I’m looking for telephoto conversion lenses and I have a question…
some indicate a magnification factor (x1.7 and x2.0 seem to be the most common) but some don’t give a magnification and instead indicate what I’m guessing is a focal length. Is there some kind of conversion to determine what 1300mm means in terms of magnification?
A rough estimate would be to divide the focal length by 50mm, since that’s the focal length that most corresponds to the normal human eye. So a 1300mm telephoto would give you roughly a 26x zoom.
However, this is all dependent on the lens and camera your lens is attached to. If it’s a 35mm film camera or 24x36mm sensor camera, then everything’s fine.
If it’s attached to a APS-C sensor camera (smaller than 24x36), then you have to multiply your focal length by 1.6 first, since the smaller sensor gives an apparent magnification of 1.6x using a lens designed for a 35mm camera.
If it’s an APS-C sensor lens(Canon EF-S, for example), then you’re fine, but your calculation changes; you’d divide by about 30mm instead of 50mm, since on an APS-C sensor, a 30mm focal length is closest to what the eye would see, instead of 50mm, which is effectively the same thing as multiplying by 1.6 and dividing by 50mm.
So… a 1300mm lens on a 35mm camera = 26x. 1300mm lens, APS-C sensor = 42x
A “normal lens” for 35mm film format is around 45-50mm. Normal in this sense means that the perspective and area of coverage is about the same as your eye. A rough way to figure magnification is to divide the lenses focal length by 50.
None of this holds true for digital cameras unless they have a “full sized” sensor, which most do not. That’s why you’ll often see a conversion factor listed. For example on my Canon 7D the conversion factor is 1.5. So a 50mm lens on that camera will give the same effect as a 75mm lens on a 35mm film camera.
Obligatory Wikilink
Yes, 50mm is “normal” for a 35mm camera. Digital cameras have an enormous variation in sensor size (in fact sensor size, density of each pixel sensor, is another camera feature. The larger/less dense the pixels on the sensor, the less noise usually in the picture, better low-light performance, etc.).
What you typically will see is “35-mm equivalent” quoted. A tyical small digital camera may say it has the 28mm-140mm equivalent zoom (5x zoom). You have to get a feel for what are practical lens sizes. A 28mm is a decent wide-angle; 85mm is good for portraiture, not in-your-face to get a head shot. 135mm is decent zoom; 300mm or 400mm is excellent (huge) zoom, but now at the point where unless it’s bright sunlight camera shake can be an issue.
As mentioned previously, the new APS-C is making inroads; for my Canon T1i I have a 10-20mm, which is a very wide zoom. I can stand on the other side of a narrow NYC street and get a whole 3-story brownstone in the picture (with some distortion). At the other extreme, one zoom goes up to 270mm which is 400mm equivalent; I can get a decent picture of the home plate group from the upper reaches of Yankee Stadium, but it’s hard to hold that steady.
Also, the longer the zoom, the higher the f-stop unless you get an incredibly big lens; a higher f-stop means less light, which means you need better sensor performance in low light. Everything is a trade-off.
I’m starting to think in terms of Canon EF-S lens sizes rather than 35mm equivalents.
Unless you are getting into the fancy removable-lens cameras, they typical point-and-shoot starts at about 28mm equivalent, because zoom wider than that is hard to engineer into a lens that also does decent telephoto. 4x zoom is typical, giving you decent telephoto shots. As long as a camera has a decent range of about 4x and you are not mainly interested in telephoto in sunlight, I would spend more time looking at lower-light picture quality, which is related to sensor size/density.
WOW! Lots of good info - thanks!
Just for the record I have a new Panasonic Lumix DMC-LX5.
I guerss I’ll have to spend some time looking at the specs.
Any lenses you for that camera attach in front of the existing zoom lens. You need to first buy the conversion lens adapter that attaches to the front lens ring, and then you attach the conversion lenses to it.
The effective (translated to the 35mm film standard) focal length of this camera is 24mm to 90mm, which is quite good on the wide angle end but not much on the telephoto end. I could see a 2x converter being helpful but nothing beyond that. This camera takes high quality images by having a large sensor and a fast good lens. Any converters will eat light and degrade image quality. As it is, you will be spending a lot to get something worthwhile for this camera; anything cheap will be crap.
Looking online I don’t see any telephoto lenses for this camera that I would bother with. The Opteka brand is crap. No, worse than crap. You might as well be shooting through wax paper. Panasonic sells a wide angle conversion lens (.75x) but they don’t seem to sell a telephoto converter.
At best, you’ll get up to 180mm, which isn’t bad. But you’ll degrade some of the best features of the LX-5 - namely good low light performance and sharp image quality, plus you’ll make the camera much bulkier. IMO, conversion lenses only make sense in very limited situations. What do you want to do with this?
Thanks Telemark, I’ve seem the glass in the Opteka brand lenses comapred to Coke bottle bottoms in terms of optics. 
I have the converter and a few filters so I’m covered there. I’m considering the wide angle lens as well.
Panasonic actualy makes a 1.7x conversion lens but doesn’t say it’s for the LX5 but it looks like it will fit the converter so I may try it. I’ve even seen people online claiming to get good results with this Raynox 2.2x.
I don’t see myself using a telephoto converter very often but thought it might be nice to bring along on vacation and stuff like that.
Raynox is a solid brand, and the 2.2x has a pretty good reputation. My concern would be how much light it consumes but for outside shooting it should be fine.
Perfect! That’s exactly what I’d be using it for. Thanks so much!
OK - one last bump just to follow up…
For grins I bought a Zeikos 3.5x c onversion lens just to see how it would work (it was only $30 so I figured what the hell).
Widest lens setting - camera alone
Max zoom on camera - Zeikos lens attached
So while not optimal at least it works. I think the results would be much better with a tripod or at least resting the camera on something stable.
Nasty chromatic aberration on that.
Yeah - like I said it’s a $30 lens - it was just an experiment.
Based on those results, I’d never use that lens. Sorry, the image quality is unacceptable for any use to me. You’d do much better by cropping and using software to add pixels if you need a larger image.
Sorry, a “normal” lens is not called that because it matches your eye. A normal lens is one where the focal length matches the diagonal of the format. On 35mm film this is about 45mm. Normal perspective requires a longer lens, 90 to 135mm. Coverage of width would take a wide angle; I don’t have specific info on that. I can’t figure what is meant by a 1300mm lens. With that an object 100 ft away would appear to be 3.9 ft away. Not usually found in amateur equipment. Or is that meant to indicate a zoom range?
I don’t really plan on using it - I’m saving for the Raynox. I’m just playing with it.
I understand, and if you enjoy playing with it that’s all that matters.