For initial testing purposes maybe it would be interesting to try ordinary close-up lenses from regular photo manufacturers. They come already with a standard threaded mount and are quite inexpensive, compared to those PCX lenses
The values usually available range from +1 to +5 diopters and we need something from 0.15 to 0.8 but there’s a Nikon 52mm. No. 0 close-up of 0.7 diopters ( 1.4mtr) and a Proxar for Hasseblad of 2.0mtr. Both could be useful for testing shorter wideangles, like the Biogons ZM 21, 25 and 28.
BTW I own a couple of close-up lenses ( +1 and +2) and they are meniscus. I don’t know if this is always the case.
Another source of P-C elements are cheap, old lenses: just tear them apart and scavenge! We do need some background research to identify the lenses of interest.
artur5 wrote:
For initial testing purposes maybe it would be interesting to try ordinary close-up lenses from regular photo manufacturers. They come already with a standard threaded mount and are quite inexpensive, compared to those PCX lenses
The values usually available range from +1 to +5 diopters and we need something from 0.15 to 0.8 but there’s a Nikon 52mm. No. 0 close-up of 0.7 diopters ( 1.4mtr) and a Proxar for Hasseblad of 2.0mtr. Both could be useful for testing shorter wideangles, like the Biogons ZM 21, 25 and 28.
BTW I own a couple of close-up lenses ( +1 and +2) and they are meniscus. I don’t know if this is always the case. ...Show more →
The values 1.4mtr and 2 mtr for close up lenses refer to the close focus range after adding them to a taking lens. They are not the focal lengths which are normally around 0.4mtr.
As Harihiko detailed, the ones needed for corrections here are over a meter in FL and they are special order items.
Sam_W wrote:
I wonder how the Contax Hologon G behaves with its ND filter when on an A7-series camera. Anyone have the two and an adapter to do some corner tests?
It is known (Hologon 16/8). Except for color shifts, it is a sharp lens. The corner smearing issue is of importance in lenses with fast apertures.
Old topogon or its clones such as W-Nikkor 2.5cm f/4 and the Orion-15 28/6 do not pose any corner smearing issues.
realVivek wrote:
The values 1.4mtr and 2 mtr for close up lenses refer to the close focus range after adding them to a taking lens. They are not the focal lengths which are normally around 0.4mtr.
As Harihiko detailed, the ones needed for corrections here are over a meter in FL and they are special order items.
At least for the Nikon No.0, this is not true. In the case it's clearly stated that the power of this close-up lens is 0.7 diopter (= 1.4m of focal length).
How the manufacturer would refer to the close focus range after adding the taking lens if they don't know beforehand which focal length we'll use ? It would be absurd and misleading.
artur5 wrote:
For initial testing purposes maybe it would be interesting to try ordinary close-up lenses from regular photo manufacturers. They come already with a standard threaded mount and are quite inexpensive, compared to those PCX lenses
The values usually available range from +1 to +5 diopters and we need something from 0.15 to 0.8 but there’s a Nikon 52mm. No. 0 close-up of 0.7 diopters ( 1.4mtr) and a Proxar for Hasseblad of 2.0mtr. Both could be useful for testing shorter wideangles, like the Biogons ZM 21, 25 and 28.
BTW I own a couple of close-up lenses ( +1 and +2) and they are meniscus. I don’t know if this is always the case. ...Show more →
For initial testing, I think they will be good.
Actually I own Proxar B50 f=2m. This is also meniscus lens.
I don't have good equipment to measure its curvature, but it looks having around 70-75mm curvature both side.
Previously I tested this Proxar with my G21/G28 and it also improves smearing, when putting it reversed in front of primary lens. However it was not as good as 1.5m PCX.
And I found another interesting thing.
Using my roughly estimated curvature/thickness, simulation tells the Proxar may also improve ZM1.4/35.
It doesn't work well at f1.4 but at f1.7 or higher, MTF looks very good.
[Update] The image here was removed to avoid misleading. I confirmed that Proxar is not good to improve ZM1.4/35's corner IQ. I also found my model had some flaws to handle meniscus lens and the solution is still under investigation.
You can find some cheap Proxar 2m on ebay, so if you (or someone here) have ZM1.4/35 and some disposable money, it would be interesting to try it .
However please don't blame me if you couldn't get good result .
Another thing that came to my mind. I'm doing some astrophotography when I can like many of us. Often we are confronted with chromatic aberration which can be corrected with ease. But other aberrations like coma and astigmatisme are a more concerning.
Astigmatisme is often present on wide angle lenses when used wide open and I've found this to be the case with my 35 and 45mm Contax G lenses.
Even very expensive lenses are confronted with the same problem (Nikon, Canon, Fuji,...).
So should it help to try to correct this astigmatisme with a correction glass ?
Or will I need to take these lenses to the ophthalmologist ??
Just letting everyone know I'm still waiting for my 1500mm PCX to arrive. I have also ordered a Zeiss Proxar 0.5m, 1.0m and 2.0m B50 lenses off eBay. I think this may be a more cost effective way of finding out what works, then buying various PCX lenses. Problem with buying optosigma PCX lenses for the experiment I want to do with my ZM collection is , if they don't work well, I can't return them, and they don't seem to go well on eBay.
I will be sure to try the B50 2.0 Proxar installed reverse and see what happens with my 35mm ZM Distagon at f1.4 thru f8.0.
I got the 24 Elmarit-M. To my surprise, it's much improved on the a7rII- big gains over the a7m and a7II. Still not as good as it is on the M9 in the corners at f/5.6 but, as I noted in another thread, once you correct for barrel distortion, you end up chopping most of the poor performance away anyway. Still, I think there are some gains to be made at lower apertures, so I'm still in on the experimentation. I also picked up a used ZM Distagon 35 to test simultaneously.
However, Opto-Sigma (which has a US office in California) is quoting a two-to-five week lead time depending on the focal length, so that would put my delivery in the two months when I won't have any time to play anyway, so I think I'll hold off ordering until mid-December, as I'll have plenty of time for it in January and February.
Just a qucik update, I received my set of Proxar lenses today.
I tried them on both the ZM 35mm Distagon and the ZM 28mm Biogon:
With the Distagon, the 2m Proxar mounted normaly ( not reversed) seemed to work best. The corners sharpened up very slightly to my eyes. Wide open at f1.4, its not really noticeable, but from f1.7 to f2.0, there begins a boost in sharpness. F2.8 appeared to be the sweet spot with very sharp corners.
Reversing the 2m Proxar did not yield good results. Still waiting for the 1500mm Planoconvex to arrive.
With the 28mm Biogon ZM, the 1m Proxar seemed to work best. With this lens, there was a substantial boost in sharpness in the corners, really quite amazing, very similiar to Haruhiko's results. Trying the 0.5m and the 2m were less effective, and sometimes worse then no Proxar filter being used.
If I have time this weekend, I can try to photograph some test scenes showing with the 2m Proxar on the 35mm Distagon and without. And the same for the 28mm Biogon and the 1m Proxar.
Now, for the kicker, while both Proxar lenses seem to help with each respective lens, you drastically loose the ability to focus to infinity. Even with the Techart Pro, I was barely able to focus several meters away at best with the Proxar lenses attached.
But they did prove that corrective lenses can help clean up the corners.
For those that are optical savory.. What are the differences between say a Zeiss 2m B57 Proxar lens, and say a 2000mm Planoconvex from Optosigma? If any?
BTW, the old Hasselblad/ Zeiss Proxar lenses are really good quality. They definately have multicoatings, and did not cause the Zeiss ZM,s to flare when attached.
What I did to get them mounted onto the ZM lenses, is I took the actual lens out of the Proxars mount, and placed it into a 49mm to 52mm step up ring. I then used a 52mm inner ring from a cheap 52mm UV filter and used that to screw down the Proxar lens into the step up ring. This directly mounted onto the Distagons front filter thread.
As for the Biogon, I used a 46 to 49mm step up ontop of the setup above.
candreyo wrote:
For those that are optical savory.. What are the differences between say a Zeiss 2m B57 Proxar lens, and say a 2000mm Planoconvex from Optosigma? If any?
Best Regards,
candreyo
It depends what form the proxar lenses are. If they are planoconvex, then they will be multicoated where an uncoated lens from Optosigma will not me. Otherwise, no difference other than the mechanics. If they are a best form lens, they are better corrected for spherical aberration than a planoconvex. At small apertures, there would be no difference in that case.
I cannot imagine they would be any other form.
No lens will provide a better correction than a meniscus lens for the field curvature and astigmatism caused by the coverglass. Those may be somewhat difficult to source.
Anybody here owning a Hawks Leica-M to Sony-E helical adapter ?.
If so, can you confirm that this model has user adjustable infinity ?. (meaning that the infinity hard stop can be modified by some margin back or forth from the standard registry distance )
This feature might be very useful when we add a PCX corrective element. Probably 1mm. backwards would be enough and, in many combinations, even 0.5mm. will do.
artur5 wrote:
Anybody here owning a Hawks Leica-M to Sony-E helical adapter ?.
If so, can you confirm that this model has user adjustable infinity ?. (meaning that the infinity hard stop can be modified by some margin back or forth from the standard registry distance )
This feature might be very useful when we add a PCX corrective element. Probably 1mm. backwards would be enough and, in many combinations, even 0.5mm. will do.
I have 3, starting from v1 to v2.5. None will do what you want.
artur5 wrote:
Anybody here owning a Hawks Leica-M to Sony-E helical adapter ?.
If so, can you confirm that this model has user adjustable infinity ?. (meaning that the infinity hard stop can be modified by some margin back or forth from the standard registry distance )
This feature might be very useful when we add a PCX corrective element. Probably 1mm. backwards would be enough and, in many combinations, even 0.5mm. will do.
I have the version 5 which lets you do it. Dont know however whether the margin is big enough
Thanks for the feedback guys. So, only the last version of the Hawks has adjustable infinity. I guess that to know for sure if the margin is enough or not will be a case per case affair. I haven't the optical knowledge required for calculating exactly that margin but probably up to 0.3-0.4mm. would cover most combinations of main lens and corrective element.
Hi all, I just registered here because of this highly interesting thread. Have three short questions to begin with ...
1. Is it really astigmatism that is to be corrected, or coma?
2. I understand that a simple lens with f=1m or even f=2m etc. reduces the chance to get to infinity as it basically works like a weak closeup lens, so what it does (apart from counter correction of the error that is introduced by the sensor glas) is that it basically shortens the lens' effective focal length.
Now I understand that even the Contax G lenses probably won't have sufficient "back focus" to work around this. And other lenses have a hard stop at infinity so are even more affected.
However, the samples posted by HaruhikoT indicate that it was not a problem to get a sharp picture of that bridge, which surely is so far away you can assume it to be in "infinity" for a 21/28mm lens. So the f=1.5m correction lens was so weak it still enables the Contax G lens to reach infinity?
But if you use a stock f=1m Proxar lens instead of that f=1.5m lens, the ability to focus is already reduced from "practically infinity" to just a few metres?
3. Could (in theory) a two-lens corrector be designed (instead of a simple lens) that would not change the infinity setting at all?
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