Is a lens designed for a crop sensor camera essentially a better choice than a FF lens

[arie_vandervelden1]

<p>Scott the OP asked about using EF vs EF-S lenses on a crop camera. Not whether a FF camera with a 24-105 mounted on it is better or worse than a 7D with 17-55. </p>

[victor_oyarzun]

<p>Thanks all for all the responses, I am glad that generated a discussion that I can not participate because my knowledge is limited. However, they give a better understanding of the matter. <br>

What I take from the responses is that there is no significant image quality advantages in the lenses designed for crop sensor cameras.<br>

Regards.</p>

[sarah_fox]

<p>I think "significant" is the key word here. This is obviously a controversial subject. There are a few people on this list who are optical engineers and could address this issue better than any of us, but they haven't weighed in. I'd sort of hoped they would. Ah well...</p>

<p>Scott is correct that I've introduced a few points of of conjecture in some of my discussions. I'm not an optical engineer and don't have an intimate working knowledge of the compromises in optical formulae that must be considered in lens design. However, I do know this: Wide angle lenses are awkward and difficult to design, as compared to "normal" and tele lenses. The wider the lens, the more awkward and clumsy the design. A FF lens on a crop body has a wider/clumsier design than it really needs to have, considering the smaller image circle requirements of a crop sensor. That can't be helpful for image quality. But yes, that's partially conjecture! ;-)</p>

[scott_ferris]

<p> I think if you own a crop camera/s alone it makes sense to maximise your lenses for than format. Even if you are of the mindset that you might get a "FF" camera at some point in the future. If you own a dual format kit there is no IQ disadvantage to getting lenses to use across your formats. But as Arie points out, crop camera lenses focal ranges really are better designed for crop cameras and are a better idea than trying to fit the square peg of "FF" lenses into the round hole of the crop format.</p>

<p>Sarah,</p>

<p>I can't hold a decent discussion on lens design, but, in the interests of a pleasant conversation, the problems I have with your thoughts on vibration didn't, I believe, take two important factors into account. One, the relationship of sprung to unsprung mass of crop camera mirror and shutter mechanisms when compared to that of their "FF" cousins. And two, the necessity to keep the crop camera more steady for a give enlargement. I can't satisfactorily work the figure out for myself, but as a minimum the crop camera has to move 1.6 times less than a "FF" one to get the same subject blur (assuming a static subject), but that figure might arguably be closer to 2.6 times steadier.</p>

<p>Just a thought :-) Scott.</p>

[dcstep]

<p>Using the same focal length of lens on both a FF and a crop-sensor body will result in the same amount of image stabiliization for both. Expressed another way, the adequate shutter speed for a particular image on a FF camera will also be adequate on a crop-sensor camera. The focal length is the same on both cameras and the crop-sensor merely has a narrower angle of view.</p>

[sarah_fox]

<p>Thanks, Scott! I'll have to go back, now, and see what I said about vibration. ;-) </p>

[scott_ferris]

<p>David,</p>

<p>If you consider the same size print or screen image size, a crop camera capture has to be enlarged 2.6 times more, that means any movement will be enlarged more too.</p>

<p>If you use the same focal length but do not crop the FF image (obviously making the fov and image different) the crop camera needs to be at least 1.6-2.6 times more stable for the same camera movement as a percentage of sensor size.</p>

<p>If you crop the FF image to match the crop image camera movement is equal, you are enlarging the same area of sensor capture and also camera movement.</p>

<p>If you do what most people do and use the correct focal length to frame your subject the same through both viewfinders and reproduce both images the same size, the crop camera, again, must be kept at least 1.6-2.6 times more stable.</p>

[dcstep]

<p>Scott,<br>

To get an image equivalent to a 16mm lens on a FF sensor, you'll use a 10mm lens on a 1.6x crop-sensor, requiring less IS, although the difference will be very small. Going to supertelephoto, to get a print with subject the same size as on 1.6 crop-sensor with a 500mm lens you'll need a 800mm lens on a full frame camera, requiring considerably more IS.</p>

<p>OTOH, you correctly said:</p>

<blockquote>

<p>If you crop the FF image to match the crop image camera movement is equal, you are enlarging the same area of sensor capture and also camera movement.</p>

</blockquote>

<p>Hence, for the same subject size in the same size print, IS is equal if the same lens is used.</p>

<p>Dave</p>

 

[scott_ferris]

<p>Let me try to explain my thought process better.</p>

<p>Scenario one: You use the same lens on both cameras from the same place. The framing is different but the subject is reproduced on both sensors the same size. In print or on screen if you want the subject the same size the enlargement ratio is the same, though the full frame image in total is larger. Because of that, any camera shake is enlarged the same, the camera systems are equal. In that instance you have just cropped the FF image down to the same size as the crop camera to make just the subjects printed the same size, so all movement is equal. In this instance, say wildlife shooting with your longest lens, the crop camera should show an advantage due to the higher number of pixels landing on the subject. My testing showed it does, in optimal circumstances, though not by anything like the numbers say it should.</p>

<p>Scenario two: If you use the same lens from the same place with both cameras and make the enlargement of the total capture the same size, ie you make two 8x12 prints of your full captures, you end up with two differently framed images, but the crop camera motion blur is enlarged 1.6-2.6 times as much. Ergo the crop camera needs to have been kept steadier than the FF one. In this instance you may be using your widest wide angle to get as much of a scene as possible in one shot, a ball game and crowd or something, a scene setter.</p>

<p>Scenario three: You have a 70-200 on both cameras. You shoot a subject for optimal framing, with the crop camera you are at 100mm for the same framed image with the FF camera you have to use 160mm. To make two more 8x12 prints you have to enlarge the crop camera capture by 2.6 as much to get those prints. You do have to use 1/100 of a sec for the crop and 1/160 for the FF, but that is only a 60% difference, not a 260% difference. Again, to my reckoning, you need to keep the crop camera 1.6-2.6 times steadier, minus the 60% allowance for focal length changes, or 100-200% steadier. Very common scenario, portraits, macro etc, anywhere you have the focal length to get the framing and perspective you want.</p>

<p>The difference between a 500 and an 800 is again 60%, you always need a 60% faster shutterspeed for the FF camera to negate the additional focal length leverage on camera shake, but FF camera equivalence allows you 100% gain, or one full stop, in iso anyway for the same noise levels. So you actually gain another 40% working those two figures in. What you can't get round is that for the same sized print the crop capture has to be enlarged 2.6 times as much.</p>

<p>This is all just talk though, I am not suggesting for one second that you can't get sharp images out of a crop camera. It was just a logical extension of my thought process, and as I am currently stuck in the middle of the Caribbean Sea I don't have much else to do :-)</p>

[sarah_fox]

<blockquote>

<p>I am currently stuck in the middle of the Caribbean Sea I don't have much else to do :-)</p>

</blockquote>

<p>Scott, you are a truly sick person! ;-)</p>