[Kguru]

So, which lenses do take into account the crop factor? Am I right in assuming that the DA/* aren't affected by the crop factor?

Crop factor is result of the sensor size, not dependent on the lens designation.

Say you use 50mm lens on a film camera, take a group shot & can fit 12 persons side-by-side into the photo. Now the same group shot from the same spot with the same 50mm lens but a smaller sensor only captures 8 persons. When viewed in the same photo size the 2nd shot looks like the 1st shot with 75mm lens "zoomed in" to the middle 8 persons. Hence it's called 1.5x crop factor (12 persons cropped to 8), or some people say 50mm lens on APS-C is equiv to 75mm on film.

It's along the same line as digital zoom in a pocket camera, diff being digital zoom is optional while crop you're stuck with.

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Last edited by Kguru; 12-24-2007 at 07:26 AM.

[Eaglerapids]

All of them, even the DA's. I know it's confusing but a 50mm is a 50mm like others have pointed out. It's the camera's sensor that has changed relative to the FOV of the lens.
Just a rough analogy:
Let's say that it takes an image circle the size of a quarter to cover the 35mm film plane and it takes an image circle the size of a dime to cover the sensor of our K10D. A FA 300/4 lens, to be able to project an image circle the size of a quarter will have to be bigger and heavier (more glass) than a DA 300/4 that only has to cover a dime. They are both 300mm lenses but the FA is covering a large area that is going to waste (the area not covered by the dime) in the DSLR.

[Lowell Goudge]

So how does a Full frame sensor fit into all of this?

It doesn't

pentax doesnt make one and any new pentax lenses are designed to cover the circle filled by a 16 x 24 mm frame. Same is true for sigma DC lenses.

To echo someone elses complaint about wide angle, thier 24-88 became a 36-120. Although the salse hype is always pushing the "longer" side of crop factor, wide angle fans have had to go oout and get wider lenses.

Having said that, however, I pity those who are buying into the 4/3 systems with the 2x crop factor. A 7-14mm zoom from olympus does exist, but the cost of that lens exceeds the cost of a K10D and 12-24mm lens combined.

[Eaglerapids]

Here is an explanation of
The DA lens is designed with the crop factor in mind, the older ones are not. At least that is my understanding.

HTH

IF I am correct in my understanding (and that's a big if) Fritz, The DA series is designed with the crop factor in mind ONLY in the fact that they have to cover only the dime and not the quarter in my previous analogy. The DA 16-45/4 is STILL a 16-45mm lens!
Now here is where I may get into trouble. We take a 35mm negative and blow it up to a 4x6, ok? In Kguru's example 12 people are in the frame. Now we put that lens on our 1.5 crop sensor, take the same picture at the same focal length and now only 8 people are in the frame.
Why? Because we took the area of the DIME and enlarged it to 4x6! That's why we say the 50mm is now a 75mm on the cropped sensor camera, but the lens itself has not changed, the sensor changed.

[Canada_Rockies]

So, which lenses do take into account the crop factor? Am I right in assuming that the DA/* aren't affected by the crop factor?

The DA* lenses, as with all DA lenses are reduced in size and weight by virtue of only having to cover the area of the sensor on the Pentax digital SLRs. All full frame (a full 35 mm frame is 24x36mm) lenses cover the area of the Pentax sensors (about 16x24 mm), but the DA series will not cover the full 24x36 frame.

If all you have is a dSLR, don't sweat it. We old timers will confuse you with our constant references to FF equivalent and 35mm equivalent fields of view. Just ignore us. The lens is the same focal length no matter what camera it is mounted on. Only the part of the image projected at the rear of the lens that is projected onto the sensor counts. You have no problem if the lens is rated for dSLR APS-C sensors or larger. And all Pentax lenses are dSLR or larger.

[Eaglerapids]

Having said that, however, I pity those who are buying into the 4/3 systems with the 2x crop factor. A 7-14mm zoom from olympus does exist, but the cost of that lens exceeds the cost of a K10D and 12-24mm lens combined.

When I was researching my DSLR I looked at the 4/3 system and quickly dismissed it for that very reason. I don't understand why Olympus went that route.

[tux08902]

See, I don't have any film SLRs anymore, which is why I don't really compare. I had a Canon A-1 and a Canon Rebel SII, but I sold those.