blackest Loc: Ireland

No a 300mm lens is a 300mm lens, on non interchangeable lens camera's they may give a 35mm Equivalent focal length but that is because they are fixed and the sensor is tiny.

SX2002 Loc: Adelaide, South Australia

Won't see anything at 200 meters..if it doesn't work at my selected distance then it's not a true 300mm lens, who takes pics with a 300mm lens at 200 meters even my 500mm is too short at that range...my Nikon lenses are ok at 15-20 meters, both of them take identical shots at that distance and after comparing my shots to my Mate's, we both have the exact size image...very much identical to shots I've compared mine to on a few sites...as far as I'm concerned, if it's sold as a 300mm lens it should work at any range...

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Apaflo Loc: Anchorage, Alaska

Go back and read more of the articles in this thread. The marked focal length of a lens is defined as when focused at infinity. Try focusing on the moon! But as suggested anything at 200 meters or more will do. Most modern lenses are a much shorter focal length when focused at close distances. Some are perhaps only 60% of the marked focal length.

That is not a bad thing either. It is something to be aware of though.

oldtigger Loc: Roanoke Virginia-USA

not true at all

mwsilvers Loc: Central New Jersey

As I said. Focus breathing. Very common. That's why it pays to compare similar zoom lenses at various distances to identify the effects of focus breathing for each lens and find the lens that works best for you under real world conditions.

mwsilvers Loc: Central New Jersey

rehess Loc: South Bend, Indiana, USA

No! The focal length of a lens is constant. A "conversion factor" is appropriate only when determining how the sensor handles/presents what it receives through the lens. Thus if I mount a 200mm lens on my "1.5 crop factor" Pentax K-30, it will provide the same image I would get by mounting a 300mm lens on my "FF" Pentax Super Program film camera. The 200mm lens is always a 200mm lens; the 300mm lens is always a 300mm lens. But the difference of how the respective sensors handle/process/interpret light results in the same image from each of those systems.

Peterff Loc: O'er The Hills and Far Away, in Themyscira.

So can you actually identify a source that specifies exactly what is an accepted formal standard for Exif data that excludes other meta data?

This is all immaterial, and the data fields that I quoted are all available and very clearly conflicting using your cited tool of choice Exiftool as well as others. It is all metadata, and it is all presented in the Exif format, including the proprietary maker notes. What part of "TAMRON 28-300mm F/3.4-6.3 Di VC PZD A010" and "Canon EF 90-300mm f/4.5-5.6" and "Canon EF100-300mm f/5.6" and "or Tamron Lens" do you not understand to be contradictory or confusing? It's all there in the same file and extracted by ExifTool and other software.

Pay attention Floyd, and I reiterate, when talking about FF and APS-C sensors in either a generic or Canon context do not use ther terms FX and DX, they are Nikon specific and not relevant here. Do your homework, you still have enough twilight left.

rehess Loc: South Bend, Indiana, USA

Sorry, but you are wrong in this case.

My first DSLR was a Canon Rebel; now I'm using a Pentax K-30. The terms FX and DX mean absolutely nothing to me - they communicate absolutely nothing to me. I cannot even use them in a sentence; if I don't have an example in front of me, I'm as likely to use the terms FX and GX as the terms FX and DX.

added: you are correct that this discussion is about using lenses on Canon cameras; that is why your choice of terms is so unfortunate, because the terms are totally foreign to the topic, and so it creates confusion and discord. That would be similar to specifying prices in Nevada using Euros.

Apaflo Loc: Anchorage, Alaska

Slow down and pay attention to detail, and stop making unwarranted assumptions that are not logical.

The credible source has already been identified as Exiftool. Using the -G option shows exactly the type for each displayed data record. Those records can be, for example, Exif, IPTC, File, JFIF, MakerNotes or one of over 40 different types of meta data that Exiftool can display.

Here are a few lines of Exiftool output to show you how to find that information,
Of course the ultimate source for information about specifically Exif data, and Phil Harvey the author of Exiftool is intimately familiar with this document, is the standard published by the Japan Electronics and Information Technology Industries Association titled, "JEITA CP-3451 Exchangeable image file format for digital still cameras: Exif Version 2.2". If you ever choose to actually research any of this, the Standard is available for download from a number of sites.


Again, slow down and look at what the data actually is and what it says. And you personally are not a credible source for this information, hence if you contradict Exiftool and/or the Exif Standard... we can automatically assume you are not correct. That is not immaterial!

You are quoting information that is not from the actual meta data, but rather is the synopsis of whatever program you are using, or worse it is your own summary of what different programs provide. As I showed, Exiftool will actually extract verbatim the exact data from the meta data in the file, by using it with a -b option. By now we should expect that you would have downloaded Exiftool and actually tried it to see if what I say is true, rather than repeatedly insisting that I'm the one who hasn't done the research!

Again there are two records that relate to the lens,
That is exactly what is in the file. Anything other than those two line has been added by a program or your own imagination. What the first item is says is that the lens is identified by the number 213, but what the programs are telling is that is ambiguous and could be one of multiple different lenses. The data is not claiming, as you are, that that record is definitive or that it might be just any of those lenses known to use that ID number. Your assumption that the meta data actually identifies the lens as a Canon EF 90-300mm f/4.5-5.6 is invalid and unwarranted because it is not a logical reading of the actual data.

The second record, "Lens Model" clearly and unequivocally identifies the lens model, yet you choose repeatedly to ignore that and described in incorrectly as ""somewhat lacking in detail".

Apaflo Loc: Anchorage, Alaska

That is a matter of opinion, not fact. I disagree. But you are certainly entitled to you own opinion.

waegwan Loc: Mae Won Li

Sorry no update today. I worked until past dark and it has been pouring rain all day. This has certainly been a lively thread though. I'll post some hopefully worthy comparisons in a day or two. Thanks to all who have enlightened me so far.

Streets Loc: Euless, TX.

OUCH! Remind me to stay away from Tamron lenses.

oldtigger Loc: Roanoke Virginia-USA

some tamrons are excellent, some not so much.
research the lens before you buy

steve_stoneblossom Loc: Rhode Island, USA

Focus breathing is not necessarily as bad as some would have you believe. It just needs to be taken into consideration, like any limitation your equipment might have. If not for the mechanics that cause the focus breathing in my 28-300 lens, I would not be able to focus as close as 18 inches. So there is probably minimal difference in the resultant image with that lens shot at 18"/300mm (130mm effective) and 36"/true 300mm.