Linkert
Established
Title says a lot. The aperture ring on my Jupiter-8 feels sort of uneven, no resistance. It's kind of "jittery", especially around f2 and between f4–8. Also it moves three or four millimetres lower than f2.
Are there any nice guides to follow when taking something like a Jupiter-8 apart? There are three super tiny screws on the aperture ring, could it be the solution?
Are there any nice guides to follow when taking something like a Jupiter-8 apart? There are three super tiny screws on the aperture ring, could it be the solution?
wolves3012
Veteran
Here's the best resource for dismantling/cleaning/re-lubing the Jupiter 8:
http://pentax-manuals.com/repairs/j8service.pdf
Those three grub-screws are not quite the answer you were thinking so read up before starting. The part you'll need is towards the bottom of the page.
If the aperture is loose or uneven, it's almost certainly because the grease has dried up to nothing. You'll need to partially dismantle the front of the lens and unscrew the aperture ring (after removing the set-screw that holds it) at least most of the way off to sort the problem.
As for going "beyond" f/2, that's pretty usual but the other end should line up with f/22. If it doesn't, either the optical module needs to be unscrewed/screwed to correct it or the middle ring needs moving - that has three tiny grub-screws too.
http://pentax-manuals.com/repairs/j8service.pdf
Those three grub-screws are not quite the answer you were thinking so read up before starting. The part you'll need is towards the bottom of the page.
If the aperture is loose or uneven, it's almost certainly because the grease has dried up to nothing. You'll need to partially dismantle the front of the lens and unscrew the aperture ring (after removing the set-screw that holds it) at least most of the way off to sort the problem.
As for going "beyond" f/2, that's pretty usual but the other end should line up with f/22. If it doesn't, either the optical module needs to be unscrewed/screwed to correct it or the middle ring needs moving - that has three tiny grub-screws too.
Linkert
Established
Thank you very much! Looks like I need to be quite sober for this task
"Firmly grip the lens unit and unscrew it from the focus unit."
I have the fourth type of J-8 in this guide, and I'm a bit scared to take this very first step. 'Lens ring' and 'Lens unit', any difference in this case? I feel a bit lost on the autonomy of the lens. I should be alright after I cross this step.
Edit: okok, now I understand what the lens unit is. Basically twist the lens unit clockwise (towards below 1m focus). Or am I way off?
wolves3012
Veteran
Hold the focus ring/whole lens barrel and unscrew the lens unit by means of the aperture ring - as you're looking at the front element turn counterclockwise. They can be pretty tight but really, it does just unscrew. Once you've got that out, if you're only doing the aperture you can skip down to "Lens Units" in that guide.
apostasiometritis
Established
Grab lens from camera side with left hand, from aperture ring with right hand, twist counterclockwise.
It may actually take a lot of strength to do it, but don't be afraid. I've never had a Jupiter get damaged in this way, they seem to be quite resilient.
As for the tightening of the ring, I'm afraid I am not aware of a mechanical way of tightening the aperture action. Note that the aperture ring screws are *tiny* and very fragile.
What I have done in the past and worked is to apply 1-2cm of electrical tape (0.5cm wide more or less) in a way that grips on both the fixed and rotating parts. It will make sense when you open up the lens.
You may have to experiment with different lengths (and possibly tapes).
It may actually take a lot of strength to do it, but don't be afraid. I've never had a Jupiter get damaged in this way, they seem to be quite resilient.
As for the tightening of the ring, I'm afraid I am not aware of a mechanical way of tightening the aperture action. Note that the aperture ring screws are *tiny* and very fragile.
What I have done in the past and worked is to apply 1-2cm of electrical tape (0.5cm wide more or less) in a way that grips on both the fixed and rotating parts. It will make sense when you open up the lens.
You may have to experiment with different lengths (and possibly tapes).
jammcat
Lick My Lens Cap
Just a tip from someone who recently made one working J8 from cannibalizing two copies.
The easiest way to remove the optical unit from the focusing unit is by utilizing a rubber kitchen glove for grip. Don't wear the glove, but sandwich the lens between a folded glove and the start to twist.
The issue isn't so much resistance with the lens, but rather, the fact that there is simply nowhere to get a solid grip on the lens otherwise.
Tightening the focus ring is pretty easy. Just be sure to do it on a piece of black velvet or similar so that you don't lose any screws. Good luck!
The easiest way to remove the optical unit from the focusing unit is by utilizing a rubber kitchen glove for grip. Don't wear the glove, but sandwich the lens between a folded glove and the start to twist.
The issue isn't so much resistance with the lens, but rather, the fact that there is simply nowhere to get a solid grip on the lens otherwise.
Tightening the focus ring is pretty easy. Just be sure to do it on a piece of black velvet or similar so that you don't lose any screws. Good luck!
wolves3012
Veteran
There is a way, as per above - re-grease the threads. It's a 5 minute job and a lot less trouble that trying to stick bits of tape on it. No disrespect, what works for you works for you but it's not exactly the "proper" way.
Linkert
Established
Thanks for all the help Got one smooth Jupiter-8 now!
Got one smooth Jupiter-8 now!
apostasiometritis
Established
Which threads would they be?
No offence taken, but to be honest tape isn't exactly gonna ruin your lens. Losing/damaging any of those three screws is not easy to rectify and happens very easily as they are seemingly made out of butter.
wolves3012
Veteran
The aperture ring is actually on a thread. If you look lower down on the guide I linked to, you'll see. To get it off and re-grease requires (at worst) removing the actuating pin of the aperture. You can actually work grease into the gap without doing so - provided there's no congealed, old grease to be removed first. I've done this on several lenses and it's quite an easy job.
The manufacturers used grease not strips of tape and dry threads. The guide I linked to is clear, correct, well-written and well-illustrated and was compiled by Kim Coxon, who is a former RFF user and something of a lens guru. He doesn't suggest the tape method either. However, feel free to use whatever method suits you. I don't disagree with your sentiments on the tiny screws but with care and the proper tools it's not usually a problem unless some PO has tinkered.