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Old Jan 7, 2008, 4:04 AM   #11
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Thanks to Tim, Penolta, and Ed, you've satisfied my curiosity, I did try a search on google, but didn't get very far. ... Jack
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Old Jan 9, 2008, 9:54 AM   #12
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jachol wrote:
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Thanks to Tim, Penolta, and Ed, you've satisfied my curiosity, I did try a search on google, but didn't get very far. ... Jack
Here are a couple of places to look Jack!

http://web.archive.org/web/200512140...rd/mounts.html

Case Study in Variations - Vivitar TX Lenses
  • Vivitar 24mm f/2.8 TX lens (#37xxxxxx)
    • less than +1 % distortion (vs. 4% standard) [/*]
    • aperture f/2.81 [/*]
    • focal length 24.1mm [/*]
    • weight = 10 ounces [/*]
    [/*]
  • Vivitar 28mm f/2.5 TX lens (#37XXXXXX)
    • less than -1 % distortion (vs. 2.5% standard) [/*]
    • aperture f/2.6 [/*]
    • focal length 28.3mm [/*]
    • weight = 10.5 ounces [/*]
    [/*]
  • Vivitar 35mm f/2.5 TX lens (#37XXXXXX)
    • less than -1 % distortion (vs. 2.5% standard) [/*]
    • aperture f/2.62 [/*]
    • focal length 36.2mm [/*]
    • weight = 11 ounces [/*]
    [/*]
  • Vivitar 135mm f/2.5 TX lens (#37XXXXXX)
    • less than +1 % distortion (vs. 2.5% standard) [/*]
    • aperture f/2.58 [/*]
    • focal length 134.3mm [/*]
    • weight = 19 ounces [/*]
    [/*]
  • Vivitar 200mm f/3.5 TX lens (#37XXXXXX)
    • less than +1 % distortion (vs. 2.5% standard) [/*]
    • aperture f/3.68 [/*]
    • focal length 198.0mm [/*]
    • weight = 21 ounces [/*]
    [/*]
The point of listing the above figures is to illustrate how close to marked focal length and aperture most prime lenses really are, even old ones like these Vivitar TX lenses. Distortion is also under 1%, well under the typical 2.5% acceptable range (and 4% for wide angle lenses like the 24mm lens here). Few consumer zooms could match this precision!

How did these lenses perform on sharpness? The 24mm lens turned in center sharpness that was very good to excellent (57-64 lpmm), while corner sharpness was good (1) to excellent (5 out of 6; 32 to 51 lpmm). Usually, you would expect the 24mm to be the hardest lens to design, and the worst performer. Actually, it is rated as the best of the litter here!

The 28mm lens was also very good (3) to excellent (3 out of 6) at the center (53-66 lpmm). Surprisingly, the corner performance was above average, with one very good mark and 5 excellent ratings (33 to 47 lpmm). Surprise again, as usually you might expect corner performance to be the worst performer for a low-cost 28mm wide angle prime lens.

The 35mm was excellent on corner sharpness (39-50 lpmm) at all stops, but only excellent at f/2.5 and f/11 and f/16. The mid-range settings dropped to very good at f/4, acceptable at f/5.6, and good at f/8 at the center.

The latter 35mm lens performance is a good example of why I admonish folks to actually test their lens rather than rely on assumptions about lens performance. Perhaps this lens was a bad example, a lemon? But if you expected the 35mm to perform better than the 24mm or 28mm, being a simpler design, you would be wrong here.

Moreover, you would normally expect the best performance in the f/5.6 to f/8 mid-range apertures, right? For this 35mm lens, you would get the worst performance.

You would expect wide open to be the worst, but it was excellent.

You might also expect the corner sharpness to be rated worse if the center was only good or acceptable, but here it was uniformly rated as excellent.

In short, this lens shows why it is critical to test your lens for variations in performance!

How did the Vivitar TX telephotos fare for sharpness? The 135mm f/2.5 fast telephoto was excellent in the corner, but ranged from excellent wide open to good in the mid ranges, then excellent at f/11 and f/16.

Again, these results are somewhat surprising. You would normally expect a low cost telephoto non-APO lens to do poorly wide open and in the corners. But the 135mm f/2.5 did excellently in the corners, and also wide open or stopped all the way down to f/16 and beyond. Where you might expect it to be sharpest, it did the worst!

Similarly, the 200mm f/3.5 Vivitar TX lens is very good from f/3.5 to f/11 in the corner, but only good stopped down to f/16 and f/22. And the center sharpness is very good wide open but falls to good at f/8 and f/11 and f/22.

Surprise again! This telephoto lens is relatively sharpest wide open and gets worse as you stop down. The optimal range is from wide open to about f/8.

In summary, these Vivitar TX lenses violate most of our assumptions about how lenses generally should perform:
  • The 24mm was the best performer, not the worst. [/*]
  • The wide angle lenses did relatively best wide open or at f/11 and f/16, not in their mid-ranges. [/*]
  • Both telephotos were best wide open (or stopped down to f/11-16 for the 135mm lens). [/*]
  • Corner sharpness was rated generally excellent or very good on all lenses (except 200mm at f/16-22). [/*]
  • Center sharpness varied more, usually with the middle f/stop ranges having the lowest rating. [/*]
Unless you tested these lenses, how would you know how they really performed?

My final point is about the relative value of these prime lenses. Note how many excellent and very good ratings they garnered. Check out the low distortion values. Consider sharpness wide open and in the corners. That's where you need it most. That's where these lenses perform best. So how come you can often buy these lenses for $20 to $35 US from dealers (without TX adapter)?

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Old Jan 9, 2008, 10:36 AM   #13
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Thanks Ed, I've been on Robert Monaghans site many times, but I've never seen that page. ... Jack
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Old Jan 9, 2008, 12:24 PM   #14
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jachol wrote:
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Thanks Ed, I've been on Robert Monaghans site many times, but I've never seen that page. ... Jack
Pages on that site seem to go out for weeks or months sometimes. I recently missed out on a 400mm TX mount lens with a K mount to TX mount on one end. Would have loved to get it as my 300 has a M42 to TX mount. Could have had a K mount for both the 400mm and the 300mm. Oh well!! LOL

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Old Jan 9, 2008, 1:40 PM   #15
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ed,
do you have a link to robert's archived home page. it's a shame he took this off line as it was one of the most comprehensive photography sites i've ever seen. a lot of the links no longer work.

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Old Jan 9, 2008, 5:54 PM   #16
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I have a couple of TX mount lenses (didn't realize what they were until I read this thread). One is a Vivtar 135mm f2.8 and the other is a Soligor 300mm f5.6.

So how exactly do you take the adaptor off? Mine looks a little different than Dawgs. The lever is all enclosed inside the housing. I've tried and can't get them to budge. I would guess that you depress the silver lever and turn couter-clockwise but that's not working.

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Old Jan 9, 2008, 6:12 PM   #17
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As you are looking at the camera end of the lens...Depress the lever and turn counter clockwise. Your 300mm is the same as mine. I don't know about a cap over the lever as I've never seen that. Would help keep from hitting it at the wrong time! I think it's counter clockwise anyway...I'm at work right now and my feeble brain can't remember for sure. I'll check again when I get home. I don't have that here at work but I'll see if I have that URL when I get home. Keep those TX's as they are very good lens and will get rarer as the days go on!



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Old Jan 9, 2008, 6:33 PM   #18
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It's just the housing for the switch. It looks like yours has been cut away maybe. Mine look like this...



I would guess that "O" means open and "L" means lock so I'm thinking counter-clockwise would be right.

Just got it figured out on the Soligor. The Vivtar still won't budge, though. I'll take it to work with me where I have some tools that might help.

Thanks Dawg!
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Old Jan 9, 2008, 8:16 PM   #19
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Either broken or cut away for sure...Works just fine though!



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Old Jan 10, 2008, 3:04 AM   #20
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Try these Roy!

http://www.robertstech.com/sitemap.htm

http://www.robertstech.com/pentax.htm

You can manuever around after you get there!

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