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01-10-2010, 12:04 PM   #1
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Five TC's plus AD-2 SP 300/2.8 - comments

Continuing the saga, I compared five TC’s on the SP 300/2.8 today. Again, the following comments are purely subjective and by no means a ‘test’. And again, there ain’t gonna be IQ pictures, just comments for the moment, confirming the I’m too lazy to upload dozens of pix theory. If someone needs a particular image I can provide / PM. (See: https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/86318-four-tc%...-comments.html for the AD-2 180/2.5 results. )

The Adaptall SP 300/2.8 lens is well documented. If you can live without auto focus and prefer to spend about half the new cost of an equivalent lens, get one. IMO the Mdl 360 is preferred. The usual technical data can be found on the Adaptall-2 web site.

Conditions were brighter than for the 180/2.5 comparison -- about F/11+ on a “Sunny Sixteen” hazy day using a tripod and 2-second delay. Results were reviewed/compared in Faststone Image Viewer. All apertures were as read via the camera using AV mode.

K200D with the SP 300/2.8 (#360) w/hood using default, best quality JPG settings, AV mode and ISO 200
Tamron Ad-2 teleconverters: SP 1.4X (#140F) , 2X (#01F) and SP 2X (#200)
Tamron-F 1.4X Pz-AF MC4
Tokina EL 2X PK/A

Equivalent APS-C focal lengths:
300 = ~420mm
1.4X = ~590mm
2X = ~840mm

At F3.5 (ie, minimum aperture plus one click): All five TC’s again offered about the same degree of sharpness with the three AD-2 elements providing slightly ‘cleaner’ bokeh and contrast. F2.8 was usable in a pinch.

At F4: As with the 180mm lens, the dedicated TC’s were noticeably better in both sharpness and contrast but post processing still brought all images to about the same level of quality. Without close comparison I couldn’t reliably differentiate between the AD-2 and non-AD-2 units after suitable post processing.

At F8: The AD-2 TC’s begin to stand out as the lens approaches the optimum aperture settings and I was confident I could differentiate between the two types of TC’s without direct comparison of the images.

At F16: Noticeable degradation begins to appear above F11 with or without the TC’s. and contrast was definitely beginning to suffer. The choice of TC’s didn’t seem to be a controlling factor compared to the effect of the smaller aperture.

General conclusions: If you’re serious about using TC’s to extend the range of this 300mm lens, the dedicated AD-2 elements seem to be noticeably better in the sweet spot between F4 – F11. Above or below that range I didn’t see a significant difference in overall quality after post processing. Avoiding camera shake and precise focus were overriding factors in consistently good results. The 1.4X TC’s provided better than expected results and seemed more consistent across the range of useful apertures. Under brighter conditions than with the 180/2.5 comparison, PF was somewhat more apparent in high contrast situations, especially wide open and above F11. As might be expected, the Tokina was the least desirable 2x TC and cropping unquestionably became a viable alternative and perhaps preferable even without direct comparisons. The SP200 TC certainly lived up to its reputation as the preferred 2X tele extender for this lens with the most pronounced differences in the OOF areas and edges. The AD-2 SP 140 TC was very satisfactory and somewhat easier to use.

If I had to choose just one of these five TC’s, I’d choose the AD-2 1.4X SP140 since this is a non-AF lens and my personal limit for consistent field use seems to be less than 600mm; also, the 2X SP200 won’t fit the companion 180/2.5. If you need 800+mm, however, you won’t go wrong having the SP200 .

Yes, you can find PF with this lens, especially using TC’s, and invariably if you insist on shooting bare tree branches and highlight reflections to prove it. But for my uses, PF was minimal and easily corrected in those conditions where a tele extender was preferable to other options.

H2

Edit: Interesting side note: Shooting against a different background I find noticeable green fringing with this lens below F11. Since the intensity and pixel width of the fringe doesn't seem to change with the SP 200 TC, I attribute this effect to the lens itself, not the TC's.

It would likely be a trade-off in the chromatic compensation group as it is similar to PF in effect but associated with different color edges; eg, it does NOT appear around bare branches against a clear blue/grey sky but does show at brown/yellow edges. I believe I've seen other notes to this affect in the past. It can be cleaned up using the usual post processing techniques.


Last edited by pacerr; 01-10-2010 at 02:47 PM. Reason: add info
01-10-2010, 12:52 PM   #2
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Very interesting. Thanks for taking the time to do this.
01-10-2010, 02:32 PM   #3
Ash
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Great work - this should become an article.
Well done and thanks for sharing.
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