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05-10-2017, 11:57 AM   #1
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Focal lengths and crops...

Evening. I am a little curious about the seemingly varied effects of crop sensors and longer focal length lenses.

To use an example, my wife, a Nikon user, has a D5500, and the Nikon 200-500 f5.6 lens. When she shoots the same subjects as me when I use the 150-450, it seems that she is far closer, almost as if the 500mm is nearer 600, because even with the 1.4 Tele added, she is not far behind me, even though I am effectively at 630mm (I am aware that small subjects at distance suffer from compression of perspective on long lenses)
However, I have also seen shots of the same subject that I shot, taken with the Sigma 150-600 on a Nikon, and they seem miles closer than mine, despite the photographer being in the same place.

Can anyone explain this at all?

Thanks

05-10-2017, 12:19 PM   #2
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Established that: 200-500 on crop = 300-750 FoV equivalent.

Assuming you use your K3, that 150-400 = 225-600 FoV equivalent. 150-600 on crop = 225-900mm FoV equivalent.

Now add a 1.4x tele. 300-750mm FoV = ([300*1.4]-[750*1.4]) 420-1050mm

If she is getting handheld, sharp BiF photos at 1050mm in anything less than perfect light, buy her some roses-she's a keeper.
05-10-2017, 12:28 PM   #3
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QuoteOriginally posted by bigoak Quote
Established that: 200-500 on crop = 300-750 FoV equivalent.

Assuming you use your K3, that 150-400 = 225-600 FoV equivalent. 150-600 on crop = 225-900mm FoV equivalent.

Now add a 1.4x tele. 300-750mm FoV = ([300*1.4]-[750*1.4]) 420-1050mm

If she is getting handheld, sharp BiF photos at 1050mm in anything less than perfect light, buy her some roses-she's a keeper.
She's not using the TC , I am . I already bought her that lens So the 150 -450 with TC should be around 935 on a K3?
05-10-2017, 12:40 PM   #4
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If comparing are you using objects at essentially infinity? If not many zoom lenses will be at shorter FL than indicated.

BTW if you want to research more--it is termed "focus breathing."


Last edited by dms; 05-10-2017 at 12:42 PM. Reason: add term focus breathing
05-10-2017, 12:56 PM   #5
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QuoteOriginally posted by dms Quote
If comparing are you using objects at essentially infinity? If not many zoom lenses will be at shorter FL than indicated.

BTW if you want to research more--it is termed "focus breathing."
Not infinity per se, but at the very end of focal length, and with a subject say 20 feet away (a tree creeper to use an example, people shots on the Sigma 600 are closer than mine on the 450 + TC)
05-10-2017, 01:41 PM   #6
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QuoteOriginally posted by Kevriano Quote
Not infinity per se, but at the very end of focal length, and with a subject say 20 feet away (a tree creeper to use an example, people shots on the Sigma 600 are closer than mine on the 450 + TC)
Does it feel like you get 30% more magnification with the Sigma @ 600mm, such as for example 900mm?
05-10-2017, 02:14 PM   #7
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Comparing a crop camera to an FF camera is like 1.5 TC (without the optical quality loss). It makes quite a difference.
The other things to consider is that it is a zoom lens, so it really depends on what focal length it was zoomed at for the photo.
Focusing is another issue. Many lenses are prone to actually changing the FoV at some focusing distances. I think this is especially true for zoom lenses with internal zoom or internal focusing mechanisms. So you can loose a lot of the reach due to the socalled Focus Breathing effect.
For such extreme telephoto you probably need super fast shutter speed. Better yet, a sturdy tripod, 2 sec timer, and remote trigger.

Bottom line: FF = wider FoV
Lenses are different from each other, some have more pronounced focus breathing
Do a controlled test at maximum telephoto and near infinity focus.
05-10-2017, 10:05 PM   #8
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QuoteOriginally posted by biz-engineer Quote
Does it feel like you get 30% more magnification with the Sigma @ 600mm, such as for example 900mm?
I wouldn't say 30%, I'm suspicious that there has been some cropping, but the other photographer says not. I'll get some comparison pictures up.

Re the next reply. I've not mentioned FF, both cameras used are APS C sensors. I know there are magnification differences between Canon, Nikon and Pentax though, but that's minimal I would have thought.

05-11-2017, 08:03 AM   #9
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Afaik another factor that comes into play outside of the focal length difference is the Nikkor 200-500 used on a dx camera has a narrower angle of view throughout its range @ 800-310' than the 150-450 Pentax 16.5-5 . That narrower angle will give the appearance of a subject being closer than that of the Pentax lens.
05-11-2017, 10:09 AM   #10
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QuoteOriginally posted by Oldbayrunner Quote
Afaik another factor that comes into play outside of the focal length difference is the Nikkor 200-500 used on a dx camera has a narrower angle of view throughout its range @ 800-310' than the 150-450 Pentax 16.5-5 . That narrower angle will give the appearance of a subject being closer than that of the Pentax lens.

You've completely lost me there 😟
05-11-2017, 12:09 PM   #11
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QuoteOriginally posted by Oldbayrunner Quote
Afaik another factor that comes into play outside of the focal length difference is the Nikkor 200-500 used on a dx camera has a narrower angle of view throughout its range @ 800-310' than the 150-450 Pentax 16.5-5 . That narrower angle will give the appearance of a subject being closer than that of the Pentax lens.
in other words, slightly different crop yields slightly different field of view.
05-11-2017, 02:28 PM   #12
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In other words, 200mm is a longer FL than 150mm, and 500mm is a longer FL than 450mm. Both lenses at 300mm will have the same angle of view. The info I have seen for Pentax APS-C is a 1.53x crop factor.

I also suspect the "focus breathing" phenomenon is the likely culprit here. 20 ft is nowhere near infinity focus. With IF zoom lenses, there can be substantial FL losses at lesser distances. The closer the distance, the greater the loss. But sometimes such a lens is capable of very close focussing, so if you get right up to the subject, you'd still get a large closeup. This is another factor that causes me to prefer the older DA 55-300mm over the newer model. I have the non-PLM HD DA 55-300mm WR, and it does a great job of good closeups without having to get very close!
05-11-2017, 10:57 PM   #13
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QuoteOriginally posted by mikesbike Quote
In other words, 200mm is a longer FL than 150mm, and 500mm is a longer FL than 450mm. Both lenses at 300mm will have the same angle of view. The info I have seen for Pentax APS-C is a 1.53x crop factor.

I also suspect the "focus breathing" phenomenon is the likely culprit here. 20 ft is nowhere near infinity focus. With IF zoom lenses, there can be substantial FL losses at lesser distances. The closer the distance, the greater the loss. But sometimes such a lens is capable of very close focussing, so if you get right up to the subject, you'd still get a large closeup. This is another factor that causes me to prefer the older DA 55-300mm over the newer model. I have the non-PLM HD DA 55-300mm WR, and it does a great job of good closeups without having to get very close!
Yes, I know that 200 is longer than 500., but 600 is not longer than the 630 ish I should get with a TC. And 500 definitely isn't, hence my original question. I am going to put some examples up. I didn't get chance last night.
05-11-2017, 11:45 PM - 1 Like   #14
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QuoteOriginally posted by Oldbayrunner Quote
Afaik another factor that comes into play outside of the focal length difference is the Nikkor 200-500 used on a dx camera has a narrower angle of view throughout its range @ 800-310' than the 150-450 Pentax 16.5-5 . That narrower angle will give the appearance of a subject being closer than that of the Pentax lens.
The angle of view you are quoting for the Pentax 150-450 is for a FF camera. On an aps-c camera like the K3, the angle will be similar to the Nikkor.
05-12-2017, 09:53 PM   #15
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QuoteOriginally posted by pschlute Quote
The angle of view you are quoting for the Pentax 150-450 is for a FF camera. On an aps-c camera like the K3, the angle will be similar to the Nikkor.
Exactly. And I do not think this situation is about a difference in angle of view spec which is or should be done in lab conditions at infinity focus, to determine any difference between lenses. Pop Photo provides an actual measured focal length of a lens they test, compared to the FL the manufacturer rates it as. Often, the finding is less than claimed. An 85mm lens might prove to be an actual 82mm or even 78mm- there is some degree off of what is claimed that is allowable. For instance, the Pentax DA 70mm Limited, as I recall, tested as around 65mm. The FA 77mm Limited, I definitely recall, tested virtually right on.

The same lab could measure the degree of change in a lens that changes angle of view, while maintaining the same FL, at various distances other than infinity- "focus breathing".
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