question regarding Roundshot cameras

Hi plungefrog

If you drive the take up spool at constant speed the film speed will increase linearly with time (because of the increasing diameter of spool). This means the exposure will decrease and there will be a horizontal distortion of the image. Both effects will be considerable (factor >2 comparing film-start and film-end).

You have different possbilities to minimize/avoid this effect:

(a) Increase the size of the take up spool
Use of own construction instead of a standard spool. The larger the diameter, the less the diameter will change (less film layers), the film-speed will be more constant.
It will not avoid the effect but reduce it so much it is not recognizable by eye on the print. I have constructed a medium format 360° Panoramic camera this way. I can post pictures if you want.

(b) Control the rotating speed of the take up spool
Most probably not easy to achieve, but doable using stepper motors and digital circuits/sensors.
This will avoid the effect if adjusted precisely.

(c) Drive the film itself
Drive the film instead of driving the spool(s). I guess this is rather complicated for 120 film, but for sure possible - It will fully solve the problem.

(d) Use a lens with small focal distance
The length of the negative for a 360° shot will be shorter, thus the effect less dramatic. However it will not avoid the problem completely.

I guess the simplest approach is (a) in combination with a coupling of the take up spool and the camera rotation (without having a second motor). This way you do not need to align the speeds of the two motors and you can use the rotating speed and the slit size to control exposure.

I quickly googled pics for the Roundshot 220VR I assume the drum is moving the film, so it will be of type (c); most probably driven by a dedicated motor with constant speed depending on the focal length.

-Zishe

 

The take-up spool can have a tensioning motor. You basically want to have something which holds a tension, and as that tension is relieved (i.e. the drum advances film), the take-up mechanism brings the tension back to par. This can be done using a clockwork mechanism. Perhaps it may be easier just to have a torque sensor which automagically (dis)engages the take-up motor.

 

Roundshot and Lookaround

Hello - I have a roundshot 65/220/70 and a Lookarund for testing
complete different stuff.

If i were you i would use the lookaorund-book-free for download now- to construct the cameras. alan has multiple versions there.
one can also use 35mm unperforated(better)-he shows also motor-constructions.

Roundshot 70/220 is working like this..
Yes film is pressed against a flat rubber-ring below. Pressure plate has one stiffer o-ring below and a loose thinner one above to press film against a second surface which is standing still against the film. Just talked to seitz about replacement of that main film-rubber-surface. is must be adjusted infactory to get precise distance to lens. Its a simple but delicate mechanisme. if the tensions are not right(worn-out o-ring) film-transport is not ok. One must work very precise.

film-takeup. its a special mechanisme which is connected to the main-o-ring.
except for the film-contact surface, all other rings are o-ring. two of them are holding the spool in place to avoid lateral movement.
vertically there is a spring-takeup for using both 220 and 70mm-spool.
btw: the pressure-plate has two positions for 220 and 70mm. the surface where the film is slipping over can be moved for 70m and 220 width. 60 and 54mm(53mm) images.
most interesting is how distances are set:
1. lens is shifted about 2-3degr. to increase DOF.
2. slit is moving when distance are changed. It will change the position towards the film/lens.
3. sharpness of slit is most important. there are instructions on the net how to do this.
If you dont mind carrying around large camera or weight i would get one of the roundshots 70/220 or better 220vr on ebay.

one can get filmslitters to cut down 70mm-film. Ilford announced unperforated delta 100 and hp5 plus for this year.

see here a roundshot-panorama- 4 secs around-1/60 second) 65mm grandagon.
www.auschwitzpanorama.tk

 

If i were you i would get roundshot 220vr with tilt-head. its much easier and best quality. i have seen a lot of crappy panoramas with all these DIY-cams. get new sigma dp2Quattro(45mm equiv.) and stitch. huge panoramas possible. dp1q(28mm) and dp3q(75mm equiv. will come. compact quite cheap each and superbe color and resolution. see images at dpreview/sigma-forum.
if you want to shoot like this yes then you need a 360 rotapancam: rs 65/70/220 at 1/60(4 sec around)
www.auschwitzpanorama.tk