Re: Dennis's wide angle optics (Re: MF Expo)

[Dennis Selwa <dselwa@xxxxxxxxxxxx>]

At 03:56 PM 5/3/99 -0600, you wrote:
>> Greg,
>> The lens wasn't designed from the ground up. Two dublets were mounted in a
>>barrel in what is called a symetrical arrangement.The two dublets were
>>chosen from a stock assortment by some guy in cherry hill NJ--I forget his
>>name. Supposedly it is better than just a single doublet.I guess its
>>possible to engineer the optimum lens and have them ground and cemented but
>>it would be quite expensive. It would be nice to talk to a real optics
>>engineer and find out what the state of the art is capable of.
>> You dont see any real wide eyepoint lenses.I guess there are limitations
>>on wideness of apparent view without distortion.
>
>  Is this a double (cemented) achromat system?
>(Similar to the double 36x94mm achromats Alan
>Lewis and I are using to view full frame 35mm).
>

GREG,
 There are two doublets with an air space between them. Its 60 mm. FL and
50mm. diameter. The 645 format is viewabe with eyeglasses. Not much room to
spare though.Im going to measure my eyepiece diameter again to make sure I
got the right numbers. I just remember it to be 50mm.
 Wow 50mm. FL and 36mm. dia  That sounds like a real wide view.

Dennis



>  Or is a doublet an airspaced achromat? (Not
>totally up on my terminology).
>
>  Getting a wide angle AND large diameter
>viewer lens is optically difficult (I hear).
>Usually you are limited to f2 or smaller (ie
>80mm FL by 40mm diameter or the Red Button
>44mm FL by 20mm diameter). To get past that
>you have to go to more elements and the symetrical
>one ofter works well.
>
>  Alan's and my 50mm FL by 36mm diameter double
>achromat works out to be f1.4.
>
>Greg
>
>