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01-25-2015, 11:39 AM   #1
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Crop or 2X extender

I just did a little experiment with a 300mm SMC Takumar on my K5. Both pictures shot from the same distance.

The left picture was shot with the raw lens 300mm and cropped. The picture on the right was shot with a Chinon 2X extender and not cropped.
Which is the sharper picture? It is clear, in this case the 2X extender gave superior results. Comments please.

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01-25-2015, 12:07 PM   #2
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The benefit comes when the detail is smaller than the resolution for cropping.
01-25-2015, 12:20 PM   #3
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Normally I would assume a 2x just would not cut it but those images tell a different story.

However, was the lens mounted on a tripod and nothing moved when the 2x was added? If not then the difference might be slight miss-focus between shots.
01-25-2015, 12:43 PM   #4
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The left shot doesn't look right to me. Focus or movement.

You say the right shot was not cropped, but it isn't in the K5 aspect ratio. Is it more correct to say that both images are cropped, but the left one twice as tightly? What percentage crops are they?

01-25-2015, 06:42 PM   #5
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Thanks for sharing. I have often wondered which is better. I suppose the test should be accompanied by all the usual disclaimers - all things being equal. Quality of lens and extender, technique, etc. may all have a role. If I understand it, the photo on the left has one-half the pixels that the one on the right has - correct? So, yes, at some point one may run of out of pixels to have a good quality image. I have also wondered, should one run out of pixels, can a person do a file enlargement and "recover" some image quality? Maybe that would be the next test. As an aside, I also often wonder how little gear (numbers of pieces, cost, range, quality, weight) one can get by with and still get a great photo by using the computer.
01-25-2015, 07:38 PM   #6
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Sharper yes but under what conditions? Tripod? Bright, or cloudy-dull? Handheld with a moving subject on a cloudy day in Winter might tell a completely different story. Horses for courses.

I am still learning when to use my Pentax HD 1.4 converter and when not to bother... good as it is, even that is not always the best choice on my DA*300! But on a tripod or a bright sunny day, it always wins.
01-25-2015, 10:47 PM   #7
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QuoteOriginally posted by GlennG Quote
If I understand it, the photo on the left has one-half the pixels that the one on the right has - correct?
No that is not correct. Anytime you double the Focal length, you divide the visual field by 1/2 vertically and horizontally. leaving you with 1/4 the visual area. when you crop a picture to a related size, you crop both horizontally and vertically. Leaving you with 1/4 the pixels.

this type comparison only shows that you do not lose any resolution when using a 2X tele-converter versus cropping the image. A better test is to compare a x00 mm lens using a tele-converter, and a prime lens of equivalent focal length without a tele-converter. Given the usual disclaimers and testing and variations in lenses of course.

Last edited by promacjoe; 01-25-2015 at 11:40 PM.
01-26-2015, 08:01 PM   #8
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QuoteOriginally posted by promacjoe Quote
No that is not correct. Anytime you double the Focal length, you divide the visual field by 1/2 vertically and horizontally. leaving you with 1/4 the visual area. when you crop a picture to a related size, you crop both horizontally and vertically. Leaving you with 1/4 the pixels. this type comparison only shows that you do not lose any resolution when using a 2X tele-converter versus cropping the image. A better test is to compare a x00 mm lens using a tele-converter, and a prime lens of equivalent focal length without a tele-converter. Given the usual disclaimers and testing and variations in lenses of course.

Thanks for clarifying. Another possible comparison might be to use a 6 MP with 2X extender and compare to a 24 MP cropped down to 6 MP. Now that, would be interested to see as well.

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