[J.Scott]

I understand that focal length is what it is, but I don't understand why Pop Photo said this lens would have a conversion to 82.5mm / 450mm for digital use, when it was designed for digital use. The lens is marketed as 55-300mm, so why would there be a conversion for it?

It is, and always will be, and only can be, a 55-300mm lens - period. If I put it on my MZ-5N it will be a 55-300mm lens; on my K10D it is a 55-300mm lens. Any lens placed on a Pentax DSLR will have a 'crop factor of 1.5X. Until DSLR's catch up and become 'full frame' there will be a crop factor involved.

This one is marketed as a 'Digital Lens' not for it's focal length but for the fact that the image created by this lens will fit perfectly on an APS-C sized sensor.

I think I understand your argument, ' If it can only be used on a DSLR then why not market the lens in it's 'converted' or 'cropped' focal length?' In fact, Pentax does market it as such; this is from their own website, "Developed specifically for PENTAX digital SLRs, the DA 55-300mm ED zoom has a focal length equivalent to 82.5mm to 450mm in the 35mm format." If Pentax cameras changed their crop factor to 1.6X (like Canon) then this lens would have a 'converted' focal length of 88-480mm, but it still is a 55-300mm lens.

Quite simply - focal length is a lens measurement and conversion or crop factor is a camera measurement.

Does that help?

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Last edited by J.Scott; 08-27-2008 at 04:45 AM.

No, the front element does not rotate during zoom or focus.

because this is a Pentax not Canon lens!


Radu (sorry I couldn't let that one pass)

[Tom S.]

It is, and always will be, and only can be, a 55-300mm lens - period. If I put it on my MZ-5N it will be a 55-300mm lens; on my K10D it is a 55-300mm lens. Any lens placed on a Pentax DSLR will have a 'crop factor of 1.5X. Until DSLR's catch up and become 'full frame' there will be a crop factor involved.

This one is marketed as a 'Digital Lens' not for it's focal length but for the fact that the image created by this lens will fit perfectly on an APS-C sized sensor.

I think I understand your argument, ' If it can only be used on a DSLR then why not market the lens in it's 'converted' or 'cropped' focal length?' In fact, Pentax does market it as such; this is from their own website, "Developed specifically for PENTAX digital SLRs, the DA 55-300mm ED zoom has a focal length equivalent to 82.5mm to 450mm in the 35mm format." If Pentax cameras changed their crop factor to 1.6X (like Canon) then this lens would have a 'converted' focal length of 88-480mm, but it still is a 55-300mm lens.

Quite simply - focal length is a lens measurement and conversion or crop factor is a camera measurement.

Does that help?

Yup, that nailed it for me. Thanks!!

[jamesm007]

I also liked the review and believe its one of the Pentax lens that offers a lot for the money. When Photozone reviews it, I believe it will be between the N/C and the new Sony 70-300mm in overall resolution at 300mm. CA/PF will be a toss up. The Pentax does start at 55mm and offers very good quality at that focal length so it one ups those lens that start at 70mm, and makes for a very versatile lens. Now those others have much faster AF, thats the downside, but the Pentax fires back costing less than half as much as the Sony. So 3 stars for IQ, 3 stars for build, and 5 stars for performance/price. Thats my best guess. Doing lots of tests. Cant wait to see the review, even though I know as well as other know that its a great lens for the money.