rji2goleez wrote:
Wow, that's a subtle difference isn't it? I can feel the difference but the rocking side to side is so small that if you lay it on something like a this micro fiber cloth, there is no rocking on either side. However, once I laid it on the tissue paper on a hard surface the difference can be felt.
Thanks John.
Bob
Just place a pencil/pen on top one of the surfaces. The convex side will have more space on the edges. The plano side will be 100% flat.
Just ordered my SLB-50-5000PM today, I was able to order it from the Canadian distributor Optikon, great service from these guys! Turnaround time is fairly long according to my contact however, there is no Canadian stock and apparently none in Japan aswell so it's a 5-7 week wait period.
Keh had the ElPro 3 in stock so I ordered one of those, thanks Fred for the setup for the OEM hood.
navmannz wrote:
Wow - can you point me to them, Jim? if so, it means that performance is independent, as it certainly has the desired effect this way.
-John
edited - just found KaruhikoT's post on this, and you are right - I'll have to test more. The advantages of a group
second edit - just back from a quick test, and it appears that with the curved face towards the lens, there is a slightly weaker effect than with it facing the subject, as assessed by focus distance anyway.
GMPhotography wrote:
Mine faces out to subject. Now you guys got me all confused. Lol
I think that you're probably right, Guy - interestingly I went back to your post to check on shims for the ZM 35. When I removed the rear mount on mine I found two gold shims (c. 0.2 mm), and removing one doesn't quite get me to infinity, but removing both is way too much. Looks like I'll have to buy some shim material and get out the nail scissors...
navmannz wrote:
I think that you're probably right, Guy - interestingly I went back to your post to check on shims for the ZM 35. When I removed the rear mount on mine I found two gold shims (c. 0.2 mm), and removing one doesn't quite get me to infinity, but removing both is way too much. Looks like I'll have to buy some shim material and get out the nail scissors...
-John
I've just done two sets of four images infinity focused with the camera tripod-mounted and using apertures in the range F/1.4 through F/4 in one-stop increments - I had the curved face towards the lens in the first set, and towards the subject in the second. After importing them into Lightroom and using its compare facility zoomed into 1:1, I can possibly see slightly better resolution in the first set than the second. Based on that result, I'll be sticking with the curved face towards the lens. YMMV...
navmannz wrote:
I've just done two sets of four images infinity focused with the camera tripod-mounted and using apertures in the range F/1.4 through F/4 in one-stop increments - I had the curved face towards the lens in the first set, and towards the subject in the second. After importing them into Lightroom and using its compare facility zoomed into 1:1, I can possibly see slightly better resolution in the first set than the second. Based on that result, I'll be sticking with the curved face towards the lens. YMMV...
rji2goleez wrote:
Can you see a difference in infinity focusing?
Very, very slight, Bob - based on my experience, when the curved face is towards the subject, the shimming needs to be reduced slightly more than when it is faced towards the lens - but the difference is very minimal! That suggests to me that when the curved face is towards the subject, it is inducing a slightly stronger correction effect, increasing the focal length just a tiny bit more.
navmannz wrote:
Very, very slight, Bob - based on my experience, when the curved face is towards the subject, the shimming needs to be reduced slightly more than when it is faced towards the lens - but the difference is very minimal! That suggests to me that when the curved face is towards the subject, it is inducing a slightly stronger correction effect, increasing the focal length just a tiny bit more.
-John
I would love for HaruhikoT to weigh in on this subject. On my setup, I have the convex side facing forward. With a single bronze colored shim left in place, I can reach a hard stop infinity focus, but just barely.
robgo2 wrote:
I would love for HaruhikoT to weigh in on this subject.
Rob
In the case of the Contax 28G, based on @HaruhikoT's simulations, reversing the 1.5m front-lens changed its strength to about 1.3m.
For the 35/1.4 ZM, the 5m front lens seems to be a better correction when not reversed. (Meaning, convex side facing away from the camera)
Fred Miranda wrote:
In the case of the Contax 28G, based on @HaruhikoT@'s simulations, reversing the 1.5m front-lens changed its strength to about 1.3m.
For the 35/1.4 ZM, the 5m front lens seems to be a better correction when not reversed. (Meaning, convex side facing away from the camera)
Is that last suggestion of yours based on actual testing, Fred? My comparison did suggest the opposite, but I'm keen to establish a bit more evidence for whether there is one way that delivers better performance than the other.
navmannz wrote:
Is that last suggestion of yours based on actual testing, Fred? My comparison did suggest the opposite, but I'm keen to establish a bit more evidence for whether there is one way that delivers better performance than the other.
Reversing the front-lens would change these numbers and affect the simulation but honestly I didn't test it.
Did you get better results reversion the 5m front-lens?
Reversing the front-lens would change these numbers and affect the simulation but honestly I didn't test it.
Did you get better results reversion the 5m front-lens?
In a word yes. When I discovered that I had mounted it the 'wrong way' round, I inverted it and shot some more images, which seemed very little different. I then did a more careful test (here) which suggests a very slight edge to those shot with the curved surface facing to the lens. It would be interesting to see results from a simulation done with it in this mode.
navmannz wrote:
In a word yes. When I discovered that I had mounted it the 'wrong way' round, I inverted it and shot some more images, which seemed very little different. I then did a more careful test (here) which suggests a very slight edge to those shot with the curved surface facing to the lens. It would be interesting to see results from a simulation done with it in this mode.
-John
Thanks for the info John. Now I got curious and will test this out.
Fred
Very poor results from a test with a Hoya 46mm +1 diopter. Even after removing 3 shims from the rear of the lens, the focus would not reach to infinity.
Using the Optosigma 2000 lens however gives very good results. Removing 2 shims wasn't enough but with 3 shims out the focus reaches past infinity and gives a MFD of 7"! This is an unexpected bonus.
The only downside is no hard stop for infinity.
I used both a Techart and Hawk's adapter to check for infinity results on an A7Rii
Regarding that 35mm + PCX 5m, orientation of the corrective lens made no visible difference in my simulated MTFs. No difference in infinity focus position, too.
Something that my simulation doesn't take into account may cause John's experimental results but I'm not sure.
Curious about how does the difference looks like. Comparison images would be appreciated.
Very poor results from a test with a Hoya 46mm +1 diopter. Even after removing 3 shims from the rear of the lens, the focus would not reach to infinity.
Using the Optosigma 2000 lens however gives very good results. Removing 2 shims wasn't enough but with 3 shims out the focus reaches past infinity and gives a MFD of 7"! This is an unexpected bonus.
The only downside is no hard stop for infinity.
I used both a Techart and Hawk's adapter to check for infinity results on an A7Rii
Do you mean poor results *and* it won't focus to infinity, or poor results *because* it won't focus to infinity?
It's perfectly possible for the best results to come with a filter which won't focus to infinity on your adapters, depending on a combination of facts about the filter, the adapters and the tolerances of the lens.
Ideally you would test for the best results focussed as far away as you can focus, and use the filter that gives that best result, and then mess with adapters and or shims to get infinity focus.
