Pentax variable aperture Zoom Lenses and their open aperture characteristics

**acoufap** · 11-30-2022, 01:29 PM - **3 Likes**

Compared some pentax variable aperture Zoom Lenses and their open aperture characteristics at recorded focal lengths. - Looks like the presentation of a music sequencer in portrait orientation. The apertures are the notes and the focal lengths are the bars.

The zooms are DA18-135, DA20-40Ltd, DA55-300PLM and DFA28-105.

Interested?

The following table shows the set of all recorded focal lengths in the rows and open apertures in the columns. Every lens is represented by a color, color legend above the table.

Every zoom has a couple of bars which show their open apertures at recorded focal lengths. Since the zooms are variable aperture zooms, their color is present in more than one column.

If you like, please feel free to discuss your conclusions.

**UncleVanya** · 11-30-2022, 01:33 PM

Why aren’t the ranges for a given zoom at the same f stop continuously represented? For example f4.5 da18-135 shows gaps. Why not solid green from 31-68?

---------- Post added 11-30-22 at 03:37 PM ----------

One conclusion is that from about 78mm the 55-300 is faster than the overlapping lenses that start at a wider focal length. That’s useful to know. It seems to justify my use of the 20-40 + 55-300 PLM vs 18-50 / 55-300 as my more carried option.

**acoufap** · 11-30-2022, 01:45 PM

Originally posted by UncleVanya

Why aren’t the ranges for a given zoom at the same f stop continuously represented?

Although the zoom mechanism works fluently analog, apertures are recorded in jumps in the exif data. While zooming you can see this also in the info panel of the back display of the latest cameras.

yep, from this chart DA20-40 and DA55-300PLM looks like a good combo. Although the small open aperture differences may not be decision critical. But this combo also is very lightweight ...

mikesbike · 11-30-2022, 07:24 PM

Indeed, the DA 18-135mm can keep to f/3.5-4.5 all the way out to about 70mm. Pretty good range! The DA 55-300mm PLM also has a good range. My DA HD 55-300mm WR lens can keep to f/4-4.5 all the way out to about 200mm, which can be seen as only about one stop off those big, expensive 70-200mm f/2.8 lenses- not bad! Both certainly do match well with the DA HD 20-40mm Ltd lens, for a fine kit. Then also having the DA HD 15mm Ltd tucked away makes the kit even better!

Not a Number · 12-01-2022, 01:20 PM

Originally posted by UncleVanya

Why aren’t the ranges for a given zoom at the same f stop continuously represented? For example f4.5 da18-135 shows gaps. Why not solid green from 31-68?

Program line for the lens?

11-30-2022, 01:29 PM - 3 Likes	#1
acoufap Site Supporter Join Date: Jan 2011 Location: Munich, Germany Photos: Gallery \| Albums Posts: 3,520	Pentax variable aperture Zoom Lenses and their open aperture characteristics Compared some pentax variable aperture Zoom Lenses and their open aperture characteristics at recorded focal lengths. - Looks like the presentation of a music sequencer in portrait orientation. The apertures are the notes and the focal lengths are the bars. The zooms are DA18-135, DA20-40Ltd, DA55-300PLM and DFA28-105. Interested? The following table shows the set of all recorded focal lengths in the rows and open apertures in the columns. Every lens is represented by a color, color legend above the table. Every zoom has a couple of bars which show their open apertures at recorded focal lengths. Since the zooms are variable aperture zooms, their color is present in more than one column. If you like, please feel free to discuss your conclusions.

11-30-2022, 01:33 PM	#2
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 24,458	Why aren’t the ranges for a given zoom at the same f stop continuously represented? For example f4.5 da18-135 shows gaps. Why not solid green from 31-68? ---------- Post added 11-30-22 at 03:37 PM ---------- One conclusion is that from about 78mm the 55-300 is faster than the overlapping lenses that start at a wider focal length. That’s useful to know. It seems to justify my use of the 20-40 + 55-300 PLM vs 18-50 / 55-300 as my more carried option. Last edited by UncleVanya; 11-30-2022 at 01:38 PM.

11-30-2022, 01:45 PM	#3
acoufap Site Supporter Join Date: Jan 2011 Location: Munich, Germany Photos: Gallery \| Albums Posts: 3,520 Original Poster	Originally posted by UncleVanya Why aren’t the ranges for a given zoom at the same f stop continuously represented? Although the zoom mechanism works fluently analog, apertures are recorded in jumps in the exif data. While zooming you can see this also in the info panel of the back display of the latest cameras. yep, from this chart DA20-40 and DA55-300PLM looks like a good combo. Although the small open aperture differences may not be decision critical. But this combo also is very lightweight ... Last edited by acoufap; 11-30-2022 at 01:51 PM.

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11-30-2022, 07:24 PM	#4
mikesbike Pentaxian Join Date: Dec 2016 Location: Southeastern Michigan Posts: 4,193	Indeed, the DA 18-135mm can keep to f/3.5-4.5 all the way out to about 70mm. Pretty good range! The DA 55-300mm PLM also has a good range. My DA HD 55-300mm WR lens can keep to f/4-4.5 all the way out to about 200mm, which can be seen as only about one stop off those big, expensive 70-200mm f/2.8 lenses- not bad! Both certainly do match well with the DA HD 20-40mm Ltd lens, for a fine kit. Then also having the DA HD 15mm Ltd tucked away makes the kit even better!

12-01-2022, 01:20 PM	#5
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 9,627	Originally posted by UncleVanya Why aren’t the ranges for a given zoom at the same f stop continuously represented? For example f4.5 da18-135 shows gaps. Why not solid green from 31-68? Program line for the lens?

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