Beginner lens numbers / size and abbreviations..(a very basic question)

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Paul Buckley

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hi I'm brand new to the camera world and I was trying to make sense of the abbreviations like stm, or ef use that you see on different lenses.
I was also wondering what the size relates to like 18 -55. Or 100 mm for instance what does it mean..?

I've bought a eos750d with a stm 18 55 lens set.. one of my main interests is marine livestock, and I want to capture close ups of my coral from a reef tank.. could someone try and give me some novice advice on what to look for.
Ideally I'd be at the front of the glass tank focussing around 125 mm to 450 mm min and max..

Thanks
 
Are you on Ultimate Reef Paul? There's a couple of useful guides there in the Photography sub-forum.
 
18, 55 and 100 are focal lengths. The larger the number the larger the magnification and the smaller the field of view. Looking at it in simple terms, wide landscape use short focal length (small number), bird at a distance use long focal length (bigger number). Your lens is an 18-55, a very common short 'kit' zoom. The focal length is 18 at one end of the zoom range, 55 at the other. Your 750D has a 'cropped sensor' (smaller than a full frame dslr which is the equivalent of the old 35mm film format). To equate your focal length to that of 35mm/full frame you need to multiply by the Canon 'crop factor' which is 1.6, but I wouldn't worry about that. Someone, though, is bound to mention it...........STM refers to the type of autofocus motor. Again nothing to worry about. EF and EFS are types of lens mount. Both are Canon but EFS lenses are designed specifically for crop sensor cameras. You can use both EF and EFS lenses on your camera, however you can't use EFS lenses on a full frame camera, which is why anyone who intends eventually upgrading from a crop sensor to full frame is advised only to buy EF lenses. If you intend shooting at 125mm range you may find you can't focus, as it may be too close for the minimum focussing distance of the lens. I say 'may' as I've never used a lens that short for close up.
 
Jannyfox said:
18, 55 and 100 are focal lengths. The larger the number the larger the magnification
Click to expand...
Incorrect. Focal length has a weak (frequently negative) relationship with magnification. The minimum focusing distance is more relevant for determine the magnification. Focal length defines the angle of view.
 
Alastair said:
Incorrect. Focal length has a weak (frequently negative) relationship with magnification. The minimum focusing distance is more relevant for determine the magnification. Focal length defines the angle of view.
Click to expand...

That and 'crop factor'?

@Paul Buckley
There's no need to concern yourself with crop factors, you only need to know that the 18-55 is a moderate wide angle to short telephoto, it's a general purpose lens, wider than 18mm would be described as ultra wide, longer than 55mm would be telephoto.*

*technically 'telephoto' doesn't actually equate to focal length, but it's an accepted norm.
 
You might need a 'macro' lens for the small objects close up.

Lenses are usually named macro, I'd recommend a second hand Tamron 90mm as a great value start.

There's an abbreviations page here somewhere, but be aware that all manufacturers use abbreviations in product names, you've no way of remembering all of them.
 
Phil V said:
There's no need to concern yourself with crop factors
Click to expand...
^ that, Jan's discussion of crop factor is irrelevant to the question and unnecessarily confusing.

One of the reasons I suggested the Photography section on Ultimate Reef* is that on there are discussions of taking exactly the type of shot that Paul wants to take - equipment used, sample shots with suggested lenses, lenses to avoid**, technique, etc.


* ok, I had a look and it's not the most active area of UR at the moment and hasn't been for a while. But I know the information is there, in part because I contributed some of it too many years ago ;)
** any zoom lens with the word "macro" should be avoided for reef photography, they're all useless for the subject (and the exceptions to the rule are so obscure you're unlikely to consider them)
 
Yes The ultimate reef does/ or did a photo of the month competition which I liked the idea of.. although not many on the forum participate... probably cos they spend so much time like me.. trying to keep the tank maintained..lol

Ok that sums up and clarifies a few things, although I don't understand why the macro lens wouldn't be best suited to my subject, is it to do with the refraction off glass or water..
I had a go with my 18 -55 stm lens and got a reasonable shot.. better than my iPhone anyway..6243826912_IMG_0046.JPG
 
A genuine macro lens would be good, it's the zoom macro lenses (particularly the ubiquitous 70-300mm "macro" lenses) that are a poor choice - because the zooms are not true macro lenses and the minimum focusing distance is too long.

I personally preferred a prime macro lens around 100mm (I used to use Sigma 105mm) for reef tank shots, others preferred something around 60mm. There is a "macro lens thread" on UR that lists various lenses that were available up to a few years ago, with links to reef tank shots people had taken with them.
 
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