Question About Zoom and Focal Distance

*Ari* · 10-18-2009, 03:07 PM

I m concerned about the behavior my new da 60-250 lens is exhibiting, and wanted to see if anyone has any information about it. It seems I can use the full focal length, but am having trouble with any focal legnths between 220 and 250mm. I red somewhere that focal length is limited at short focal distances on the long end. So far, I have only tested this lens indoors. Is that true, or is this a defective copy?
Thanks for any hel on this!
P.S> - I am referring to this thread at dpreview about the subject - it seems the poster is having the same trouble as me:Problem with my (?) 60-250.: Pentax SLR Talk Forum: Digital Photography Review

*Wheatfield* · 10-18-2009, 03:27 PM

Are saying you can't zoom from 220mm to 250mm?

*Ari* · 10-18-2009, 03:36 PM

Yes-thanks for saying that better than me

Anything between 220 and 250 just shows up (in EXIF) as either 220 or 250, even if I'm moving the barrel in between the focal lengths.

*Ash* · 10-18-2009, 04:12 PM

I believe Richard Day's response to this concern on your dpreview thread answers your question clearly.

The 60-250 is IF and may 'lose' focal length at close focusing, whereas the 55-300 does not because it is not IF. It shouldn't be a big deal, though - the 60-250 should not be considered a macro lens by any means...

Lowell Goudge · 10-18-2009, 04:27 PM

virtually all high ratio zooms (>3:1) only hold the maximum focal length at infinity focus, as you move in and focus closer the maximum focal length goes down.

It would be really interesting if owners of all the super zooms could run some tests to show this, bu photographing known size objects from different distances and then counting pixels on the sensor to accurately measure them as image height

*Ari* · 10-18-2009, 05:03 PM

So I guess my question is, when do I get that zoom range back? Outdoors at really long distances? And why would I lose that +om range and not any at 250mm? Really confused.....

**Marc Sabatella** · 10-18-2009, 06:19 PM

Originally Posted by Ari

Yes-thanks for saying that better than me Anything between 220 and 250 just shows up (in EXIF) as either 220 or 250, even if I'm moving the barrel in between the focal lengths.

That's totally normal for most zoom lenses - it is very typical for them to only report focal length in specific steps. This has nothing to do with the issue that is also being discussed here, where the actual focal length might be shorter than reported at short focus distances (which is also totally normal for most zoom lenses). That is, even outdoors, focused on the horizon ("infinity"), chancess are your zoom will continue to not report all the intermediate focal lengths. Doesn't mean it isn't using them; just that the mechanism for reporting focal length to the camera likes to round things off.

All this is to say, there is nothing to be concerned about here.

*Ari* · 10-18-2009, 06:23 PM

Thank you Marc! I was really hoping to hear that

But why would it only round off in that focal length area? From 220-250mm?

**Marc Sabatella** · 10-18-2009, 06:43 PM

Are you sure that's the only place it rounds off? My zoom lenses all round off a lot more than that. But I don't own the 60-250, so maybe it's unqiue in that. Anyhow, the fact that it shows you 250 at proves that it is reporting focal length in "relative" terms, not absolute - that is, it is showing the focal length as 250mm even though when focused close it isn't really that long. That's in keeping with how other lenses work, too - although their real focal length does get shorter when you focus close (not that you'd normally have any way of knowing without getitng out a tape measure and performing some calculations), they continue to report their maximum in the EXIF.

*Ari* · 10-18-2009, 06:51 PM

It seems to be the only spot. I am going to take a boatload of reference pics to see. Just odd that it can report 89mm, 102, mm.....but between 220 and 250 nothing....

*Ari* · 10-19-2009, 04:24 PM

Well, after calling Pentax, it seems the lens is defective - they said there shouldn't be that much rounding up. Ugh. I hate the return process....mailing back and forth.....I think I am going to forego this lens and start thinking about an alternative. I don't want to get caught in a loop of returning things. I think I may forego a zoom altogether.....I have only had luck with 2 zooms - the da*50-135 and the 16-50. Just would like the practicality of a good zoom range for certain jobs. But the complaints I hear 'round here of build quality on both the tamron and sigma 70-200 make me sooooo nervous....

**Marc Sabatella** · 10-19-2009, 09:07 PM

Originally Posted by Ari

Well, after calling Pentax, it seems the lens is defective - they said there shouldn't be that much rounding up.

You might try asking other owners of this lens if there's does the same - the person you spoke with might be simply misinformed.

But also consider - really, who cares what number goes into the EXIF? Either the zoom ring turns all the way to 250 or it doesn't, and that should be plainly visible in the viewfinder. And if it turns all the way to 250, it's got to pass through 230 and 240 and 241 and 242, and so on. So far, aside from potentially less-than-recise EXIF information, I don't see any evidence at all that anything is actually *wrong* here.

**Marc Sabatella** · 10-19-2009, 09:08 PM

Originally Posted by Ari

It seems to be the only spot. I am going to take a boatload of reference pics to see. Just odd that it can report 89mm, 102, mm.....but between 220 and 250 nothing....

So it reports 89 and 102 - does it also report 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, and 101?

*Ari* · 10-19-2009, 09:10 PM

All good points, Marc. I think part of the problem is that I may be obsessing over this because I spent so much money on it.

*Ash* · 10-19-2009, 09:33 PM

Is the lens optically good Ari?
If the EXIF data is not a big deal to you then try not to worry about this little detail.
It will not affect your image results.