Dumb Question re SMC Pentax Reflex Zoom 400-600mm F8-12.

**Fastback67** · 08-10-2022, 01:44 PM

I recently picked up an SMC Pentax Reflex Zoom 400-600mm F8-12.
Question is : How do you change the focal length on this lens. Mine appears to be locked at 400mm, and I don't see any magic buttons or rings to zoom it out to 500mm or 600mm. there is a ring at the base with the focal lengths 400mm, 500mm, 600mm marked on it, but it does not appear to rotate. The focusing ring is just that, the focusing ring. The red barrel line for focusing distance is always at 400mm as well. I'm use to using a lens that has a separate zoom ring and a focus ring. Probably a dumb question I know, but I can't seem to locate any information concerning this lens. Any assistance here would be greatly appreciated.

Last edited by MarkJerling; 08-11-2022 at 12:45 AM. Reason: Fleshed out title.

jcdoss · 08-10-2022, 01:51 PM

The zoom ring is the thin ring near the lens mount. The lens will markedly extend when zooming to longer focal lengths.

**Fastback67** · 08-10-2022, 02:00 PM - **2 Likes**

Yes, I would expect that, however, the zoom ring near the lens mount does not rotate in any direction. It appears to be frozen at 400mm

---------- Post added 08-10-22 at 05:02 PM ----------

Hey!!! I just got it freed up!!! Good to go! Thank you very much! I didn't want to force it and break something without asking first.

gatorguy · 08-10-2022, 02:20 PM - **4 Likes**

Originally posted by Fastback67

Yes, I would expect that, however, the zoom ring near the lens mount does not rotate in any direction. It appears to be frozen at 400mm

---------- Post added 08-10-22 at 05:02 PM ----------

Hey!!! I just got it freed up!!! Good to go! Thank you very much! I didn't want to force it and break something without asking first.

Glad to see you got it sorted.

By the way, anytime you don't understand something about your photography or gear just ask away. There are no dumb questions, only dumb not to ask if you don't know.

jcdoss · 08-11-2022, 01:12 AM

Originally posted by Fastback67

Hey!!! I just got it freed up!!! Good to go!

Glad to hear that the problem has been resolved! Please make sure to post some images from that lens, especially ones with some excellent donut bokeh! 😁

steephill · 08-11-2022, 02:54 AM

I bought one which had the same issue so that means that based on a sample of two they all do it!. I couldn't free it off and sent it in for service. It had to go back to Pentax in Japan and came back clean and smooth although it is quite a tight movement - no chance of zoom creep!

Check that yours has a rear filter fitted.

**Fastback67** · 08-11-2022, 04:28 AM

Nope... No Rear Filter installed as yet. If memory serves there use to be a number of rear filters available for this lens. I'll have to look around.
Thanks guys!

jcdoss · 08-11-2022, 04:52 AM

I bought mine right at the beginning of this COVID crisis, and the zoom ring has always worked fine. I wouldn't say it's stiff, but it stays where I put it for sure. Just adding a new data point!

**mlag** · 08-11-2022, 03:07 PM

Originally posted by jcdoss

The zoom ring is the thin ring near the lens mount. The lens will markedly extend when zooming to longer focal lengths.

Mine is also quite reluctant to zoom, you need to apply more than usual force to rotate the ring, unlike any other lens ring. Lucky the focus ring is swifter. On the good side, the zoom doesn't creep if you point up or down, and you won't mess up the zoom while focussing.
But it is not the lens for swift zoom tracking a fast subject.

**Fastback67** · 08-14-2022, 04:56 AM

So I picked up a standard 40.5mm UV Filter for the rear of the lens, but it doesn't fit? It just sits and spins with no apparent thread engagement. Is there something special about these rear filters that I'm not aware of? Longer neck to threads, smaller outer barrel diameter?
Couldn't I just mount a 67mm UV Filter on the front instead?

Thank You

---------- Post added 08-14-22 at 08:29 AM ----------

Okay, so I broke out the calipers this morning and took a few measurements.
The thread size is indeed 40.5mm at the rear of the lens. The acceptable outer diameter for any filter to be inserted at the rear of the lens is 42mm.
The UV filter I picked up has the required 40.5mm thread, but the outer barrel diameter is 43mm, so it just sits there and spins, never touching the threads.
I've never seen filters sold with both Outer Dia. and Thread Dia....

sota · 04-27-2023, 06:51 PM

to add a data point:
my reflex zoom is also stupidly stiff to turn the zoom ring. so much so that the previous owner dislodged the rubber ring. Ironically, mine will zoom nicely using a push/pull on the focusing ring!

I haven't looked into the rear filter situation yet.

08-10-2022, 01:44 PM	#1
Fastback67 Site Supporter Join Date: Aug 2012 Location: New Hampshire, USA Photos: Gallery Posts: 348	Dumb Question re SMC Pentax Reflex Zoom 400-600mm F8-12. I recently picked up an SMC Pentax Reflex Zoom 400-600mm F8-12. Question is : How do you change the focal length on this lens. Mine appears to be locked at 400mm, and I don't see any magic buttons or rings to zoom it out to 500mm or 600mm. there is a ring at the base with the focal lengths 400mm, 500mm, 600mm marked on it, but it does not appear to rotate. The focusing ring is just that, the focusing ring. The red barrel line for focusing distance is always at 400mm as well. I'm use to using a lens that has a separate zoom ring and a focus ring. Probably a dumb question I know, but I can't seem to locate any information concerning this lens. Any assistance here would be greatly appreciated. Last edited by MarkJerling; 08-11-2022 at 12:45 AM. Reason: Fleshed out title.

08-14-2022, 04:56 AM	#10
Fastback67 Site Supporter Join Date: Aug 2012 Location: New Hampshire, USA Photos: Gallery Posts: 348 Original Poster	So I picked up a standard 40.5mm UV Filter for the rear of the lens, but it doesn't fit? It just sits and spins with no apparent thread engagement. Is there something special about these rear filters that I'm not aware of? Longer neck to threads, smaller outer barrel diameter? Couldn't I just mount a 67mm UV Filter on the front instead? Thank You ---------- Post added 08-14-22 at 08:29 AM ---------- Okay, so I broke out the calipers this morning and took a few measurements. The thread size is indeed 40.5mm at the rear of the lens. The acceptable outer diameter for any filter to be inserted at the rear of the lens is 42mm. The UV filter I picked up has the required 40.5mm thread, but the outer barrel diameter is 43mm, so it just sits there and spins, never touching the threads. I've never seen filters sold with both Outer Dia. and Thread Dia.... Last edited by Fastback67; 08-14-2022 at 05:30 AM.

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08-10-2022, 01:51 PM	#2
jcdoss Pentaxian Join Date: Nov 2012 Location: Ingelheim am Rhein, Germany Photos: Gallery \| Albums Posts: 6,769	The zoom ring is the thin ring near the lens mount. The lens will markedly extend when zooming to longer focal lengths.

08-10-2022, 02:00 PM - 2 Likes	#3
Fastback67 Site Supporter Join Date: Aug 2012 Location: New Hampshire, USA Photos: Gallery Posts: 348 Original Poster	Yes, I would expect that, however, the zoom ring near the lens mount does not rotate in any direction. It appears to be frozen at 400mm ---------- Post added 08-10-22 at 05:02 PM ---------- Hey!!! I just got it freed up!!! Good to go! Thank you very much! I didn't want to force it and break something without asking first.

08-10-2022, 02:20 PM - 4 Likes	#4
gatorguy Moderator Join Date: Feb 2015 Location: Central Florida Photos: Gallery Posts: 6,092	Originally posted by Fastback67 Yes, I would expect that, however, the zoom ring near the lens mount does not rotate in any direction. It appears to be frozen at 400mm ---------- Post added 08-10-22 at 05:02 PM ---------- Hey!!! I just got it freed up!!! Good to go! Thank you very much! I didn't want to force it and break something without asking first. Glad to see you got it sorted. By the way, anytime you don't understand something about your photography or gear just ask away. There are no dumb questions, only dumb not to ask if you don't know.

08-11-2022, 01:12 AM	#5
jcdoss Pentaxian Join Date: Nov 2012 Location: Ingelheim am Rhein, Germany Photos: Gallery \| Albums Posts: 6,769	Originally posted by Fastback67 Hey!!! I just got it freed up!!! Good to go! Glad to hear that the problem has been resolved! Please make sure to post some images from that lens, especially ones with some excellent donut bokeh! 😁

08-11-2022, 02:54 AM	#6
steephill Pentaxian Join Date: Nov 2018 Photos: Gallery Posts: 586	I bought one which had the same issue so that means that based on a sample of two they all do it!. I couldn't free it off and sent it in for service. It had to go back to Pentax in Japan and came back clean and smooth although it is quite a tight movement - no chance of zoom creep! Check that yours has a rear filter fitted.

08-11-2022, 04:28 AM	#7
Fastback67 Site Supporter Join Date: Aug 2012 Location: New Hampshire, USA Photos: Gallery Posts: 348 Original Poster	Nope... No Rear Filter installed as yet. If memory serves there use to be a number of rear filters available for this lens. I'll have to look around. Thanks guys!

08-11-2022, 04:52 AM	#8
jcdoss Pentaxian Join Date: Nov 2012 Location: Ingelheim am Rhein, Germany Photos: Gallery \| Albums Posts: 6,769	I bought mine right at the beginning of this COVID crisis, and the zoom ring has always worked fine. I wouldn't say it's stiff, but it stays where I put it for sure. Just adding a new data point!

08-11-2022, 03:07 PM	#9
mlag Loyal Site Supporter Join Date: Jul 2021 Location: Zuiderkempen - Grote Netewoud - Belgium Photos: Gallery \| Albums Posts: 1,399	Originally posted by jcdoss The zoom ring is the thin ring near the lens mount. The lens will markedly extend when zooming to longer focal lengths. Mine is also quite reluctant to zoom, you need to apply more than usual force to rotate the ring, unlike any other lens ring. Lucky the focus ring is swifter. On the good side, the zoom doesn't creep if you point up or down, and you won't mess up the zoom while focussing. But it is not the lens for swift zoom tracking a fast subject.

04-27-2023, 06:51 PM	#11
sota Forum Member Join Date: Apr 2023 Location: NJ Posts: 64	to add a data point: my reflex zoom is also stupidly stiff to turn the zoom ring. so much so that the previous owner dislodged the rubber ring. Ironically, mine will zoom nicely using a push/pull on the focusing ring! I haven't looked into the rear filter situation yet.