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02-22-2012, 03:56 PM   #106
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And the one final test.....

We agreed that it could be justifyably questioned if my tests showing up-samled crops of images taken without TC were "fair". Now, this was in order to get identical fields of view, (which is the general argument for cropping rather than using TCs, though maybe not on such a small scale).

The previous tests were made at a constant object-to-sensor distance.

But there is of course also the test where one changes the distance in order to have the same field of view for the entire image frame. So here goes.

I have used the same gear as previously and again I have let Catch-in-Focus determine when to relase shutter (and built-in flash). This time, crops are NON-RESIZED 400 X 266 sensor pixel selections from the original images taken with and without TC.

Admittedly, we are quite far from something absolutely reproducible, but I think we can agree, that the image taken with TC isn't that bad, considering that it was taken at twice the distance of that taken without TC.

Can't we.......?

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Last edited by Stone G.; 02-22-2012 at 04:01 PM.
02-22-2012, 04:17 PM   #107
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It may be my monitors but the face closeup and the fabric seem to have better sharpness and contrast with the TC.
02-22-2012, 04:28 PM   #108
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QuoteOriginally posted by demp10 Quote
It may be my monitors but the face closeup and the fabric seem to have better sharpness and contrast with the TC.
No, it's not your monitors - it is showing the same on mine...
02-22-2012, 04:53 PM   #109
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Well, I don't know how much weight to give to that. (I see the same). As said: fofuc was left to CIF; the lens was stopped down when used without TC to f/22 (perhaps past its optimum?) while it was at f/9 when used with TC. I had to stop down the lens that much because of the flash and the closeness to the subject. Main point is: THIS TC doesn't exactly degrade IQ with THIS lens!

02-22-2012, 05:55 PM   #110
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I suppose we are seeing the effects of diffraction at F22. With the APS-C sized sensor anything narrower than f10 (more or less) will start showing degradation due to diffraction.

The exposures seem to be a bit different also on the first pair of images with the one without the TC having a bit darker background.

Regardless, the quality with the TC is very good on its own.
02-22-2012, 06:11 PM   #111
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Honestly, it doesn't matter to the original topic if one is a little better or a little worse. There are a lot of variables that can make an image a little better or a little worse (as aperture or who knows what might have here). Long store short, teleconverters can be worth using. They have many of the other limitations of lenses like poor glass will typically give poor results. They may have their own limitations such as working well with some lenses and not with others. Lenses themselves may have variations where one copy may work well with your camera and another may not. In the end, all things considered, teleconverters can sometimes do a great job and or provide excellent image quality. Very good quality glass may cause minimal loss of image quality but so many other things can do the same , its hard to even test. They look close enough to me. This thread pretty clearly shows teleconverts can perform as well as any other photo eqipment and all photo equipent will have their good and bad.
02-22-2012, 07:34 PM   #112
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QuoteOriginally posted by ripit Quote
Honestly, it doesn't matter to the original topic if one is a little better or a little worse. There are a lot of variables that can make an image a little better or a little worse (as aperture or who knows what might have here). Long store short, teleconverters can be worth using. They have many of the other limitations of lenses like poor glass will typically give poor results. They may have their own limitations such as working well with some lenses and not with others. Lenses themselves may have variations where one copy may work well with your camera and another may not. In the end, all things considered, teleconverters can sometimes do a great job and or provide excellent image quality. Very good quality glass may cause minimal loss of image quality but so many other things can do the same , its hard to even test. They look close enough to me. This thread pretty clearly shows teleconverts can perform as well as any other photo eqipment and all photo equipent will have their good and bad.
The real test is , without telling someone you used a TC or not, whether they like your image or not. After that who cares
02-22-2012, 08:07 PM   #113
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Stone G, you've done some nice work showing that TCs can do nicely.

My questioning of up-sampling to 200% was that it may have been an unfair comparison because it resulted in each display pixel containing fewer than one sensor pixel. I think a better comparison of TC & no TC shot at the same distance would be the no TC image displayed at 100% and the TC image cropped to the same overall magnification.

But that's a small detail.

Thanks again for your good work.

02-22-2012, 08:14 PM   #114
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Has anyone tried some of those tests on distant subjects separated from the camera by a field, lake, valley ... ?
[Distant = more than 50 metres away.]
My belief is that such distant subjects will be "subject to" ground moisture, haze, that sort of thing.
Using a TC under those circumstances might affect IQ, or is this foolish to think it would?

Under a "controlled" environment, such as indoors, would you not have "better results" with the TC attached to a tele-lens?

JP
02-23-2012, 02:31 AM   #115
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QuoteOriginally posted by jpzk Quote
Has anyone tried some of those tests on distant subjects separated from the camera by a field, lake, valley ... ?
[Distant = more than 50 metres away.]
My belief is that such distant subjects will be "subject to" ground moisture, haze, that sort of thing.
Using a TC under those circumstances might affect IQ, or is this foolish to think it would?

Under a "controlled" environment, such as indoors, would you not have "better results" with the TC attached to a tele-lens?

JP
That is certainly NOT foolish to think, as the effects of the factors you describe increase with focal length - which any amateur astrophotograper will confirm, (: we shoot through several scores of sometimes turbulent and hazy atmosphere). And that's is also, why the demonstrations of "TC Degradation" taken under such circumstances should be taken with a grain of salt. Camera body / sensor and pixel size-Optics-Ambient conditions, they all matter for the results of "tests"!

And I do agree with Lowell Goudge: After all, it is the result that matters - not how I achieved it.
02-23-2012, 01:05 PM   #116
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yes they are worth it!
02-23-2012, 01:59 PM   #117
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there are good exapmples of 2X TC use with F*300/4.5 here:
Pentax-F*300/4.5 + Tamron 2X TC. (5 imgs): Pentax SLR Talk Forum: Digital Photography Review
04-06-2012, 11:16 AM   #118
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QuoteOriginally posted by normhead Quote
I guess I just have to keep posting this..



As Mark said... the lens is over $1000 and has amazing MTF numbers....(DA*60-250), the converter cost me over $300 (Pentax A 1.7)

The results mean about 50% more sharpening in post production, when you consider it turns my F4 60-250 into a 425 mm 6.7 lens, this is the bargain of the century. Using a DA lens on an FA converter you're definitely making use of the best part of the converter. I had a Sigma 120-400, and I like these images better, the combination is lighter and I still have a razor sharp 60-250 when the teleconverter isn't on the lens.
That is nice! Will check out the 1.7 converter.
08-05-2012, 11:37 PM   #119
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Reviving an old topic to see what people think. I have a Pentax K-r, and am considering a TC. The two lenses I would be using it on are the M 50mm f1.7, and a Tele-astranar 400mm f6.3. The 400mm is only decent, I expect quite a bit of IQ loss. But how would a cheap TC perform on an M lens? Am I better off cropping? I wanted to turn my 50 into a bit more of a tele portrait lens. Do TC's effect bokeh at all? I'm trying to find cheap 1.4's or 1.7's, but the majority are 2x's.
08-06-2012, 04:47 AM   #120
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I've found that a cheap 1.4x on the Pentax-A 400/5.6 is no better than cropping, and that lens is more than decent. (The Pentax-A 1.4x-L converter, on the other hand, is excellent with this lens.) The M50/1.7 is sharp enough that I suspect you would be better off cropping for those times you want a tight head shot while avoiding perspective distortion.
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