[kentster]

I have 2 Tamron Lenses. 1) 18-200mm A14 2) 70-200 F2.8 on a K20D.

I believe both are designed for crop sensor cameras.....so i'm thinking 200mm should be the same on each camera ...correct?

The 70-200 seams to to bring the subject in much closer then the 18-200.

Also - I'm looking to add a wider lens to the collection. Does anyone make a 8 to 17 mm lens that doesn't have the crop factor? Or is that even possible.

[esrandall]

Hi there, not dumb questions at all. 200 should be 200 when used on the same camera. The Tamron 70-200 is actually a FF lens, but used on the same camera, should be apples to apples. Regarding a FF ultra wide, there is the Sigma 15-30 (there's one for sale in the Marketplace, actually). Anything wider than that for FF is getting into fisheye territory (with the exception of the Sigma 8-16 = 12-24 on APSC). The widest Pentax prime I know of is the old 15mm f/3.5 (think there's one for sale in the Marketplace -- very rare lens to be found).

[K(s)evin]

Crop factor is a function of the sensor, not the lens. 18-200 will be 18-200 always.

Pentax has 14mm f/2.8 prime.

[rawr]

The 18-200 is a crop lens (ie designed for use on crop bodies), the 70-200 is a full-frame lens.

Sigma make a 8-16mm crop format lens which is very well regarded, as well as two 10-20 mm zooms. Tamron make a 10-24mm crop zoom.

All those lenses have user reviews in the lens review section of Pentax forums.

[Adam]

Also - I'm looking to add a wider lens to the collection. Does anyone make a 8 to 17 mm lens that doesn't have the crop factor? Or is that even possible.

Like a full frame lens that's that wide? I think 14mm is about as wide as it gets outside of fisheyes. Pentax's widest FF prime is still the SMC and SMC A 15mm F3.5. This would give you the same field of view as a 10mm lens on a crop body.

[calsan]

The Sigma 12-24 is a full frame lens, which is equivalent to the Sigma 8-16 (no longer available for Pentax) on APS.
As for why does the field of view change between '200mm' lenses - a few reasons - manufacturers round to whole numbers, field of view changes with focal distance, and something known as 'focal breathing'. Give it a google, I can't explain.

[UncleVanya]

Focus breathing may be to blame. Is the difference noticed with subjects at infinity or subjects closer than 30' or both? If only seen under roughly 20-30' then it is probably focus breathing. This is a property of a lens (typically internal focus lenses) where the magnification decreases as you focus closer. This makes the apparent focal length drop. My 18-135 does it, my 60-250 does it... My takumar bayonet (135) doesn't.

[Abbazz]

I have 2 Tamron Lenses. 1) 18-200mm A14 2) 70-200 F2.8 on a K20D.

I believe both are designed for crop sensor cameras.....so i'm thinking 200mm should be the same on each camera ...correct?

The 70-200 seams to to bring the subject in much closer then the 18-200.

Also - I'm looking to add a wider lens to the collection. Does anyone make a 8 to 17 mm lens that doesn't have the crop factor? Or is that even possible.

As stated by others, a 200mm lens is always a 200mm lens and you should see no difference between the 18-200 and the 70-200. Except that the Tamron 18-200 is not a 200mm anymore when focused closer than infinity. It's called focus breathing. In fact, the Tamron 18-200, when set at 200mm and focused close, is more like 150mm in actual focal length. See this thread:

Re: Focal length ain't what it used to be.: Micro Four Thirds Talk Forum: Digital Photography Review

There are expensive lenses performing much worse. For example, take the Nikon 70-200/2.8 VR II; when used at 200mm and focused close, its actual focal length becomes 134mm:

70-200mm AF-S VR II Lens Review by Thom Hogan

Cheers!

Abbazz

[EDIT] Sorry for the duplicate, I didn't see Uncle Vanya's post.[/EDIT]

[UncleVanya]

As stated by others, a 200mm lens is always a 200mm lens and you should see no difference between the 18-200 and the 70-200. Except that the Tamron 18-200 is not a 200mm anymore when focused closer than infinity. It's called focus breathing. In fact, the Tamron 18-200, when set at 200mm and focused close, is more like 150mm in actual focal length. See this thread:

Re: Focal length ain't what it used to be.: Micro Four Thirds Talk Forum: Digital Photography Review

There are expensive lenses performing much worse. For example, take the Nikon 70-200/2.8 VR II; when used at 200mm and focused close, its actual focal length becomes 134mm:

70-200mm AF-S VR II Lens Review by Thom Hogan

Cheers!

Abbazz

[EDIT] Sorry for the duplicate, I didn't see Uncle Vanya's post.[/EDIT]

Yours is clear and concise. It helps me and I know how this works. Lol b

[excanonfd]

Samyang lenses (and all the rebadge brands) are all FF, including 8/3.5, 14/2.8, 85/1.4 (that's all I have). The new version of 8/3.5 with removable hood will not vignette on a FF while the older version with a fixed hood definitely does vignette - a lot.

[yucatanPentax]

The Sigma 12-24 is a full frame lens, which is equivalent to the Sigma 8-16 (no longer available for Pentax) on APS.
As for why does the field of view change between '200mm' lenses - a few reasons - manufacturers round to whole numbers, field of view changes with focal distance, and something known as 'focal breathing'. Give it a google, I can't explain.

At least in the USA, the Sigma 8-16 is still available in Pentax mount, new, from Sigma.

8-16mm F4.5-5.6 DC HSM | Sigma Corporation of America

[i_trax]

you can still preorder them from CRKennedy in AU, that is what I did to get mine.

[pathdoc]

My takumar bayonet (135) doesn't.

Well if it's a prime (which I'm assuming it is, given the single quoted number), it can't.

Samyang lenses (and all the rebadge brands) are all FF, including 8/3.5, 14/2.8, 85/1.4 (that's all I have).

This is something to bear in mind. IIRC the P/K mount ones are all also aperture-priority capable, yes? If so,then at least the aperture should be written into the EXIF even if the focal length has to be set manually for SR.

[UncleVanya]

Well if it's a prime (which I'm assuming it is, given the single quoted number), it can't.

That is not my understanding. My understanding is that any lens can exhibit this and that it is not limited to zoom lenses. It is related to focusing not zooming. Focus/Lens Breathing: What Is It and Does It Matter?

If you have a source that indicates otherwise please share. The lens in question is not internal focus which I think is necessary component to focus breathing. So not at all surprising that it does not - but not because it is prime.

[kentster]

I'm learning new stuff everyday... Thanks everyone for your responses