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04-24-2009, 07:27 PM   #1
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Lens/TC comparison project

Having recently retired, Iíve got a little spare time to play with the lenses accumulated over 40-plus years of Pentax LBA. We didnít have a diagnosis way back then - we just hid the results from the spouse. ď What? That olí thing? Why, my Dear, itís been around as long as that purse Iíve never seen before. Would you like to go out for dinner tonight?Ē

The first project is to compare M42 lenses at each useful F-stop, including whatever TCís are available. Iíll work on the newer stuff later. Eventually, Iíd like to record other variables and effects such as extension rings, diopter filters and hoods. May take a while as I have to borrow ďfingers aní toesĒ from all three dogs to count all the possibilities as it is.

The first trial run was just to figure out what was useful and worth the time and effort. For example, is F-min, F-min + 1, and F 8 enough, or is it useful to record every F-stop?

Iíve accumulated enough preliminary data to make some risky observations. Your experience may be different. If so, please contribute, because if anything, Iíve discovered that lens/TC combinations are much more varied than I suspected.

Hereís a list of the planned M42 lenses and TCís:

(PST = Pentax Super Takumar Ė M42)

PST 35/3.5
PST 50/1.4
PST 55/1.8
PST 105/2.8
PST 135/3.5
PST 200/4.0
Accura Supertele 200/3.9 PS
PST 300/4.0
Tele-Takumar 300/6.3 PS
Vivitar(Tokina) 400/5.6 T-mount
Focal 80-200/4.5
Tokina 80-200/3.5-4.5
Sears 135/2.8
Sakar 135/1.8
Asanuma(Tokina) 2x TC
Vivitar 2x TC #1
Vivitar 2x TC #2

Based on preliminary (learning curve) experience with the PST 105, 135, 200 and 300, Iíve formed a few opinions:

- * TCís have very different ďpersonalitiesĒ with different lenses and with different focus distances on the same lens. Of the screw-mount TCís I have available, Iíve no doubt that Iíd chose one over another depending on the lens and intended application. *

- I have one TC thatís poor on more than one lens at all distances. This is the only one Iíd discard on general results Ė and even it may prove better on other lenses.

- A steady, vibration-damped support and 2-second shutter delay makes as much difference in sharpness as any other single effect Ė no surprise, but the comparisons are exceptionally consistent.

- Split-prism focusing is MUCH more consistent than any other mode.

- Itís all too easy to confuse pure sharpness with other undesirable lens attributes such as lack of contrast, poor bokeh, bloom, CA/PF, etc. Likewise, motion blur hides sharpness.

- Bright, high contrast scenes degrade ALL my TCís to some extent, but - even those with very noticeable CA or PF perform much better in low contrast, cloudy or shady situations. One TC Iíd not consider using in bright sun is acceptable in open shade.

- The widest F-stop (F-max) on every lens is notably worse than ĎF-max plus 1í. No surprise here and the soft presentation does have advantages in some situations, especially when combined with the associated bokeh effects.

- I believe recording at F-max, F-max plus 1 and F 8 will be satisfactory as the results among other F-stops seems very small and is quite predictable even with TCís.

- I'm gaining a new appreciation for TC's when used within their limits.

Does anyone have any innovative suggestions as to how I might eventually ďpublishĒ pictorial results so they might be of use to others. Iím not interested in building a web site, but the potential number and the organizing and pairing of comparison shots seems a little much for typical upload sites.

H2

04-24-2009, 07:35 PM   #2
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A great project; one that I have thought of doing but never found the time to get into. I look forward to seeing your results and comparing them to my own experience.

Regards, Jim
04-24-2009, 07:47 PM   #3
F16
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I don't know that I can offer much advice, but I think this is a fun test. I wish that I had a DSLR as doing extensive tests of this kind with a film SLR isn't as practical, and I also have a lot of lens/TC combos that I'd like to test eventually. I don't see many higher end M42 TCs but I have a rare Tamron SP 7 Element M42 TC, can't imagine that there are many of those floating around. And for that matter, I don't know if I've ever even seen a 1.4x/1.5x TC in M42 mount, and not surprising that these shorter TCs tend to give much better results.

Some good starting points with a test like this would be things like a very stable tripod (obviously), self-timer, maybe a beanbag resting on the lenses, stationary test subjects and/or high shutter speeds, etc. 100% crops near the center and maybe 2/3rds of the way to the edge of the frame would be good ways to check results. Maybe 'focus bracket' each shot with 2 or 3 shots just to be sure you can choose an image that is closest to having proper focus. Results at small apertures probably won't interest many people, showing results wide open and maybe 1 & 2 stops down would be most useful.

P.S. - it would also be useful if you had a modern 2x 7 element TC of good quality such as Tamron, Sigma, Kenko, etc to compare with. It would be interesting to see how the older TCs compare.

Last edited by F16; 04-24-2009 at 07:53 PM.
04-24-2009, 07:48 PM   #4
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Hey, Jim, send my old 85/1.8 back for a visit and I'll include that one too. I miss it. H2

04-24-2009, 07:59 PM   #5
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Pacerr - PM me. I might be able to host a comparison for you.
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