|
Forum: Pentax DSLR Discussion
11-02-2017, 11:46 AM
|
| |
A friend once said the 60-250 was the perfect soccer lens. Wide enough to shoot from the sidelines when the action was near and long enough to get the shot from cross field. He never found the SDM speed an issue but then again he and I grew up shooting manual focus on sports.
|
|
Forum: Pentax DSLR Discussion
11-02-2017, 11:40 AM
|
| |
Then look no further! That's a nice lens. The other option would be to look at the DA* 60-250 f/4 - if speed is not a huge requirement and SDM focusing speed is acceptable. The lens is lighter and smaller and offers a great deal of very high quality optics. The DA* 50-135 is another option but gives up range for speed (f/2.8). Neither lens works on a full frame completely - though the DA* 60-250 can be modified to make it very very good on Full Frame (not quite perfect - some would say).
Other options are the 100-300 f/4 Sigma (expensive and hard to find) and the Tamron and Sigma 70-200 f/2.8 variants that are cheaper and lighter than the DFA option.
|
|
Forum: Pentax DSLR Discussion
11-02-2017, 11:35 AM
|
| |
Still not sure what you are saying. The 70-200 will be the same as setting the 55-300 to 70-200 but will offer better optical quality, and f/2.8 for low light use even at 200mm which the 55-300 will not. It will be heavier and larger and more expensive. It will also work well should you ever want to use a K-1 since it is full frame. It will NOT appear to be equivalent to the 55-300 set to 100-300. That is what I am trying to convey. Sorry if that hasn't been clear and sorry if you already understood that.
|
|
Forum: Pentax DSLR Discussion
11-02-2017, 11:11 AM
|
| |
No no no...
The f/2.8 "through the entire range" is referring to ONLY the widest opening option. Many lenses have a variable aperture that is wider on one end of the range and narrower (effectively) on the longer end. The DA 55-300 is one of those variable aperture lenses. All of these have f/stops that are much narrower.
Also I want to address the "full frame lens vs. crop lens". The focal length doesn't care what the lens was made for. The way the lens appears in the viewfinder and on the sensor cares.
So if I put a 300mm lens on an 8x10" view camera - that lens put on a crop body will give the same basic image as a 300mm crop frame lens. The crop frame lens on an 8x10" view camera will not work - as it will fail to cover the entire area of the camera negative but the portion that will be illuminated will in fact look the same as it would from the original 300mm view camera lens.
The portion you see when using a lens is a lot like a window in the wall of your house. Imagine you have a 2x3' lens and you are seated 10' from it. If you then enlarge the window to 4'x6' you will see more things in the window - the window will show a wider amount of stuff. Effectively the window will give you a wider angle view without any change in the outside world or the "lens" (glass with no optical impact in the window).
This is why if I put a 300mm lens on a "full frame" camera that is a full frame lens and covers the entire area (like the 70-200 f/2.8 DFA) it will appear LESS telephoto in terms of what is captured than it will on a "crop frame" camera like the K-70. The crop frame lens on the other hand at the same focal length still shows the same image on the crop frame camera as the full frame lens. So if you put the DFA 70-200 f/2.8 on the K-70 at 100mm and the DA 55-300 at 100mm the basic image will be similar (quality and exposure available may vary but the overall view of the subject will be similar). The DA 55-300 placed on a K-1 will fail to cover the entire sensor and will vignette badly or even black out entirely in the corners and edges because it is not designed to have a large enough area covered by the light going through it to be used on a Full Frame sensor.
Any other arguments about equivalence and so forth are all about comparing perspective - but NONE of those are about the LENS being a different type - only about using the focal lengths on the various sensors. Any lens of XYZ focal length is going to give the same basic image view on any sensor as long as it has an image circle (fancy name for a window) that covers the full size of the sensor.
---------- Post added 11-02-17 at 02:14 PM ----------
Yes but what is missing is that the DA 55-300 also offers an equivalent view of 82.5mm - 450mm - the equivalence isn't based on the lens being full frame it is based on the size of the sensor relative to the focal length on some standard size that you are measuring against. The implication that the DFA will appear longer than it is on the D70 relative to a similar DA is just confusion and is what I think the OP has in his head.
Put another way - any 200mm will have a 300mm equivalent field of view when used on a crop (APSC) sensor - RELATIVE to a 200mm or 300mm placed on a Full Frame sensor. It is simply NOT true that a DFA lens will look longer at a given focal length than a DA lens of the same focal length when viewed on any sensor. (The DA will of course fail to cover the full sensor of anything larger than a crop sensor in most cases).
|
