[normhead]

That's perfectly possible. However, a lens designed for the smaller sensor would have exact same advantage.

It's main advantage is that it would be lighter. And that is why most of us treasure our APS-c lenses.

Sigma 70-300 550gm
Pentax 55-300 PLM 442

And the Pentax is by far the superior lens. I use it with care to avoid vignetting on my K-1 FF (which it does at some focal lengths, but not all). I'd rather use an APS_c lens on FF (and do on a regular basis) than a similar FF lens, because of the weight, where the APS-c lens is good enough to give good results.

[Sidney Porter]

I think I am struggling with the premise. The lens is just a series of pieces of glass. The issue that a ff lens "wastes" the edges in a apsc doesn't make what is captured and used any less. If anything the center of a ff lens is the typically the best part.

[normhead]

My advice is: Just enjoy shooting ... and rest assured that FF-lenses will work without quality issues on APS-C.

Seriously, this is it. You have to shoot with a lens to know if it's for you. Prejudging based on the sensor size it was developed for should be a non-starter.

In fact, MTF charts have no effect on my decision to buy or use a lens.

But if you've found something to be true, MTF charts with accompanying distortion and CA graphs can help explain a point.

I'm always amused when people assume because I use MTF charts in my explanations that they are a big part of my life. At this point, already owning over 20 lenses, what I look at most is how smooth the out of focus areas are. Overall sharpness is over-rated, but, all other things features being equal, I might use MTF as the tie breaker, but I'd be more likely to use price.

Honestly, most of the time I only use MTF charts to back up my observations when explaining things here on the forum. Not doing so may precipitate unnecessary arguments. Anyone can argue with me. Test chart data makes it more difficult.

[Sidney Porter]

Slight hijack

At some point does a apsc lens stop making sense to design because of physics? For example it doesn't seem like a (apsc only) 70-200mm at f/2.8 exist. They seem to be ff and usable on the apsc. Is this because physics dictate in order to have the aperture large enough at that focal length the image circle will end up being large?

[aslyfox]

My wife is into photography and steals my favourite lenses for her own use. .. . .

big hijack

IMHO [ 30th anniversary will be Sept 7 2021 ] a good marriage is made up of compromises

[normhead]

Slight hijack

At some point does a apsc lens stop making sense to design because of physics? For example it doesn't seem like a (apsc only) 70-200mm at f/2.8 exist. They seem to be ff and usable on the apsc. Is this because physics dictate in order to have the aperture large enough at that focal length the image circle will end up being large?

That's partially true, but consider that the 50-135 2.8, a favourite on APS_c is the same field of view of the 70-200 on FF, maybe not the same lens but the same capability.

The 70-200 on APS-c would be 100-300mm on FF, those exist, but they are much less popular. It's the functional 35mm focal length that's important, not the actual FL of the lens.

The DA*50-135 is much lighter than a DFA*70-200. Telephoto is where APS-c really starts to make sense over FF in terms of weight.

[stevebrot]

The total number of "pixels" that the lens projects onto an APS-C sensor is going to be 1.5 times less.

Hmmmm...I don't think I my lens projects pixels or even latent pixels, but...

The proof of the pudding is in the eating and I only have one crop-format lens in my bag for use with my K-3, a Sigma 17-70/2.8-4 (C) that is my walk-around zoom. Everything else is FF and I have done some pretty good work with those, even the "vintage" stuff*. Below is a link to my Flickr page; see if you you can pick out the photos with the wasted pixels.

fotostevia | Flickr


Steve

(...flux to the frame is the same for any given focal length regardless of image circle...)

* Believe it or not, most of my "vintage" lenses are more than up to the challenge of the pixel pitch on the K-3.

---

Last edited by stevebrot; 02-12-2021 at 11:43 AM.

[Sidney Porter]

The 70-200 on APS-c would be 100-300mm on FF, those exist, but they are much less popular. It's the functional 35mm focal length that's important, not the actual FL of the lens.

I often shoot at poorly lit highschool athletic fields so I often benefit from the field of view and the f2.8 that I get from my tamron 70-200. I was wondering if it could be even made physically smaller for an apsc. I understand comparing field of view between the 2 formats.

It has been awhile since I have shot the larger format. I don't have a k1 and the last film I shot was in 2011. At this point my minds eye is apsc. The only time I even think equivalent is for forum post.

[Dan Rentea]

We can use full-frame lenses on APS-C cameras, but that sounds like an awful idea, since only the center of the lens would be used. The total number of "pixels" that the lens projects onto an APS-C sensor is going to be 1.5 times less. Let's say a full-frame lens has a resolution of 2000 lp/ph. On an APS-C sensor that would become 1333 lp/ph. That's in linear dimension. Over the area of the sensor, that would be a 2.25-fold decrease in resolution. That's enough to turn and awesome lens into trash.

I understand that lens "resolution" is not the same as resolution of the lens+camera, but a 2.25-fold decrease in resolution of one part of the system is going to have a dramatic effect on the final image.

I also appreciate that a cropped sensor would "benefit" from using only the center of the FF lens where resolution is better than at the border, however, this is not nearly enough to compensate for using only a fraction of the image projected by a FF-lens. Border resolution is typically 10% less than resolution in the center, while the sensor size is 33% different (in linear dimension).

What is your real-life experience of using FF-lenses on APS-C camera vs using an APS-C lens?

I see that SMC-FA 35mm f/2 has glowing reviews. How would it do on an APS-C camera relative to SMC DA 35mm F2.4?

This thread confirms this, but the author did not actually state what camera he was using.

I haven't seen a Canon APS-C lens outperforming the 85mm f1.4L on a crop camera. Or a 70-200mm f2.8L lens. Or a 16-35mm f2.8 lens. Or...

Same with Nikon. I haven't seen a Nikon APS-C lens outperforming the Nikon 105mm f1.4 lens for example on a crop camera.

The reason why APS-C lenses are being bought has to do with weight and price, both of them being less than an equivalent lens on a full frame. Personal opinion of course.

[stevebrot]

For example it doesn't seem like a (apsc only) 70-200mm at f/2.8 exist.

It is called the DA* 50-135/2.8, same FOV on APS-C as 70-200 on FF.


Steve

[Sidney Porter]

It is called the DA* 50-135/2.8, same FOV on APS-C as 70-200 on FF.


Steve

I understand fov between formats.

My question is could a 70-200 f2.8 be made with only a apsc image circle?

Not resolution, but total pixels projected onto a sensor.

The problem is there are fewer of those "best" pixels. Would you still insist the same if we used a FF-lens on a phone-size sensor?

---------- Post added 02-12-21 at 11:52 AM ----------


Would you care to elaborate which step in my logic is faulty?

pixels are not projected on to the sensor; pixels are discrete electrical sensors organized in a two-dimensional array that collectively make up the camera's sensor. Light isn't a collection of discrete eleiments, it is continuous (hence the utility of both wave-theory and particle-theory to describe how light works). A lens modifies the path that light travels, and as it does so, can redirect, magnify, or diminish the light. The light that comes through any particular lens is going to come through that lens in exactly the same way regardless of the characteristics of the target (sensor). The fact that some of the light that could, in theory, be captured by a sensor will not be so collected is irrelevant to that which is captured. An APS-C sensor is collecting exactly the same light that a full-frame sensor will collect in its subset of light sampled. I believe your logic error is in mistaking the light that the sensor is collecting for the available light coming through the lens, since the sensor acts as a filter, selectively capturing the available light in discrete picture-elements ("pixels").

[normhead]

The reason why APS-C lenses are being bought has to do with weight and price, both of them being less than an equivalent lens on a full frame. Personal opinion of course

Exactly, if APS_c has enough resolution and noise characteristics, for telephoto for your shooting you'd be silly to carry around FF gear in long focal lengths. That being said, if I'm out shooting with my 300 2.8 and 1.4 TC and the subject is a bit tight, switching to my K-1 is always an option, although when I've done it I rarely see any advantage to the K-1 images, they are just harder to get. But hey, you gotta experiment. Otherwse you don't know as much as you could.

It's amazing how many misconceptions can be cleared up by a bit of experience.

[redrockcoulee]

big hijack

IMHO [ 30th anniversary will be Sept 7 2021 ] a good marriage is made up of compromises

Very true. I stayed with Pentax even though I was working at a all Nikon shop with a staggering array of lens because my wife wanted the K10D instead of a Nikon.

We share equipment from Pentax, Hasselblad and large format. She allows me to buy whatever gear I wish, knowing I'm a miser, but frowns on me selling anything. 45 years and counting. Pentax for the entire time starting with matching black Spotmatic F.

[stevebrot]

My question is could a 70-200 f2.8 be made with only a apsc image circle?

Definitely, and Nikon, Canon, Sony, and Pentax all make APS-C lenses in that general zoom range, though not as fast as f/2.8. It seems that the smaller image circle does not make that much difference in bulk/weight with faster lenses.


Steve