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#11 |
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As one who has used them in the past, the attachment lens I think you're talking about produce mediocre to terrible images. Generally, CA is very prevalent, sharpness & focus is, in most cases, extremely difficult to achieve. Not too bad if you like fuzzy rainbows, not so good otherwise.
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#12 | |
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Join Date: Mar 2005
Location: Extreme Northeastern Vermont, USA
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One thing to be careful of when using a fisheye type lens, and especially the conversion lenses, is extraneous light sources. Since the lens is picking up light from such a wide area, sometimes lights we don't really notice or think of as being a problem, can create some strange effects. |
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#13 |
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Join Date: Jan 2013
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Hi,
This is a learning experience for me. I started by trying to throw something together from a box of lenses, collected, over the years, from cannibalized cameras and lenses; but the best I can get is about 120 degrees. This doesn't really have the extreme distortion of the ones I've seen on the net. By the way, what's the difference between a semi and a (regular) fish eye lens? The semi's I seen on the net look pretty good. ... john |
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#14 | |
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Join Date: Jan 2011
Location: Australia, New South Wales central coast
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May I "confuse" you a bit more ... Aperture numbers - just like shutter speed number are fractions A shutter speed of 1/500 second is often shown as '500', and an aperture of 1/16 is shown as 16, but with an 'F' in front to separate it from shutter speed numbers and because the fraction comes from the Focal Length of the lens in use Aperture numbers are a fraction, where the fraction comes from the diameter of the hole the light goes thru vs the mm's of the lens in use. For example - if a 100mm lens had an aperture hole of 25mm, then 25/100 = 1/4 = F4 As you zoom a lens, the mm's change but the hole the light comes thru does not change - leading to an alteration in the fraction Try this sketch for size ... ![]() So - if your lens was a 100-300mm zoom, and at the 100mm position the aperture was F4 [from above], then at the 300mm position the math becomes 25/300 = 1/12 = F12 We are lucky today in that our lens designers can make lenses which are actually shorter than the 300mm stated. The optical design is called 'telephoto' rather than the original 'long' lens. This means that the resulting fraction is less than 1/12 [from above], possibly down to 1/6 to 1/9. Therefore the information on the lens barrel will say something like "F = 4 : 9" ... meaning as you zoom the aperture changes from 1/4 the mm's to 1/9 the mm's of the lens Does this help at all? Phil
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Has Lumix mirrorless & superzoom cameras and loves their amazing capabilities Spends 8-9 months each year travelling Australia Recent images at http://www.flickr.com/photos/ozzie_traveller/sets/ |
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#15 |
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Join Date: Jan 2013
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Alright. It's starting to come into focus
![]() I have a chance to buy a Pentax Takumar Spotmatic M42 lens, from an old film camera. The seller says that it has an adjustment that will allow it to be used on many cameras. It's a screw on, so I should be able to adapt it to one of my cameras. I will try it before buying; but would like an opinion as to whether this is a good (fisheye) lens. Thanks, ..... john |
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#16 |
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Join Date: Jan 2011
Location: Australia, New South Wales central coast
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G'day John
The 'old' M42 threaded lenses can be used on almost any camera these days via the use of an M42 to [canon/nikon/pentax/m43 etc] bayonet adapter The 'fisheye' part comes from the mm's of the original lens - if this old lens is on the 8mm to 16mm region is will be wide angle to very-wide angle. If the old lens is over 24mm then it will merely be a regular wide angle lens One thing to double check with any adapters is the need to focus to infinity ... I have one particular adapter whose thickness is 'one paper sheet too thin' and thus the lens focuses beyond infinity - ie: with lens set to infinity & the stuff on infinity goes out of focus, and I have to back off a bit to get it right. With this adapter, 'infinity' comes into focus with the lens on about 30m Hope this helps Phil
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Has Lumix mirrorless & superzoom cameras and loves their amazing capabilities Spends 8-9 months each year travelling Australia Recent images at http://www.flickr.com/photos/ozzie_traveller/sets/ |
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#17 |
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Join Date: Jan 2013
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Hi Phil,
First - Thanks for your help in understanding the lens numbers. It did help. I won't pretend to understand what you're talking about wrt focusing of this lens. I think there are two things I want to ask you. 1. You mention an adapter. Will I have to get a bayonet adapter to get it to fit my 52mm or 58mm lens thread? 2. Would the best way of checking the focus of this lens wrt to my camera(s), be to hold it up to the camera and see if I get a sharp picture? ...... john P.S. He wants $40 for the lens. It sounds like a great price to me, if it works. |
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#18 |
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Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
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Focusing shouldn't really be much of an issue. When a lens has a short focal length, as is the case with fisheye lenses, the depth of field is huge, so everything is usually in focus.
It's actually hard to get something out of focus when using a fisheye lens.
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#19 |
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I'm completely lost trying to follow this conversation.
A fisheye "conversion" lens screws on the front of another lens and the aperture is irrelevant. The .5x, .7x is the conversion factor. A 50mm lens would seem like a 25mm lens at .5x and 35mm with .7x. You need to know the focal length and the filter thread diameter as a baseline. An M42 lens is a lens that adapts to an interchangeable lens body in place of the original lens. You can't just screw it on the front of another lens. What camera are you using? It seems from your posts in the past, you have P&S cameras. |
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#20 | |
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Location: Washington, DC, Metro Area, Maryland
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Conversion lenses are most often used for video, which has a much lower resolution than still images, so the field curvature isn't as noticeable.
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