Fixed Size (dimensions) Lens?

**FarmerJim** · 10-04-2017, 10:13 AM

I really like the fixed size of my DA* 50-135 lens. When zooming or focusing the lens barrel does not extend (or rotate). It seems like this enhances the weather sealing of the lens, and without the air being pulled into or pushed out of the lens when extending or contracting, a design that "causes" less dust to appear in the lens.

Do my thoughts make sense? Is this something that can be measured?

Does Pentax make any other fixed length (zoom or prime) lenses that do not extend when changing focal length or focusing (internal focusing and internal zooming)?

Thanks for any thoughts or information!

Last edited by FarmerJim; 10-04-2017 at 10:35 AM. Reason: Edited for clarity

**boriscleto** · 10-04-2017, 10:38 AM

The term you are looking for is internal zoom. Only one other current zoom is an internal zoom, the D FA* 70-200/2.8. The FA* 80-200/2.8 & F*/FA* 250-600/5.6 were internal zoom.

**aslyfox** · 10-04-2017, 11:08 AM

using the lens search tool you can access under " Lenses " above and filtering for " internal zoom " this is the result I got for zoom lenses both in and out of production

https://www.pentaxforums.com/lenssearch/?type=Zoom&inproduction=0&iz=1

six total

HD D FA 15-30mm F2.8

DA★ 50-135mm F2.8

HD D FA★ 70-200mm F2.8

the following are marked no longer in production:

FA★ 80-200mm F2.8

F★ 250-600mm F5.6

FA★ 250-600mm F5.6

**boriscleto** · 10-04-2017, 11:49 AM

@Adam

The D FA 15-30 doesn't have the Int. Zoom icon in the database.

Adam · 10-04-2017, 11:59 AM

Originally posted by boriscleto

@Adam

The D FA 15-30 doesn't have the Int. Zoom icon in the database.

Added, though those icons will soon be replaced since we have the lens specs in the new system. Thanks!

The 15-30mm is borderline IZ in my opinion, since the length doesn't change but you can see the element moving within the outer hood.

Na Horuk · 10-04-2017, 12:32 PM

Internal zoom and internal focus. These features have their own pros and cons. It seems like most high end lenses these days have these designs. Some designs actually use both, moving the barrel as well as adjusting the ratio between elements. Lens barrels can be very complicated
In theory the internal mechanisms have some drawbacks I don't like, especially since I don't really use WR. But in practice, these are not very noticeable, at least not to most people

**FarmerJim** · 10-04-2017, 12:33 PM

Thanks for the info.... I guess I hadn't noticed that I could select "Internal Focusing" and "Internal Zooming" on the lens search page.

10-04-2017, 10:13 AM	#1
FarmerJim Site Supporter Join Date: Oct 2012 Location: Oregon, USA Photos: Albums Posts: 63	Fixed Size (dimensions) Lens? I really like the fixed size of my DA* 50-135 lens. When zooming or focusing the lens barrel does not extend (or rotate). It seems like this enhances the weather sealing of the lens, and without the air being pulled into or pushed out of the lens when extending or contracting, a design that "causes" less dust to appear in the lens. Do my thoughts make sense? Is this something that can be measured? Does Pentax make any other fixed length (zoom or prime) lenses that do not extend when changing focal length or focusing (internal focusing and internal zooming)? Thanks for any thoughts or information! Last edited by FarmerJim; 10-04-2017 at 10:35 AM. Reason: Edited for clarity

10-04-2017, 11:08 AM	#3
aslyfox Seeker of Knowledge Join Date: Aug 2016 Location: Topeka, Kansas Photos: Gallery \| Albums Posts: 24,581	using the lens search tool you can access under " Lenses " above and filtering for " internal zoom " this is the result I got for zoom lenses both in and out of production https://www.pentaxforums.com/lenssearch/?type=Zoom&inproduction=0&iz=1 six total HD D FA 15-30mm F2.8 DA★ 50-135mm F2.8 HD D FA★ 70-200mm F2.8 the following are marked no longer in production: FA★ 80-200mm F2.8 F★ 250-600mm F5.6 FA★ 250-600mm F5.6 Last edited by aslyfox; 10-04-2017 at 11:20 AM.

10-04-2017, 11:59 AM	#5
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,593	Originally posted by boriscleto @Adam The D FA 15-30 doesn't have the Int. Zoom icon in the database. Added, though those icons will soon be replaced since we have the lens specs in the new system. Thanks! The 15-30mm is borderline IZ in my opinion, since the length doesn't change but you can see the element moving within the outer hood. Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

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10-04-2017, 10:38 AM	#2
boriscleto Loyal Site Supporter Join Date: Dec 2009 Location: North Syracuse, NY Photos: Gallery Posts: 16,475	The term you are looking for is internal zoom. Only one other current zoom is an internal zoom, the D FA* 70-200/2.8. The FA* 80-200/2.8 & F/FA 250-600/5.6 were internal zoom.

10-04-2017, 11:49 AM	#4
boriscleto Loyal Site Supporter Join Date: Dec 2009 Location: North Syracuse, NY Photos: Gallery Posts: 16,475	@Adam The D FA 15-30 doesn't have the Int. Zoom icon in the database.

10-04-2017, 12:32 PM	#6
Na Horuk Veteran Member Join Date: Feb 2012 Location: Slovenia, probably Photos: Gallery \| Albums Posts: 11,186	Internal zoom and internal focus. These features have their own pros and cons. It seems like most high end lenses these days have these designs. Some designs actually use both, moving the barrel as well as adjusting the ratio between elements. Lens barrels can be very complicated In theory the internal mechanisms have some drawbacks I don't like, especially since I don't really use WR. But in practice, these are not very noticeable, at least not to most people

10-04-2017, 12:33 PM	#7
FarmerJim Site Supporter Join Date: Oct 2012 Location: Oregon, USA Photos: Albums Posts: 63 Original Poster	Thanks for the info.... I guess I hadn't noticed that I could select "Internal Focusing" and "Internal Zooming" on the lens search page.

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