Full frame, crop frame "crop factor," resolution, cropping etc

[FlyingSquirrel]

I've been trying to research full frame sensors vs crop frame sensors, the so called "crop factor / magnification factor," resolution, cropping. The problem I'm having is that I am running into conflicting information and opinions...

To summarize what I want to know: For photography where having good reach is important (wildlife photography), what is really the difference between having a 1.6 crop factor sensor vs having a full frame sensor and cropping the photo in post processing? While I am aware that generally a full frame sensor will have better image quality / lower noise, I think a huge factor that needs to be considered is actually resolution / number / size of pixels, and what it really looks like when cropped.

I've read, the crop factor is really just basically showing a cropped portion of what would be captured on a full frame sensor, so you are not really getting the magnification that you think you are, you are instead getting a pre-cropped image. In these next statements, I'm not claiming that I am correct or that what I am saying is accurate, I am only stating what seems logical to me... The thing about that which doesn't make sense to me is that, you have a large amount of pixels packed into that smaller area, so it really is not like a crop of a full frame sensor because you have the higher resolution within that area. And so when they say a full frame sensor could be cropped to get the same image quality or better as a crop frame sensor, it would seem to me that you'd need the equivalent resolution of pixels for that cropped area. It doesn't seem to me that most full frame sensors have enough resolution/pixels to allow a cropped image of the same resolution that you would get with a crop sensor. To come down to a specific example, though not to limit the discussion, imagine I am comparing my Canon 7D 1.6 crop to a full frame 5d Mark III. I just can't imagine being able to crop a full frame image from the 5D down to what I'd get with the 7D and have the cropped image have enough resolution to equal out.

Additionally, I've read that the larger pixels in a full frame sensor don't carry as much fine detail when you crop down, so the cropping of a full frame sensor would not have the same apparent resolution as a crop sensor image of the same apparent magnification.

Once again, this is all just what I've read and my own thoughts on what it seems to indicate, but I don't claim to know if it's accurate, so I'm asking this question to get input from people with experience and better information then me. I really want top image quality, but I also need as much reach / as little cropping as possible, or at least for a cropped image to have high enough resolution and quality. Thanks for any input or help!

[pnodrog]

A full frame sensor is apx 36x24mm in size or 864sq mm. A canon crop sensor is apx 22.2x14.8mm or 329sq mm. To keep the same pixel density the full frame sensor needs to have 2.626 time more pixels than the cropped camera.(If pixels were 1mmsq the ratio is 864 over 329)

e.g. If the cropped sensor camera is 20mgpx the full frame will need to be 52.52mgpx to have the same resolution in the cropped area. At present it is only the Nikon D800 that comes close.

Note: The above factor of 2.626 is for canon the value is a bit lower for nikon as the cropped area is slightly larger. If you square the crop factor you also get an approximate factor to use to convert from croped area to full frame. For nikon it is 1.5x1.5 = 2.25. A 16.2mgpx D7000 (16.2x2.25=36.45mpx) is just about the same as the D800 in the cropped area.

[NorthernFocus]

You are correct in your reasoning. Don't let yourself get confused by all marketing terminology. At the end of the day, it all comes down to how many pixels comprise the image. "Cropped sensor" cameras (i.e. sensors smaller than 36x24mm) typically have higher pixel density. So for a given lens magnification, you get more pixels in an image than with a "full frame" sensor using the same lens from the same distance. The trade off for the higher pixel density is typically more noise at higher ISO settings. That is simply because whith higher pixel density the photosites on the imaging sensor in the camera are smaller therefore are exposed to less light than larger photosites on lower density sensors.

The previous post gave the example for 1.6 crop Canon sensors vs. full frame. Nikon's ratio is 1.5 so an FX sensor has 2.25 (1.5x1.5) times the total area of their DX sensor. The D800 is a 36MP FX sensor. It has a DX shooting mode which produces 16MP images which are the same size as the Nikon D7000 images. You are correct that one could shoot the D800 in FX mode then crop in post processing to get exactly the same image with the same number of pixels.

The whole magnification effect of cropped sensor cameras is purely a marketing strategy. However, one advantage one rarely heres about is that if one shoots a cropped sensor camera with full frame lenses, the light that falls on the sensor is the middle portion of the image which tends to be the sharpest area for most lenses.

[pnodrog]

Sorry Dan you put your post up while I was editing mine due to a silly input error when doing my original calculation. I added a bit more before exiting and on reviewing see you made the same D7000 to D800 comparison. Reassuring that we agree.

[William W]

To summarize what I want to know: For photography where having good reach is important (wildlife photography), what is really the difference between having a 1.6 crop factor sensor vs having a full frame sensor and cropping the photo in post processing? While I am aware that generally a full frame sensor will have better image quality / lower noise, I think a huge factor that needs to be considered is actually resolution / number / size of pixels, and what it really looks like when cropped.

Yes.

It is not an "huge" factor. But it is one of the factors required for an accurate comparison: and it is often the factor which is omitted from the conversation - so, omitting it, makes it 'huge' in that sense.


***

I've read, the crop factor is really just basically showing a cropped portion of what would be captured on a full frame sensor, so you are not really getting the magnification that you think you are, you are instead getting a pre-cropped image.

Yes.

A lot of the confusion is brought about by that word.

There is no "magnification" happening when you take the 200mm lens off the 5D and then plonk it onto the 7D.

Magnification (in Photography Terms) is independent of sensor size.

*

To come down to a specific example, though not to limit the discussion, imagine I am comparing my Canon 7D 1.6 crop to a full frame 5d Mark III. I just can't imagine being able to crop a full frame image from the 5D down to what I'd get with the 7D and have the cropped image have enough resolution to equal out.

Correct.

I have a dual-format kit comprising 5D’s and APS-C Bodies.

It is indeed worthwhile having an 18MP 1.6-factor body (e.g. a 7D) to supplement the 5DIII (22MP), just in terms of the 'reach'.

It can also be very sensible discussing the pros and cons of buying a 5DMkIII to supplement a 7D, for other reasons.

But, it's not really a sensible conversation extolling the value of 'the extra reach of the crop factor', when one is considering an 8MP body (e.g. a 20D & 30D) and comparing those cameras to a 5DMkIII.

And it is scarcely worth having that same conversation using a 40D (10MP) as an example: because 22MP on the 5DMkIII when cropped to the 1.6-factor is around-about 10MP and the 5DMkIII is superior in so many other factors.

So when the "buy APS-C for the extra reach" conversation begins, it is always advisable to know what cameras are being compared.

*

It appears to me that you’ve got a pretty good handle on it, Matt.

WW

[NorthernFocus]

Sorry Dan you put your post up while I was editing mine due to a silly input error when doing my original calculation. I added a bit more before exiting and on reviewing see you made the same D7000 to D800 comparison. Reassuring that we agree.

Not to worry. There are quite a few knowledgealbe people on this site. On some other sites that I frequent there would have already been half a dozen wrong answers, as many informed ones, and then it would degenerated into an arguement over who has the biggest .... well you know what I mean.

[Glenn NK]

For photography where having good reach is important (wildlife photography), what is really the difference between having a 1.6 crop factor sensor vs having a full frame sensor and cropping the photo in post processing? While I am aware that generally a full frame sensor will have better image quality / lower noise, I think a huge factor that needs to be considered is actually resolution / number / size of pixels, and what it really looks like when cropped.

I've read, the crop factor is really just basically showing a cropped portion of what would be captured on a full frame sensor, so you are not really getting the magnification that you think you are, you are instead getting a pre-cropped image.

I think you've got it.

I have both the 30D (1.6 crop), and the 5DII bodies; the 30D sensor has about 8.2 MP, the 5DII about 21.1 MP.

Shooting with the same lens on both bodies from the same position at the same image, when I crop the 5DII image to the same size, the remaining number of pixels (resolution) is very close to being the same as the number of pixels in the 30D image.

21.1 divided by the square of 1.6 = 8.2 MP (pretty close eh?)

When doing macro/closeup work, I use either body - the 5DII has one advantage: it has live view. The difference in the images in negligible - at least I can't tell them apart.

Glenn

[William W]

. . . and then it would degenerated into an arguement over who has the biggest .... well you know what I mean.

haha

[DanK]

so it really is not like a crop of a full frame sensor because you have the higher resolution within that area. And so when they say a full frame sensor could be cropped to get the same image quality or better as a crop frame sensor, it would seem to me that you'd need the equivalent resolution of pixels for that cropped area.

Exactly right. This is why I stay with a crop sensor for macro work. At minimum working distance with a 1:1 macro lens, a given subject occupies the same physical area on the sensor, regardless of sensor size. Crop a FF image, and you end up with far fewer pixels.

There are some clear advantages of FF, such as less high-ISO noise (there are advantages to the larger photosites) and shallower DOF for a given aperture. However, for my uses, the reach of a crop more than offsets them.

[FlyingSquirrel]

Thank you, to everyone who replied. It feels good to finally get a handle on all of this, after struggling a bit with the concepts (and, the math ). It's also nice to know that my gut instincts were correct, and my suspicions have been confirmed regarding cropping and resolution, etc. I'll stick with my 7D until Canon comes out with a 50mgpx full frame body (...er...then again, if they did it would probably cost at least $10K )

Now the only disappointment is that I am left with my 7D's unsatisfactory noise levels and slightly less than professional performance and capabilities. Boooooo

[dan marchant]

Now the only disappointment is that I am left with my 7D's unsatisfactory noise levels and slightly less than professional performance and capabilities. Boooooo

Seriously? The 7D is a great camera. If you don't like it feel free to send it my way.

[Adrian]

Excellent info in this thread. We happen to have a 5DIII and a 7D and have frequently (though informally) made this comparison with the same lenses. Leaving aside the basic mathematics, is your point about how the pictures actually look. In practice in decent light, you can crop the 5DIII and get what appears on screen or a print up to A4 size (I never print larger than that) IQ that is extremely similar.

I do a lot of street photography and in that role I find the full frame a big advantage. A wide angle lens really is wide on a FF. I have also done a lot of night photography this year (Aurora) and the FF wins hands down.

On the other hand, we did a trip to Asia and a good deal of wild life photography from a boat. Crop camera was better for that as our longest lens is only 300mm. Horses for courses. 7D is a great tool.

[William W]

I do a lot of street photography and in that role I find the full frame a big advantage. A wide angle lens really is wide on a FF. I have also done a lot of night photography this year (Aurora) and the FF wins hands down

. . . and wide lens for 135 Format ('Full Frame') Cameras can be really FAST (Max Aperture): which is a much appreciated asset for both Street Photography and Nightscapes, sans star-trails.

WW

[rpcrowe]

A 5Diii + 7D would be a nice combination. However, I opted to stay with the 1.6 factor cameras and purchased a second 7D (I always shoot with two cameras).

Previously I used a 30D + 40D for a trip to China. I liked using the same batteries + memory cards for both cameras.

When I began using a 7D + 40D combination, I needed to bring a second type of battery and charger on any trip (although both cameras used the same CF memory cards). This is not a big problem but, since I believe in redundancy, I would bring two chargers for each battery type (A friend left a charger in a hotel room on a trip to China and had the Devil's own time replacing it). Bringing two chargers is easier than bringing four chargers.

Different batteries can be a logistical problem. I was shooting deep in the Carlsbad Caverns of New Mexico when to my chagrin, I realized that rather than bring a replacement battery for each camera down into the caves, I had brought two batteries for my 350D.

I absolutely love my 17-55mm f/2.8 IS lens and use it quite effectively as a low light lens (due to the constant f/2.8 aperture and great low light auto-focus). I don't usually need to travel with a faster lens like I used to. The 17-55mm f/2.8 IS lens is one reason I remain with crop format equipment. Another reason is that the quality I get using top-line lenses satisfies my needs quite well.

I am not a great fan of UWA imagery. I have a 12-24mm f/4 Tokina which gives me all the side to side coverage I need (actually, the 17mm side of my mid-range zoom is wide enough for most of my coverage). I am however, a great fan of long focal lengths.

Although I have always shot with a pair of digital cameras, this is the first time that I have had the luxury of shooting with identical cameras. I have not had this luxury since shooting with a pair of Leica M-2 rangefinder cameras in the 1960's. I have always been shooting with cameras one model or more apart: 10D + 350D that was a terrible combination; 10D + 30D; 40D + 30D; 7D + 40D. Now, I have a pair of identical cameras and since I will be 73 in the next week, these will probably satisfy my needs for the rest of my life. It is nice to have all the dials, menues, etc. identical between the two cameras. I have even found out that the RRS L-bracket for my 40D will fit my 7D relatively well. I cannot access the door for the remote cable (without loosening the L-bracket) when using the 40D bracket on the 7D but, I can live with that...

By the way, I don't really worry about crop factors and equivalent focal lengths. I know what I get with my lenses on my 1.6x gear and that is all I need to know...

[Cantab]

A 5Diii + 7D would be a nice combination. However, I opted to stay with the 1.6 factor cameras and purchased a second 7D (I always shoot with two cameras)....

Richard, you've got me wondering about whether my next luxury purchase should be a second camera I'm currently shooting with a Canon 60D. Two cameras would reduce the need to swap lenses but I suppose might be a bit more to lug around or, more realistically, carry out to the car.

[NorthernFocus]

...By the way, I don't really worry about crop factors and equivalent focal lengths. I know what I get with my lenses on my 1.6x gear and that is all I need to know...

Amen!

I've been wondering when we're going to stop talking about crop vs full frame sensors and simply talk about resolution. Recall when the industry started the notion of additional reach of digital cameras, there were no full frame sensors on the market from the majors. The discussion was a marketing concept and a way to explain relative to 35mm film format which at the time was the standard. However, now with multiple models of cameras in multiple formats with various pixel densities, as discussed in this thread, the idea of a cropped sensor having more "reach" is no longer a given.

Let's all agree to be specific and say, Camera X has more reach than camera Y. And when an uninitiated person asks why, let's reply, "because the sensor has higher pixel density", not "because it is a cropped sensor camera".

[ajohnw]

I haven't read all of this thread but there are factors other than pixel count to think about. As an example I have recently switched almost exclusively to micro 4/3. It started with a humble olympus E-PL1 more or less out of curiosity. That is a 12mp sensor that is significantly smaller than aps. I found that as far as PC screen photo's go I could crop them directly out of a full frame image. This a link to one using the standard zoom lens that comes with the camera.

http://www.23hq.com/ajohnw/photo/8090641/original

This is a full frame shot taken with a 100mm Pentax manual film macro lens on the same camera. Forgive me for the slight out of focus at the wing extremes. Manual focusing needs 7x magnification at least and only part of the subject is in view. Click on it to expand it opened in another tab.

http://www.23hq.com/ajohnw/photo/8059501/original

Being happy with the format I now have an OM EM-5. I can carry 12-600mm via 3 lenses easily. 2 by Olympus and 1 by Panasonic. Total weight is just on 2kg and the stuff fits in a small thick canvas shoulder bag. I've also added auto extension tubes to get round macro focusing problems and will probably use them with the Panasonic 100-300mm lens. The OM also offers full time image stabilisation which will make manual lens focusing a lot easier if I feel the need.

In my view from this there is a lot of scope on sensor size but the only format that offers a real advantage crop factor magnification wise and weight wise is micro 4/3. Curiously Olympus's cheaper mostly plastic lenses are rather good. I don't rate Panasonic's to 200mm zoom other than that it's cheap.

The OM is a 16mp camera. This is another area. In real terms other than in camera tests the move from 12 to 16mp doesn't really make any difference. The lens is the main limitation which ever make you buy these days apart from perhaps the very high end full frame cameras coupled with very high end very long focal length lenses. These cameras tend to have lower pixel densities than say APS. Part of this is down to manufacturing problems which the producers strive to improve. Compacts with absolutely tiny sensors with masses and masses of pixels illustrate this. Sounds odd but after a fashion and within certain limitations the smaller the sensor the higher the pixel density can be. It will be interesting to see if they ever manage to match the OM's pixel density on APS.

I'm not suggesting you buy an OM. Just using them as an example of the variations and gains if any from sensor size. My full frame lens which gives me around 500mm on aps probably weighs the same as my entire micro 4/3 kit. I've taken a lot of shots with the Pen and there is a learning curve. Mostly exposing for high lights with care and bringing out the dark end later. Not much done with the OM over the winter but I have a feeling it's different in that respect. This may be due to the use of a Sony sensor rather than the previous one which was by Panasonic. I feel it's likely to be an easier camera to use.

John
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[rpcrowe]

Richard, you've got me wondering about whether my next luxury purchase should be a second camera I'm currently shooting with a Canon 60D. Two cameras would reduce the need to swap lenses but I suppose might be a bit more to lug around or, more realistically, carry out to the car.

Yes, an extra camera is definitely extra weight. My 7D cameras weigh 1.8 lb / 816 g each, so that is the price that I pay in weight for the ease of shooting with two cameras. I am willing to lug the extra weight because I really enjoy having a focal range of 17-200mm at my finger tips without switching lenses. I shoot with 17-55mm f/2.8 IS and 70-200mm f/4L IS lenses which are to me perfect. I don't miss the 55-70mm gap between the lenses.

There are several other advantages other than having that focal range.

I will be able to get shots very quickly if I need a different focal length

The sensors on my cameras seldom need cleaning because the cameras are seldom without lenses attached.

Excellent image quality and, fast, accurate autofocus throughout the range

IS capability throughout the range

Constant f/2.8 aperture in my mid-range 17-55mm zoom and constant f/4 in my 70-200mm tele zoom

Since I am shooting with two cameras I have 32 Gb of memory before changing cards (16 Gb card in each camera)

I have more images before changing batteries. I could use a battery grip to get extra images. However, a battery grip adds over 15 ounces or about half the weight of a second camera. Few people think twice of using a battery grip but, many think that an extra body is too heavy.

The extra body does cost more. However, I used a 40D paired with my 7D for a long time and used a 30D paired with the 40D before that. An extra 40D or 50D body would not be that expensive. I got my extra 7D body refurbished and on sale at Adorama. Plus, I didn't have to pay shipping or state sales tax on the purchase. A refurb 60D runs $579 USD from Adorama. I don't know about taxes or shipping up north.

An important aspect of having a second camera is that the second body is an insurance policy against missing out on photography due to a malfunctioning camera. I fell on a slippery slope in Alaska and broke my 40D. However my 30D saved the trip photographically. A fellow tour member fell in front of the Xi'an, China City Walls and broke his Nikon DSLR. He had no backup camera and missed out on photography until the tour arrived in Hong Kong several cities later when he bought a replacement camera (with no USA warranty).

This is the first time I have had the luxury of shooting with two identical cameras. It's not a great problem but, it is nice when all the buttons and dials are in the same place on both cameras.

I carry my two cameras in two different ways.

When there is little chance of a snatch and grab thief, I use an OPTECH Dual Harness. I carried my cameras that way during my two week trip to China. Even in crowds like this...


I will also carry one camera (with my 17-55mm lens) on a security strap (incorporating a metal cable to foil a cut-purse thief) around my neck and the second camera (with the 70-200mm lens) in a Tamrac Holster case. I have a hand strap on that camera and a hood on the lens. It is ready to shoot as I draw it from the holster. The rest of my gear is distributed through the pockets of my photo vest.

I have been sold on a two camera system and have been shoting with two cameras for years...

[ajohnw]

My spare camera is an Olympus Pen E-P3. I suspect this may be the best Pen they have made. Same lenses and apart from situations where I may need a touch of manual focusing for one reason or the other in many cases it's as capable as the OM but smaller, lighter and not moisture proofed. It's certainly fine for all what might be called normal photography where AF is likely to be ok.

Scene wise this isn't a very well post processes shot, dull wet rainy days but it gives some idea of the formats capabilities

http://backup.cambridgeincolour.com/...98480/original

John
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[Manfred M]

One other "downside" of crop frame versus full-frame shooters is that you get a wider DoF, by around 1 stop with crop frame. In other words, shooting f/2.8 on a crop frame gives you roughly the same DoF that f/4 does on a full-frame.