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Using eyepiece lenses

 
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LordV



Joined: 22 Nov 2007
Posts: 1561
Location: UK

PostPosted: Wed Mar 10, 2010 1:20 am    Post subject: Using eyepiece lenses Reply with quote

I'm showing my total ignorance of optics here but is there any way of using just microscope or telescope eyepiece lenses on a DSLR as a high power macro lens ?
I thought the answer was no but no doubt someone will correct me
Brian v.
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 18170
Location: Richland, Washington State, USA

PostPosted: Wed Mar 10, 2010 2:00 am    Post subject: Reply with quote

Hold it up to your eye the normal way 'round and see if there's enough front-end clearance to use it as a loupe. If there is, then you can probably mount it on the end of a long extension and use it as a macro lens.

With a microscope eyepiece, this probably won't work. Most of them are designed to focus inside the body of the eyepiece tube. Turn them around and you'd have enough clearance, but then the aberrations would get pretty bad.

Telescope eyepieces, I don't know about.

In either case, they're not going to be terribly high power. The focal length of an eyepiece is basically 254 mm divided by the nominal power. So a typical 10X microscope eyepiece is about 25 mm focal length.

From a standpoint of aberrations, an eyepiece is corrected for infinity focus on the eye side. Put one of these on a bellows, and there'll be some spherical aberration to live with also.

--Rik
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LordV



Joined: 22 Nov 2007
Posts: 1561
Location: UK

PostPosted: Wed Mar 10, 2010 2:28 am    Post subject: Reply with quote

rjlittlefield wrote:
Hold it up to your eye the normal way 'round and see if there's enough front-end clearance to use it as a loupe. If there is, then you can probably mount it on the end of a long extension and use it as a macro lens.

With a microscope eyepiece, this probably won't work. Most of them are designed to focus inside the body of the eyepiece tube. Turn them around and you'd have enough clearance, but then the aberrations would get pretty bad.

Telescope eyepieces, I don't know about.

In either case, they're not going to be terribly high power. The focal length of an eyepiece is basically 254 mm divided by the nominal power. So a typical 10X microscope eyepiece is about 25 mm focal length.

From a standpoint of aberrations, an eyepiece is corrected for infinity focus on the eye side. Put one of these on a bellows, and there'll be some spherical aberration to live with also.

--Rik


Thanks Rik,
I wasn't planning on trying this but someone asked me on another forum whether it was worth buying some fairly cheap objectives to do this with- I answered probably not.
Brian V.
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Charles Krebs



Joined: 01 Aug 2006
Posts: 5760
Location: Issaquah, WA USA

PostPosted: Wed Mar 10, 2010 11:17 am    Post subject: Reply with quote

Brian,

If someone already had one then go ahead and try it... but it will need to be reversed (eye end facing subject) and the image will be pretty sad. (May work out as a "dreamy" special effects optic Wink)

Buying some eyepieces to try is, in my mind a non-starter. I just saw a very nice Nikon CF BD Plan 10/0.25 go for $75. That's a proven piece (21.2mm focal length) that can do fantastic work.

There are certainly other 10X objectives that will do fine work, but when you can get something like that, at that price, it doesn't make sense to even experiment with cheap 10X "unknown" objectives. You may luck out and get one that works well, or you could end up with a few mediocre paperweights.
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