the lens and focused on the sensor is the same on both bodies. Let's assume the image is of a square box and the image presented to the sensor is 10 by 10 mm i.e. 100 sq mm.

On a FF this image will cover approximately 11% of the total sensor size. On a crop nearly 30%. The key difference is in the no of pixels used to record the box. On a FF 6D approximately 2.4 megapixels will be used. On a crop 70D approximately 5.9 megapixels. Of course to misquote Orwell "not all pixels are equal"

Sorry if I'm banging on about it, but this to me is an important insight, which I've now come to understand.

The issue then resolves to whether the IQ of the fewer no of 6D pixels surpasses that of 2.5 times as many 70D pixels. Always assuming I go round photographing square boxes!

Thanks again for all your feedback.

[Cyberman]

Re: Understanding Cropped & FF cameras

The issue then resolves to whether the IQ of the fewer no of 6D pixels surpasses that of 2.5 times as many 70D pixels.

I think having seen the 6D and 70D in action the 6D is definitely a great camera, and in some cases it will out perform my 70D hands down.
But I think you have two questions to ask yourself...
1. Is the difference in price an issue? The difference is not inconsiderable.
2. Will you need/use the extra imaging capabilities of the 6D?
Obviously I don't know enough about where you are on your photographic journey to answer either.

I have been thinking about whether at the moment if I had the option i would get a 6D to supplement or replace my 70D, and I don't honestly know. I think with where I am personally I would probably leave it a bit, but then again I might well give in to temptation!

[Wayne Els]

Re: Understanding Cropped & FF cameras

I prefer a wider lens for use with my FF, and I will eventually buy a wider lens starting either at 10mm or 12mm & going up to either 24mm, 30mm or 35mm.

Nat what lenses are you actually looking at? 10-12mm is über wide on a FF. This old thread may be of help. http://www.eos-magazine-forum.com/sh...-Angle-on-a-FF

Russell, having had a quick look at your flickr I think you'd be ok with a 6D but then I don't know what direction you'd like to go in with your photography.

[Nathaniel]

Re: Understanding Cropped & FF cameras

Whatever you decide on,contact Panamoz who might give you a 5% discount if you make a bank to bank transfer. They did this with my 6D. So ask them first.

Dr.Jon. Excellent resume,so much so I have printed that out for my "photo Tips" file. Thanks.

[Columbarius]

Re: Understanding Cropped & FF cameras

Thanks Cyberman, Wayne & Nat,

Where am I going with photography? What a good question! I got back into it a couple of years ago after a long break from film, b&w developing & printing,etc. in the '60s. I guess we had all watched David Hemmings in "Blow Up" & thought this is for me! Then life got in the way & photography fell by the wayside.

I started with a 550D and the kit 18-135mm lens & managed some acceptable images from the viewpoint of composition, but nothing like the sharpness & clarity that I wanted. So, following the advice on this & similar forums I started to invest in better glass & I now have the EF 24-105mm f/4.0L IS USM, EF 70-200mm f/4.0L IS USM, and Extender EF 1.4x III. Which I used on the SA trip. I was quite pleased with some of the results.

When it comes to where I want to go with photography, I'm working at two extremes on the one hand I'm keen on wildlife, particularly birds and insects. I keep bees & I'm working on a portfolio of bee related images (& yes I want a "proper" macro lens). On the other hand I do a fair amount of "reportage" work for my choir & the charity I work with.

So my current thinking is:

1: Buy a 6D and the 100mm L macro lens
2: Wait until the 7D Mark 2 (whatever it's called) is finally announced (sometime in 2014) & available & the price has stabilised. The spec will need to beat the 70D but it will probably incorporate many of the 70D features. Add that to the armoury.
3: Keep the 550D as backup until then

The combination of the two will almost certainly cover any shoots I'm likely to tackle & last me through whatever time I have left, and I won't be able to blame the tools!

That's the thinking. Does it make sense?

[colin C]

Re: Understanding Cropped & FF cameras

That's the thinking. Does it make sense?

Very logical, but don't put too much credibility on a 2014 7D MKII.

Canon's semi-pro range generally change every two years, with their Pro range somewhat longer. The 7D was introduced in 2009, so logically should have changed in 2011 and there have been regular rumours of a new model since 2011. As the 7D is twice as old as its siblings, you would have thought a new model was imminent, but then it should have been in 2011, 2012 and 2013.

Over the years I have learnt not to second guess Canon with logic. Look at some good lenses that urgently need an update, such as the 50mm f1.4 introduced in 1993. So what do they do, bring out a 50mm f1.2L alongside it. Same with the 100mm f2.8 macro, you get the 100mm f2.8 L macro alongside it.

Canon has stated that 2014 will be the year of the lens, so on the basis that Canon usually launch around three lenses a year, we are probably looking at six plus for 2014. Hmmm, there I go again second guessing Canon ............ that'll end in tears!

[Wayne Els]

Re: Understanding Cropped & FF cameras

Thanks Cyberman, Wayne & Nat,


That's the thinking. Does it make sense?

Definitely. The 6D with one of the macro's - I'm interested in the 100L but I guess maybe the 180 would be better for your bees, would be excellent. It (the 6D) would only really be challenged if you were doing BIFs and such like (IMHO).

[S_J_P]

Re: Understanding Cropped & FF cameras

To illustrate the differences between crop/full-frame when cropping-in to compensate for the different field of view, I did an unscientific test a little while ago which I posted here.

The comparison was using a 60D/6D at various ISO, and was designed to show both a comparison of image-quality and of ISO performance. It's not directly comparable with a 70D/6D as they're more evenly matched in both pixel-count and ISO performance, but I was surprised how comparable the results are when cropping-in on the Full-Frame