I want more telephoto

[Joshonator]

My solution past 300mm is an old tamron adaptall 2 mount 70-210 with an adaptall 2 to m42 converter. Then I attach two m42 2x extenders and attach to camera with an m42 to eos adapter. that's 840mm before taking into account the crop sensor, and the results I got weren't too bad. Of course a tripod is highly recommended and the aperture is roughly f8. But handheld is easily possible with one extender attached and probably possible with two on a bright day or with the ISO cranked beyond the point of usability.

Bear in mind the lens was 15$, the extenders were about 20$ each and the adapters costed about 15$ for both.

 

[480sparky]

What's so gawd-awful wrong with a mirror lens?

 

[bobandcar]

My solution past 300mm is an old tamron adaptall 2 mount 70-210 with an adaptall 2 to m42 converter. Then I attach two m42 2x extenders and attach to camera with an m42 to eos adapter. that's 840mm before taking into account the crop sensor, and the results I got weren't too bad. Of course a tripod is highly recommended and the aperture is roughly f8. But handheld is easily possible with one extender attached and probably possible with two on a bright day or with the ISO cranked beyond the point of usability.

Bear in mind the lens was 15$, the extenders were about 20$ each and the adapters costed about 15$ for both.

if that was a crack at me see attached photo.



if it wasnt a crack at me, why would you try that?

 

[KmH]

A)As Keith stated, who seems to have some experience with these things, they're not totally awful.

B) They're basically good for shooting pictures of the moon or other stellar objects. (not really, not enough magnification or aperture) ...weird background highlights effect Keith talked about (like the donut looking background highlights in 480sparky's giraff photo)

For the price the Opteka mirror lens is tough to beat.

 

[Joshonator]

My solution past 300mm is an old tamron adaptall 2 mount 70-210 with an adaptall 2 to m42 converter. Then I attach two m42 2x extenders and attach to camera with an m42 to eos adapter. that's 840mm before taking into account the crop sensor, and the results I got weren't too bad. Of course a tripod is highly recommended and the aperture is roughly f8. But handheld is easily possible with one extender attached and probably possible with two on a bright day or with the ISO cranked beyond the point of usability.

Bear in mind the lens was 15$, the extenders were about 20$ each and the adapters costed about 15$ for both.

if that was a crack at me see attached photo.



if it wasnt a crack at me, why would you try that?View attachment 12857View attachment 12858

My post wasn't intended to have any meaning to you. But when i get a chance to use it we should compare shots of our setups . The main reason I got the 2x extenders was for macro actually.

 

[TCampbell]

The doughnut-shaped bokeh you get from the central obstruction in a mirror lens (aka catadioptric lens) is always a nice artistic touch.

It's challenging to make a long focal length lens with a low focal ratio using glass. The focal ratio (f-stop) is the area of clear aperture of the lens divided into the focal length. That means in order for a 500mm lens to offer f/4 the area of clear aperture has to divide into the focal length four times... which requires a diameter of 125mm (about 5").

When a "glass" lens is used, problems with chromatic aberration become severe at that size and you have to use exotic low dispersion elements and achromatic doublets in an attempt to "reduce" the impact. This means the lens is not only physically large, but it's also going to be heavy. Canon likes to use fluorite crystal for their low dispersion elements. Fluorite has to be synthetically "grown" in a kiln and in order to make a crystal large enough to grind into a optical grade lens requires a very long time in a kiln.

Basically there's no "cheap" way to do this and get a lens that isn't garbage. The "long" glass telephoto lenses tend to be f/5.6 (because split-prism & phase-detect focusing still works at f/5.6) but much above that and it basically doesn't work anymore. I have an old 35mm camera with manual focusing and the split prism focus aid. You can't even focus that above f/5.6 because half of the mirror will almost always be black. You can only look at the image and try to visually make the image as good as possible.

A catadioptric lens (basically works like a Schmidt-Cassegrain or Mak-Cas telescope) uses parabolic mirrors to focus light rather than passing the light through a lens. Since the light only "bounces" off a mirror rather than passing through a lens, it doesn't have a CA problem (thank Isaac Newton for discovering this.)

Catadioptric scopes work fabulously on deep space objects (no bokeh). But not so well on terrestrial objects because the "blur" always takes on the shape of the clear aperture. Catadioptric scopes always have a central obstruction. This means the area of "clear" aperture is always in the shape of a doughnut -- so you get circular "bokeh" with a black center.