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dkCambridgeshire

Leitz EPIS 1000mm f3.5 lens 20x24 inch LF camera

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On 12/8/2018 at 1:45 PM, Ambro51 said:

A superb lens for him to use IF he wants absolutely perfect “landscape” images,, in focus corner to corner, is a single achromat.   With the recent influx of Chinese refractors, these lenses are plentiful.   I’d suggest a 3” or 4” diameter lens from F 12 to F 15.  A washer stop is needed in front of the lens, placed one lens diameter in front, with an opening 1/3 of the lens diameter.  The lens is ‘reversed’, so the convex side faces the plate.    While the aperature is small,  exposures for positives will be about 30-60 seconds.   ••••••  this lens will give “Ansel Adams” type of clarity and focus.......and Yes with 25 years doing Wet Plate and building cameras, I know what I’m talking about.

Could you possibly please post an image made using an achromat with a single front mounted 'washer' stop' ? 

dunk 

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Yes.  Probably under “Wet Plate Leica”.   I hardly use it, but from tests it functions like any wet plate camera.  Outdoors, by the cap, 4 seconds at F 8 gave a nice image on black glass.  On clear glass a bit longer exposure would give a printable negative.  By the grainless collodion process the print will be higher quality than a silver gelatin negative.

Edited by Ambro51

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I probably have a few old civil war re-enactment group shots.  They were done using a common practice of the day (and what I’m suggesting re. Prior posts) of using the single front achromat of the petzval lens reversed and installed in place of the removed rear element.  A stop was inserted, focal length much longer and pin sharpness.  

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14 minutes ago, dkCambridgeshire said:

Could you possibly please post an image made using an achromat with a single front mounted 'washer' stop' ? 

dunk 

Hi Dunk

 

I should be able to do this before long too (just building a front panel/shutter to use an 1850s lens). From my reading the position of the front stop is a compromise because its placement changes aberrations, and the position is a trade off of increasing one at the same time as decreasing another. I think that Kingslake mentions this but I can't find the section at the moment - I'll have another look later.

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Paul, There are three Kingslake books . Can you please advise which one you refer to? 

Optics in photographyRudolf Kingslake booksOptical System Design

A history of the photographic lens

Rudolf Kingslake

 

Lens design fundamentals

Rudolf Kingslake

 

Optical System Design

Rudolf Kingslake

Thank you

 

dunk 

Edited by dkCambridgeshire

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Dunk. I will send you an extract from the Lens Vademecum which covers, inter alia, the Grubb lenses which are mainly Aplanatic rather than achromatic. It does, however, go into some detail about the variable effects when using central washer stops. Both of my Grubb lenses have holders for such stops. If you feel it is worthwhile, feel free to pass it on to Tony and give him my best regards. 

The Grubb Section starts at about page 66 out of 74 of what I am sending to you.

William

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2 hours ago, willeica said:

Dunk. I will send you an extract from the Lens Vademecum which covers, inter alia, the Grubb lenses which are mainly Aplanatic rather than achromatic. It does, however, go into some detail about the variable effects when using central washer stops. Both of my Grubb lenses have holders for such stops. If you feel it is worthwhile, feel free to pass it on to Tony and give him my best regards. 

The Grubb Section starts at about page 66 out of 74 of what I am sending to you.

William

Thank you very much William … a wealth of information and have passed on to Tony  … and will also study myself.

Regards

dunk  

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