Strange question but do you think the strength of a lens filter can decrease or increase being closer or further away from the front element. This may explain this
What made you think about trying the PCX 5m on your ZM 25!!
Now you started a whole issue for us because it performed noticeably better than the meniscus +1 lenses....and you were handholding the lens!
The closest you can get to the PCX 5m is the Proxar 2m. Based on your tests, it should perform better than the Proxar 1m.
Otherwise, the PCX 5m will be the choice for the ZM 25 as well. (It looked way better on your infinity comparison at all apertures)
Perhaps the ZM 25 has an exit pupil distance that makes up for the difference in focal length and require the same PCX as the ZM 35....Perhaps @HaruhikoT can comment on this.
The take away was that the ZM 25/2.8 was already great and now got superb.
Fred
Fred Miranda wrote:
What made you think about trying the PCX 5m on your ZM 25!!
Now you started a whole issue for us because it performed noticeably better than the meniscus +1 lenses....and you were handholding the lens!
The closest you can get to the PCX 5m is the Proxar 2m. Based on your tests, it should perform better than the Proxar 1m.
Otherwise, the PCX 5m will be the choice for the ZM 25 as well. (It looked way better on your infinity comparison at all apertures)
Perhaps the ZM 25 has an exit pupil distance that makes up for the difference in focal length and require the same PCX as the ZM 35....Perhaps @HaruhikoT@ can comment on this.
The take away was that the ZM 25/2.8 was already great and now got superb.
Fred
I wonder if the issue is that meniscus filters are very touch about alignment, less so that PC lenses.
I wonder if a different focal length PC filter would be even better? After all a +1 (1M) was calculated as the right strength for the 25; maybe a PC with a shorter focal length than 5m is worth trying....
DavidBM wrote:
I wonder if the issue is that meniscus filters are very touch about alignment, less so that PC lenses.
I wonder if a different focal length PC filter would be even better? After all a +1 (1M) was calculated as the right strength for the 25; maybe a PC with a shorter focal length than 5m is worth trying....
One member reported that the 1.5m PCX was best for the ZM 25 and ZM 28. I had this PCX lens for a while and tried it with the ZM 28. (results were posted on this thread)
It worked great with it but at the end of the day I didn't think the ZM 28 was such a great lens to begin with, especially when comparing it to the ZF 28/2....so I sold both ZM 28 and 1.5 PCX lens.
If you check Guy's infinity tests, the PCX 5m is noticeably better than the meniscus choices (Proxar, B+W, Hoya,etc..)
on the ZM 25.
It would be interesting to know which PCX is optimal for this lens but we already know that the PCX 5m is better than the close-up +1 meniscus choices.
My first initial thoughts are a ZM 35 has more field curvature than the ZM 25 but than you got exit pupil stuff involved so as a non engineer I'm getting lost on this stuff in a way. Logical thinking is I need less correction on the ZM 25 than I do on the ZM 35. Even without the lens filter this 25 is damn good out of the gate.
Well I got the PCX from the 35 mounted in the proper filter setup so I don't have to hold it. I'll run the B+W against it again the morning. I want to be sure holding it in front had no effect.
Fred Miranda wrote:
One member reported that the 1.5m PCX was best for the ZM 25 and ZM 28. I had this PCX lens for a while and tried it with the ZM 28. (results were posted on this thread)
It worked great with it but at the end of the day I didn't think the ZM 28 was such a great lens to begin with, especially when comparing it to the ZF 28/2....so I sold both ZM 28 and 1.5 PCX lens.
If you check Guy's infinity tests, the PCX 5m is noticeably better than the meniscus choices (Proxar, B+W, Hoya,etc..)
on the ZM 25.
It would be interesting to know which PCX is optimal for this lens but we already know that the PCX 5m is better than the close-up +1 meniscus choices....Show more →
That was the point I was trying to make; we know the 5m PCX (thanks Guy) is better than the 1m meniscus.
But don't know whether that is because of the focal length, or PCX vs meniscus.
So it seems like it's worth trying other PCX focal lengths...especially as 5m seems a bit long according to the simulation.
DavidBM wrote:
That was the point I was trying to make; we know the 5m PCX (thanks Guy) is better than the 1m meniscus.
But don't know whether that is because of the focal length, or PCX vs meniscus.
So it seems like it's worth trying other PCX focal lengths...especially as 5m seems a bit long according to the simulation.
The only other member who tried this was @candreyo
Ah, my mistake! I thought I remembered Haruhiko having shown us a simulation that said 1m was the right focal length. All bets are off then. And yes, puzzling...
Haha please don't call me so many times. I haven't tried simulations yet particularly for ZM25. I will try it later and will post something to answer your questions.
I'm kidding whenever you get a chance that be great. I'm going crazy over here. Lol
I'm trying to think like a engineer that's not a good thing you know. HaruhikoT wrote:
Haha please don't call me so many times. I haven't tried simulations yet particularly for ZM25. I will try it later and will post something to answer your questions.
sebboh wrote:
good eye, there are 3 explanations i can think of:
1) decentered filter - pretty sure it was very close to well centered and there doesn't seem to be any asymmetry across the frame.
2) it was raining for this series but not the previous pcx comparison so everything is a little less sharp in the new series (especially at greater distance).
3) i didn't quite reach infinity with the pcx filter on this test - i tuned my g28 to hit infinity right at the stop with the pcx filter on my a7, but i used nehemiah's a7 for this test since mine is now converted. it's possible that flange to sensor distance between our 2 a7s is slightly different which threw my focus off (i just used the stop to try and make focus as consistent as possible between tests, but perhaps that was the wrong decision). i will check into this when i get a chance. ...Show more →
Thank you. My G28+PCX1.5m made great sharpness across frame on my A7RII especially when stopping down F4-F8, so I think if weather condition and infinity focus were ideal, that midzone difference between UT and PCX would be not so much. Anyway I completely agree the UT solution is impressive.
1) For ZM25 I expect PCX 2.5m (SLB-50-2500PM) is optimal.
Interestingly, unlike the case with ZM35 and G21/28, ZM25 accepts very wide range of PCXs. Not only 2.5m but also 1.5m and 5m shows good MTF in my simulation. 5m seems to be a bit lack of correction, though.
Difference between 1.5 and 2.5 seems be small so I prefer 2.5m that should be easier to achieve infinity focusing.
ZM25 has 37.3deg chief (exit) ray angle that is smaller than G28 having 38.9deg, that's why ZM25's optimal filter is weaker than G28 despite 25mm is shorter than 28mm.
2) As I wrote in the previous post, correction effects of the meniscus lenses such as Proxar and Hoya+1 are more complicated than that of PCX.
I can't tell exact difference of attributes between those meniscus and PCX in simple words.
But a sure thing is, not always but in some cases, meniscus gives weaker correcting effect to astigmatism and field curvature than PCX having the same diopter.
This may be the reason why @candreyo's Proxar 1m works on ZM25 and Proxar 0.5m works on ZM18, while PCX 1m and 0.5m should be too strong (over-correction) for those.
Also this should be why many close-up lenses are meniscus, I think.
For close-up usage, they need filters which give sufficient diopter but doesn't affect AST and FC. So meniscus is optimal.
In contrast we A7x + RF WA owners need filters give adequate correction to AST and FC but having less diopter which affects its FL and infinity focus. So PCX is preferable for this purpose in many cases.
I haven't tried simulations yet particularly for ZM25. I will try it later and will post something to answer your questions.