[UncleVanya]

@mtkeller I have had at least two customers send me lenses with weird focusing issues. These lenses looked like they had good sdm but would fail to focus in challenging situations. The camera or the lens would get close then stop trying. My own lens (same model) with good sdm wouldn’t fail in the same scenarios. After screwdrive conversion both customers lenses would reliably focus on the exact same situations that they were unable to before. In those cases the failure to lock focus was in low light with a target that wasn’t very easy to focus on.

[mtkeller]

Thanks, @UncleVanya. That sounds a lot like what I'm experiencing with mine. I will first endeavor to get my hands on a body that can be used to follow the instructions here on screwdrive conversion, and if I don't find something that looks workable, I will be in touch about sending you my lens.

[UncleVanya]

Thanks, @UncleVanya. That sounds a lot like what I'm experiencing with mine. I will first endeavor to get my hands on a body that can be used to follow the instructions here on screwdrive conversion, and if I don't find something that looks workable, I will be in touch about sending you my lens.

No worries. Just let me know if you need any advice. My favorite camera for conversion is the k100d but there are plenty to choose from.

[mtkeller]

No worries. Just let me know if you need any advice. My favorite camera for conversion is the k100d but there are plenty to choose from.

I have leads on a K-r and a K100D Super. It sounds like an advantage of the K100d is that it doesn't support SDM so it would allow me to confirm that the screwdrive AF is working before I go through the process of mucking about with the ROM files. Am I understanding correctly? Would that be particularly useful, or could I just go with the K-r or K100D Super?

[cooks333]

Even in AF.S, it often refuses to lock focus.

I've had similar focusing issues with mine. A few years ago, autofocus pretty much stopped working all together and so I sent the lens away to get fixed. Turned out to be an SDM problem if I remember correctly. It came back and worked properly again for a while, but has now fallen back into less-than-optimal performance. The motor isn't running and so I pretty much use it as a manual focus lens. The red AF lights in the viewfinder will still flash when something comes into focus, so at least there's that. I use the lens mostly for stills and haven't used it a ton recently (perhaps because of the focusing!), so it hasn't been the end of the world for me. But I can remember trying to shoot some wildlife while these issues were going on and it was really frustrating. Long story short, you're not alone and I feel your pain.

[mtkeller]

I've had similar focusing issues with mine. A few years ago, autofocus pretty much stopped working all together and so I sent the lens away to get fixed. Turned out to be an SDM problem if I remember correctly. It came back and worked properly again for a while, but has now fallen back into less-than-optimal performance. The motor isn't running and so I pretty much use it as a manual focus lens. The red AF lights in the viewfinder will still flash when something comes into focus, so at least there's that. I use the lens mostly for stills and haven't used it a ton recently (perhaps because of the focusing!), so it hasn't been the end of the world for me. But I can remember trying to shoot some wildlife while these issues were going on and it was really frustrating. Long story short, you're not alone and I feel your pain.

I'm glad to hear that someone else has experienced it. Sorry that SDM repair didn't seem to fix it long term, but I guess that gives me even more of a basis to just try the conversion to screwdrive rather than first sending somewhere for repair. The K-3 iii and Tamron 70–200mm f/2.8 screwdrive have proved an effective tracking pair for me with sports. I would not mind running this lens as a screwdrive lens for BIF, especially since most reports are that it is quieter than other screwdrive lenses (perhaps because it's a star prime).

[UncleVanya]

I have leads on a K-r and a K100D Super. It sounds like an advantage of the K100d is that it doesn't support SDM so it would allow me to confirm that the screwdrive AF is working before I go through the process of mucking about with the ROM files. Am I understanding correctly? Would that be particularly useful, or could I just go with the K-r or K100D Super?

Correct. Unless you plan to convert a lot of lenses that's probably not a priority. Also the K100D (not super) does not require any special SD card files to go in/out of debug mode. The K100D only needs a series of keys pressed. Very helpful for converting a lot of lenses... But I have used my K100D Super for conversion - it works fine. The only reason I ended up with the K100D is a mistake I made originally when trying to get the K100D Super into Debug mode. AFTER I bought the K100D and figured out what to do I figured out what I had done wrong on the K100D Super. It was a very slight typo and a misunderstanding of the menu structure once in Debug mode.

[AfterPentax Mark II]

It’s definitely the lens and not the camera. As I noted, none of my other lenses act up on the K-3 iii. I also put the DA*300mm back on the K-70, and it exhibits the same behaviors.

---------- Post added 05-03-21 at 06:50 ----------

Of course I just sold the K-7 that came attached to the DA*300mm to MPB, so I no longer have a body on hand capable of doing the screwdrive conversion. I’m thinking that by the time I pay for shipping and @UncleVanya’s time, I might as well stake out a low cost older body to try the screwdrive conversion myself. I could sell the body on again if things get sorted. Of course, if the fact that the lens isn’t focusing quite as precisely as it could in live view is a potential sign of something larger that might be wrong, then it may make the most sense to send the lens in to someplace that can properly look it over for repair.

Glad that you have now ascertained that it is the lens that is at fault. Hope that you get it to work again!

[mtkeller]

Glad that you have now ascertained that it is the lens that is at fault. Hope that you get it to work again!

Me, too. Just sent payment for a K-r that was listed here on the Marketplace, since I'd rather support another member on here than buy a used K100D Super from UsedPhotoPro/Roberts. I will come back with an update once I give screwdrive conversion a try!

[mtkeller]

K-r arrived today. Immediately put it to work doing the conversion to screwdrive. Afterward, I could successfully do the AF tuning on my target in the basement. The issue I’d noted with the focus in live view not being spot on has been resolved by the screwdrive conversion. No more jittering back and forth. Yeah, it’s not as quiet, but it now swiftly locks focus. I’m calling this a success. Now I guess I just need to see if anyone wants to buy a used K-r that I’ve owned for a day

[UncleVanya]

K-r arrived today. Immediately put it to work doing the conversion to screwdrive. Afterward, I could successfully do the AF tuning on my target in the basement. The issue I’d noted with the focus in live view not being spot on has been resolved by the screwdrive conversion. No more jittering back and forth. Yeah, it’s not as quiet, but it now swiftly locks focus. I’m calling this a success. Now I guess I just need to see if anyone wants to buy a used K-r that I’ve owned for a day

Success is always awesome to hear about!

[mtkeller]

Success is always awesome to hear about!

I appreciate all the experience members here (especially you) have shared to make this something I felt confident doing. Now I’m looking forward to going out and enjoying this lens focusing properly with my K-3 iii! I did catch a robin flying off a power line in my back yard tonight, and the combo tracked really nicely.

[caliscouser]

How's the noise with the screw-drive? I have a screw drive DA*200, but I haven't used it in a while.
From what I remember it's a little more subdued and damped than most screw drive lenses, but certainly not quiet.

[mtkeller]

Quieter than my F 100–300, but that’s a pretty low bar to clear

I wouldn’t call it quiet, but it’s tolerable. Maybe I’ll record a comparison clip tomorrow; I have the Tamron 70–200 as well.

[UncleVanya]

Quieter than my F 100–300, but that’s a pretty low bar to clear

I wouldn’t call it quiet, but it’s tolerable. Maybe I’ll record a comparison clip tomorrow; I have the Tamron 70–200 as well.

The DA* lenses are well sealed and that may help cut some noise