lamiaceae Loc: San Luis Obispo County, CA

Yes, I also feel "Apaflo" has a good handle on this issue. I have a lot of SLR/DSLR lenses, around 28 I believe. Many have the same or overlapping focal lengths. So it would be an interesting experiment to compare them the way weagwan did. I have a screw mount Pentax Super-Takumar 35mm f/3.5, a K-mount smcPentax-A 35mm f/2.8, and a digital smcPentax-DA 35mm f/2.8 Macro Limited prime lenses. Their marked distance scales are all different for minimum focus. And likewise, I have many 50mm lenses, different speeds, different focus properties. I also have three Zoom lenses that can cover 18mm, 28mm, 35mm, 50mm, and two beyond. So they can be compared to several primes.

After thinking about the presented issue for a while I think I have it figured out. I've worked with view cameras, 4x5" and 8x10". Learning view camera photography you get some insight into optics. At infinity focus the magnification is only dependent on the focal length of the lens (and in a way of the format relative to cropping. But since we were talking about different lenses on the same camera, that is not an issue). The magnification of a lens at other than infinity focus is also a function of bellows extension or the optical distance between the (rear) node of the lens and the film or sensor plain. To get 1:1 Magnification the bellows extension is 100mm for a 50mm lens. To actually get this one can use extension tubes or a bellows. That is also with the lens set to "infinity focus". The problem is in most modern cases we do not know the bellow extension or throw or whatever you want to call it. As stated many lenses have internal focus (prime and zoom) and others have lenses that rotate or coil out or physically move to focus (again for both prime and zoom designs). So the "zone" between infinity and minimum focus it where this gets confusing.

Related to all this and the OP's issue, I've noticed that when using my old vintage film lenses the distance scales on the lens are wrong when used on a digital APS-C body. The lenses actually focus fine and even focus is indicated with non-AF lenses when the camera is set to AF. In fact Pentax has a cool trick when using manual focus lenses on a AF engaged body. For non-Pentax owners and readers out there, you may research it. So if and when I my lenses I am sure I'll notice differences. I am fairly sure I have lens designs of all the various types.


Where this effect might also show but I don't have the equipment to test it is were I to compare my vintage smcPentax 100mm f/4 Macro lens to a Nikon (film) 105mm f/2.8 Macro lens I am sure I would find the described magnification anomaly because Nikon lens of that type have internal floating element focus and Pentax lenses of that type are conventional with extending focus. Not as nice or convenient for many applications. My belief though again I have no way to test this, I figure focus stacking is easier with many Nikon vs Pentax lenses.

Apaflo Loc: Anchorage, Alaska

Wonderful. But not one word of it relates to this thread, where the topic is the difference between two lenses of the same focal length. Your entire discussion would applied to either lens in exactly the same way and does not explain the difference the OP demonstrated and asked about.

blackest Loc: Ireland

hmm which cool trick? The lens code or green button or something else?

stevetassi

I would speculate that they have different reproduction ratios.

lamiaceae Loc: San Luis Obispo County, CA

Something else. Hmmm, try to find a discussion...

...Here is someone else’s explanation (a bit long winded). Logic would dictate that if you are shooting with a manual focus lens you should switch the camera into manual focus mode and this is the case most of the time. When shooting in MF with a manual lens you will still get focus confirmation when your subject is in focus via the center focus point illuminating red briefly in the viewfinder, the focus indicator lamp lighting (also in the viewfinder) and the audible focus lock beep (assuming it is enabled). From what I can tell, the camera will only use the center focus point with older manual lenses (A and M). You can select other focus points with modern AF lenses when in MF mode. I always use the center point, focus, recompose, then shoot anyway. But that’s just the way I roll. Dialing in accurate focus can be tricky as the range of movement of the manual focus lens’ focus mechanism and front/back focus issues can throw the focus sensor off. The focus indicator will often stay illuminated over several degrees of focus ring rotation (in-focus range). This can be especially frustrating when using fast lenses with extremely short depths of field while trying to achieve critical focus on a specific point of the subject. Trial and error with lots of high magnification LCD review is the best way to get it right. Each lens will likely have its own characteristics that will need to be learned. A good excuse to take lots of pictures :D Here’s an article covering MF technique.

Another focus technique with manual lenses is “catch-in-focus” or “focus trap.” With this technique you set the camera to AF-S mode, fully depress the shutter then manually dial in the focus. As soon as focus is achieved the shutter will release. Problem is that it will either fire at the beginning or at the end of the in-focus range (depending on which direction the focus ring is being rotated) and the actual desired focus point may be somewhere else within the in-focus range. Also, if you are shooting at the slow end of hand-holdable shutter speeds you can actually get what I’d call “focus blur” as you focus through the desired focus point while the shutter is open. I find the focus trap technique most useful when trying to catch action shots and/or when shooting at smaller apertures in bright light. I find it basically useless when shooting wide open and/or in low light.


I'd be surprised if something similar did not work also on higher end Nikon cameras.

lamiaceae Loc: San Luis Obispo County, CA

catchlight.. Loc: Wisconsin USA- Halden Norway

Again as said the obvious answer is focus breathing...

There are big differences between brands and especially how much money you spend. Check the test ratings to find the best lenses for your budget. Independent testers offer the best information.

Bear2 Loc: Southeast,, MI

Ditto, that would be my guess also, crop vs full frame.

Duane

Apaflo Loc: Anchorage, Alaska

That would have zero effect. 300mm is 300mm, regardless of the FX or DX notation.

dleebrick Loc: Indian Land, South Carolina

Man! I learn something new everyday. Never would have expected that kind of effect.

cactuspic Loc: Dallas, TX

There is a substantial difference in the amount of focus breathing in various zoom lenses. Whereas the the Canon 70-200 II tests at headshot distance as a 195mm lens, the Nikon 70-200 II at headshot distances tests at 135. While it may not matter to some, it does change the amount of facial compression and background blur if you fill the frame to the same extent with the subjects head. The Tamron and the Sigma versions show similar focus breathing as the Nikon. This says nothing about the be build quality, chromatic aberration, sharpness or other qualities we look at in choosing a lens. All of the listed lenses are internal focus lenses. The amount of focus breathing a lens undergoes in closer focus distances is just another design consideration for lens manufactures.

https://northrup.photo/gear-basics/lens-features/focus-breathing/
https://petapixel.com/2014/09/04/why-i-want-to-switch-to-nikon-but-cant-tony-northrup-throws-gas-on-the-canikon-debate/. At about the 8:50 mark

romanticf16 Loc: Commerce Twp, MI

You just illustrated the issues Nikon had with their 70 to200 f2.8 VR lens and why it has been redesigned optically several times.

NikonCharlie Loc: Kansas USA

Many lenses of say zoom to 300mm are 300mm only at infinity focus.
The 70-200 VRII Nikon is one such example, at focus of 15 feet, lens setting to 200mm it is about 165mm field of view

steve_stoneblossom Loc: Rhode Island, USA

You might get the results depicted, however, if the lens stayed the same and you changed cameras, one FX and one DX. Just thought I would muddy the waters even more since that seems to be the trend.

Apaflo Loc: Anchorage, Alaska

I think you will find the Canon lens is much less than any 195mm at head shot range.

Tony Northrup's rants on this topic are technically so flawed as to be hilarious. He claims the Canon lens doesn't have focus breathing and that he uses it most often at greater than 180mm for close up portrait shots. He just doesn't understand that it isn't 190mm just because that is what it says. It cannot be set to both 10 feet focus distance and 190mm. He has never shot with the focal lengths he claims, and clearly cannot tell the difference.

Find better sources of information than Northrup and Rockwell.