Comparing lenses for full frame vs. APS-C sensors

[xpatUSA]

Originally Posted by xpatUSA hello Tom. How do you measure resolution?

Pixels per image.

Oh, I see. I haven't seen that definition before ... interesting.

[ajax]

... (I don't think that "upgrading" is a helpful way of looking at this -- most FF Nikons would be a downgrade from my current camera.) ...

It looks like the D500 is priced at or above some entry level FF mirrorless cameras and well above my entry level APS-C from Canon. This also includes some from Nikon (e.g., Z5). Can you elaborate on why a FF would be a downgrade? I suppose that might be the same as asking what makes the D500 (APS-C) worth that much more than the much less expensive APS-C cameras?

I think I've been guilty of thinking that FF is just part of what you get if you're willing to spend enough money.

[tclune]

Oh, OK. I haven't seen that definition before ... interesting.

Well, definitions that boil down to that idea are common -- lp/ph (line pairs per picture height) and lw/ph (line widths per picture height) are routinely used in reviews. In any case, talking about "resolution" of a camera body will necessarily be pretty loosey-goosey no matter what units you decide to employ. But, in the context of discussing the resolution of an image, using a metric that omits the total number of pixels seems pretty uninformative. And anything that would seem to suggest that a 20 MP image has higher resolution than a comparable 45 MP image would require some very fancy footwork to explain.

[ajax]

If you were to go full frame, David, what would you do with your current kit? Ditch/sell it and start again? ...

I'm a little slow but I do have an answer for that question. This is something I've had in mind for some time now. What triggered the desire to act is that I have a granddaughter who is studying photography in school and wants a real camera as opposed to a phone. She is saving to buy something like what I have. With a worthy replacement she could have mine and even if NOT brand new the price might be enticing.

[ajax]

Have you thought about hiring or borrowing some new kit to try it out before you buy?
...

That is a GREAT idea but I'm afraid I have no idea about how to do it. When you say "hiring" that makes me think you might mean rent. How might that be done?

[xpatUSA]

Well, definitions that boil down to that idea are common -- lp/ph (line pairs per picture height) and lw/ph (line widths per picture height) are routinely used in reviews. In any case, talking about "resolution" of a camera body will necessarily be pretty loosey-goosey no matter what units you decide to employ. But, in the context of discussing the resolution of an image, using a metric that omits the total number of pixels seems pretty uninformative. And anything that would seem to suggest that a 20 MP image has higher resolution than a comparable 45 MP image would require some very fancy footwork to explain.

Thank you for clarifying your view, which by "comparable" appears to mean exactly the same image size on the same medium with no resampling and the same zoom percentage. The statement however only makes sense with your definition - "pixels per image" and your definition can not apply to all images, even if equal in all respects.

I too find the common "lp/ph" to be quite "loosey-goosey", preferring instead to think of MTF (Modulation Transfer Function) at a given level or frequency ... similarly to lenses, which have no idea what height an image is or how many pixels it contains.

[ajax]

My original post had a much narrower purpose than where this discussion has ended up going which does seem to remain focused on the difference between FF & APS-C sensors.

Something else that I've always attributed to full frame cameras is better quality lenses. In that, APS-C provides a way to reduce cost/price which creates a need to keep the cost/price of lenses lower. From a technical point of view, a simple minded way to think about it is that smaller is less costly to produce. Now that I've taken a little deeper dive I'm thinking it matters, at least as much and possibly more, what lens is being used. Something else that's become apparent is that there are lots of different options for lenses. Apparently, this includes both full frame and APS-C ones which may be what I hadn't previously appreciated. While some differences in lenses have to do with application (i.e., portrait, landscape, etc. etc.) image quality is also a relevant factor. This suggests that some consideration needs to be paid to limitations of both the body/sensor & lens when deciding how to mate them. I'm afraid I have very little idea on what to look for in that respect. Are there some thing to keep in mind when doing that?

Intuitively, I feel like zoom lenses are necessary for what I'm doing and I would suspect that some sacrifice in quality accompanies that. This might add up to I should be emphasizing the quality of the zoom lens over the camera body. Is there any merit to that idea?

By the way, terms like "crop frame", "crop sensor", "crop mode" etc. appear in this discussion. I'm NOT familiar with the term but have deduced that it refers to a sensor that is smaller than a full frame (i.e., 24x36mm) such as an APS-C sensor. Is that correct? Is there more to it?

[Tronhard]

I am rather late to the conversation, but I have tried to assimilate all of the posts... The relationship between sensor size and image quality is, as has been well expressed, quite a complicated one. For me ANY change in gear boils down to a series of question that I have outlined in the following document:
https://1drv.ms/b/s!Au9RK1jLnjMSjHqMYZ6kzq_QIryB

In the case of choosing to go full-frame or not, of significance is the question of the types of subjects you intend to shoot, particularly: are your subjects likely to needs very wide angle performance, or long telephoto performance. The reason behind these considerations is explained in the following article I wrote on Equivalence:
https://1drv.ms/b/s!Au9RK1jLnjMSjHzc...pJwyb?e=5aJKCA

So, if you work your way through those documents, there are two issues that come to the fore when considering whether to go crop of Full Frame:
If you are predominantly going to shoot wide-angle, then a Full-Frame sensor has advantages because it does not apply a sensor crop to the image: i.e. the number written on the lens is a metric for what the (sensor + lens) combo will deliver. A crop sensor will be disadvantaged in this area - as per the examples in my second link

If, on the other hand, you shoot at the long telephoto end, a crop sensor MAY render benefits, because it has already 'cropped' the image to provide a FoV Equivalent to that of using a longer telephoto lens. Basically what happens is that the image area is reduced, but when we see it in a viewfinder, a digital display, or print it to a standard size, it will appear to be 'zoomed in' (note the quotes) but that actually reflects the increase in magnification of the output media.

Where this may be advantageous is in the area of pixel density: so two cameras, each with say 30MP, where one is a 1.5 crop sensor and the other is a FF sensor. To give both images the same Field of View from the same lens focal length, the FF output would be cropped and blown up in display or print. The number of pixels thus used is reduced by the square of the crop factor (CF is linear, pixels available is an area), so to make a 30MP FF sensor's output look like that of the crop sensor, the resultant number for pixels available would be 30/(1.5x1.5)=13MP. On the other hand the output for the same size display or print would remain at 30MP - which is not an insignificant difference.

As regards renting a lens, I recommend looking at lensrentals.com - they appear to be the best known and biggest player in the area and seem to have an excellent reputation. I have no financial interest in them as I live in New Zealand.

[xpatUSA]

...
By the way, terms like "crop frame", "crop sensor", "crop mode" etc. appear in this discussion. I'm NOT familiar with the term but have deduced that it refers to a sensor that is smaller than a full frame (i.e., 24x36mm) such as an APS-C sensor. Is that correct? Is there more to it?

I hate that term when is applied to equipment, not images.

Even worse is "crop factor" where bigger is smaller and hence more frowned upon. It also implies that 36x24mm is the gold standard when everybody knows that that is an 8x10" piece of sensitive glass.

[Geoff F]

[QUOTE=ajax;768499]Intuitively, I feel like zoom lenses are necessary for what I'm doing and I would suspect that some sacrifice in quality accompanies that. This might add up to I should be emphasizing the quality of the zoom lens over the camera body. Is there any merit to that idea? [QUOTE]

Yes, in most cases the lens is the most important item in any camera set up. Better to have a good lens on a cheap camera than the other way around.

At one time, a long time ago in film camera days, the early zoom lenses tended to be either very expensive or somewhat poor in quality. So people were advised to use a fixed size lens and 'zoom with their feet' which meant moving closer or further away from the subject. Modern zooms are considerably better and reduce the need for constant lens changes. Zooming with your feet was always risky when standing on a cliff edge or with your back against a wall.

[Tronhard]

I hate that term when is applied to equipment, not images.

Even worse is "crop factor" where bigger is smaller and hence more frowned upon. It also implies that 36x24mm is the gold standard when everybody knows that that is an 8x10" piece of sensitive glass.

I agree with you to a fair degree Ted. Frankly, as I have expressed in my article on Equivalence, the whole thing is IMHO a bit of a mess, caused by the colloquial use of terms like: 'large format', 'full-frame' and 'crop sensor', and worst of all, the description of what is produced by a camera (be it film or digital) is directly related to the focal length alone, which the output (which is what matters) is a combination of what the lens projects and what the medium captures. That is why, when I wrote my article, I placed a definition of MY terms at the start of the article.

If you read my article, I hope you see that I don't see one as better or worse than the other, but more a factor of what one wants from the equipment - i.e. horses for courses...

[pschlute]

By the way, terms like "crop frame", "crop sensor", "crop mode" etc. appear in this discussion. I'm NOT familiar with the term but have deduced that it refers to a sensor that is smaller than a full frame (i.e., 24x36mm) such as an APS-C sensor. Is that correct? Is there more to it?

"crop sensor" refers to a sensor that has the same size as the aps-c format (a film format). So yes, smaller sensor than a FF sensor.

Crop mode means that the FF camera can take an image using just a portion of its FF sensor...ie an aps-c sized portion. The resultant image will be exactly the same as a FF image cropped in post. So a 36MP FF camera can produce a 16MP crop image either by using "crop mode" or by simply cropping the FF image in software.

I have no idea what "crop frame" means (unless it is the same as crop sensor)

[Tronhard]

I agree with Geoff here, and again I emphasize that MUCH depends on what you are going to produce.

As Manfred has said, he produces large, detailed, fine Art prints and, to get the best results, it requires a higher investment than for someone producing images for social media, digital display or more modest-sized prints. I am predominantly a Canon shooter and FOR MY PURPOSES, which are mostly digital and prints up to A2 size, I have found that good quality zoom lenses do an adequate job. Especially considering that much of my shooting is done in the wild, where I am not likely to have control over over where I can be placed relative to my subject: e.g. shooting a male grizzly bear is not likely to be a situation where one can move around and very close to the animal without IT moving (preferably not AT one). If one is shooting a range of subjects a good zoom lens can be a great solution. You just have to make sure that the lens' plus camera performance is good enough for your purposes.


[QUOTE=Geoff F;768502][QUOTE=ajax;768499]Intuitively, I feel like zoom lenses are necessary for what I'm doing and I would suspect that some sacrifice in quality accompanies that. This might add up to I should be emphasizing the quality of the zoom lens over the camera body. Is there any merit to that idea?

Yes, in most cases the lens is the most important item in any camera set up. Better to have a good lens on a cheap camera than the other way around.

At one time, a long time ago in film camera days, the early zoom lenses tended to be either very expensive or somewhat poor in quality. So people were advised to use a fixed size lens and 'zoom with their feet' which meant moving closer or further away from the subject. Modern zooms are considerably better and reduce the need for constant lens changes. Zooming with your feet was always risky when standing on a cliff edge or with your back against a wall.

[Tronhard]

David: To respond to your comments: mine responses in italics...

Something else that I've always attributed to full frame cameras is better quality lenses. In that, APS-C provides a way to reduce cost/price which creates a need to keep the cost/price of lenses lower. From a technical point of view, a simple minded way to think about it is that smaller is less costly to produce. Now that I've taken a little deeper dive I'm thinking it matters, at least as much and possibly more, what lens is being used. Something else that's become apparent is that there are lots of different options for lenses. Apparently, this includes both full frame and APS-C ones which may be what I hadn't previously appreciated. While some differences in lenses have to do with application (i.e., portrait, landscape, etc. etc.) image quality is also a relevant factor. This suggests that some consideration needs to be paid to limitations of both the body/sensor & lens when deciding how to mate them. I'm afraid I have very little idea on what to look for in that respect. Are there some thing to keep in mind when doing that?

Looking at the range of lenses available today, I think it is fair to say that lenses designed for 'crop sensor' cameras are of not necessarily of less quality than those designed for FF sensors. In each grouping there are better and less well-performing units, and that is not necessarily tied to cost - there are some cheaper lenses that render great results - again, depending upon what you want to produce.

Life can get complicated when one puts lenses designed for one format onto another: e.g. put a wide-angle FF sensor on an APS-C body. In this case the optics have significant complex curvatures and cropping the projected image will likely have quality issues. On the telephoto end, one is less likely to have issues as the image fields, and thus optics, are flatter. As an example, I refer you to an article I wrote comparing Canon EF 70-300mm lenses. https://1drv.ms/b/s!Au9RK1jLnjMSjHsu...48oMt?e=bPuEmU

Intuitively, I feel like zoom lenses are necessary for what I'm doing and I would suspect that some sacrifice in quality accompanies that. This might add up to I should be emphasizing the quality of the zoom lens over the camera body. Is there any merit to that idea?

Really, resultant image is a combination of the skill of the user (which is very significant), lens type and quality, and body design and quality. So, each has a role to play.

However, if I was looking at an investment, I would tend to focus on the glass - lenses last longer and hold their price much more than bodies that may change every couple of years. A good lens will last decades. When I was shooting film, I often used a combination of Canon and Nikon bodies, but with the same Tamron Adaptall SP lenses that could fit on either body, using an adapter. When I went digital, I chose Canon for the lenses that I considered superior in the areas of my interest.

By the way, terms like "crop frame", "crop sensor", "crop mode" etc. appear in this discussion. I'm NOT familiar with the term but have deduced that it refers to a sensor that is smaller than a full frame (i.e., 24x36mm) such as an APS-C sensor. Is that correct? Is there more to it?

These are essentially colloquial terms that have evolved over time - more of a result of marketing than precise technological roots. Back in the middle of the last century, when cameras became more of a consumer product, and in particular those using 35mm film, that format became known as FULL-FRAME, to distinguish that format from smaller ones used in cameras like the instamatic.

APS-C format was a new format that was developed in the 1990's by a consortium of camera makers, but driven mostly by Kodak. That used a smaller film size but had many features to add information to the film and to safeguard the film from inadvertent exposure. It was essentially killed by the rise of digital technology around the start of the new century. In the case of Canon, they produced the world's first APS-C sized CMOS sensor - and pivotal development that reduced the cost of DSLRs by about a factor of 10, and with the CMOS sensor (previous were CCD sensors) it used much less energy and was less likely to attract dust to the sensor - all things that were much appreciated. While the early Canon DSLRs had APS-C sensors, they still used the full-frame EF lens mount. It was not until the Canon 20D (released in 2004) that the EF-S lens mount and optical format was produced.

[DanK]

Crop sensor is a standard term for a sensor that is moderately smaller than a "full frame" (i.e., 36 x 24 mm) sensor. It is typically applied to sensors that are 1/1.5 to 1/1.3 times FF size in length and width. It's generally not applied to smaller sensors. They are labeled by their inverse, e.g., 1.6 crop. AFAIK, the 1.3 crop has long since disappeared. This is an arbitrary convention, but I don't think it will help the OP to debate its strengths and weaknesses.

OP: as Tronhard pointed out, the area on crop sensors is obtained by squaring the crop factor, as it's cropped in both directions. So your camera, which is 1.6 crop (also called APS-C), has an area that is 1/(1.6x1.6)=0.39 the size of a FF sensor.

Longer focal lengths capture narrower angles of view, hence smaller areas. Given any focal length, the area captured by an APS-C is 39% as large as with a FF. A corollary of this is that to capture the same area across the entire sensor, a FF camera needs a lens that is 1.6 times as long. So if your longest lens is 300mm, you would have to crop the image from a FF camera down to 39% of its full size to have the same framing as you would get with an APS-C camera. This is why pixel density matters so much. Crop sensor cameras typically have more pixels per cm^s, so you can get the same number of pixels on the subject with a shorter focal length. This is why people talk of "greater reach".

Additional factors are cost and weight. For comparison, here are three cameras I have looked at recently, with their kit lenses:

Fuji X-T4, 1.5x crop factor, 26 MP: $2100.
Canon R6, FF, 20 MP: $3,600
Canon R5, FF, 45 MP: $5,000

If you cropped the R5 image to the size of the Fuji image for a given focal length, you would have 19 MP.

Can you print 13 x 19 well with 22 MP (what I had with my 5D Mark III): yes, with no problems at all. I've obtained good prints at 17 x 22. Would they have had finer detail with 45 MP? Sure. Would you notice? Not all that likely. I had a 17 x 22 print of an image I took with the 5D Mark III hanging in a museum for a few months last year. No one said that the resolution was insufficient.

Unless directly asked, I never tell people what I think they should buy. However, if I put the question differently and ask, 'have you made a strong case that FF is worth it for you?' I think I would say, 'not yet.' If you are outgrowing your current equipment, I would say to put FF and any other categories out of mind at first and ask: what would I like my new gear to do better? That will be a guide as to what's worthwhile for you. The answer may well be FF, but it might not be.

[Tronhard]

I accept this diverging from the original intent of the thread, so apologies!

I have got the R5 and R6 and I am hugely impressed by the animal eye tracking and IBIS - both is which are extremely helpful for the kind of images I take. I am hoping for a pro / prosumer-level R7, with much the same specs as the R6, but with something like a 35MP sensor. Frankly, at the telephoto end, at least, I don't see a need for them to come out with a special mount for such a configuration, and they have cheaper glass for lower end models - apart from the RF 24-105L and 100-500L, I tried the RF 24-240 and was hugely impressed: lens tech has come a long way, especially now that software is an inherent part of the correction built into lenses.

It is interesting to note that DPReview have just announced that they are going to, by default, include lens correction algorithms into their lens reviews as so many of the new generation of lenses incorporate those by default and without them lenses would not perform as we would normally experience them.

It seems so. I think all they publicly announced is the end of the 1 DX flagship line, but it's been assumed for a long time that the next rung down, the 5D series, is also dead.

I don't see a compelling reason to upgrade my current 5D Mark IV now, but if I were shopping from scratch now, given the level of equipment I use, I would only consider mirrorless. However, the consumer level DSLR market seems reasonably robust for the moment.

[Tronhard]

Hi Dan, I am rather with you on this. While I have 95% of my gear in Canon, I have decided to try the Fujifilm X-T4 as it seems to have the lead in the APS-C sensor market: it's sensor seems to be excellent, the IBIS is helpful and the classic dial interface is something I have always liked. Their glass is good too and their gear is small and light.
I have coming (it's celebrating its third week stuck in transit in Oz), the X-T4, +16-80 lens, and I just went mad and decided to try the new, and very promising Tamron 18-300 - something that is rather novel, considering Fuji seems to have been reluctant to open up their format to 3rd party lens makers. All the reviews I have seen of this lens indicate it is far superior to what we have come to expect from super-zoom lenses: I wait to be pleasantly surprised.

[tclune]

Can you elaborate on why a FF would be a downgrade? I suppose that might be the same as asking what makes the D500 (APS-C) worth that much more than the much less expensive APS-C cameras?

I tried to answer this in my original post. First and foremost, my primary application is bird photography. So I have a relatively specific set of things that I want to optimize in a camera. The most important thing is pixels on subject -- birds tend to stay away from people and many are quite small. With all the reach I can get out of a long tele, I still need to crop most of my images -- often significantly. For a typical low-end FF camera, I would end up with about half as many pixels on the bird as I get with the D500 (BTW, I would get pretty much the same results with the less expensive DX Nikons as I do with the D500 in this regard.) The low end FF Nikons have about the same number of pixels as the DX cameras, but the sensor is over twice the size. So the pixel density is much less. That's a serious disadvantage SPECIFICALLY FOR BIRDING with FF cameras. However, as I mentioned in my original post, the lovely D850 has about the same pixel density as my D500, so it can give you the density when you need it and the massive number of pixels when you want that (as is typical of landscape photography.)
The next huge issue, with BIF especially, is the ability of the AF system to acquire focus and track fast-moving critters. The lower-end cameras typically are much slower at acquiring focus and often have fewer modes for tracking an acquired object. The number of focal points on the D500 is much greater than the lower-end cameras, too -- so it can track further out from the center of the frame. BTW, one big advantage of mirrorless is that it can typically track all the way across the frame, unlike DSLRs. The bad news with mirrorless systems is that their focal points are linear, not cross-type. So they are notorious for being unable to acquire focus at all in environments that have strong horizontal features, But that should resolve itself in a few years as the mirrorless AF systems get better.
The UI on the D500 is a dream -- I can set up single point continuous AF on one button, dynamic focus on another, and group focus on a third. If a bird is flying across a clear sky, I just use the group focus and it tracks that bird instantly. If the bird is on a tree branch and moving between leaves, I can use the dynamic button to keep the bird in focus through difficult circumstances. If the bird is just sitting in plain sight, I can use single point focus. All of these options are right at my fingertips and the engine in the D500 is much faster and more precise than those on the less expensive Nikons.
With BIF, burst capture is often the thing you need -- an Osprey diving to catch a fish is hard to keep in focus at all, let alone snapping the shutter at just the right instant. The D500 can capture up to 200 shots at a time at up to 10(?) frames per second, so I can concentrate on following the action, not clicking the shutter at the right instant. Less expensive Nikons just don't have that ability.
I find the D500 to have terrific dynamic range. With birding, you will often be out in the early morning or late afternoon light, or shooting in shaded woods. You really need to be able to pull detail out of marginal lighting conditions. I find the D500 to be a champ at that.
Notice that all of these things are virtues for the kind of shooting that I like to do. The D500 is not worth the price for many other kinds of photography. Indeed, the DX format, the limited number of pixels, and even the lack of a built-in flash might be detriments in other shooting contexts.
FWIW

[Tronhard]

Tom, I have a somewhat similar situation to you. If you read any of my posts you will be aware that I am a wildlife shooter (I don't think this is limited to just bird shooters) and having the greatest ability to isolated a subject by using a crop sensor is hugely advantageous, and as we both agree, pixel density from using a crop sensor is a huge benefit.

While I have shot with Nikon since about 1980, my last Nikon purchase was the brilliant Df - which I loved for its combination of classic dials and the brilliant sensor from the D4, tweaked for low-light work. I still have a couple. That said, I continue with Canon and as I posted the R5 and R6 are brilliant for wildlife, especially bird photography because of the animal eye tracking and IBIS - but Nikon is doing great stuff in those areas too. I wish I could afford an R3, but over here it's about $11k and there are no units in the country, or likely to be so for a while!

[DanK]

The bad news with mirrorless systems is that their focal points are linear, not cross-type. So they are notorious for being unable to acquire focus at all in environments that have strong horizontal features,

I had never heard this. I think this may no longer be true of some mirrorless cameras. I just searched, and it seems not to be true of the Canon R5:

100% horizontal and 100% vertical with Face + Tracking and Auto Selection modes 100% horizontal and 90% vertical with manual selection and large zone modes

https://www.canon.co.uk/cameras/eos-r5/specifications/


I have no idea if this is true of other new mirrorless models.