Why 300mm ain't the same on different lenses?
Feb 20, 2017 07:49:58 #
waegwan wrote:
The Canon 100-300 is a discontinued EF model and one of the earliest EF lenses, that is why I say old. Condition wise it works great and I really like it, it is Canon 100-300 f/5.6L. the other lens is Tamron 28-300 Di VC PZD also in excellent condition.
The field of view at close focus may be different, but the significant difference is that a 10x zoom range lens has vastly more compromises than a 3x zoom. That is very apparent in the much sharper image from the Canon lens! It is a good demonstration of why most advanced photographers just won't use a 10x superzoom.
Feb 20, 2017 07:53:18 #
waegwan wrote:
That makes sense, thanks :) I'll do some infinity shots tomorrow or the next day when I get a chance and post them.
That would be nice! Also interesting might be a couple fairly tight crops that let us see the difference in sharpness. It might not be as much at longer focus distances.
Feb 20, 2017 07:56:48 #
waegwan wrote:
The Canon 100-300 is a discontinued EF model and one of the earliest EF lenses, that is why I say old. Condition wise it works great and I really like it, it is Canon 100-300 f/5.6L. the other lens is Tamron 28-300 Di VC PZD also in excellent condition.
I was leaning in the same direction travisdeland was until I looked up the 6D after I posted and found it had a full-frame sensor. Sounds like Apaflo has a great handle on your observations.
Feb 20, 2017 07:57:15 #
If you set the lens on infinity anh mount it on the bellow at rhe same distance yoi have higher magnification
Feb 20, 2017 08:12:13 #
waegwan wrote:
Yea I know the door handle ain't interesting and t... (show quote)
Focus breathing. In an effort to keep the lens from extending as you get close to the minimum focus distance and/or to get lenses to not rotate the front element they use an internal focus design which shortens the focal length to give a shorter minimum focusing distance.
At infinity the two lenses should be pretty similar in focal length and you won't see much of a difference.
Focus breathing is not just a "feature" of zoom lenses, it happens to primes as well. It affects internal focus lenses for the most part. The video in this article includes an 85mm F1.4, at 3:45, to show that non-zoom IF lenses have that issue. Lenses intended for cinematic use tend to be less susceptible to breathing, but will cost considerably more than even top quality popular lenses.
http://www.imaging-resource.com/news/2014/12/17/what-is-focus-breathing-and-how-does-it-affect-your-images
Zeiss will sell you an 85 T1.5 for $4500 which has very little breathing:
https://www.bhphotovideo.com/bnh/controller/home?O=&sku=857814&gclid=CjwKEAiAxKrFBRDm25f60OegtwwSJABgEC-ZhqnOlIG1RMuOPcO0y63FoGPJrw0hQa8W7MIsUjYUbxoC5BXw_wcB&Q=&ap=y&m=Y&c3api=1876%2C92051678642%2C&is=REG&A=details
Feb 20, 2017 08:12:37 #
BebuLamar wrote:
If you set the lens on infinity anh mount it on the bellow at rhe same distance yoi have higher magnification
And almost certainly higher astigmatism. Other aberration may also increase. It probably will have visibly lower image quality to an unacceptable degree.
Feb 20, 2017 08:12:46 #
travisdeland wrote:
Is one lens designed for crop sensor, and the other for full frame?-THAT would make a considerable difference.
Nope!
Feb 20, 2017 08:18:16 #
Apaflo wrote:
That would be nice! Also interesting might be a couple fairly tight crops that let us see the difference in sharpness. It might not be as much at longer focus distances.
I'll use a 6D for the infinity shots, it will be a lot sharper than the Rebel xs. I'll play with cropping and see how it goes.
Feb 20, 2017 08:24:33 #
Picdude wrote:
I was leaning in the same direction travisdeland was until I looked up the 6D after I posted and found it had a full-frame sensor. Sounds like Apaflo has a great handle on your observations.
I didn't use the 6D for these, I used a Rebel xs. I'll do the next set with the 6D. But either way it is the same camera and same distance with different lenses set at the same focal length. I'm sure Apaflo got it right. Still I didn't expect that much difference.
Feb 20, 2017 08:24:34 #
Gene51 wrote:
Focus breathing. In an effort to keep the lens from extending as you get close to the minimum focus distance and/or to get lenses to not rotate the front element they use an internal focus design which shortens the focal length to give a shorter minimum focusing distance.
Those are all side effects, or artifacts, and none are the reason Internal Focus has become almost universal.
IF is an effort to design a lens with better control of astigmatism over a longer range of focus.
Remember when it was always mentioned that macro lenses were optimized at close focus and were not as sharp at longer distances? That made them nice portrait lenses too. The Internal Focus design makes it possible to be sharp at 1:1 magnification and also when focused at infinity. That is not the goal for a 10x zoom, but control of astigmatism is the primary target.
Feb 20, 2017 08:30:15 #
travisdeland wrote:
Is one lens designed for crop sensor, and the other for full frame?-THAT would make a considerable difference.
No, I used a crop sensor Rebel for this comparison but both lenses are regular EF lenses
Feb 20, 2017 16:47:52 #
Apaflo wrote:
Those are all side effects, or artifacts, and none... (show quote)
Not sure how many lenses you have designed but all of the above are totally valid reasons why lenses are mostly internal focus.
https://en.wikipedia.org/wiki/Internal_focusing
And this thread that also mentions faster AF performance because you are moving less mass, and when working at very close distances in macro, not having a lens that changes physical length ensures that you won't have the front element contact the subject while focusing. Helping keep environmental "stuff" out of the lens is another cited benefit to having an internal focus lens as opposed to the alternative.
http://photo.stackexchange.com/questions/22183/what-is-the-benefit-of-an-internal-focus-lens
So, we are both correct, only my answer is a little more complete - I wouldn't call these all side effects - it's all part of the design decision making process, and I am sure the accountants and marketing people weigh in as well.
Play nice and please don't take this thread down your rabbit hole as you are so prone to doing. Anyway, you can argue with yourself if you want - I'm off to get some pictures of a NYC sunset.
Feb 20, 2017 18:21:48 #
IIRC, internal focus lenses sometimes create problems for tele-converters, because the lens may move back into an area that is empty on the camera but used by the tele-converter.
Feb 21, 2017 05:32:46 #
waegwan wrote:
Yea I know the door handle ain't interesting and t... (show quote)
The focal length in a lenses name is only an estimated length, the real numbers (which usually are quite different), are found in the spec sheets!!
Feb 21, 2017 06:01:16 #
A little update for today, as Apaflo suggested, there is no noticeable difference at infinity. That is the frame fill at 300mm appears to be the same on both lenses. The shots I took were hand held and not clear so I am not going to post tonight. I hope tomorrow I will be able to set up a tripod and not only do an infinity comparison but a few others between minimum focus distance and infinity. Again, this is not intended to be a focus or lens quality discussion. I just was surprised, as a novice, that there was that much difference at close range in how much of the subject filled the frame at the same focal length. I think it will be interesting to see what some of the mid range differences are if any. Lots of folks on UHH ask for lens suggestions for traveling. Maybe some of the posts here will help the decision process. I think when I set up the tripod outside I'll do the comparisons with both a FF (Canon 6D) and a Crop (Canon Rebel xs)
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