SMC 50mm 1.4 simple repair question

madguru · 04-22-2018, 04:12 PM

Hi,

I've been using this forum to learn about great lenses for quite a while, and finally had a question.

I have a Pentax 50mm smc 1.4. The front ring has become loose and the screws have fallen out that keep it in place. Nothing is damaged. I wanted to know what kind of screws those are and what kind of screwdriver I need as well.

Thanks,

Adnan

**aslyfox** · 04-22-2018, 04:20 PM

welcome

according to this thread, you will need JIS screws and JIS screw drivers:

Cross-head screws - a caution: - PentaxForums.com

not sure of the size of the screws sorry

**Bob 256** · 04-22-2018, 07:06 PM

If you have a small piece of soft wood like balsa, you can shape it about the size of the existing screw holes and then screw it in (make sure it's not too snug a fit so it doesn't break off). Unscrew the balsa and you should have an imprint of the thread which if you have the proper tools, you can determine the thread pitch. You should also be able to measure the diameter of the portion that went in the screw hole for a diameter - chances are pretty high they're metric. That should allow you to order some replacements if you find a source.

Not a Number · 04-22-2018, 10:27 PM

Which model is the lens? K, M or A, e.g. Pentax, Pentax-M, Pentax-A?

The A's use M1.7 × 4 screws (1.7mm wide - 4mm long). Thread pitch doesn't matter at these sizes as only one pitch is used per diameter. Engineers love to use the same components as much as possible so I don't see these changing much from lens to lens. M1.7 wide screws are the most common size screws you'll find in Pentax lenses and camera bodies. The length varies depending on the application.

You can try these:
M1.7x4 Black Zinc Pan Head Machine Screw #21528 [21528] : Metric Screws!, We have the screws you need!

The only reason the front ring would be loose and the screws missing is that the lens was taken apart or very badly abused. It must have been taken apart for a reason so there are probably problems or other missing parts.

**aslyfox** · 04-23-2018, 04:45 AM

if the screws just " fell out"

is that might be an indication that stripping has already occurred

if so

what then?

madguru · 04-23-2018, 08:46 AM

Thanks for all the replies. The lens is a SMC Pentax M 50mm 1.4. So, it would make sense for the screws to be JIS screws, but the M1.7x4 seems like they could be a good fit. Hmmm. Not quite sure. The M1.7x4 that is flat on top in the link look like they could be a good match. Perhaps I should get three of those and the JIS screw driver set?

Adnan

04-22-2018, 04:12 PM	#1
madguru New Member Join Date: Apr 2018 Posts: 2	SMC 50mm 1.4 simple repair question Hi, I've been using this forum to learn about great lenses for quite a while, and finally had a question. I have a Pentax 50mm smc 1.4. The front ring has become loose and the screws have fallen out that keep it in place. Nothing is damaged. I wanted to know what kind of screws those are and what kind of screwdriver I need as well. Thanks, Adnan

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04-22-2018, 04:20 PM	#2
aslyfox Seeker of Knowledge Join Date: Aug 2016 Location: Topeka, Kansas Photos: Gallery \| Albums Posts: 24,581	welcome according to this thread, you will need JIS screws and JIS screw drivers: Cross-head screws - a caution: - PentaxForums.com not sure of the size of the screws sorry

04-22-2018, 07:06 PM	#3
Bob 256 Site Supporter Join Date: Jun 2008 Location: Idaho Photos: Gallery Posts: 2,375	If you have a small piece of soft wood like balsa, you can shape it about the size of the existing screw holes and then screw it in (make sure it's not too snug a fit so it doesn't break off). Unscrew the balsa and you should have an imprint of the thread which if you have the proper tools, you can determine the thread pitch. You should also be able to measure the diameter of the portion that went in the screw hole for a diameter - chances are pretty high they're metric. That should allow you to order some replacements if you find a source.

04-22-2018, 10:27 PM	#4
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 10,526	Which model is the lens? K, M or A, e.g. Pentax, Pentax-M, Pentax-A? The A's use M1.7 × 4 screws (1.7mm wide - 4mm long). Thread pitch doesn't matter at these sizes as only one pitch is used per diameter. Engineers love to use the same components as much as possible so I don't see these changing much from lens to lens. M1.7 wide screws are the most common size screws you'll find in Pentax lenses and camera bodies. The length varies depending on the application. You can try these: M1.7x4 Black Zinc Pan Head Machine Screw #21528 [21528] : Metric Screws!, We have the screws you need! The only reason the front ring would be loose and the screws missing is that the lens was taken apart or very badly abused. It must have been taken apart for a reason so there are probably problems or other missing parts.

04-23-2018, 04:45 AM	#5
aslyfox Seeker of Knowledge Join Date: Aug 2016 Location: Topeka, Kansas Photos: Gallery \| Albums Posts: 24,581	if the screws just " fell out" is that might be an indication that stripping has already occurred if so what then?

04-23-2018, 08:46 AM	#6
madguru New Member Join Date: Apr 2018 Posts: 2 Original Poster	Thanks for all the replies. The lens is a SMC Pentax M 50mm 1.4. So, it would make sense for the screws to be JIS screws, but the M1.7x4 seems like they could be a good fit. Hmmm. Not quite sure. The M1.7x4 that is flat on top in the link look like they could be a good match. Perhaps I should get three of those and the JIS screw driver set? Adnan