Jupiter 9 service notes

[Kim Coxon]

At long last and with thanks to Roland for donating the guinea pig, I have done the repair notes for the Jupiter 9. This covers a full strip and re-build of the focus unit. Another one will follow on the collimation aspects.

If anyone has any comments on any readability issues I would appreciate it so I can make it more understandable.

Download from here http://pentax-manuals.com/repairs/j9service.pdf

Kim

 

[Branestawm]

Kim, your article looks very good. I rebuilt one of these lenses recently and had been toying with the idea of doing a write up but you beat me to it! Just a couple of observations to add from experience with my 1959 lens:

A mark accross the lens mount/outer barrel makes lining up easier otherwise on re-assembly it can be tricky to locate the dimples fo the grub screws.

To make fitting the rf cam easier I took a measurment of its height when on infinity after removing the mount(see pic). From memory I think this was about 0.4"

On my lens the middle helix has two tapped holes for the stop screw. You can guess which one I tried first when putting the lens back together.

I initially used grease for lubrication but found the drag from three threads moving together made the focusing action too heavy for my taste. I have now cleaned this out and used a thin layer of engine oil which gives nicely weighted action and is less effected by changesin temperature.

Hope this is of help and I look forward to seeing your article on optical setting

 

[Kim Coxon]

I started out by marking but I find it easier not to now. With some of them there are so many marks it just gets confusing. If you follow it my way it's less easy to make a mistake by getting the wrong marks.

As far as the cam is concerned, it will be in the right place if you add the extra 1/2 turn. Another way to judge is against another lens.

It doesn' matter which hole you use because there should be a corresponding slot on the other side. It is the amount you turn the units back and the right start thread that is important.

I would never use oil in a lens and very rarely in a camera. Oil is designed to spread. If you use oil, it will end up initially on the diaphraghm which is not too much of a prblem in an RF lens but more importantly on the glass. If this happens, you are into another strip and having to use solvents to clean the elements. I use a very light weight silicon based grease for such threads put on sparingly. Too much will cause drag. I use a much thicker graphite based grease if I need a damping effect such as on the diapraghm ring of J8's etc.

Kim

Kim, your article looks very good. I rebuilt one of these lenses recently and had been toying with the idea of doing a write up but you beat me to it! Just a couple of observations to add from experience with my 1959 lens:

A mark accross the lens mount/outer barrel makes lining up easier otherwise on re-assembly it can be tricky to locate the dimples fo the grub screws.

To make fitting the rf cam easier I took a measurment of its height when on infinity after removing the mount(see pic). From memory I think this was about 0.4"

On my lens the middle helix has two tapped holes for the stop screw. You can guess which one I tried first when putting the lens back together.

I initially used grease for lubrication but found the drag from three threads moving together made the focusing action too heavy for my taste. I have now cleaned this out and used a thin layer of engine oil which gives nicely weighted action and is less effected by changesin temperature.

Hope this is of help and I look forward to seeing your article on optical setting

 

[Branestawm]

Thanks for your comments Kim, I hope I didn't sound too critical in my previous post but felt that a few observations may be in order. However, just to clarify a couple of points:

It does matter which screw hole you use for the stop screw. As you say it is possible to make the lens focus correctly whichever one is used but the focusing collar fits on the middle helix and is secured by three screws locating in dimples on its periphery. If the middle helix is 180 degrees out the focusing ring will not locate in its correct position unless you drill new dimples for the grub screws.

I should have stressed that when using oil I used it very sparingly; just enough to provide a lubricating film. I also used a synthetic oil and these tend to creep far less than mineral oils. A quick check on the lens in question shows no signs of oil migration from the helicals in the couple of months since it was serviced. But yes oil can cause all sorts of problems if not used properly and I hope I didn't give the impression that I was just slopping it about!

Incidentaly I'm in Grantham, if you're ever in the area your are welcome stop by for a cuppa and a chat.

Cheers
Paul

 

[Kim Coxon]

Hi Paul,
Not at all. In many ways it was the sort of feedback I was looking for. When you get used to doing something, you sometimes take things for granted and forget that some doing it for the first time might need a fukker explanation. So far, I have tried to produce notes that depict the vagaries of each lens rather than a complete DIY guide aimed at people who have done the odd lens but not that type.

Soon I hope to produce a "general" guide with a few comments about tools, cleaners, grease etc on the re-lube side followed by a section on collimation. It is this sort of feedback that will help that. As to the oil, IMHO a very light grease will always be better and last much longer. Oil, even the synthetic stuff is designed and as the adverts put "engineered" to flow to cover all the moving parts. Used in very small quantities it won't get everywhere very quickly but it won't last that long either. Most things that use oil have to be lubricated far more frequently than things that are greased. I enjoy doing lenses but not that much! Put a drop of oil on a pond and it soon spreads to a huge circle perhaps a moleculr thick. Drop og lump of grease and it tends to stay as a lump for a long time. If I get down to Grantham, I will bring you a small tub of the grease I use.

I thought you were refering to the guide pin on the inner helix. All this carries is the lens unit. The dimples for the aperture ring are on the middle one. The only hole in this should be for the limit screw which doesn't ride in a slot like the guide pins. All the ones I have done have only had the one hole for this at the top. If you come across one with 2, it would make sense to mark it. I might have to amend that.

Until about a week ago, I thought I was the only RFF member in this area. I then found out another member works just across the airfield and is a Nav and now there is another 15 miles down the road. We may even end up with a Lincolnshire group 😱

Kim

Thanks for your comments Kim, I hope I didn't sound too critical in my previous post but felt that a few observations may be in order.

Paul

 

[Branestawm]

There's another member, can't remember his name, in the north of the county. This fascination with obsolete equipment must be a Lincolnshire thing.

We don't like change around 'ere!