Having trouble putting a new lens in a Dahua Starlight turret

[orrd]

I bought a Dahua Starlight IPC-HDW4231EMP-ASE and I wanted a higher focal length lens so I bought a 16mm M12 lens like this: Sunvision CCTV HD 5MP 16mm Monofocal Fixed Iris 17⁰ AOV Board / M12 / MTV Lens | eBay

But now I'm having trouble installing the new lens. I was able to remove the old one, but the new one won't screw on. It almost starts, but then immediately gets too tight to go on. When I look at the new lens and the old one, it almost looks like maybe the threads on the new lens are smaller.

Is it possible this lens has a different threading? I thought all M12 lens were supposed to be compatible?

 

[alastairstevenson]

When I look at the new lens and the old one, it almost looks like maybe the threads on the new lens are smaller.

You can confirm that if you hold the 2 lenses together with the threads touching and see if the thread pitch is the same.

 

[orrd]

I don't know, I can't really tell. The threads seem to maybe fit together when I hold them next to each other. But the threads are so small, it's just hard to tell.

I just wonder if different threads are even a possibility? I just thought it was a standard and they would all be the same.

 

[alastairstevenson]

The threads seem to maybe fit together when I hold them next to each other.

I maybe should have said 'with each lens facing the other way' so that the threads can be right against each other.
That way it will be very clear if they are the same pitch. Which from the picture they do appear to be.

Are you sure you weren't starting to cross-thread the new lens when starting to screw it in?

 

[Fastb]

orrd,
based on the section of "no threads" on the old lens, I suspect the lens was held in place with a set screw. This set screw would lock the lens in place (after focusing) by pushing onto that unthreaded channel of the lens.

If your camera indeed has a set screw, make sure it is retracted enough. The set screw, if protruding enough, could make it hard to screw in the replacement lens.

Judging by the pic, the thread pitch appears to be the same.... Nestling the two lenses together, one upright while the other is upside, should let you see if the thread pitch is exactly the same.

Eg:

 

[orrd]

Yeah, even when I hold the lenses that way, I can't quite tell. They kind of seem to fit together I think. I tried to get a picture of that but it didn't turn out well. I'm pretty sure it doesn't have a set screw, but I'll double-check (the lens replacement videos I've watched for the Dahua didn't mention that).

I don't think I'm cross-threading it because the threads and socket look undamaged and the old lens still goes in just fine with no problem.

I'm getting a 25mm lens soon, so I'll try that one. I suspect the threads on this one might just be not quite right.

 

[Fastb]

orrd,
My Dahua didn't use a setscrew. Instead, after focusing, an epoxy was used to retain lens position.
Try twisting the lens backwards (CCW). With a light touch, you may feel when the leading edge of the thread on the lens drops down over the last thread on the lens holder. That will be the point where the two parts can be threaded together. And lets you focus on getting the thread started in the right region, ie: a 5 to 10 degree neighborhood, of the 365 total.

Lastly, examine the leading edge of the first thread on the lens. That "nose" is what finds the "recess" of the lens holder. The leading edge of the first lens thread is critical. If it's damaged at all, you might file down a little bit, to restore that leading "nose" to be straight, clean, and ready to mate.

That M12 size of the lens is big and wide. Getting cross threaded is very easy.

It sounds as if the lens holder is okay, since the original lens threads right in. So I'd scrutinize the new lens, specifically, the threads.

 

[orrd]

In case anyone is wondering, I tried a couple other lens, and I couldn't get any of them to thread onto the Dahua. I ended up having to use a Hikvision instead. I don't know if there was something just not right with that particular Dahua Starlight IPC-HDW4231EMP-AS or what. I ended up putting the lens that it came with back in and used it for another purpose. After a while I may order another one and try again.