[y0chang]

The 18-35mm is an odd lens, its too short of a range for a zoom, its too heavy for a replacement for a prime, and its neither long enough nor short enough for APS-C. It has found a niche for video shooters in other mounts, but that is moot point for pentax. I think you are trying to fit a square peg into a round hole in finding justification for the 18-35mm. I think you might want to consider a DA 16-85mm. That lens has great image quality, will cover a huge range, it is great for travelling, its water resistant and will be cheap enough that if you wanted the 50-135 later, it would be a complement. Or if you don't mind a little worse corner quality, the 18-135mm is a good lens as well.

[Serkevan]

No, he is saying that the DOF will be somewhat comparable to a 85mm lens at F5.6.

I was not, I was saying that he would lower the resolution from 24 to 5 or 6 MP.
I did not address DOF at all (Although most things will look definitely further out of focus as the magnification from the crop is much higher for the same print size).

[y0chang]

I don't understand what you typed yet but I'm going to try to figure it out . I'm going to read the links Serkevan put above . I still have a lot to learn . So sorry if my questions and requests are stupid .

---------- Post added 11-01-19 at 07:11 AM ----------


Kozlok will you take a photo with the 18-35 at 35mm and the sharpest f stop and then take the same photo with the 16-85 at 85 mm with the f stop at 2.8 . them crop the 35 mm photo so you see the same thing as you do with the 85mm . And post it here so I can see the difference in the two .

---------- Post added 11-01-19 at 07:21 AM ----------


I know the 200mm photo is better than the cropped 35mm to the same size fov as the 200mm and I can see it when I zoom in on flikr and lightroom but not zooming in it looks pretty close . I was just hoping to get 2 photos from you professionals that know what your doing to let me see what the difference is between a 18-35mm lens at 35mm cropped to the same fov as the pentax 50-135 at 135mm . or even the 85mmm from the 16-85 mm lens .

This an example of the difference in field of view between 35mm and 135, its is unlikely that that quality will remain from 35 to 135mm. That would be trying to crop the barn in the 35mm to the field of view of the 135mm image. I find past a 2x crop, you lose too much detail no matter the resolution of the lens nor sensor.

[AstroDave]

As long as you are using the same camera with the two lenses, the change in megapixels is just the square of the ratio of focal lengths.

For your 35 mm compared to 135 mm, the ratio of focal lengths is 35/135 = 0.26

Square that: 0.0672

Now multiply the K3's 24 megapixels by that, and you have an equivalent 1.6 MP camera!

As others have said, if you want the reach, just get the 50-135!!

[AggieDad]

I guess I am crazy. Why not just get the 18-135 mm lens? Have it all. Is there really that much difference in the IQ?

[ChristianRock]

I don't understand what you typed yet but I'm going to try to figure it out . I'm going to read the links Serkevan put above . I still have a lot to learn . So sorry if my questions and requests are stupid .

---------- Post added 11-01-19 at 07:11 AM ----------
42

Kozlok will you take a photo with the 18-35 at 35mm and the sharpest f stop and then take the same photo with the 16-85 at 85 mm with the f stop at 2.8 . them crop the 35 mm photo so you see the same thing as you do with the 85mm . And post it here so I can see the difference in the two .

---------- Post added 11-01-19 at 07:21 AM ----------


I know the 200mm photo is better than the cropped 35mm to the same size fov as the 200mm and I can see it when I zoom in on flikr and lightroom but not zooming in it looks pretty close . I was just hoping to get 2 photos from you professionals that know what your doing to let me see what the difference is between a 18-35mm lens at 35mm cropped to the same fov as the pentax 50-135 at 135mm . or even the 85mmm from the 16-85 mm lens .

Well, when you are cropping you are throwing part of the picture away. When you crop a 35mm image to 200mm you are throwing away over 80% of the image - you are cutting it off. That is why you end up with a little over 4 megapixels on a 24 megapixel image. and 4 megapixels was state of the art... about 20 years ago when digital cameras first started and everybody still shot film.

Having said that, if you are printing 8x10 images, I would say anything over 8 megapixels is actually going to look fine. So you could be ok cropping to 85 or even 100mm. And if you are printing 4x6 then you are probably fine even with the 4MP image! Also, if you are just looking at a picture on a cell phone or small old laptop, you might be fine cropping to 200mm and still seeing a nice image. But if you have a 4K monitor the 4MP image will not look great.

The problem is, you are probably better off with a small $100 dollar point and shoot that goes to 300mm equivalent rather than having a DSLR and a big expensive lens like the Sigma 18-35, and cropping 82% of your picture off.

It's just mathematics...

EDIT: The 200mm crop would actually be around 0.7 megapixels, so fine only for cell phone viewing.

[taktoon]

Well, when you are cropping you are throwing part of the picture away. When you crop a 35mm image to 200mm you are throwing away over 80% of the image - you are cutting it off. That is why you end up with a little over 4 megapixels on a 24 megapixel image. and 4 megapixels was state of the art... about 20 years ago when digital cameras first started and everybody still shot film.

Having said that, if you are printing 8x10 images, I would say anything over 8 megapixels is actually going to look fine. So you could be ok cropping to 85 or even 100mm. And if you are printing 4x6 then you are probably fine even with the 4MP image! Also, if you are just looking at a picture on a cell phone or small old laptop, you might be fine cropping to 200mm and still seeing a nice image. But if you have a 4K monitor the 4MP image will not look great.

The problem is, you are probably better off with a small $100 dollar point and shoot that goes to 300mm equivalent rather than having a DSLR and a big expensive lens like the Sigma 18-35, and cropping 82% of your picture off.

It's just mathematics...

I think when you crop from 35mm to 200 mm you loose far more then 82%. Maybe even almost 97%. But I need to check it with mathematics.

[AstroDave]

I think when you crop from 35mm to 200 mm you loose far more then 82%. Maybe even almost 97%. But I need to check it with mathematics.

Yes, indeed - 97%. See my earlier post on this. You are now down to a 0.7 MP K3 camera.

[ChristianRock]

I think when you crop from 35mm to 200 mm you loose far more then 82%. Maybe even almost 97%. But I need to check it with mathematics.

bdery just did the math for us in the previous page.

If the loss was 97% then we would end up with a 0.7 megapixel image. As I said, it's just math, so it's important to do the math

[taktoon]

bdery just did the math for us in the previous page.

If the loss was 97% then we would end up with a 0.7 megapixel image. As I said, it's just math, so it's important to do the math

Maybe he forgot about something in his math.

[mikesbike]

I would say both would be a good pairing, if you need that fast f/1.8 for low light. Otherwise, I am very happy with my Sigma 17-50mm f/2.8 to pair with the DA* 50-135mm f/2.8, a combo which I don't find prohibitively bulky for vacationing, even for biking around. For that, however, I prefer to go with yet smaller lenses when possible.

[ChristianRock]

Maybe he forgot about something in his math.

Well if you know better math than him (he is an optical engineer by trade) why don't you do the math then and point out what he's doing wrong? Instead of just saying "I *think* his math is not right" or "maybe he did something wrong".

[taktoon]

Well if you know better math than him (he is an optical engineer by trade) why don't you do the math then and point out what he's doing wrong? Instead of just saying "I *think* his math is not right" or "maybe he did something wrong".

He calculated the horizontal angle of view. 38 degrees for 35mm lens and 6.9 on 200mm lens on APS-C sensor. Then he made proportion with image size. The cropped one lost 82% of it size. But which size? The proper answer is 82% of the width and 82% of the height so 97% of the surface (mega pixels). I still can be mistaken.

[bdery]

I know the 200mm photo is better than the cropped 35mm to the same size fov as the 200mm and I can see it when I zoom in on flikr and lightroom but not zooming in it looks pretty close . I was just hoping to get 2 photos from you professionals that know what your doing to let me see what the difference is between a 18-35mm lens at 35mm cropped to the same fov as the pentax 50-135 at 135mm . or even the 85mmm from the 16-85 mm lens .

Well of course, if you zoom out enough all cameras and lenses produce comparable images.

Respectfully, if that's how you intend to use your camera you'd be better off with a compact superzoom. There is no point in using expensive and large equipment to later cripple its results.

A DSLR is full of disadvantages. Its advantages are resolution, noise handling, DOF control and having the ability to select the right lens for the job. What you're asking is what would happen if you threw all of this away.

[bdery]

bdery just did the math for us in the previous page.

If the loss was 97% then we would end up with a 0.7 megapixel image. As I said, it's just math, so it's important to do the math

Maybe he forgot about something in his math.

Well if you know better math than him (he is an optical engineer by trade) why don't you do the math then and point out what he's doing wrong? Instead of just saying "I *think* his math is not right" or "maybe he did something wrong".

He calculated the horizontal angle of view. 38 degrees for 35mm lens and 6.9 on 200mm lens on APS-C sensor. Then he made proportion with image size. The cropped one lost 82% of it size. But which size? The proper answer is 82% of the width and 82% of the height so 97% of the surface (mega pixels). I still can be mistaken.

Guys, I did a quick and dirty estimate (and said so) to give the OP an idea of what he was throwing away. Please don't quote me too severely on it