# Optical Forums > Optical and Ophthalmic Equipment >  Topcon vt-5

## Jims

How do you set or align the cylinder lenses when reassembling this phoroptor
jims

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## Optitech USA

Jim,

They should have been marked at 180 prior to removing the banks. Putting them back in unmarked is very difficult next to impossible.

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## Jims

Jason,
thanks. They all have a factory mark (a black dot) but there is no corresponding markings on the lens holder disc. I do not have manual to indicate in what position you orient these dots eg. Facing inward on the 180 meridian which I intuitively tried or dots off-set 57 degrees counterclockwise (left side) power nob rotates a total of 630 degrees through all 11 positions +0.25D to +2.50D and one open slot (630 divided by 11= ~57 degrees)
tried but was found to be incorrect. Only one side disassembled but am reluctant to scramble the good side for a look-see. Would rather experiment a few more times to try & deduce correct assembly

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## Optitech USA

Jim,

From the factory they are set at 180 or 90, ive seen both. If you use a lensometer on all the lenses and put a line across them at 180. Line that 180 line on the factory markings they have on the metal frame and try that. if that is still incorrect try it at 90. Its going to be one of the two. I gotta ask, why did you remove the entire banks anyways?

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## Jims

> Jim,
> 
> They should have been marked at 180 prior to removing the banks. Putting them back in unmarked is very difficult next to impossible.


Jason,
thanks again for your help on this. I solved the problem and will write it up in case anyone has a
similar problem in the future. I have photos but don't know how to post here and don't want to bother. Thought I would compose a brief PDF on a forgotten piece of information with pics and 
Pearls about disassembly of this instrument that could prevent this problem from arising. Also I have figured out the exact math of gear movements. It is way more complex than aligning all the axises with total rotation of each cylinder lens of 3300 degrees for one full cycle thru pwrs. There is no alignment of the axises per se rather a *specific offset of 300 degrees counterclockwise for L* beginning with the first lens (0.25D.) each lens disc has 42 gears so when you check accuracy you can adjust axises by 8.57 degrees by moving the lens forward or back by one gear., There are no marks on lens gears for set-up; the axises are marked which is some help but leads nowhere if you assume they should all be aligned in some sort of  symmetry. This offset creates a continuously variable location for each successive lens axis. 
james skudlarick OD
honolulu
808 395-5945

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