Arthritis troubles with my M 50 1.7 HELP!

Imp · 12-24-2015, 07:36 PM

Help!

I've got a lovely M 50 1.7 that was my dad's lens before I started using it. Just about... 10 minutes ago I was taking some macro pictures of some christmas lights, using a set of extension tubes, and suddenly I found that I cannot focus to infinity. The focus ring begins to feel resistance around 2.5 meters, and stops at 6 feet. No closer to infinity!

Has anyone else ever encountered this issue? What might be the problem? I don't think its an issue with the extension tubes, because I've used them with the M 50 1.7 quite often before.
Should I send it to Eric? If so, does someone have his website handy for me? Or do you think Pentax will repair a lens this old?

Thanks, and Merry Christmas!

**monochrome** · 12-24-2015, 08:11 PM

I would trust Eric to diagnose and cure your lens. His website address is Home

**TwoUptons** · 12-24-2015, 08:15 PM

With the lens mounted on the extension tubes, you shouldn't be able to focus to infinity, but I'm not sure from your post if that's the real problem...

Are you saying the focus ring won't move to the infinity position or that the lens won't actually focus to infinity. The latter isn't unexpected...

I know for some lenses the rear element moves around a lot with focusing, but I would expect any reasonable set of extension tubes to have plenty of clearance for that (As opposed to some teleconverters which may have their own optics in the way). But you said you didn't think that was a problem.

I have a very stiff-focusing Super-Tak 50mm f1.4 that fell off the back of a truck, so it is fairly arthritic in about the same range, but it literally fell out of a truck, so I'm a bit surprised it focuses at all... but you could have some impact damage you didn't know about (or even have) before.

Will it focus to infinity when not mounted to the tubes?

-A different Eric

**dms** · 12-24-2015, 08:21 PM

From your description it sounds like you are trying to focus at infinity with the extension tubes installed. That is not possible. The only method of getting more magnification, and still retain infinity focus, is with teleconverter--which adds optics as well as extension.

Imp · 12-24-2015, 08:56 PM

Originally posted by dms

From your description it sounds like you are trying to focus at infinity with the extension tubes installed. That is not possible. The only method of getting more magnification, and still retain infinity focus, is with teleconverter--which adds optics as well as extension.

Sorry if I was unclear, the problem is that my lens cannot focus beyond 6ft WITHOUT the extension tubes on. I just noticed the problem while using extension tubes, thats all.

**UncleVanya** · 12-24-2015, 10:53 PM

Originally posted by Imp

Sorry if I was unclear, the problem is that my lens cannot focus beyond 6ft WITHOUT the extension tubes on. I just noticed the problem while using extension tubes, thats all.

To be clear you mean the focus ring will not turn past the 6' Mark and it appears the distance is accurate it hasn't slipped to where the 6' Mark would be infinity.

Not a Number · 12-25-2015, 01:39 AM

The lens may only need a CLA (Cleaning, Lubrication and Adjustment). The helicoid grease may have dried out. Grease is usually a mixture of oil, and emulsifier (soap) and a carrier (typically clay). If the oil and emulsifier has dried that leaves you mostly with clay which can block the threads preventing the focus from turning.

Imp · 12-25-2015, 05:52 AM

Originally posted by UncleVanya

To be clear you mean the focus ring will not turn past the 6' Mark and it appears the distance is accurate it hasn't slipped to where the 6' Mark would be infinity.

No, i think its jammed at 6', because I know it is not becoming as compact as it should.

Not a Number · 12-25-2015, 08:38 AM

Does the focus ring turn at all? If it does the screws that hold it to the helicoid barrel may just be loose.

Imp · 12-25-2015, 09:18 AM

Originally posted by Not a Number

Does the focus ring turn at all? If it does the screws that hold it to the helicoid barrel may just be loose.

Yes, the ring turns from its closest focus until about 6', at which point there is a LOT of resistance - I don't want to force it.

Mothballs · 12-26-2015, 11:31 PM

Yeah, don't force it. It barely took anything for the screw in my Soviet MIR-1 37mm (RIP) focus to break off inside the lens.

Imp · 12-28-2015, 05:16 PM

Originally posted by dcshooter

so unless you are doing the repairs yourself

Would that be difficult to do, considering I've no clue how to do it? I wouldn't mind trying it just to experiment. Would you start by unscrewing the screws on the lens mount? Curious how it might be done.

Not a Number · 12-28-2015, 05:35 PM

Look through the links in the lens assembly database thread to see what the typical disassembly is for cleaning the helicoid. While this particular lens does not have a link listed there are several M series lens that do.

You'll need a good quality JIS screwdriver and a good helicoid grease at the very least. Typically you remove the trim ring on the front of the lens, remove the screws holding the filter ring, then loosen/remove the screws securing the focus ring to the helicoid barrel. Then you just unscrew the helicoid. Depending on the lens you may not even have to remove the lens mount.

**UncleVanya** · 12-28-2015, 08:24 PM

Originally posted by dcshooter

This thread shows some of the rear disassembly:
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/310415-arth...-1-7-help.html

Groundhog day?

Imp · 12-29-2015, 05:29 AM

Originally posted by UncleVanya

Groundhog day?

yeah...

12-24-2015, 07:36 PM	#1
Imp Pentaxian Join Date: Nov 2014 Location: Washington, DC Photos: Gallery \| Albums Posts: 1,749	Arthritis troubles with my M 50 1.7 HELP! Help! I've got a lovely M 50 1.7 that was my dad's lens before I started using it. Just about... 10 minutes ago I was taking some macro pictures of some christmas lights, using a set of extension tubes, and suddenly I found that I cannot focus to infinity. The focus ring begins to feel resistance around 2.5 meters, and stops at 6 feet. No closer to infinity! Has anyone else ever encountered this issue? What might be the problem? I don't think its an issue with the extension tubes, because I've used them with the M 50 1.7 quite often before. Should I send it to Eric? If so, does someone have his website handy for me? Or do you think Pentax will repair a lens this old? Thanks, and Merry Christmas!

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12-24-2015, 08:11 PM	#2
monochrome Loyal Site Supporter Join Date: Mar 2008 Location: Working From Home Photos: Gallery \| Albums Posts: 26,276	I would trust Eric to diagnose and cure your lens. His website address is Home

12-24-2015, 08:15 PM	#3
TwoUptons Loyal Site Supporter Join Date: Nov 2015 Photos: Albums Posts: 4,225	With the lens mounted on the extension tubes, you shouldn't be able to focus to infinity, but I'm not sure from your post if that's the real problem... Are you saying the focus ring won't move to the infinity position or that the lens won't actually focus to infinity. The latter isn't unexpected... I know for some lenses the rear element moves around a lot with focusing, but I would expect any reasonable set of extension tubes to have plenty of clearance for that (As opposed to some teleconverters which may have their own optics in the way). But you said you didn't think that was a problem. I have a very stiff-focusing Super-Tak 50mm f1.4 that fell off the back of a truck, so it is fairly arthritic in about the same range, but it literally fell out of a truck, so I'm a bit surprised it focuses at all... but you could have some impact damage you didn't know about (or even have) before. Will it focus to infinity when not mounted to the tubes? -A different Eric

12-24-2015, 08:21 PM	#4
dms Site Supporter Join Date: Aug 2011 Location: New York, NY Photos: Gallery Posts: 2,192	From your description it sounds like you are trying to focus at infinity with the extension tubes installed. That is not possible. The only method of getting more magnification, and still retain infinity focus, is with teleconverter--which adds optics as well as extension.

12-24-2015, 08:56 PM	#5
Imp Pentaxian Join Date: Nov 2014 Location: Washington, DC Photos: Gallery \| Albums Posts: 1,749 Original Poster	Originally posted by dms From your description it sounds like you are trying to focus at infinity with the extension tubes installed. That is not possible. The only method of getting more magnification, and still retain infinity focus, is with teleconverter--which adds optics as well as extension. Sorry if I was unclear, the problem is that my lens cannot focus beyond 6ft WITHOUT the extension tubes on. I just noticed the problem while using extension tubes, thats all.

12-24-2015, 10:53 PM	#6
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,459	Originally posted by Imp Sorry if I was unclear, the problem is that my lens cannot focus beyond 6ft WITHOUT the extension tubes on. I just noticed the problem while using extension tubes, thats all. To be clear you mean the focus ring will not turn past the 6' Mark and it appears the distance is accurate it hasn't slipped to where the 6' Mark would be infinity.

12-25-2015, 01:39 AM	#7
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 10,526	The lens may only need a CLA (Cleaning, Lubrication and Adjustment). The helicoid grease may have dried out. Grease is usually a mixture of oil, and emulsifier (soap) and a carrier (typically clay). If the oil and emulsifier has dried that leaves you mostly with clay which can block the threads preventing the focus from turning.

12-25-2015, 05:52 AM	#8
Imp Pentaxian Join Date: Nov 2014 Location: Washington, DC Photos: Gallery \| Albums Posts: 1,749 Original Poster	Originally posted by UncleVanya To be clear you mean the focus ring will not turn past the 6' Mark and it appears the distance is accurate it hasn't slipped to where the 6' Mark would be infinity. No, i think its jammed at 6', because I know it is not becoming as compact as it should.

12-25-2015, 08:38 AM	#9
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 10,526	Does the focus ring turn at all? If it does the screws that hold it to the helicoid barrel may just be loose.

12-25-2015, 09:18 AM	#10
Imp Pentaxian Join Date: Nov 2014 Location: Washington, DC Photos: Gallery \| Albums Posts: 1,749 Original Poster	Originally posted by Not a Number Does the focus ring turn at all? If it does the screws that hold it to the helicoid barrel may just be loose. Yes, the ring turns from its closest focus until about 6', at which point there is a LOT of resistance - I don't want to force it.

12-26-2015, 11:31 PM	#11
Mothballs Senior Member Join Date: May 2015 Posts: 275	Yeah, don't force it. It barely took anything for the screw in my Soviet MIR-1 37mm (RIP) focus to break off inside the lens.

12-28-2015, 05:16 PM	#12
Imp Pentaxian Join Date: Nov 2014 Location: Washington, DC Photos: Gallery \| Albums Posts: 1,749 Original Poster	Originally posted by dcshooter so unless you are doing the repairs yourself Would that be difficult to do, considering I've no clue how to do it? I wouldn't mind trying it just to experiment. Would you start by unscrewing the screws on the lens mount? Curious how it might be done.

12-28-2015, 05:35 PM	#13
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 10,526	Look through the links in the lens assembly database thread to see what the typical disassembly is for cleaning the helicoid. While this particular lens does not have a link listed there are several M series lens that do. You'll need a good quality JIS screwdriver and a good helicoid grease at the very least. Typically you remove the trim ring on the front of the lens, remove the screws holding the filter ring, then loosen/remove the screws securing the focus ring to the helicoid barrel. Then you just unscrew the helicoid. Depending on the lens you may not even have to remove the lens mount.

12-28-2015, 08:24 PM	#14
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,459	Originally posted by dcshooter This thread shows some of the rear disassembly: https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/310415-arth...-1-7-help.html Groundhog day?

12-29-2015, 05:29 AM	#15
Imp Pentaxian Join Date: Nov 2014 Location: Washington, DC Photos: Gallery \| Albums Posts: 1,749 Original Poster	Originally posted by UncleVanya Groundhog day? yeah...