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Old Aug 19, 2003, 5:48 PM   #1
djb
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Default mirror tele lenses

i'm sure this has been hashed over before and i'm just too lazy to go looking for the info but, has anyone used one of those old mirror telephoto lenses from 35mm days. most were around 500mm and f/8. if i'm not mistaken, i think they were fixed focus too. anyway, does anyone remember who made the best mirror lens? does anyone remember the mathematics as to figuring real focal length, f/stop, etc. when connecting a camera with it's own lens via an adapter?? would using a mirror lens and also the digital camera's zoom be feasible?? i guess it would be sort of an afocal system without the eyepiece??? if anyone has used this setup has it been successful?? any comments about it??? thanx!!!

dennis
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Old Aug 19, 2003, 11:20 PM   #2
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Default Re: mirror tele lenses

Quote:
Originally Posted by djb
does anyone remember who made the best mirror lens? does anyone remember the mathematics as to figuring real focal length, f/stop, etc. when connecting a camera with it's own lens via an adapter??
The best mirror lenses I have ever seen are the Carl Zeiss 500mm F4 and 1000mm F5.6. The former has a price tag, if my recollection is right, of $30,000-40,000 and the latter is > $60,000. When such a lens is used with a camera it supports, the marked aperture is the maximum and minimum aperture you can get. They do not need an adapter.

Quote:
Originally Posted by djb
when connecting a camera with it's own lens via an adapter?? would using a mirror lens and also the digital camera's zoom be feasible?? i guess it would be sort of an afocal system without the eyepiece???
All mirror lenses designed for SLR camera use have a fixed focal length. This means the subject is FOCUSED on the image plan. To be used with a consumer digital camera that does not have the interchangeable lens capability, a mirror lens (and any other SLR lens) must be converted to an afocal system, a system that does not have a focal point (or the focal point is at infinity), so that the scene is PROJECTED onto the camera lens. Some companies such as Minolta and Nikon produced scope adapter that can be used with their own lenses, converting them to monoscopes. Otherwise, you have to find some way to attach an eyepiece. If the mirror lens is a telescope, an eyepiece is already available. Check www.scopetronix.com for various adapters.

CK
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Old Aug 20, 2003, 1:12 PM   #3
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If you are talking about putting a mirror lens on a SLR (or DSLR) camera, you are in luck. Go to your local library and see if they subscribe to popular photography. In the last month or two they just did an article on mirror lenses.

Eric
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Old Aug 20, 2003, 2:23 PM   #4
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thanx for the info!!! $30K to $60K+ is just a tad out of my budget. just a tad!!! ha ha ha ha!!!! i remember some russian optics and i do remember the article on mirror lenses. i'll have to find it and read it again. i have a fuji s602z. i was thinking of using a t mount
to 55mm adapter to mount between the lense and my camera. i thought but, wasn't sure, that i could focus via my cameras autofocus mechanism or manual focus and my zoom function. that's why i asked about the mathematics involved in calculating actual focal length. thanx guys!!

dennis
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Old Aug 20, 2003, 3:55 PM   #5
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Quote:
Originally Posted by djb
i remember some russian optics and i do remember the article on mirror lenses. i'll have to find it and read it again. i have a fuji s602z.
If you use a T-mount ring to 55mm adapter, it means you will not use any eyepiece, and, as a result, the mirror system is NOT afocal and cannot focus on your Fuji s602z. If the article you were referring to is H. Kepler's published in Pop Photo a couple of months ago, that is a very cheap one made by Samyang with a price tag around $100 on eBay and Adorama http://www.adorama.com/catalog.tpl?o...4&sku=SY5008XX This one is definitely not working with T-mount to 55mm adapter (because it has no eyepiece to convert it to an afocal system). Adorama also sells a Pro-Optic 500mm F5.6 mirror lens that comes with an eyepiece http://www.adorama.com/catalog.tpl?o...4&sku=PRO500SS To use this one, you will need an adapter. Check www.scopetronix.com for the details. IMO, the optical quality of this Pro-Optic mirror lens is only average. I had one and use a William Optic eyepiece that can be directly mounted on a Nikon Coolpix 9xx/4500. Or, you can buy any spotting scope or telescope.

Quote:
Originally Posted by djb
i thought but, wasn't sure, that i could focus via my cameras autofocus mechanism or manual focus and my zoom function. that's why i asked about the mathematics involved in calculating actual focal length.
As mentioned above, your digital camera can only work fine with an afocal system. If an eyepiece is available, then you must focus roughly with the mirror lens and allow the camera AF system to fine tune the focus. Yes, this is a two-stage procedure. So, forget using it for action shoot. The math for calculating the focal length is simple. If the mirror lens has focal length of Xmm and the eyepiece has focal length Ymm, the magnification of the mirror lens is X/Y. For example, the above mentioned Adorama Pro-Optic mirror lens has a focal length of 500mm. If you choose to use a 25mm eyepiece, the magnification is 500/25=20. The effective maximum focal length when this combo is mounted on you camera is 20*(the longest zoom focal length). For example, if your cam has a maximum focal length of 200mm, then the combo will have an effective focal length of 20*200=4000mm! However, you have to make sure that your zoom lens will not hit the eyepiece and this is the reason a compatible adapter is needed.

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Old Aug 20, 2003, 4:37 PM   #6
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Quote:
i'm sure this has been hashed over before and i'm just too lazy to go looking for the info but, has anyone used one of those old mirror telephoto lenses from 35mm days. most were around 500mm and f/8. if i'm not mistaken, i think they were fixed focus too.
It does not sounds that complex like above! Actually several vendors still sell theses mirror lenses. The only fix thing about theses lenses are their aperture! ... and you are right, they are around f/8 and available in most mounts ($379):
http://www.adorama.com/catalog.tpl?o...&sku=SG6008EOS
http://www.adorama.com/catalog.tpl?o...&sku=SG6008MAX

At theses aperture, the AF in most camera will not work, hence all theses lenses are manual focus only, ie you focus it manually with a ring! I had a 500mm for my older AF SLRs and the nice feature about theses lenses are their defocus detail tend to show up as circles!

For T-Mount ($99):
http://www.adorama.com/catalog.tpl?o...XX&promocode=A
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Old Aug 20, 2003, 5:11 PM   #7
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Shene and others, thanx much for the info. after thinking about it i guess i will need to use an eyepiece.

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Old Aug 20, 2003, 5:35 PM   #8
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Default A less expensive and perhaps better alternative....

There are a number of "digiscoping" alternatives where relatively inexpensive telescopes can be used as a mirror lens.

Since you didn't say which fixed lens camera you have, it's important to know that this afocal solution works best with the small lens cameras like the Nikon CP series. These cameras have very small lenses with 28mm filter threads. Several companies such as William Optics (DCL-28 ) as mentioned in the thread and ScopeTronix make eyepieces which have 1.25" barrels and work with many different astronomical type telescopes.

These telescopes have various fixed focal lengths. For example, the Meade ETX-90 has a 1250mm focal length at F13.8. Some of the larger scopes have shorter fixed focal lengths and some are longer. With an eyepiece such as the 24mm William Optics DCL-28, you can shoot at up to about 6000mm with excellent results on reasonably close targets (not too much atmosphere between the lens and subject) and with good lighting.

If your camera has a larger objective, there are eyepieces available with large exit pupils, but expect vignetting at all but full zoom. If you are serious about digiscoping, visit the digiscoping forum here and get more information.

Lin
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Old Aug 20, 2003, 5:44 PM   #9
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Lin, i did post that i have a fuji s602z. i have the 55mm adapter tube and a couple of filters for it. i'm just trying to figure the best way to get 3x to 5x the focal length with reasonably good results.
the 210 mm equivalent FL is just not long enough for me. hey i may wait a year or so and get me a dslr and some really fine macro and tele lenses. look wht the eos rebel 300 is going for with a lense. amazing!!!! i have a 4 1/2 inch reflector telescope and have a bunch of adapters to use afocally but, i don't seem to be able to focus well. the camera wants to focus on the secondary mirror and all i see is the image of the primary mirror with the secondary obstruction in the center. oh, that's a different matter. anyway, i just would like to be shooting in the 35mm equivalent of 600mm to 1000mm for wildlife. just can't get close enough to birds and squirrels and chipmunks with what i have. thanx!!!

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Old Aug 20, 2003, 6:57 PM   #10
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Quote:
Lin, i did post that i have a fuji s602z
I see that in a later post - I only read the initial one. With the S602Z, the only working 3x solution I know of is the Olympus TCON-300 which does work well with the S602Z. To use it, however, you have to fabricate a mount and the telephoto must be focused indepdently of the camera.

The TCON-300 was made for the Olympus E10/E20 and is a superior optic, but comes with an adapter brace which connects to the camera's tripod mount and by way of a "sole plate" to the lens which simply sets in very close proximity to the camera's objective.

Unfortunately, even at today's reduced prices (the original cost was over $600) the TCON-300 is usually over $400. Add another $100 or so for the fabrication of the mount (the one for the E10 won't work) and you are back to nearly the price of the S602Z.

I use the TCON-300 with my Olympus E10, Sony F707, Olympus C2100UZ, Olympus E-100RS and Fuji S602Z, but truthfully, you would be money ahead in the long haul to get the new Canon dSLR so you can use a wide variety of quality lenses for this purpose.

Best regards,

Lin
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