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05-30-2009, 11:55 AM   #1
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28mm Lens test: Three Vivitars and Two Pentaxes

About two years ago, I had settled on a couple of 28mm prime lenses, but acquired some others along the way. I am going to test them to see if I still like my favorites and figure out how good the inexpensive newcomers are.

The lenses, Vivitar numbers from the Bestiary:
  • Vivitar 28mm f2.0 K mount K12, MFD 0.3m, filter 55mm, 260g
  • Vivitar 28mm f2.5 TX mount T91, MFD 0.25m, filter 58mm, 290g
  • Vivitar 28mm f2.8 T4 mount T93, MFD 0.25m, filter 58mm, 270g
  • Pentax-F 28mm f2.8, KAF mount, MFD 0.3m, filter 49mm, 180g
  • Pentax-DA 18-55mm f3.5-5.6 V1 at 28mm, MFD 0.25m, filter 52mm, 230g

Vivitar 28mm f2.0 K12 - Made by Kiron, it's one of my favorite lenses to carry. The maximum aperture is the big reason. I have compared this lens to the Tokina-made Series 1 28mm f1.9, and it was quite a bit sharper. Six aperture blades make it one better than most of the Pentaxes, though I can't say I see the difference. It was my only 55mm filter ring for a while, so I use a stepdown ring and 52mm caps. Focus ring is stiff, but f2 makes getting precise focus very easy. The ring turns 270 degrees. All of these Vivitars focus in the opposite direction than all Pentax lenses, and aperture rings turn in the Pentax direction. Minimum aperture on all the Vivitars is f16.

Vivitar 28mm f2.5 TX mount T91 - I think all of these TX lenses are made by Tokina, so this is a different lens than the other f2.5 Vivitar I've seen on eBay. It's cheap if you have the TX mounts already. Eight aperture blades, bokeh must be great! The focus is a little light and it's hard to turn the aperture ring without sometimes turning the focus ring. The ring turns 180 degrees. I used the TX K-mount on this one and the weight includes that mount. The aperture ring doesn't click at f2.8 so I set the ring in between f2.5 and f4 to try to get f2.8. It only clicks at full stops from f4 to f16 and wide open.

Vivitar 28mm f2.8 T4 mount T93 - Also made by Tokina, and reminds me of other old 28mm lenses. It has the older metal focus ring and red /white markings. It's cheap if you have the T4 mounts already. Eight aperture blades like the other Tokina. The focus is just right. The ring turns 270 degrees. I used the T4 M42 mount on this one, modified for manual aperture operation, and the weight includes that mount. The aperture ring only clicks at full stops from f2.8 to f16.

Pentax-F 28mm f2.8 - This is the same optical formula as the Pentax-A, which I liked. I stumbled on this one for a great price and sold my Pentax-A copy, so I have autofocus now. I liked the A construction and focus ring better, but this F is not bad. It's clearly a lot smaller and lighter than the Vivitars. The ring turns 90 degrees and has a sticky feeling at close distances, some issue with this copy that I haven't investigated. The minimum aperture is f22.

Pentax DA 18-55mm version 1 - I included this as a control. It only opens to f4 at 28mm. I let the lens tell me where 28mm was rather than trying to match the image size to another lens. That's a more repeatable setting. The minimum aperture at 28mm is f27.

Sharpness and distortion test - I have a brick wall so I waited for a clear day for consistent light. My *ist DS was mounted on a tripod about 10 feet from the wall. I used the 2 second delay for all shots. I took a test shot with the DA 18-55 at f8 and 1/250 to get a nice histogram, and used that exposure as a baseline for all the exposures. I also used the color temperature from this shot to set all the lenses to the same temperature in Adobe Camera RAW - obviously I took all the photos in RAW. I focused manually for all the lenses. I focused each lens, then adjusted apertures and shutter speeds for shots from wide open to f16 at each full stop. Since focus is so important for sharpness, I went through the group three times and chose the best-focused set of images to compare. (Even with a split-prism screen, my focus was not perfect every time.) It took about 40 minutes for almost 100 shots.

I created the sharpness composite images by choosing a set of the best focused images. Then I opened them in Adobe Camera RAW v3.7 and set the color temperature and tint to match the test image. I used Photoshop Elements 4.0 to copy sections from the center and upper right corner of each image, and pasted them into the composite image. I had to convert the images to 8 bit to add text labels produce a JPG composite.

Flare test - The camera was on a tripod. I framed the image so the sun was just barely in the upper right corner with the first lens, the Vivitar K12. I used that lens for the baseline exposure (f2, 1/4000) and adjusted all the other expoosures for each lens wide open (e.g., f2.8, 1/2000). Although each lens might have a slightly different field of view, they are all designed for a 24x36 format except for the DA 18-55, so even if the sun isn't quite in the image, the sun is certainly hitting the front element and bouncing around the interior. I opened them in Adobe Camera RAW v3.7 and oddly the color temperature and tint were all the same as the test image. I turned down the exposure one stop on each lens because the flare showed up better. I used Photoshop Elements 4.0 to resize the images to 600x401, convert to 8 bit, sharpen slightly to compensate for downsizing, copy each image, and paste into the composite image.

Test image links, lens photos and more talk in my next posts.

05-30-2009, 12:06 PM   #2
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These test images are pretty big, up to 2.86Mb and 2600x1600. You'll have to look at them full-size to avoid resizing issues.

Centers composite

Corners composite

Flare composite

Distortion composite
05-30-2009, 01:09 PM   #3
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The group photo. The Vivitars are all the same height, but the K12 is not as fat. The F28/2.8 is much shorter. I assume everyone knows what the kit lens looks like.





05-30-2009, 02:54 PM   #4
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Nice job! My quick impressions on this are:

- The Vivitar 28/2 looks surprisingly small and performs quite well
- Corner performance is much worse than center on the 2.5 that I wonder is field curvature isn't to blame
- EDIT: I originally wrote "The F28/2.8 does not fare so well"; I should have said Z93 - I had the order mixed up
- the kit lens looks way better than a kit lens "should"


Last edited by Marc Sabatella; 06-02-2009 at 05:05 PM.
05-30-2009, 04:41 PM   #5
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Wow, I love that lens flare off the K12! Totally over the top loveliness.

Thanks for this comparison. It conforms with my expectation that the T-mount lenses of this type are not up to the standard of the K-mount.
05-30-2009, 07:23 PM   #6
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QuoteOriginally posted by Marc Sabatella Quote
Nice job! My quick impressions on this are:

- The Vivitar 28/2 looks surprisingly small and performs quite well
- Corner performance is much worse than center on the 2.5 that I wonder is field curvature isn't to blame
- The F28/2.8 does not fare so well
- the kit lens looks way better than a kit lens "should"
You may be right about the f2.5 (T91). I figured 10 feet was far enough away to minimize the effects of field curvature, but I just measured the width of the field here. It's not quite 8 feet, more than I thought. That lens was also easy to bump out of focus, though I don't think I did.

The F28/2.8 doesn't take tests well. Last time I tried this, I had similar results with an A28/2.8, so I think my tests were OK. I do end up using it in the real world and liking the results. However, the DA 18-55 can match it in good light and the 28/2 K12 can match or better it in low light, so it ends up just being small and light.
05-30-2009, 07:47 PM   #7
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QuoteOriginally posted by Just1MoreDave Quote
The F28/2.8 doesn't take tests well. Last time I tried this, I had similar results with an A28/2.8, so I think my tests were OK. I do end up using it in the real world and liking the results. However, the DA 18-55 can match it in good light and the 28/2 K12 can match or better it in low light, so it ends up just being small and light.
My gut feeling, from the little I've used it, is that my A28/2.8 is in the middle of the Vivitar pack. It does not distinguish itself particularly and is definitely bettered at f/2.8 by some of the f/2 lenses. I might even have done some casual tests that support that contention.
05-31-2009, 06:55 PM   #8
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I just noticed something unusual about the Vivitar 28mm f2.0 K12. The front element turns when you focus it. I don't think any of my other prime lenses do this, including the otherwise similar Kiron 24mm f2. I guess it doesn't bother me; Ive owned it for 2 years without noticing.

05-31-2009, 07:03 PM   #9
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am I the only one that think the F lenses just looks super cool.

this 80's retro futuristic look is just awesome.. I wish Pentax will re use this design and make a camera to go with it
06-01-2009, 07:28 AM   #10
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QuoteOriginally posted by redpigeons Quote
am I the only one that think the F lenses just looks super cool.
It's good we're all different!

I don't own any lenses from that era because I really dislike the cheesy plastic look. I haven't even bought the FA50 for that reason. I also hate the gaudy rings and plastic Canon design of the DA*55, so I'll give that a pass too.

Understated black metal for me! I love the FA Limiteds.
06-01-2009, 07:34 AM   #11
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You really ought to try the SMC PENTAX (k) 28mm F3.5 lens. This is the K version, not the later M version. Its a killer lens. The SMC Pentax (k) 28mm F2.0 is damn good too, maybe better at close range but not as good at infiinity as the F3.5 version. Both these lenses are hard to find unfortunately.
06-01-2009, 10:09 PM   #12
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QuoteOriginally posted by jco Quote
You really ought to try the SMC PENTAX (k) 28mm F3.5 lens. This is the K version, not the later M version. Its a killer lens. The SMC Pentax (k) 28mm F2.0 is damn good too, maybe better at close range but not as good at infiinity as the F3.5 version. Both these lenses are hard to find unfortunately.
I had both the f3.5 lenses and tested them a couple of years ago, along with the same K12 and DA 18-55, plus an A28/2.8 and a couple of others. That test was not as careful as this one, but that K28/3.5 was really ordinary. The M28/3.5 was the best performer, the K12 behind but not that far.

The K28/3.5 results are nowhere near anyone else's for that lens, so something was off. But even if it was great, it has to be the biggest 28/3.5 lens ever. It's 50% longer and 50% heavier than the Takumars before it or the Pentax-M. I know I don't need tremendous speed at 28mm but f3.5 is really slow for a prime. It was just too big and too slow for me. I would like to see a comparison between M and K versions. The Pentax f2.0 primes are probably great too but in a different price category than me.
06-02-2009, 09:59 AM   #13
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thanks for the comparison, when I get to a computer I will have to have a good look. Sounds like the F28/2.8 didn't fair too well - that would be in keeping with my experience of an A28/2.8 on film, which at times could be unexpectantly soft and suffering from, I think, a lot of coma and CA.
06-02-2009, 10:31 AM   #14
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QuoteOriginally posted by Duncan J Murray Quote
Sounds like the F28/2.8 didn't fair too well - that would be in keeping with my experience of an A28/2.8 on film, which at times could be unexpectantly soft and suffering from, I think, a lot of coma and CA.
And I thought this activity was supposed to involve visual and not auditory perception. Did you actually look at the pictures? F28/2.8 was the sharpest in the corners, very good in the center and had the lowest flare. The main difference in the brick shots was white balance. If white balance was set with a white/gray card, the center crops would look nearly identical >f/2.8.

The occasional softness you experience is your fault.
06-02-2009, 10:42 AM   #15
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QuoteOriginally posted by rparmar Quote
It's good we're all different!

I don't own any lenses from that era because I really dislike the cheesy plastic look. I haven't even bought the FA50 for that reason. I also hate the gaudy rings and plastic Canon design of the DA*55, so I'll give that a pass too.

Understated black metal for me! I love the FA Limiteds.
I'm curious whether people irrationally discriminate between lenses solely based on the "Made in..." label. In the 50s, in the US, "Made in Japan" was synonymous with cheap crappy flashlights and toys.
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