To comment further on the best way to know which side of the lens is plano and which is convex. (to make sure we don't install them incorrectly when building the filter system)
I previously mentioned placing a flat object on the lens surface (like a pencil) and watch the edges of the lens. If there is a tiny gap, that's the convex side. (The plano side should be completely flat)
I had asked this question to OptoSigma a few days ago and got an answer today:
"Comments from my engineers
There is so little power on the lenses that if you install it backwards it will not matter.
It’s very difficult to tell which side is which."
The 5000mm lens is even more difficult to know which side is which than the 1500mm lens.
I don't know about the 5m. Optosigma lens but with the 1m. and 1,4m filters that I tried, reversing the lens was like night and day, for what concerns corner sharpness.
"Another way to do it is to shine a laser pointer at a glancing angle on both surfaces. If the reflected beam is larger (not by much) that will be the convex surface"
artur5 wrote:
I don't know about the 5m. Optosigma lens but with the 1m. and 1,4m filters that I tried, reversing the lens was like night and day, for what concerns corner sharpness.
Fred Miranda wrote:
...
"Comments from my engineers
There is so little power on the lenses that if you install it backwards it will not matter.
It’s very difficult to tell which side is which."
...
Ah, what?
I don't understand a lot about the physics of optics and lenses, but if when you install it backwards, it doesn't matter... that to me implies a flat piece of glass (planoplano?) that wouldn't help you one bit no matter how you installed it.
I tried with a laser pointer from an old airgun and for sure the reflected beams of the two sides of the filter are different but not in the way they told you. Although my lenses are meniscus, not planoconvex, so they have a convex and a concave side (instead of flat) but the reflected beam from the convex side are several short lines and from the concave a single longer line. Maybe I'm not doing it right. The shapes of the reflected beams change a lot with a minimal variation of the angle of incidence of the laser on the filter.
Anyway, with meniscus filters is very easy to tell apart the convex and the concave side.
On a side note, I've just lost an auction on eBay for a ZM25. It was a half hearted bet from my part, as I'm not really convinced until reading Guy's repport on the performance of this lens with the 1m filter.
Nevertheless, the final price was lower than I expected for a copy apparently in great shape : 463 euro i.e. less than $500.
artur5 wrote:
I tried with a laser pointer from an old airgun and for sure the reflected beams of the two sides of the filter are different but not in the way they told you. Although my lenses are meniscus, not planoconvex, so they have a convex and a concave side (instead of flat) but the reflected beam from the convex side are several short lines and from the concave a single longer line. Maybe I'm not doing it right. The shapes of the reflected beams change a lot with a minimal variation of the angle of incidence of the laser on the filter.
Anyway, with meniscus filters is very easy to tell apart the convex and the concave side.
On a side note, I've just lost an auction on eBay for a ZM25. It was a half hearted bet from my part, as I'm not really convinced until reading Guy's repport on the performance of this lens with the 1m filter.
Nevertheless, the final price was lower than I expected for a copy in apparently great shape : 463 euro i.e. less than $500. ...Show more →
Just use my "pencil test" to determine the convex side and it's gonna be ok. It works...
Thanks for the tip Fred, but I'm my case it's quite obvious which side is which just at a glance. Meniscus filters have a very apparent curvature, both the convex and the concave side. My laser test was just pure curiosity.
GMPhotography wrote:
Thanks Fred. It's Adorama that has not shipped my used lens yet. They shipped my strobe and Hawks adapter maybe because they are new.
If you'd like to email me: [email protected] w/ your order # I will be delighted to check the status
Oh thanks Helen but they did ship last night. Should be here tomorrow. I think new comes from the warehouse and used from the store. So my guess they send it to warehouse to ship from. Maybe delayed slightly plus the holiday as well. No big deal
GMPhotography wrote:
Oh thanks Helen but they did ship last night. Should be here tomorrow. I think new comes from the warehouse and used from the store. So my guess they send it to warehouse to ship from. Maybe delayed slightly plus the holiday as well. No big deal
Hi, all these talks on checking the convex and concave sides make me wonder if I have fixed the adapter filter correctly. I have the lens from 1M Ploxia. The convex side need to be facing outward right? Just want to double check this.
I have not tested the filter on my ZM 25mm as I have not removed the shims yet. Planning of doing it this weekend.
AFAIK there's no strict rule concerning the correct instalation of the filter. It depends on the design of the main lens and also on the specific characteristics of the filter (radii of curvature, focal length..). Just in case, test your combo both ways, i.e. with the convex side facing outwards and inwards, to find out which one is better.
HaruhikoT wrote:
I tried techart AF and pixco MF adapter with the G28 + PCX1.5m reversed, both can reach infinity without modification.
I don't have the Fotodiox adapter but I expect a 90% chance of reaching infinity.
Other 10% is maybe Fotodiox's is thicker than others, but even in that case you can adjust infinity by removing shim inside the G28.
See this post: https://www.fredmiranda.com/forum/topic/1159122/0
I got the Contax 28/2.8 G and Fotodiox adapter today. Unfortunately I can't reach infinity with this adapter when using the 1.5m front-lens.
There are not many adapter options. I think the Pixco brand is not longer available.
Well I screwed up. I got a 49-55 step up instead of a 46. My 25ZM I got as a demo from Adorama is about as new as you can get. Real happy with that. I have Fred's Proxar 1m , have a Fotosy adapter as well but waiting on a few things . Hawk adapter, spanner wrench and now 46-55. Still need to buy some hoods but no hurry.
It works...