brianv Posted July 7, 2012 Share #1 Â Posted July 7, 2012 Advertisement (gone after registration) The Summarit 5cm F1.5 lens appears to be optimized for F2.8 used at close-focus, and F1.5 at infinity. This is true of four that I shot with, and all were marked 51.1mm focal length on the optical barrel. This was probably a design consideration to deal with focus shift. Â I modified a Summarit 5cm F1.5 by adding a shim to the rear group to increase the focal length. At F1.5, it now agrees with the RF of the M9 from closest focus to infinity. It back-focuses when stopped down, similar to a C-Sonnar optimized for F1.5. I know how to deal with that. Performance used close-up and wide-open is improved. Â Summarit 5cm F1.5: modify for using F1.5 at all distances Link to post Share on other sites More sharing options...
Advertisement Posted July 7, 2012 Posted July 7, 2012 Hi brianv, Take a look here Link: Modifying the 5cm F1.5 Summarit for close-up and wide-open use.. I'm sure you'll find what you were looking for!
brianv Posted July 8, 2012 Author Share #2  Posted July 8, 2012 I've been shooting with the Modified Summarit on the M9.  Wide-Open at F1.5, close-up.  flower_f1.5 modified Summarit by anachronist1, on Flickr  100% crop.  flower_f15_crop by anachronist1, on Flickr  One more.  Flower and Visitor by anachronist1, on Flickr Link to post Share on other sites More sharing options...
bpalme Posted July 8, 2012 Share #3 Â Posted July 8, 2012 I love the bokeh of these old lenses. If you get some more especially with people please post. Link to post Share on other sites More sharing options...
jaapv Posted July 8, 2012 Share #4  Posted July 8, 2012 Good examples. Btw, it has not been modified, just adjured to your wish- Leica and others have been doing that for ages with lenses that have focus shift. There are plenty of threads on this regarding the Summilux 35 asph. It is by no means certain that a random adjustment shim from a Jupiter gives the desired result. The thickness required varies with each lens. I've been shooting with the Modified Summarit on the M9. Wide-Open at F1.5, close-up.  flower_f1.5 modified Summarit by anachronist1, on Flickr  100% crop.  flower_f15_crop by anachronist1, on Flickr  One more.  Flower and Visitor by anachronist1, on Flickr Link to post Share on other sites More sharing options...
brianv Posted July 8, 2012 Author Share #5 Â Posted July 8, 2012 The thickness of the shim does vary with individual optics, depends on the exact focal length of the front group and the exact focal length of the rear group. All four Summarits that I've disassembled were scribed 51.1mm internally, and the "power" of the individual elements of the rear group were also scribed. I would be very surprised of the exact thickness of the shim fell outside of a 0.15mm to 0.25mm range. Having done this with other lenses, I just looked at it, held up the front and rear groups to get an idea of the relative power, and decided "it needs a 0.2mm shim." I was right on the first guess. If anyone runs into a Summarit scribed "51.5mm", I would leave it alone. Â I've never read of anyone else optimizing the Summarit 5cm F1.5 for close-up and wide-open work, and none of the four lenses that I took apart used shims for either the main optics module or the stand-off of the rear group. The lenses were all custom machined to work without them. Â I do consider changing the focal length of a lens as a modification of its optical prescription. It is more than adjusting the main standoff shim, or adjusting the index of a cam. The spacing between individual elements of a lens is part of it's optical prescription. This one is now different from the original design. You run the risk of undoing corrections that went into the design, field curvature is one that I've run into on other lenses. Â A more structured approach to this problem would be to measure the exact focal length of the front group and the rear group, then compute the additional standoff required to bring the lens to 51.6mm. I just did not take the time to set it up on the optics bench. Â My favorite model (daughter) is getting over pneumonia. I've been disassembling lenses while playing "Nurse". As soon as she is better, will get some portraits with the Summarit. Also shimmed a pair of J-12's for Nikon S-mount and converted a 1936 Contax Sonnar to Leica Mount. My way of dealing with being house-bound. Link to post Share on other sites More sharing options...
jaapv Posted July 8, 2012 Share #6 Â Posted July 8, 2012 Mine was adjusted by Sherry Krauter and is spot-on for all distances wide open. However, stopping down, focus shift kicks in, so it is wise to avoid 2.0, 2.8 and maybe 4.0 at distances under 3 m. Originally these lenses were adjusted to a compromise, which worked on film, but not that well on a more precise digital sensor. Link to post Share on other sites More sharing options...
brianv Posted July 8, 2012 Author Share #7 Â Posted July 8, 2012 Advertisement (gone after registration) As I did this: thought about, machine a mechanism to compensate for focus shift using an indexed cam coupled to the aperture ring, which would move the rear module out by 0.2mm at F1.5 but back to the default position at F2.8. I used to have a mechanical engineer with a CNC that worked for me. Always fought tempation to have him make camera parts. Â This mod was not hard to do, and I'm sure several technicians such as Sherry and DAG have done it on request. It took me 30 minutes to do, much longer to write-up and document online. Link to post Share on other sites More sharing options...
brianv Posted July 8, 2012 Author Share #8  Posted July 8, 2012 Summarit 5cm F1.5, wide-open,  grass2_f15 by anachronist1, on Flickr  100% crop:  Grass2_f15_crop by anachronist1, on Flickr   Summarit 5cm F1.5, at F4 on the Leica M9:  grass_f4 by anachronist1, on Flickr  100% crop of above,  grass_f4_crop by anachronist1, on Flickr  Just like a Sonnar, focus using the RF and then back-off slightly towards close-up. Link to post Share on other sites More sharing options...
brianv Posted July 9, 2012 Author Share #9 Â Posted July 9, 2012 Too funny thinking about this lens and what could have been. I learned enough about optical design to keep a few Optical Engineers within reason on projects. Â I can imagine what the lead engineer would have done. Â Hey Bernie, this lens is 51.1mm and I need it to be 51.6mm- can you take a look at it? Â Sure- hand it over. Â Two months go by.. Â Hey Bernie, have a chance to look at that lens? Â Yes, I did the design, the glass came in from Schott, sent it to Thorlabs to have cut and polished, and ordered a 0.2mm shim to increase the spacing... Â I miss Bernie. Retired a few years ago, one of the last of the old school optical engineers. Link to post Share on other sites More sharing options...
jaapv Posted July 9, 2012 Share #10 Â Posted July 9, 2012 (Nearly) All RF lenses are shimmed to enable calibration Link to post Share on other sites More sharing options...
brianv Posted July 13, 2012 Author Share #11  Posted July 13, 2012 A couple from today at the Marine Museum.  Nikki_f15_summarit by anachronist1, on Flickr  Nikki_f4_summarit by anachronist1, on Flickr  korea_f15_summarit by anachronist1, on Flickr  Korea2_f15_Summarit by anachronist1, on Flickr Link to post Share on other sites More sharing options...
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