Zeiss super speeds mkIII issue.

[John Christoforou]

Greetings,

 

I have a set of 5 Zeiss super 16 lenses, 9.5mm 12mm 16mm 25mm 50mm. The lenses were serviced two years ago and used sparingly. Today we've checked all 5 lens and 3 of them, the 9.5mm 12mm and 16mm were quite out of measure. The widest one, was about a meter off of what the tape measure was showing, infinity was out too. Should I send the lenses for service again or just ask for a collimation?

Do you think that the above issue is something common or there is something wrong with the lenses?

 

 

Thank you!

John

[Dom Jaeger]

G'day John,

 

how did you check the lenses?

 

Since all the shorter focal lengths are out it seems more likely that the camera (if that's what you used to check them) is the problem. If the camera flange depth is out it will throw the focus scale out on all the lenses, but it's more pronounced on shorter focal lengths. It only needs to be a tiny error in camera flange depth to throw off the scale on lenses as wide as 9.5 or 12mm, by the time you get up to 25mm it may not be noticeable.

[John Christoforou]

Hi Dom,

 

The lenses were mounted on the Ikonoskop dII camera, unfortunately there is no film plane sign so we took a wild guess by looking the sensor and set a point for the measurement. I purchased the lenses first and a bit later I bought the camera, so the lenses were collimated with out Ikonoskops' flange depth. What also worries me is that infinity on all 3 lenses is out too.

 

Thanks for your reply!

John

[Gregg MacPherson]

Maybe Dom is still monitoring this thread. I am really curious how they measure FFD on a digital camera. Can't exactly roll your dial guage around on the sensor surface. Can't put a refective surface behind the gate and use an autocollimator. Any simple description of how it is done?

 

Dom, if the focus scales are out by 1m doesn't that mean a big error on the FFD?

 

Cheers,

Gregg.

[Dom Jaeger]

Hi Dom,

 

The lenses were mounted on the Ikonoskop dII camera, unfortunately there is no film plane sign so we took a wild guess by looking the sensor and set a point for the measurement. I purchased the lenses first and a bit later I bought the camera, so the lenses were collimated with out Ikonoskops' flange depth. What also worries me is that infinity on all 3 lenses is out too.

 

Thanks for your reply!

John

 

I'm sure you can estimate where the sensor plane is close enough to not be an issue.

 

Judging exact focus on lenses that wide can be tricky, ideally you'd want a nice big monitor to check the image on. The camera flange depth might be only a few hundredths of a mm out, easily fixed by removing or adding some mount shims. Maybe take it to a reputable rental house (ie one with a service department) to get checked, along with the lenses. They shouldn't charge much for a collimation check. It could be that the camera is slightly out of tolerance in one direction and the lenses slightly out in the other direction, adding up to a discrepancy that shows up on the wider lenses.

 

If the camera flange focal depth (or lens back-focus) is out of tolerance the entire lens scale is thrown out, including infinity. More of a problem if the FFD is too long and the lens no longer reaches infinity, rather than too short in which case the lens will pass through it.

[Dom Jaeger]

Maybe Dom is still monitoring this thread. I am really curious how they measure FFD on a digital camera. Can't exactly roll your dial guage around on the sensor surface. Can't put a refective surface behind the gate and use an autocollimator. Any simple description of how it is done?

 

Dom, if the focus scales are out by 1m doesn't that mean a big error on the FFD?

 

Cheers,

Gregg.

 

Hi Gregg,

 

there are a few tools out there to measure FFD on digital cameras, from the rather expensive:

http://www.pure4c.de/dynasite.cfm?dsmid=102935

 

to the fairly affordable:

http://www.abelcine.com/store/NULL-Lens-Target-Optical-Collimator-Kit/#tabs

 

I used a Denz FDC for a while, until it went out of tolerance itself and we needed the special checking tool for the checking tool for only a few thousand more Euros..

 

These days I just use a couple of test lenses that I know are spot on with a chart and a big monitor.

 

Describing that the focus scale is out by a meter is not much help - at the infinity end being out by one meter is a hair's turn of the scale, at close focus it can be half of the rotation. With linear focus mechanisms like the helical threads used in Zeiss Super Speeds (where the distance that the focus group or lens moves away from the image plane is directly proportional to the angular rotation of the scale ring) it makes more sense to describe the discrepancy in measurements of the scale rotation ie 3 lines out, where a line is the thickness of the index mark for example.

 

To give an idea though, on a 9.5mm Super Speed if the focus distance was 2 meters but the scale read 3 meters you'd have a back-focus or flange depth error of about 0.025mm or one thousandth of an inch. If the distance was 1 meter but the scale read 2 meters the error would be more than twice that, maybe 0.06mm. Roughly the diameter of a human hair.

[John Christoforou]

Thank you both for your replies, really appreciated!

 

What I'll try to do is get camera and lenses for a check up. One other thing that crossed my mind is that Ikonoskop uses

the IMS system. The IMS is an interchangeable lens mount system from PS technik that allows you to change mounts.

That means there are moving parts, you take the PL mount out and add a C or any other available mount.

Maybe this has a tiny tiny effect on the FFD every time I change a lens or mount.

[Dom Jaeger]

Yes any adapter system has the potential to be a little off. P+S Technik tends to make things very well and to very tight tolerances, but all it takes is a bit of grit between mating surfaces.

[Gregg MacPherson]

 

there are a few tools out there to measure FFD on digital cameras

Thanks for the ineteresting read and links.

For S16 frame/sensor, checking the FFD using just a calibrated lens and the camera eye piece or monitor, what focal length and distance do you use? What's ideal?

 

Cheers,

Gregg

[John Christoforou]

Thank you so much Dom!

[Freya Black]

Hi Dom,

 

The lenses were mounted on the Ikonoskop dII camera, unfortunately there is no film plane sign so we took a wild guess by looking the sensor and set a point for the measurement. I purchased the lenses first and a bit later I bought the camera, so the lenses were collimated with out Ikonoskops' flange depth. What also worries me is that infinity on all 3 lenses is out too.

 

Thanks for your reply!

John

 

Did you buy the Ikonoskop recently? I was under the impression they stopped production.

I'd love to hear they bounced back as I've seen some really nice footage from the camera lately.

 

Freya

[John Christoforou]

Hi Freya,

 

 

you can read my impressions about the Ikonoskop camera here:

 

http://christoforou.blogspot.gr

 

thanks!