Lenilenapi
Carbonite Member
I had a rude awakening this week that could be of interest to everyone who is using a 35mmm adapter. If other people's experience is better let me know, as maybe I've just had bad luck and am off base with this criticism.
On a hunch I took my 3 adapters in to a camera repair department that had a collimator. If you don't know what a collimator is, it's an optical instrument that sends a pattern of cross hatched lines into a lens system so that the pattern is perceived by the imaging system as if it is coming from infinity.
Before many of you were born I used to work in a rental house checking the back focus of lenses on 35mm and 16mm packages before they went out using the collimator. It is standard procedure in a cine rental house, and I know some of you with film backgrounds *are familiar with this.
It is very easy to tell whether a lens is backfocusing correctly with a collimator by checking whether it comes in to focus at or near the infinity mark and especially by whether a zoom lens tracks focus from telephoto to *wide angle correctly. By the way I'm talking about the back focus of the 35mm lens on the adapter GG screen, not the backfocus of the video camera's lens on to the *35mm adapter from the other side. That's a different problem and easy to adjust.
It's always been confusing to know whether my adapters were backfocused correctly because the rules for still lenses are unclear. Sometimes *a still lens is supposed to hit infinity at the end of the barrell movement and sometimes it *is supposed to go past it. Some still zoom lenses are supposed to track perfectly, but it isn't considered as important for stills as it is in cine and supposedly many still lenses aren't expected to track.
I already knew that virtually every adapter I have owned - Redrock, Brevis, SGPro and *Letus have all come to me with the backfocus misadjusted. That was obvious just trying to get infinity close on each one. (BTW my SG Pro was second hand so it may not have been Wayne's fault.) *The others all came from the shop that way and in some cases I have returned them and they still came back misadjusted.
However I thought by now I had *set my Brevis and my SGPro correctly and I had just received a new Letus from Hien that he assured me was checked carefully. (Actually from my own tests I was doubtful about the new Letus but it seemed close anyway.) The annoying thing was my lovely 80-200 f2.8 Nikkor didn't track on any of them and I didn't know whether the fault lay in the lens design or the adapters.
So last week I went into Adolph Gasser's in San Francisco where I checked 10 lenses on 3 adapters and compared them to 2 Nikon bodies. (The collimator was a beautiful old optical instrument built by hand by Adolph himself in 1950. Adolph had been my boss years ago and was one hell of an inventor and designer. His son John insisted on accompanying me because he has sentimental attachment to the instrument. John got into it and kept bringing me different lenses and bodies to cross check our results.)
Well it turns out all three adapters were still misadjusted! Not as badly I'm sure as when I got them, but they were still *all off. *I was able to correct the Brevis and the SGPro with screw adjustments that are pretty simple to do, and low and behold - with proper adjustment of the mounts *- My Nikon 80-200 and my Tokina 28- 70 both tracked perfectly. *I later tested the adapters in real world situations and the collimation was accurate , the lenses performed better and tracked.
What is the problem here? I have been concerned for a long time that many if not all if our friendly manufacturers do not use a collimator *in their shops. Perhaps they never worked in a rental house.
I don't know what happens in every shop, but at least in a few I surmise from conversations that they have trusted measuring the physical distance of the mount with a depth gauge and figured that was sufficient. They may have been checking inside the shop to see whether the lenses seemed to focus at the distance markings on the lenses they were using as another test. I don't know whether the problem is that tolerances are simply too fine to easily measure or perhaps that the cheap lens mounts vary in their own depth.
Whatever methods they were using, they have often been insufficient. When I received my new upgraded Nikon mount from Letus I was astonished to find that it was not the same depth as my previous mount and hit focus at a different distances. At this rate I'm afraid to trust the reliability of interchangeable lens mounts.
A collimator is cheap! Less than $2000. *A lot of 35mm camera assistants carry one in the field . These manufacturers should be checking every unit before it goes out with a lens they know. Its fast, simple and accurate! *I sent this to Cinevate, SGPro, Letus and Redrock before posting. *Dennis at Cinevate is already investigating getting one. Wayne at SGPro just emailed me as well asking where to find one. The only manufacturer I know of is "Richter " and you can find them at <http://www.chamblesscineequip.com/catalog/richter_kollimator.htm>.
Meanwhile to you guys in the field - *See if you can find someone with an optical bench who will check your backfocus. On the phone they may tell you it won't work with your rig because they've never seen anything like it, but i can assure you it works very well.
(BTW - I just spent about 1.5 hours fumbling with my Letus and I think its finally right ( based on my known zoom lens) and I'll double check on the collimator again next week. I wish there was a better method of fixing back-focusing on the Letus. I got my directions from another user and it was a very wanky method, but maybe I just am ill informed about this one.)
Lenny Levy
On a hunch I took my 3 adapters in to a camera repair department that had a collimator. If you don't know what a collimator is, it's an optical instrument that sends a pattern of cross hatched lines into a lens system so that the pattern is perceived by the imaging system as if it is coming from infinity.
Before many of you were born I used to work in a rental house checking the back focus of lenses on 35mm and 16mm packages before they went out using the collimator. It is standard procedure in a cine rental house, and I know some of you with film backgrounds *are familiar with this.
It is very easy to tell whether a lens is backfocusing correctly with a collimator by checking whether it comes in to focus at or near the infinity mark and especially by whether a zoom lens tracks focus from telephoto to *wide angle correctly. By the way I'm talking about the back focus of the 35mm lens on the adapter GG screen, not the backfocus of the video camera's lens on to the *35mm adapter from the other side. That's a different problem and easy to adjust.
It's always been confusing to know whether my adapters were backfocused correctly because the rules for still lenses are unclear. Sometimes *a still lens is supposed to hit infinity at the end of the barrell movement and sometimes it *is supposed to go past it. Some still zoom lenses are supposed to track perfectly, but it isn't considered as important for stills as it is in cine and supposedly many still lenses aren't expected to track.
I already knew that virtually every adapter I have owned - Redrock, Brevis, SGPro and *Letus have all come to me with the backfocus misadjusted. That was obvious just trying to get infinity close on each one. (BTW my SG Pro was second hand so it may not have been Wayne's fault.) *The others all came from the shop that way and in some cases I have returned them and they still came back misadjusted.
However I thought by now I had *set my Brevis and my SGPro correctly and I had just received a new Letus from Hien that he assured me was checked carefully. (Actually from my own tests I was doubtful about the new Letus but it seemed close anyway.) The annoying thing was my lovely 80-200 f2.8 Nikkor didn't track on any of them and I didn't know whether the fault lay in the lens design or the adapters.
So last week I went into Adolph Gasser's in San Francisco where I checked 10 lenses on 3 adapters and compared them to 2 Nikon bodies. (The collimator was a beautiful old optical instrument built by hand by Adolph himself in 1950. Adolph had been my boss years ago and was one hell of an inventor and designer. His son John insisted on accompanying me because he has sentimental attachment to the instrument. John got into it and kept bringing me different lenses and bodies to cross check our results.)
Well it turns out all three adapters were still misadjusted! Not as badly I'm sure as when I got them, but they were still *all off. *I was able to correct the Brevis and the SGPro with screw adjustments that are pretty simple to do, and low and behold - with proper adjustment of the mounts *- My Nikon 80-200 and my Tokina 28- 70 both tracked perfectly. *I later tested the adapters in real world situations and the collimation was accurate , the lenses performed better and tracked.
What is the problem here? I have been concerned for a long time that many if not all if our friendly manufacturers do not use a collimator *in their shops. Perhaps they never worked in a rental house.
I don't know what happens in every shop, but at least in a few I surmise from conversations that they have trusted measuring the physical distance of the mount with a depth gauge and figured that was sufficient. They may have been checking inside the shop to see whether the lenses seemed to focus at the distance markings on the lenses they were using as another test. I don't know whether the problem is that tolerances are simply too fine to easily measure or perhaps that the cheap lens mounts vary in their own depth.
Whatever methods they were using, they have often been insufficient. When I received my new upgraded Nikon mount from Letus I was astonished to find that it was not the same depth as my previous mount and hit focus at a different distances. At this rate I'm afraid to trust the reliability of interchangeable lens mounts.
A collimator is cheap! Less than $2000. *A lot of 35mm camera assistants carry one in the field . These manufacturers should be checking every unit before it goes out with a lens they know. Its fast, simple and accurate! *I sent this to Cinevate, SGPro, Letus and Redrock before posting. *Dennis at Cinevate is already investigating getting one. Wayne at SGPro just emailed me as well asking where to find one. The only manufacturer I know of is "Richter " and you can find them at <http://www.chamblesscineequip.com/catalog/richter_kollimator.htm>.
Meanwhile to you guys in the field - *See if you can find someone with an optical bench who will check your backfocus. On the phone they may tell you it won't work with your rig because they've never seen anything like it, but i can assure you it works very well.
(BTW - I just spent about 1.5 hours fumbling with my Letus and I think its finally right ( based on my known zoom lens) and I'll double check on the collimator again next week. I wish there was a better method of fixing back-focusing on the Letus. I got my directions from another user and it was a very wanky method, but maybe I just am ill informed about this one.)
Lenny Levy
