Help with telecine lens.

Forum covering all aspects of small gauge cinematography! This is the main discussion forum.

Moderator: Andreas Wideroe

Boffee
Posts: 3
Joined: Thu Feb 16, 2012 7:18 pm
Real name: keith wilkinson
Location: Worthing, West Sussex, UK

Help with telecine lens.

Post by Boffee » Thu Feb 16, 2012 7:48 pm

I am trying to telecine without a condensor lens, ie shooting off the gate,of a Eumig 610D. However I am not having much luck, I have purchased a 1/3rd CCTV camera without a lens and a set of C-mount extension tubes but just can't seem to figure out what would be the focal length of the lens with an extension tube I would need to focus on the Super 8mm frame when the gate is 50mm from the front of the projector which is the nearest I would be able to get get with the lens on the front of the camera. Has anyone done this or know how to do the calculations? The French web site http://www.easy-transfert.com has photos of a projector with such an arrangement, so it must be possible. I have tried focal lengths of 75mm and a 25mm but does not work.

granfer
Posts: 383
Joined: Thu Jul 31, 2008 7:30 pm
Real name: Clive Jones
Location: Nr.Exeter,UK

Re: Help with telecine lens.

Post by granfer » Thu Feb 16, 2012 8:16 pm

PM me with your email address, and I should be able to help. If you know the ACTUAL dimensions of the sensor in your camera it will be easier to get the right answer.
Granfer

woods01
Posts: 822
Joined: Thu Jul 31, 2003 3:09 am
Location: Vancouver

Re: Help with telecine lens.

Post by woods01 » Fri Feb 17, 2012 7:43 am

If Granfer can't help you my advice is to start with a shorter tube extension find your focus and then slowly expand. You're in the world of macro-photography so its easy to struggle on your focus. Stop down your lens so you will have as much depth of field as possible, once you've found your spot, open up your aperture to your preferred stop and refocus.

aj
Senior member
Posts: 3538
Joined: Thu Oct 02, 2003 1:15 pm
Real name: Andre
Location: Netherlands
Contact:

Re: Help with telecine lens.

Post by aj » Fri Feb 17, 2012 1:30 pm

You need a lens with proper focal length. To get some space to keep distance and for parts.

1/3 inch (8mm) is about the same as a S8 frame.

If you have a 25mm lens the 1:1 image is achieved when the film is at 50mm from the optical centre. Ther sharp image is then available on the other side and again at 50mm from the same centre.

Standard CCTV lenses are often only 5-6 mm and leave way to little room. Apart from being b-class optics.
Best get yourself an enlarger lens (50mm) and use bellows. Plenty of sharpness and good wide aperture.
I.e. 50 mm gives 100 mm distance on both sides.
Kind regards,

André

granfer
Posts: 383
Joined: Thu Jul 31, 2008 7:30 pm
Real name: Clive Jones
Location: Nr.Exeter,UK

Re: Help with telecine lens.

Post by granfer » Fri Feb 17, 2012 6:20 pm

A 1/3 ccd sensor is NOT an 8mm diagonal, it is only about 6 mm, smaller than a Super 8 frame. See

http://en.wikipedia.org/wiki/Charge-coupled_device
so the simple 1:1 is not accurate enough. As Boffee wants to use his Extension Tubes (which he already has) the calculations will give an accurate answer.
I have prepared an explanation of how to do the calculations for ANY Focal Length lens, ANY film size and ANY sensor size and they are available to anyone who asks. Just PM me with email address.

aj
Senior member
Posts: 3538
Joined: Thu Oct 02, 2003 1:15 pm
Real name: Andre
Location: Netherlands
Contact:

Re: Help with telecine lens.

Post by aj » Sat Feb 18, 2012 8:32 pm

I wrote about the same

Super-8 = 3.68 x 4.88mm which gives a diagonal of 6,112

So a 1/3 inch chip is very near to an S8 frame.

As OP is not getting any result I think it wise to start with a simple set-up
using my intructions to try to obtain a 1:1 image. When that works he can attempt further tuning.

Very likely the lens is unsuitable. If the lens is like 6 mm and some
50mm from the chip it will work as a enlarger. I.e. the projected image is
much larger then S8 and the focus distance from the optical centre is closing in at the focal length.

So, goodluck :)
Kind regards,

André

bakanosaru
Posts: 337
Joined: Sat Mar 15, 2003 9:23 am
Location: Auckland, New Zealand

Re: Help with telecine lens.

Post by bakanosaru » Sat Feb 18, 2012 10:10 pm

Super-8 = 3.68 x 4.88mm which gives a diagonal of 6,112
Let me google that for you:Super 8 frame size

Wikipedia says Super 8 = 4.01mm x 5.79mm (diagonal = 7.04mm)

Apparently SMPTE says Super 8 = 4.22mm x 5.69mm (diagonal = 7.08mm)

Assuming one of those is actually right. It looks like you're thinking of Regular/Standard 8mm.

DonFito
Posts: 69
Joined: Tue Jan 08, 2008 4:08 am
Location: San Jose, CA
Contact:

Re: Help with telecine lens.

Post by DonFito » Sat Feb 18, 2012 10:29 pm

Found this quote from John_Pytlak:

Super-8 5.31 x 4.01 millimeters (SMPTE 154)

would give a diagonal of 6.65mm

Looking at bakanosaru's link, SMPTE 154 refers to projectable area.

--
Thread from John:
viewtopic.php?t=10972
--
Cheers,

Rafael Rivera
www.donfito.com

aj
Senior member
Posts: 3538
Joined: Thu Oct 02, 2003 1:15 pm
Real name: Andre
Location: Netherlands
Contact:

Re: Help with telecine lens.

Post by aj » Sat Feb 18, 2012 10:40 pm

Try pythagoras yourself instead of googling.

Any tips on getting images on the CCD?

The point is that is far less then then 8mm which I supposed 1/3 of a inch is.
The suggestion is to try to image 1:1 to get some result and work from there.

Good luck again with these new insights from these great contributors :)
Kind regards,

André

RCBasher
Posts: 456
Joined: Thu Jan 11, 2007 9:27 am
Location: UK
Contact:

Re: Help with telecine lens.

Post by RCBasher » Sun Feb 19, 2012 11:43 am

Splitting hairs over small dimensional errors is academic in this case because all the lens formulae are for a perfect lens of no thickness. The calculations will get close, then it will be down to good old trial and error. A very small change of extension tube length will make a big difference and also preference for how much overscan is wanted, assuming the gate has been opened up.

Here are some starting points for magnification requirements:

For Super8, assume 1/3” needs about 0.8:1, 1/2” needs about 1:1, and 2/3” about 1.5:1

Here are some real measurements off of my system for R8 and S8

Conditions
CS-mount (for C-mount, deduct 5mm from the x - to mount figures)
Lens is a Schneider Componon-S 2.8/50 enlarger lens
CCD is nominal 2/3”, so I require magnification for R8 and S8 and hence mount my lens reversed for best optical performance
Image coverage to slight overscan (sprocket holes just appearing on one edge and top and bottom frame lines just showing)

Measurements for S8
Film to front edge of camera lens mount: 186mm
Film to front surface of lens end closest to the film: 64mm
Outside edge of lens filter thread to camera mount (required extension tube length including adaptors): 83mm


Measurements for R8
Film to front edge of camera lens mount: 198mm
Film to front surface of lens end closest to the film: 57mm
Outside edge of lens filter thread to camera mount (required extension tube length including adaptors): 102mm


Basically, for R8 I add an additional 18mm extension tube and adjust the whole assembly backwards to refocus.

I chose to use 42mm standard non-auto Pentax screw thread mount extension tubes as readily available at very cheap prices. Two sets are really required to give a good selection range.
42mm to C-mount adapters are easily found, usually from star-gazing equipment websites.
To reverse mount the Componon, I used a 43mm to 52mm filter step up ring, which then enabled a 52mm to 42mm reversing ring to be used.
If mounting the lens non-reversed, a 39mm to 42mm adapter can be purchased.


Hope the above helps, obviously adaptations will be required for smaller sensors (less magnification required, so shorter extension tubes). I think somewhere in the distant past I may have given some actual figures for a 1/3" sensor here in the forum.

Frank
Off all the things I've lost, I miss my mind the most.

granfer
Posts: 383
Joined: Thu Jul 31, 2008 7:30 pm
Real name: Clive Jones
Location: Nr.Exeter,UK

Re: Help with telecine lens.

Post by granfer » Sun Feb 19, 2012 12:56 pm

RCBasher rightly points out that all calculations of distances are based on a "thin" lens, and suggests that the lengths of extension tubes are a matter for much experimentation because the construction of lenses and their mounts vary so much.
However, ALL lenses can be considered to be a "thin lens" (the "thin lens" being located at the nodal point of the lens). This actually makes it easy to determine the required extension length, not difficult.

For example, if the required "lens to sensor" distance when using a 50mm C-mount lens is 102 mm, all one has to do is remember that for a 50mm lens set to infinity the "Nodal Point" would be 50 mm from the sensor in NORMAL use. Therefore, when used with an extension tube at 102mm, the extension tube needs to be (102 - 50 mm) = 52mm.

And one can find the "Nodal Point" of any lens by subtracting the "back focus" (mounting flange to sensor distance) from the Focal length. The "Nodal Point" (effective position of a thin lens) is at the resulting dimension FORWARD of the mounting flange.

The understanding of Optics generally, and Photographic Lenses in particular, is made very much easier if one does not lose sight of the fact that the Science is governed by very simple laws.

topaz
Posts: 4
Joined: Wed Jan 04, 2012 2:32 am
Real name: Matt

Re: Help with telecine lens.

Post by topaz » Tue Feb 21, 2012 11:02 pm

Hi guys

I have just ordered a canon 1100d and plan to use it for "off the gate" telecine.

I have experimented with a 350d and have found I can get a full frame and ok focus using 2 methods.

1. Stock 18-55 lens reversed at 18 and about 2 inches from the gate.
2. Stock projector lens(canon s-400) hacked onto the 350d body with extension tube.

But ideally I would like to just use a macro lens on the 1100d. The problem is the
Slr lenses are too wide to fit flush to the gate and would ideally need to be ( can get exact distance) about 4-5 inches away.

Would it be possible to work out what type of macro lens may work? Then I could use a narrow extension tube to block out any
ambient light. It doesn't have to fill the frame exact but would be great to have some framing options.

Any help is greatly appreciated.

Cheers
Matt

luuude
Posts: 10
Joined: Tue Jul 05, 2011 2:22 am
Real name: ludvig

Re: Help with telecine lens.

Post by luuude » Tue Mar 20, 2012 10:59 am

Hi!

I use a similar setup with a 5dmarkII to get close enough I have mounted a front surface mirror att 45 degrees in front of the gate. So my camera is at 90 degrees to the projector making it like a big "L". I use a reversed nikon 50mm on a loooong bellows. To capture I use the HDMI out with a very flat gamma and also I use a custom firmware to get rid of all the OSD crap in the HDMI out called magic lantern.

here is a still frame. You can clearly see the grain so for me that is sharp enough.


Image
Image
Image

Image
Image

Ludvig

RCBasher
Posts: 456
Joined: Thu Jan 11, 2007 9:27 am
Location: UK
Contact:

Re: Help with telecine lens.

Post by RCBasher » Tue Mar 20, 2012 3:02 pm

Nice set up and captures, although what you consider to be sharp grain looks rather more like compression artifacts due to noise/grain. Real image detail doesn't look particuarly sharp IMHO.
Off all the things I've lost, I miss my mind the most.

luuude
Posts: 10
Joined: Tue Jul 05, 2011 2:22 am
Real name: ludvig

Re: Help with telecine lens.

Post by luuude » Tue Mar 20, 2012 3:40 pm

Well sir I am sorry but you are wrong. Look at the sprocket holes and the small scratches in the film. It´s just some random frames from some admittently soft footage.
There is no compression or noise in the images.There is however a lot of grain, this is 8mm film after all. Also the dynamic range of the canon sensor is very helpful in capturing the challenging reversal film.

Post Reply