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Front-End Filter Improves Corner Smearing
  
 
sebboh
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p.94 #1 · p.94 #1 · Front-End Filter Improves Corner Smearing


Fred Miranda wrote:
I remember trying a 5m PCX on it and it made corners worse.


due to the type of field curvature that the zm 50/1.5 has, the kolari UT conversion actually makes the corners worse, but the midzone much better. it's possible the PCX filter could function similarly.









Dec 19, 2017 at 09:24 PM
DavidBM
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p.94 #2 · p.94 #2 · Front-End Filter Improves Corner Smearing


Fred Miranda wrote:
I remember trying a 5m PCX on it and it made corners worse.


Thanks!
I found your post, no improvement at any part of the frame in the 1-4 meter zone.

Thatís a pity: @Sebboh tests show huge improvement with Kolari UT, so I was hoping for some of that with 5m (which I think is what Haruhiko thought would be the right strength)

I guess Sebbohís tests are at infinity, and I have never shit it at infinity except for test purposes, and likely never will...



Dec 19, 2017 at 11:02 PM
DavidBM
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p.94 #3 · p.94 #3 · Front-End Filter Improves Corner Smearing


sebboh wrote:
due to the type of field curvature that the zm 50/1.5 has, the kolari UT conversion actually makes the corners worse, but the midzone much better. it's possible the PCX filter could function similarly.

http://c1.staticflickr.com/5/4501/24169039848_a204269232_o.jpg


That would be great, donít care about corners, it was mid zone I was going for based on your tests I was looking at the other day.

Unfortunately Fredís test found no improvement anywhere in the 1-5m zone. I suppose it might be worth trying in the spirit of replication....



Dec 19, 2017 at 11:05 PM
Fred Miranda
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p.94 #4 · p.94 #4 · Front-End Filter Improves Corner Smearing


DavidBM wrote:
That would be great, donít care about corners, it was mid zone I was going for based on your tests I was looking at the other day.

Unfortunately Fredís test found no improvement anywhere in the 1-5m zone. I suppose it might be worth trying in the spirit of replication....


I don't have the ZM 50/1.5C anymore, otherwise I would post some test shots. I remembered well that the 5m PCX made the FC worse though. Perhaps it overcorrected?

The only lens I still use with a PCX front lens is the CV 35/1.7 Ultron. The sharpest 35mm I've tested to date. I tested a 2.5m, 4m and 5m front lens an the latter was definitely the best choice for it.



Dec 23, 2017 at 08:51 PM
Mathieu18
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p.94 #5 · p.94 #5 · Front-End Filter Improves Corner Smearing


Been running searches but havenít found anything... does anyone know the optimal filter for a Voigtlander M Mount 21/4? Might try it anyway, about to do a naked sensor conversion on an A7 OG, but curious if I could make it work on the R2 too.


Jan 08, 2018 at 02:16 AM
maxxprofex
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p.94 #6 · p.94 #6 · Front-End Filter Improves Corner Smearing


Hey Mathieu, that's a good question and I'm very curious if you can find out about it!

For the 25mm F4 version, I used the Opto Sigma SLB-50-1200PM (plano convex 1.2m) lens combined with a too short adapter. Results are not bad... You might want to ask Haruhiko wether he is able to run a simulation for your lens based on its geometry. But my guess would be that a PCX somewhere around the focal length of 1.2m could do the job.



Jan 08, 2018 at 05:38 PM
Scho
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p.94 #7 · p.94 #7 · Front-End Filter Improves Corner Smearing


So far I have had no luck getting infinity focus using the Contax G 28/2.8 Biogon (M mount converted) with a PCX front filter (OptoSIgma SLB-50-1500PM) using TAP, Voigtlander II, Fotodiox, and Fotodiox Pro LM-E adapters. Corners are great but can't focus sharply beyond 10-15 ft at any aperture. I'll have to open the lens and see if there are spacer washers inside that can be removed. The lens does focus at infinity without the PCX filter. The filter is mounted between step rings as described earlier in this thread, with convex side facing the lens.


Jan 08, 2018 at 08:50 PM
realVivek
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p.94 #8 · p.94 #8 · Front-End Filter Improves Corner Smearing


Carl, the cheapest part in this setup is the adapter. You can get one of the E to M adapters from China, remove the LM mount, grind th down the adapter by a mm or so, reattach the L mount . If I were you, I would not open up the M mount lens even if I do not plan on using it on a Leica camera ever.

Scho wrote:
So far I have had no luck getting infinity focus using the Contax G 28/2.8 Biogon (M mount converted) with a PCX front filter (OptoSIgma SLB-50-1500PM) using TAP, Voigtlander II, Fotodiox, and Fotodiox Pro LM-E adapters. Corners are great but can't focus sharply beyond 10-15 ft at any aperture. I'll have to open the lens and see if there are spacer washers inside that can be removed. The lens does focus at infinity without the PCX filter. The filter is mounted between step rings as described earlier in this thread, with convex side facing the lens.





Jan 08, 2018 at 09:21 PM
Mathieu18
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p.94 #9 · p.94 #9 · Front-End Filter Improves Corner Smearing


Thanks, I figure I'll start with my 1500mm PCX and see how it does. If it improves it enough I'll be content as it'll mostly be used at f/8 anyway. Did you have any trouble with infinity focus?

maxxprofex wrote:
Hey Mathieu, that's a good question and I'm very curious if you can find out about it!

For the 25mm F4 version, I used the Opto Sigma SLB-50-1200PM (plano convex 1.2m) lens combined with a too short adapter. Results are not bad... You might want to ask Haruhiko wether he is able to run a simulation for your lens based on its geometry. But my guess would be that a PCX somewhere around the focal length of 1.2m could do the job.


---------------------------------------------
If the front of the lens is similar to the native, there will be brass/aluminum spacers where the optical block attaches to the body, from the front end (remove the vanity ring and there are 3-4 screws, very simple). If it's completely rehoused, I have no idea. My native G had the same behavior when used. I'd actually recommend this first and just save the spacer, its not any significant surgery.

Scho wrote:
So far I have had no luck getting infinity focus using the Contax G 28/2.8 Biogon (M mount converted) with a PCX front filter (OptoSIgma SLB-50-1500PM) using TAP, Voigtlander II, Fotodiox, and Fotodiox Pro LM-E adapters. Corners are great but can't focus sharply beyond 10-15 ft at any aperture. I'll have to open the lens and see if there are spacer washers inside that can be removed. The lens does focus at infinity without the PCX filter. The filter is mounted between step rings as described earlier in this thread, with convex side facing the lens.




Jan 08, 2018 at 09:28 PM
 

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maxxprofex
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p.94 #10 · p.94 #10 · Front-End Filter Improves Corner Smearing


Thanks, I figure I'll start with my 1500mm PCX and see how it does. If it improves it enough I'll be content as it'll mostly be used at f/8 anyway. Did you have any trouble with infinity focus?

Great! Let us know, how it performs!

My 25/4 with the 1200 PCX performs best at F11. It's definitely better than the Kit Zoom (the FE 2870), not as good as my Nikkor AIS 24 F2.8, but much smaller and ligther.

For infinity focus, you'll need an adapter that is a bit shorter -- I bought a cheap adapter which I took to a mechanical workshop where I had 0.5mm ground off. Now, I can focus a little past infinity.



Jan 08, 2018 at 10:15 PM
Scho
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p.94 #11 · p.94 #11 · Front-End Filter Improves Corner Smearing


Vivek and Mathieu,

Thank you for the suggestions. I have no means to do precision (or even crude) grinding so adapter modification is beyond my capability. I did find a simple illustrated description of how to open a Contax G Biogon lens and it looks like I might be capable of doing what Mathieu suggested. I assume that one must align the ridge on the lens barrel with the rotating notch on the housing to allow aperture adjustment. Now to find a very small screwdriver with a magnetic tip for those tiny screws.

Thanks,
Carl

Opening the Contax G Biogon:
http://www.fredmiranda.com/forum/topic/1159122



Jan 08, 2018 at 10:38 PM
Scho
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p.94 #12 · p.94 #12 · Front-End Filter Improves Corner Smearing


I removed the 2 spacer washers (one paper thin brass and another approx 1mm aluminum) from the Contax G Biogon as described above and lens now able to focus at distance and nearby with the PCX front filter.

quick test shot out of window after lens surgery:




Jan 09, 2018 at 07:51 PM
thrice
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p.94 #13 · p.94 #13 · Front-End Filter Improves Corner Smearing


Very very impressed by the 35ZM with 5m PCX. Also had the Haida Clear Night filter on this shot, no real light pollution in the Norwegian countryside though.

Other than a little coma and strong vignetting it is arguably higher contrast at f/1.4 than my 21 Loxia at f/2.8. Both lenses are very sharp, the Loxia is probably better colour corrected.

This shot is f/1.4 ISO6400 15s foreground is an 8 image smooth reflections stack. Sky is obviously single shot to avoid trailing.

Excuse the compression, uploading from my phone in the airport to kill time.







Jan 12, 2018 at 04:06 PM
Mathieu18
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p.94 #14 · p.94 #14 · Front-End Filter Improves Corner Smearing


Scho, glad it worked out, thatís the same spacers I had to remove on the G 28.

Tried the 1500mm PCX on the CV21, and it was way, way too strong. Iíll try the PCX 5000 when I have a chance, based on what I saw from the 1500 though Iím wondering if thatíll be too strong as well. Isnít too terrible unmodified, plus I still need to pull the optical block and see if itís shimmed...



Jan 12, 2018 at 04:53 PM
uscmatt99
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p.94 #15 · p.94 #15 · Front-End Filter Improves Corner Smearing


Well after reading through the thread for the past couple of days, I'm going to try my hand at this with my ZM 25/2.8 and ZM 35/2.8. I got a set of used Proxar lenses and necessary step and retention rings to mess with and will give the 1m a go on the ZM 25/2.8. I don't recall seeing anyone post in the thread or elsewhere regarding the C-Biogon.

I found a table on Digilloyd with listed ray angles for the ZM line:
https://diglloyd.com/prem/s/ALLVIEW/SonyNEX/lenses-ray-angle-table-ZM.html

The 25/2.8 has chief ray angles listed of 40.8 and 37.3 degrees.
The 35/2.8 has chief ray angles listed of 30.9 and 35.8 degrees.

Any guesses regarding the required corrective lens for the C-Biogon? I'm going to initially play with what I've got, and will consider moving to one of the Opto Sigma PCX lenses for the ZM25 (can't remember if it's 1500mm or 2500mm) depending on how the Proxar 1m works. But at around USD $90 a pop, I'd rather not have to buy several lenses to try on the C-Biogon. Good news is that I've busted out the spanner wrench for the first time and the C-Biogon shims are just as easy to get to as the 25/2.8 shims, so it should be pretty quick to dial in the infinity focus.



Jan 13, 2018 at 01:10 PM
KlausJH
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p.94 #16 · p.94 #16 · Front-End Filter Improves Corner Smearing


I have the ZM25 and tried a Proxar 1m first. I bought it used and it was not in a very good condition. But the results were fine. Then I got the PCX 2500 from OptoSigma and the results were perfect. The longer focal length required only one shim to be removed from the ZM25. I would assume, the C-Biogon requires a similar frontend filter as the ZM25.


Jan 13, 2018 at 06:15 PM
uscmatt99
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p.94 #17 · p.94 #17 · Front-End Filter Improves Corner Smearing


KlausJH wrote:
I have the ZM25 and tried a Proxar 1m first. I bought it used and it was not in a very good condition. But the results were fine. Then I got the PCX 2500 from OptoSigma and the results were perfect. The longer focal length required only one shim to be removed from the ZM25. I would assume, the C-Biogon requires a similar frontend filter as the ZM25.


It's interesting as lenses with similar chief ray angles end up being optimally mated with different PCX lenses. For example, the ZM 25/2.8 and 21/2.8 angles differ by only 0.1 degrees, but the 25/2.8 is best paired with a PCX 2500mm lens, while the 21/2.8 is best paired with a PCX 1500mm, at least per samuli's wiki, though the 21/2.8 hasn't been simulated.

I have experience with the 25/2.8 and 35/2.8 on the vII Kolari mod on the original A7. The 25/2.8 was corner to corner sharp only at f/8, while the 35/2.8 required f/11 for the corners. This is assuming that you focus critically in the center to mid frame. I'm therefore guessing that the 35/2.8 will require "stronger" correction. I'd love to get both down to f/4-5.6. The ZM25 in particular is ridiculously sharp and will cause aliasing across the frame even at f/4 when I shot it on crop cameras. I'd actually stop it down to f/8-11 just so diffraction would mitigate against all the color maze artifact. But that was on 12mp and 16mp DX sensors.

For now I've got the step-up rings and retaining rings, just waiting on the step down rings and Proxars. I have a feeling that by the end of this I'll have a small pile of bits and bobs. Thankfully the ZM lenses are very easy to take apart and reassemble for shim adjustment.



Jan 14, 2018 at 12:18 AM
Guenther54
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p.94 #18 · p.94 #18 · Front-End Filter Improves Corner Smearing


Can reading glasses reduce corner smearing in vintage RF wide angle lenses on Sony A7R?



Thanks to HaruhikoT and candreyo for their description how to remove corner smearing in rangefinder wide angle lenses like Contax G and Zeiss ZM types. There is now much experience with planconvex lenses with foval lengths between 6000 and 1500 mm. These lenses are not everywhere available and cost about 100 $ each.

For vintage lenses like Jupiter 12 they may be helpful. As very good discussed there the J12 like his father (ore mother) Carl Zeiss Jena Biogon 2,8/3,5 cm is in the center very sharp, but suffers in the corners from smearing.

Is there another solution especially for these cheap RF Lenses Jupiter 12 2,8/35 mm, which is available in the traditional old Contax/Kiev RF Mount and also m39 (LTM) Mount?

I started a simple test by using spectacle lenses for eye glasses. These are menisci ore convex-concav not planconvex lenses. The lenses are aivailable in the interesting range of

+0,25 diopt. = 4000 mm focal length
+0.50 diopt. = 2000 mm focal length
+0,75 diopt. = 1334 mm focal length
+1,00 diopt. = 1000 mm focal length

and are ophtamological used for longsightedness (=hyperopia, hypermetropia)

These lenses are cheaper than the known planconvex lenses, have diameters between 55 and 65 mm and are available super multi coated for few money more. Mostly made of plastic, there are still more scratch resistent mineralic glasses available.

I purchased three types between 0,25 an 0,75 diopt. and tested it on the Jupiter 12 and a Sony A7R.
The best image quality is with a combination of Jupiter 12 and 0,5 diopt. in reversed position. The concave surface of the lense points to the object, the convex surface to the camera.

The diameter of the J12 filter ring is 40,5 mm.

There is a vintage close up lens from Voigtlšnder Focar 0 f=2m 342/41 AR that fits perfectly on the filter ring. Unfortunatly we need a reversed position of the convex-concave lens (less concave than eye glasses). But with some expirience I could change the direction without destroying the filter holder.



There is now a little problem. Combining a lens with 35 mm and a close up lens with 2000 mm focal length the total focal length is about 34,45 mm (1000/35 = 28,57 diopt. + 0,50 diopt. = 29,07 diopt. =34,45 mm) . The filter lens combination needs a reduction of the flange back of about 0,55 mm for adjusting to infinity.

You can shim the lens by opening it and removing spacers. But I dislike this solution, because the integrity of the lens is destroyed and when using the lens like me furthermore with classical rangefinder cameras it doesn't work.

I decided for these handicraft work:
Sony E-Mount LTM adapters are cheap and in some types you can change the flange distance by removing about 0,6 mm (better a little more than less) from the planarity. But be awere to buy a LTM adapter with a prominent thread part like
this.



If you take an adapter with no difference between the Sony E-Mount part and the LTM thread you have to remove 0,6mm material in two positions. If the flange distance is to wide, you can adjust it with thin sheets of material you like (I used baking paper ore packing foil with alu core).



These test shots are jpegs with auto white balance and without correcting color shift and vignetting.




My next step is buying a 0,5 diopt. multicoated spectacle lens from mineralic glas (the test glas is a little cheaper organic glas) and let it fit by an optometrist in a 40,5 mm filter ring. If you buy a cheap one from chinese ebay seller be aware that you order a filter with a screw socket. My test +0,5 diopt. spectacle lens was fitted in a 46 mm ring.



Unfortunatly with a step up ring from 40,5 to 46 mm the distance placement stops at 2,5 m because of the moving the outer tube of the J12. The Voigtlšnder close up lens is in this case uncomplicated. But microcontrast is less (lacking multi coating?) and there is vignetting in the corners (prominent filter ring in combination with more angle of field because of a little less focal distance?)



Jan 18, 2018 at 08:55 PM
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