8mm Forum: Help with my Scope Lens Focusing

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Posted by Colin Preston (Member # 68) on September 03, 2006, 06:53 PM:

Hi Chaps
Wondered if you could help
Just completed my cinema in the loft, and ran Grease through for the kids. [Big Grin]

My problem is this, (I have had it for a whiel but now its really getting on my wick), The center of the picture is fine in terms of focus. Pin sharp in fact, but as it moves out towards the left and right, it goes out of focus [Mad]

. Not too bad, but bad enough for it to be noticable
I know its not the film beacuse if I take away the scope lens, the picture is perfect.

In my GS I have a 1.0 lens, and my scope lens is a Kowa.
The scope lens is mounted on a swing bracket and I would say there is approx 1.5cm between the front optic on my GS lens and the rear optic on my Scope lens.

I might be being a little thick, but I am at a loss as to what to try to resolve this. [Confused]

Could it be that the scope lens needs to be closer to the GS lens?

Any help would be greatly appreciated
Col

Posted by Kevin Faulkner (Member # 6) on September 04, 2006, 07:06 AM:

Hi Colin, The scope lens needs to be as close (to the Elmo's prime lens) as possible. I take it that you have the Kowa 8Z. This has fairly large rear and front elements 43 & 52mm which is what is required for use with super 8 zoom lenses.

Once the prime lens is in focus put the scope lens in position and either focus it or set the focus ring to the correct distance from lens to screen.

If you are using a scope lens designed for 16mm you will find that the elements are smaller and will give rise to light falloff at the corners and possible focus probs at the extreme edges.

The Kowa 8Z was actually a rebadged version of the Kowa 16H or D. Not sure which it was now, but you can tell from the larger elements. The 8Z was also rebadged by Elmo as the Elmoscope-11 and no doubt under other names.

All scope lenses designed for super 8 have quite large elements for the reasons above.

Hope this all helps, Kev.

Posted by John Whittle (Member # 22) on September 04, 2006, 09:01 AM:

The best way to focus a scope lens is to use a grid chart film which can be spliced into a loop. Focus the prime lens for sharpness and then put the scope lens in place.

Slowly focus the scope lens, you'll notice that it really only changes the image in one direction and when you hit the sweet spot you'll know it. These lenses are often off from the focus marks on the lens (in fact it is very easy to move that ring by loosening a few set screws).

Kevin is right about the larger element lens for Super8. That's due to the shorter focal length projection prime lenses to get a larger picture at a shorter distance. The other problem with the short prime lens is the loss of depth of field which is shallow and the fast the lens, the more critical the focus. The Kowa 8Z is the same as the 16mm Kowa 16H. The Sankor 16D has large elements but is a longer lens and might not be as good as the Kowa in Super8 use.

The other problem common to scope lenses is if they are out of alignment. If the front and back elements are not in perfect vertical alignment, the picture will show a loss of contrast (first) and then get soft.

A good lens will have incrediable sharpness and contrast with a good print and a good prime lens.

John

Posted by Joerg Niggemann (Member # 611) on September 04, 2006, 10:59 AM:

Hi Colin,

I made my first experience with CS during the last weeks and had a similar problem. I used the GS with the standard 1,1/15,5-25 and a "Rectimascope" CS lens from Wittner. My first thought was that the Rectimascope wasn't adjusted correctly. Then I found that picture edges were slightly out of focus even without the CS lens mounted, but this was only visible with a grid chart test film.

Next I started a test with all projectors and lenses I have, using the test film. The result was that all my Elmo lenses (2x 1,1/15,5-25, 2x 1,3/15-25) are critical in terms of "edge focusing" when used at a focal length of about 20-25mmm. Unfortunately, this is exactly the range I have to use with CS.

My Bauer T610 with Xenovaron 1,1/11-30 was a good reference with a very clear and crisp projection up to the picture edges. I also learned that I shouldn't run a focus test film on my Chinon [Eek!]

.

Finally, the solution came on ebay: I got an Elmo lens 1,2/25-50 which does a perfect job with the Rectimascope: all focusing problems are gone.

I think that John is right, a grid chart test film is highly recommended to check adjustment of projector and CS lenses. Any slight focusing problem which isn't noticeable during normal projection could get magnified and visible with CS.

Joerg

Posted by Michael De Angelis (Member # 91) on September 04, 2006, 01:45 PM:

John,

Are the Grid Chart films
commercially
available through a
photographic supply
house here in the USA?

Thank you,
Michael

Posted by Kevin Faulkner (Member # 6) on September 04, 2006, 05:14 PM:

I would think you could use the SMPTE super 8 test film. Dont know if you can get it in the USA but you can certainly buy some from FFR in Germany as I got a 5m length just last month form them.

http://www.ffr-film.de/Katalog/index.htm

Kev.

[ September 08, 2006, 01:04 AM: Message edited by: Kevin Faulkner ]

Posted by Kevin Faulkner (Member # 6) on September 04, 2006, 05:14 PM:

Meant to say that you should look under this heading on their web site: "Vor & Nachspann"

http://www.ffr-film.de/Katalog/index.htm

Kev.

Posted by Dave Johnson (Member # 628) on September 05, 2006, 01:48 AM:

Hi,all
I have a similar problem with a scope lens [Isco 2000] the lens used to be ok but I have tried different focal distances but to no avail, the lens appears to be fixed focus as there is no focus ring? there is a minute tec srew on the barrel that is all, the film is sharp without the lens, projecting through a GS

Posted by Eberhard Nuffer (Member # 410) on September 05, 2006, 01:31 PM:

Joerg,

what is the problem with your Chinon? Are the test results that bad?

Eberhard

Posted by Joerg Niggemann (Member # 611) on September 05, 2006, 04:51 PM:

Eberhard, my Chinon is a SS1200 with 1,3/15-30 lens. I love the machine for its simple but reliable construction. The projection is not "that bad" and there's no problem with focusing up to the edges. In comparison to the Bauer and Elmo lenses, the picture looks slightly "fogged", although the lens is clear. Again I think you won't notice without test film (I never did). I have only one Chinon lens, maybe others perform better...

Joerg

Posted by John Whittle (Member # 22) on September 07, 2006, 02:47 PM:

quote:
Are the Grid Chart films commercially available through a photographic supply house here in the USA?

I haven't seen them, you might see if Chambliss or SMPTE have them. The SMPTE film will be very expensive. I have several 16mm loops that I had made at various labs and optical houses when I worked in post production. Labs used to run alignment registration tests of all printers every morning and I had a lab superintendent save some for me. Same with the optical houses which were camera shot pin registered prints.

Test films like these are necessary when adjusting gates, lens squareness and then focus as well. Any error will simply be magnified in scope.

John

Posted by Alan Rik (Member # 73) on September 07, 2006, 03:56 PM:

I believe you can get the SMPTE films from Wittner and they now accept credit card. Well.. thats what I heard. [Smile]

Posted by Kevin Faulkner (Member # 6) on September 08, 2006, 01:06 AM:

As I said in an Earlier thread, you can buy the SMPTE super 8 test film from FFR-Film in Germany and they can take payment via PayPal.

Kev.

Posted by Joerg Niggemann (Member # 611) on September 08, 2006, 02:19 AM:

There's a difference between the Wittner and FFR SMPTE films:

Wittner sells the "camera original" from SMPTE (5 meter --> 60 EUR), FFR a print taken from the original (5 meter --> 14,95 EUR). If you don't need a length of 5 meters, you can get 2 meters of Wittner's original for 24,00 EUR.

My own test film is a DEFA print (former east german film company) which shows a different test pattern. For my personal use, it's ok to check the CS setup.

Kevin, how is the quality of the FFR print?

Joerg

Posted by Kevin Faulkner (Member # 6) on September 08, 2006, 03:58 AM:

Joerg,

I had some old original SMPTE which I ran first then checked the FFR version. This matched the original extremely well indeed. Its on polyester colour stock and is pink looking.

I decided that it doesnt matter what it looks like as long as it does the job. It would certainly be just fine for checking checking lens focus etc and I have used it for gate and claw alignment on the Elmo with no problems.

Kev.

Posted by John Clancy (Member # 49) on September 09, 2006, 03:27 AM:

Dave, is that Isco lens the one that comes in the box with the scantily clad girl on the beach? If so, I have a pair of them and they are fixed focus. One of my lenses has fogged down the far left hand side and therefore practically useless. The other is still perfect but I always found it difficult to get all over focus with it from 8mm but it appears fine with 35mm. Get a Kowa 8Z and you'll most likely solve your problem.

Posted by Dave Johnson (Member # 628) on September 09, 2006, 08:33 PM:

Hi John
No scantily clad women came with my lens, let alone a pair!!
Yes the lens is fixed focus, what I don't understand is that it used to be ok, it has been in storage for some time, I wondered if something inside could have moved? could the lens be serviced
before I trash it? If so where? any info would help

Posted by Colin Preston (Member # 68) on September 12, 2006, 04:57 PM:

Hi
Thansk for the replies on this, Sorry I have not been back sooner. The lens I have just says Kowa Anamorphic, nothing else. The rear of the lens looks about the same size as the front on the Elmo lens

I guess I need a better scope lens with a larger rear optic, or would I get away with getting an Elmo 1.3 lens? Does that have a smaller front optic?
Thanks again guys
Col

Posted by Kevin Faulkner (Member # 6) on September 12, 2006, 05:39 PM:

Colin, It sounds to me like you have one of the smaller Kowa 16mm lenses. Changing to the Elmo 1.3 will be the answer to the problem. I think it's a change of scope lens which will solve your problem.

Kev.

Posted by Colin Preston (Member # 68) on September 12, 2006, 05:59 PM:

Thanks Kev
Understood
Don't suppose anyone out here has an 8z they dont have use for?

Col

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