**Clarification added at the bottom of the post.
We all know that a 200mm lens is always a 200mm lens whether it is installed on an Full Frame DSLR or on an APS-C DSLR (you can replace the 200mm with any focal length, it all works the same). It is the crop factor of the APS-C sensors that changes as we are losing part of the image projected from the image circle. The angle of view changes, but never the focal length. As an example, shooting with a 200mm lens using the K20D , one would have an image similar, (in angle of view), to a 300mm lens. Right? Yes indeed, but the focal length would still be 200mm.
Some are concerned that since part of the image is actually lost, the cropping diminishes the quality of the picture. It doesn't. If you were to crop an image, taken with a full frame DSLR with, say, a 14.2MP sensor, to the size of an APS-C sensor, yes there would be a loss of details. You would wind up with an image re-sized to about 9.5MP. If you take a picture with the K20D equipped with an APS-C sensor, the crop actually happens outside the image circle of the sensor and the image remains that of a 14.2MP sensor. So isn't it a benefit to be able to extrapolate 300mm out of a 200mm lens? Oh yes, the next argument I usually hear is that wide angle lenses are also affected the same way and a 20mm wide angle lens would act like a 30mm lens. That's true, but since the maximum aperture of the lens installed remains the same when used on an APS-C sensor, don't you think that it's a positive thing? You can purchase a super wide angle lens for $300.00 to $600.00, but try to purchase a 300mm f/2.8 lens for under $4,000.00. You can purchase the Pentax DA* 200mm f/2.8 for around $800.00 and on your Pentax DSLR, it's like having a $4,000.00 300mm f/2.8 lens on a Full Frame DSLR.
Theoretically, there are other things to consider. The bokeh of a 300mm lens is different than that of a 200mm lens. It is usually smoother (but not necessarily as the lens construction and the number of Diaphragm Blades also make a difference). The compression effect of a 300mm is greater than that of a 200mm. In other words, a 300mm makes objects appear closer to each other that in reality, more so than a 200mm and certainly a lot more so than a 50mm lens or wide angle lens. I wanted to test the above and find out for myself what were the real tangible differences. I am lucky enough to have the DA* 200mm and the DA* 300mm lenses. I don't have a Pentax FF DSLR (nobody does thus far), but I figured that if I were to take some photos with both lenses using my K20D, then adjust the results so that the final images were the same sizes with the same framing, I would see what the differences were. Here are my results.
Difference in Bokeh! The pictures above show an image taken with the DA* 200mm @ f/4 (top photo) and with the DA* 300mm @ f/4 (above photo). The images were re-sized to show approximately the same image framing. There is a small difference between the bokeh. The 300mm produced a little creamier bokeh. Is the difference enough to prove a point? You decide.
Difference in compression! Above, I took roughly the same picture using the DA* 200mm and the DA* 300mm both set @ f/4. The darker portions of the images represent about the same framing. The two images below show the results taken with the 200mm and the 300mm when matched to the same framing sizes. I cannot see a big difference between the two. Can you?
I ask you, did I misunderstood something or did I misunderstood everything?
** See this article about DEPTH-OF-FIELD AND FOCUS, FOCAL-LENGTH AND PERSPECTIVE, OBJECT ISOLATION, SEPERATION, COMPRESSION and LAYERS. Pay particular attention to the Perspective and Compression.
** Looking at the comments and emails received, it seems that I have confused a lot of people with this post. Maybe my "Franglish" is getting in the way. My point is simply that the pictures taken with a 200mm lens used on an APS-C sensor will be similar to the pictures taken witth a 300mm used on a full frame DSLR. If there are differences, I don't think that they are noticeable enough to bother with. The K20D with the 14.6MP CMOS sensor gives me better results than I had using "Full Frame" 35mm films. Agreeing that the picture quality of the K20D meets your requirements, one is better off with an APS-C sensor when it comes to costs. The advantage of gaining on the telephoto side outweights the benefits of gaining on the wide angle side with a FF camera. A 35mm format wide angle lens (14mm @ f/2.8 or 21mm f/2.8 when used on APS-C) ~$300 to $600 - 35mm format telephoto (200mm @ f/2.8 or 300mm still at f/2.8 when used on APS-C) ~ $1400 to $5000. It gets even better when using a 35mm format telephoto of 300mm f/2.8 on an APS-C DSLR.
12 comments:
A good run-through. I also read some to the same extend at Bjorn Rorslet's site and at Luminous Landscapes, so I would say that you seem to get it right :-)
My photography teacher had asked me to take images with all my lenses (UWA to tele) to see the perspective changes. When I was studying the perspectives of different focal length lenses I had realized that
if I move the camera back and forth to get the same FOV, then perspective changes deeply.
But on the other hand,
if I don't move the tripod and crop the images to get same FOV, then all focal length lenses gives exactly the same images perspectively.
Is that what you mean?
Dear Yvon,
Can you overlap those both cropped images?
it will give us the real answer.
Yvon, there's just one think I'd like to add. When shooting with tele-lenses, the APS-C chip gives you one very nice advantage; the larger Depth of Field of a shorter focal length in a more narrow Field Of View.
Example:
A 200mm on APS-C has the same FOV as a 300mm on 24x36.
A 200mm has always a larger DoF than has a 300mm at equal apertures.
Best,
Jostein
Dear Alunfoto,
This is what I really hate of cropped sensor:
We get a larger Depth of Field of a shorter focal length in a more narrow Field Of View.
AdnanEROL,
But since you get to keep the wider aperture, you should be able to adjust the depth of field close to your liking. From a 200mm f/2.8 you get a field of view of a 300mm but still keep the f/2.8 maximum aperture. Using a 300mm on full frame, the 300mm would likely be an f/4 or you could get a very expensive 300mm f/2.8. The benefits are even better when using a 300mm f/2.8 as you get a 450mm still at f/2.8. That's a lens that would cost a lot more in full frame. That should definitely help in the depth of field area.
"The 300mm produced a little more bokeh." You cannot have more or less bokeh. I think what you mean is that the bokeh is smoother in the 300mm case.
I agree with you on that, since tele lenses are more expensive than WA ones:
"...The advantage of gaining on the telephoto side outweights the benefits of gaining on the wide angle side with a FF camera...
One day I hope to take 2 bodies with me when going out for shooting. A FF or MF camera with WA and standart lenses, and a K20D with a tele lens on it :)
Here is what I tested, I took my Olympus OM-1 and a 300mm lens and put it on a tripod, then I installed my Sigma 70-300 on my K100D Super and also my K20D afterwards. Now I am assuming that an FF sensor is the same as my Olympus, isn't it? What came out surprised me. I pull the 300 on the Olympus to the max and then compared with the K100D. The result is simple, I need to pull back at exactly 200mm on the Pentax to have the same field of view from the Olympus. So a 200mm does become a 300mm when using a crop factor of 1.5. So what ever lens you use on a smaller sensor is incresaed by the ratio, be 1,3, 1,4, 1,5 or whatever. I tried it with 28mm for the olynpus and a 18-55 for the Pentax. Same result, it does boost the range, so a 300mm is not a 300mm it is a 450mm. Otherwise you would have the same field of view, and it's not the case, any other inputs?
For me there is a big difference in bokeh between the 200mm and the 300mm shot. The 200mm lens, though, can be opened up to f/2.8 and I'm sure that would make up some of the difference.
Thanks for posting this!
Don
Don,
Yes, there is a little difference in the bokeh. However, is it worth the difference in price? The reason I shot at f/4 is that the DA* 300mm has a maximum aperture of f/4. I wanted to compare apples to apples. The DA* f/2.8 acts like a 300mm f/2.8 on the APS-C DSLR and cost only a fraction of a 300mm f/2.8 for full frame.
By the way I'd like to see same image taken with a 200mm lens at f:2.8 and a 300mm lens at f:4 to compare bokeh.
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