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Old Jan 26, 2017, 9:03 AM   #1
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Default Fisheye conversion lens

Hi,
I'm thinking of buying a cheap conversion lens to do some fisheye pictures. (I like the spherical ones.) I've been looking on Kijiji and have no idea how to tell: if the lens will work with my camera, whether they're fisheye or wide angle, and what the numbers cited (i.e. 0.7X, 0.6X etc) mean.
Any help would be appreciated.
Thanks,
.... john
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Old Jan 26, 2017, 10:07 AM   #2
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In general, conversion lenses attach to the filter screw threads on the end of the lens barrel of your lens, so first, your camera's lens needs to have filter screw threads and they must be the correct diameter (in millimeters.) The other issue is the magnifying power (i.e. 0.7X, 0.6X etc), which affects the amount the angle of view will be increased. If your lens isn't very wide, then you would need a smaller number conversion lens (like 0.5X) to get the same fisheye effect that a wider lens would get with a larger number conversion lens (like 0.7X).

It would be hard to be more specific without knowing exactly what camera/lens you have and what conversion lenses you're looking at.
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Old Jan 26, 2017, 10:25 AM   #3
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Thanks TCav,
That helps. I was trying to save myslelf by trying different lenses, but I guess that's probably my best method.
By the way, which number on my lens tells me how wide it is?
.... john
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Old Jan 26, 2017, 12:46 PM   #4
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Hi, John;
Either on the front of the lens, or in the camera manual, you will find the focal length(s) of your lens, as well as the aperture. Usually written something like: F/2.8 - 5.6 (this is aperture) f=5 - 35mm (this is focal length). In order to tell how wide the lens is, convert the lower focal length to 35mm equivalent. There may also be a circle with a slash through it, with another number, which will be the thread diameter. You will need this to determine what size accessory lens to get.
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Old Jan 26, 2017, 3:06 PM   #5
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Hi,
Yes, alright. The camera I'm thinking about trying says 1:2.6-5.5 I've never understood the aperture thing, because the aperture settings on the screen allow 2.6-8.0 Why the discrepancy?
Thanks,
..... john
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Old Jan 26, 2017, 3:41 PM   #6
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Quote:
Originally Posted by Shinnen View Post
Hi,
Yes, alright. The camera I'm thinking about trying says 1:2.6-5.5 I've never understood the aperture thing, because the aperture settings on the screen allow 2.6-8.0 Why the discrepancy?
Thanks,
..... john
The "1:2.6-5.5" is a reference to the MAXIMUM aperture at the range of focal lengths the zoom lens is capable of. That is, at its widest viewing angle (shortest focal length), the maximum aperture is f/2.6. As you zoom in, however, and the focal length gets longer, the maximum aperture gets smaller (the f-number gets numerically larger), until finally, at full tele, the maximum aperture is only f/5.5. At any viewing angle, however, you can limit the amount of light that passes through the lens by selecting a smaller aperture, down to, apparently, f/8.
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Old Jan 26, 2017, 6:19 PM   #7
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I must be stupid. I still don't get it.
..... john
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Old Jan 26, 2017, 8:28 PM   #8
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If you set your aperture to f/2.6 at wide angle, it will change to f/5.5 when you zoom in all the way, due to the characteristics of the lens, so you may go from 2.6 to 8 at wide angle, but only 5.5 to 8 at full zoom. (assuming f/8 is as small as you can go)
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Old Jan 26, 2017, 8:31 PM   #9
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I think it's the focal length that you need to be concerned with if you want to use the fisheye converter.

You'll see more of the effect at 18mm than 55mm for example.

What makes it awkward is trying to figure out if the converter will vignette on a particular lens. If you have to zoom through it, you can lose the effect.

Take a look at the Raynox site to get some idea of how this works. A lot of the generic converters were intended for P&S cameras with small filter threads.

Raynox shows examples of what to expect.
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Old Jan 28, 2017, 8:29 AM   #10
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Hi VTphotog,
Yes. I see that. So, what is quoted on the lens is the maximum apertures for wide open and fully zoomed?
...... john
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