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03-17-2011, 06:34 PM   #1
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Critique My Lens Logic

I own prime lenses I love that cover focal lengths from 20mm to 180mm. I also own a DA 55-300 zoom, which I have been impressed with. Since I always set up with a tripod for carefully chosen shots, the only reason I've been keeping the DA 55-300 is for its focal lengths beyond my 180mm prime.

Today I started wondering if pictures taken with my excellent Voightlander 180mm were cropped to the size of the 300mm FL on the DA, would they equal or better the DA's resolution. As a test I shot a distant house with both lenses, and cropped the 180mm to match the 300mm size; in the second set I cropped the 300 quite a bit and further cropped the 180mm shot to match that (wondering how a more extreme 180mm crop would hold up against a more modest 300mm crop).

As far as I can see, the VL 180 crops easily beat the DA 55-300 at 300 Fl. and its crop. So given my shooting preferences, is there any reason not to simply use the VL180mm cropped for scenes I want to shoot far away?

The DA 55-300 full shot @ 300mm:




The Voightlander Crop:




The DA 55-300 @ 300, cropped:




The Voigtlander 180mm, extreme crop:



03-17-2011, 06:40 PM   #2
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Hi Les:

Cropping the 180 to get the effect of the 300 means you are throwing away pixels. look carefully at the fence in the middle of the first two images. You seem to have more detail in the 300mm than the 180mm cropped. It seems like the 55-300 may still be necessary. The Voigtlander seems like a nice lens though!

Regards,
03-17-2011, 07:13 PM   #3
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At web resolution, it seems like cropping will work perfectly fine. Of course, there is still a slight compression difference between 180mm and 300mm, but it wasn't really noticeable in this example.

The only problem I could see is if you wanted to make larger prints.
03-17-2011, 07:25 PM   #4
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QuoteOriginally posted by BigDave Quote
Hi Les:

Cropping the 180 to get the effect of the 300 means you are throwing away pixels. look carefully at the fence in the middle of the first two images. You seem to have more detail in the 300mm than the 180mm cropped. It seems like the 55-300 may still be necessary. The Voigtlander seems like a nice lens though!

Regards,
Hi Dave . . . after pixel peeping I see you are right about the fence, and some of the tree leaves around the center of the pictures as well. When I check out the borders of both pictures, the 180mm is quite a bit sharper. Beyond center sharpness, it appears to me that the contrast, highlights, and color rendering of the 180mm is a lot better (or at least I prefer it).

Thanks for your feedback.


Last edited by les3547; 03-17-2011 at 07:34 PM.
03-17-2011, 07:28 PM   #5
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QuoteOriginally posted by wshi Quote
At web resolution, it seems like cropping will work perfectly fine. Of course, there is still a slight compression difference between 180mm and 300mm, but it wasn't really noticeable in this example.

The only problem I could see is if you wanted to make larger prints.
Thanks wshi . . . yes, no plans for large prints at this time. I've been looking for a reason to keep the DA 55-300 because in the past I've liked it so much, but now it seems I don't really need it for the type of shooting I do.
03-17-2011, 08:22 PM   #6
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The CV image has more contrast and the microcontrast is also higher, so it looks like it holds very well against the DA. Not so surprising really - that CV is supposed to be a superb lens.

I was actually wondering today about the same thing - whether a high quality 200mm can replace a budget 300mm. Timely thread.
03-17-2011, 08:31 PM   #7
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IMHO, what you are testing here is not the lens resolution, but rather the sensor resolution. I don't think that you can compare lenses with this kind of test. It's the sensor that you are stressing.
03-17-2011, 08:56 PM   #8
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QuoteOriginally posted by jimH Quote
IMHO, what you are testing here is not the lens resolution, but rather the sensor resolution. I don't think that you can compare lenses with this kind of test. It's the sensor that you are stressing.
Hi Jim, I didn't get your meaning, could you explain more? I probably should not have used the word "resolution" since what I really care about is the overall quality of the picture.

By "stressing" did you mean "emphasized" (i.e., rather than stress in the sense wear, hardship, etc.)? If so, I am not sure what difference it makes. The end result are photos where one is either better, equal, or an inferior to the other. When I used one lens, a picture of the scene looked one way, when I used the other the scene looked another way. So clearly there is a difference in what each lens produces. What I am trying to figure out is . . . if I prefer the Voightlander cropped to the DA zoom uncropped, is there any reason (strictly in terms of picture quality) to keep the zoom?

03-17-2011, 09:46 PM   #9
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one other reason to consider though is that the 50-300 is a convenient lens to use especially if you were restricted to carry more than 1 or 2 lenses on certain occasions. the 180 would be a struggle to use less than under 180mm.
03-17-2011, 10:02 PM   #10
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that's not totally fair. The 55-300 is a great lens, but it's not the sharpest thing at its longest focal distance of 300mm. The 55-300mm is great not just because of its long reach, but also for its unusual span of focal length from 55mm, making it very versatile zoom lens for lots of situations. If you don't use the 55-300 very often at the short end, then keeping only the voightlander would make sense.
03-17-2011, 11:01 PM   #11
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The DA 55-300 is a great lens alright, my problem is that when I start to use it I know I have a prime that performs better, so I end up using a prime. The only time I haven't gone that route is the occasional 300mm shot I've taken, but looking at the 180mm crop, it looks like its overall IQ might be as good or better. I just don't know if I am overlooking something by thinking I can crop and get the same results as using the zoom's 300mm FL. One think I can think of is that I can see my subject better when I use the zoom.
03-18-2011, 03:39 AM   #12
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So use the CV when quality is more important than content, and the DA over its range when content is more important than quality. I don't expect my 18-250 to match the IQ of my 85/2 at that FL; but each has its own strength, one for flexibility, the other for specificity. As I've mentioned a few times around here, I have many many lenses. I don't approach them comparatively as THIS IS BETTER THAN THAT, but more as I LIKE WHAT I CAN DO WITH THIS. If you don't like what you can do with the 55-300, dump it.

Last edited by RioRico; 03-18-2011 at 03:58 AM.
03-18-2011, 06:49 PM   #13
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QuoteOriginally posted by les3547 Quote
Hi Jim, I didn't get your meaning, could you explain more? I probably should not have used the word "resolution" since what I really care about is the overall quality of the picture.

By "stressing" did you mean "emphasized" (i.e., rather than stress in the sense wear, hardship, etc.)? If so, I am not sure what difference it makes. The end result are photos where one is either better, equal, or an inferior to the other. When I used one lens, a picture of the scene looked one way, when I used the other the scene looked another way. So clearly there is a difference in what each lens produces. What I am trying to figure out is . . . if I prefer the Voightlander cropped to the DA zoom uncropped, is there any reason (strictly in terms of picture quality) to keep the zoom?
If you crop a photo you are taking a small portion of the image that has been registered on the sensor and you have stretched the image by cutting away many of the pixels that make up the image, thereby "stressing" the image, in other words your resulting image from a cropped photo has fewer pixels than an image produced by a longer focal length lens (and not cropped) for any given portion of the image.

The photo from the longer focal length lens should have more detail and should be clearer than an image of the same object taken with a shorter focal length lens and cropped to get the same overall coverage. Simply because the image taken with the longer focal length lens has more active pixels to draw the image.

A sensor can only produce so many pixels for a photo, if you trim a lot of the pixels away by cropping you will degrade the picture. In that manner you are stressing the sensor, so to speak.

Not so much the sensor but the image that results from the sensor. So the long and the short of it is if you want to compare lenses, you need to use the same focal length lens to get comparable quality from the sensor. If you compare a long focal length lens with a short focal length lens by cropping the image from the short focal length lens, you aren't comparing apples and apples, since one image will have a disadvantage because it was cropped while the other was not. (Clear as mud)?
03-18-2011, 08:11 PM   #14
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QuoteOriginally posted by jimH Quote
So the long and the short of it is if you want to compare lenses, you need to use the same focal length lens to get comparable quality from the sensor. If you compare a long focal length lens with a short focal length lens by cropping the image from the short focal length lens, you aren't comparing apples and apples, since one image will have a disadvantage because it was cropped while the other was not. (Clear as mud)?
But Les is not attempting to compare lenses. He is just trying to see whether he can get usable results from a shorter lens. Basically, his question is: do I need the 300mm, or can I just use the 180mm and crop. Which is a valid question.

Also, because the results from the 180mm lens actually look better to me (check the roof of the house to the left in the second set of crops), it doesn't look like the 300mm manages to fully use the sensor resolution. Hence we are not really hitting the limits of the sensor resolution here, but the limits of the resolving power of the DA lens. At least, this is what I can make from the size of these crops.
03-18-2011, 08:13 PM   #15
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QuoteOriginally posted by jimH Quote
If you crop a photo you are taking a small portion of the image that has been registered on the sensor and you have stretched the image by cutting away many of the pixels that make up the image, thereby "stressing" the image . . .
The photo from the longer focal length lens should have more detail and should be clearer than an image of the same object taken with a shorter focal length lens and cropped to get the same overall coverage . . . If you compare a long focal length lens with a short focal length lens by cropping the image from the short focal length lens, you aren't comparing apples and apples, since one image will have a disadvantage because it was cropped while the other was not. (Clear as mud)?
Yes, it is clear, thank you the detailed answer. OTOH . . .

While it all makes perfect logical sense, what if after comparing a cropped picture to the longer FL, the cropped picture looks as good or better? Now an observer has their sensory input to deal with, but no explanation if what you say is always true. In other words, either I am not seeing well, or there is another way to account for the 180mm crop looking better than the 300mm non-crop.

For example, the DA 55-300 is known to lose substantial resolution at 300mm, but the VL 180mm is optimized for its single FL. So while there may be more pixels present in the 300mm shot, they might be rendered relatively soft (compared to, say, a prime 300mm); whereas the 180mm is exceptionally capable of resolution (as tests have proven). So when cropped, though containing less pixels, the 180mm started out so much sharper that it still outperforms the zoom at its least desirable FL (just offering a hypothesis to account for observations ).

And this was actually why I started this thread, to ask if just such a thing might be possible between a superb prime lens and a mediocre lens (at 300mm anyway).

Last edited by les3547; 03-18-2011 at 09:16 PM.
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