[Sagitta]

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I'm going to have to test out my old zooms for this, just because I know of it now. Most aren't on the list or mentioned anywhere as far as I saw.

[Ex Finn.]

I was bored and decided to check my A 70-210/4
It proved harder to determine on the DA 18-55 WR, as far I can tell it is parfocal also.

[Sagitta]

Apologies if I repeat anything in here. Order is as I grab 'em from storage.

Sears (Samyang) 70-210 f/4 is, but its push/pull so basically useless as you'll shift focus unless you have impressively steady hands.

Pentax FA28-90mm f3.5-5.6 appears to be. Surprising since its a cheap 90's kit lens.

Sears (Samyang) 28-70mm f/3.5-4.5mm. Is, but again its push pull, and its also all around an awful lens.

Sigma 70-300mm f/4-5.6 DL Macro Super is not.

Sears (RMC Tokina) 75-260mm f/4.5 Close Focus IS. No push pull here so its much handier, if you don't mind big heavy zooms.

Pentax F 35-70mm f/3.5-4.5 Macro appears to be. Due to the short focal range, it could simply be a case of it not ever zooming far enough to get out of focus.

Sigma 10-20mm f/3.5 appears to be so, but again the short throw makes any positive yes/no tough.

[Ex Finn.]

Sears (Samyang) 70-210 f/4 is, but its push/pull so basically useless as you'll shift focus unless you have impressively steady hands.

I let my SMC A ride the close-focus stop.

[mgvh]

[Apparently the original editor can not edit a post after enough time has passed. I'll repeat it here and update it with the latest. Or should I just start a new thread? While I was at, I reorganized the Pentax lenses according to starting focal length.]

What zoom lenses are parfocal?
I've tracked down a couple threads that deal with the matter somewhat (here and here), but I think it would be helpful to have a list of zoom lenses that are parfocal.

Quick summary:
Parfocal lenses are ones where you can focus at any focal length and changing the zoom won't affect the focus. With the advent of autofocus mechanisms, that became less important, so many (most?) newer zoom lenses are varifocal. (Apparently it is easier to make varifocal lenses, and they are also lighter.)

Why is this significant? If you want to shoot video on most (all?) of the Pentax bodies, the focus is locked once you start shooting video. On some of the newer bodies (e.g., the K-30), you can re-focus while shooting, but it does not offer continuous focus.
SO: if you want to shoot video with your Pentax, and you plan to do any zooming, you will most certainly want a parfocal lens. (It is nearly impossible to zoom and focus at the same time.)

In any case, the lens database here doesn't seem to indicate whether a zoom lens is parfocal or varifocal, so, as one consideration when buying a lens, a parfocal zoom lens list might be helpful.

In general (and here is where confirmation from your experiences would help), I think most (all?) of the film era zooms are parfocal: K, M, A, F, FA, and FA-J lenses.
From reading the other threads, it appears that some newer lenses may almost be parfocal. (DA 16-45; DA 50-135; DA 50-200 WR; Tamron 28-75)

UPDATE (and I'll try to keep this updated as something of a sticky): Thanks to beholder3, we have something of a list being established. (See his post on page 2)

After reading this here I started a similar discussion on another forum and this is what we got so far for parfocal lenses with PK mount.

UPDATED 2015.02.19 (w/ latest info)

1. Pentax DA 16-45 F4
2. Pentax DA 18-55 mm F3.5-5.6 AL (v1)* - WR version
3. Pentax DA 18-250*
4. Pentax FA 24-90 mm
5. Pentax M 28-50/3.5-4.5
6. Pentax-F Zoom 28 - 80mm 1:3.5-4.5 MACRO
7. Pentax F 28-80 mm F3.5-4.5
8. Pentax FA28-90mm f3.5-5.6
9. Pentax M 35-70mm f2.8-3.5 (push-pull)
10. Pentax F 35-70**
11. Pentax A 35-105 mmF3.5
12. DA 50-200 WR
13. Pentax SMC-A 70-210 f4
14. Pentax M 75-150mm f4 (push-pull)
15. Pentax M 80-200 mm f4.5 (push-pull)
16. Pentax F 80-200 mm 1:4.7-5.6
17. Pentax F 100-300 mm f4.5-5.6
18. Pentax FA 100-300mm F4.5-5.6
19. Sigma 18-200
20. Tamron 17-50/2.8
21. Tamron 70-150/3.5 (20A)
22. Tamron 28-75/f2,8
23. Tamron 28-80mm F:3.5-5.6 AF Aspherical**
24. Tamron SP 35-80/2.8-3.5 (01A)
25. Tamron 28-70/3.5-4.5 (44A)
26. Tamron 70-200/2.8
27. Tamron SP AF 24-135mm F/3.5-5.6 AD Aspherical [IF]
28. Tokina 19-35/3.5-4.5
29. Tokina RMC 25 - 50 F4
30. RMC Tokina 75-150 f/3.8*
31. Tokina SZ-X 60-300mm f4-5.6 (push-pull)
32. Vivitar Series 1, 35-85mm f2.8
33. Vivitar 70-150mm f3.8
34. Vivitar MC 75-205/f3.8 (1touch Kiron)
35. Sears (RMC Tokina) 75-260mm f/4.5 Close Focus
36. Sigma EX 10-20 f4-5.6** (could be due to short throw; small range)
37. Sigma 10-20mm f/3.5** (could be due to short throw; small range)
38. Sigma 17-70/2.8-4.5*
39. Sigma 18-35 f/1.8 (NOT parfocal, but at f/4 and smaller the focus shift becomes trivial)
40. Sigma 18-50/2.8 EX Macro
41. Tamron Adaptall 70-150mm f3.5 Model QZ-150M (two touch, has manual/auto switch so can vary aperture manually whilst filming)
42. Tamron Adaptall-2 35-70mm f3.5 Model 17A (two touch)
43. Tamron Adaptall-2 70-150mm f3.5 Model 02A (two touch)
44. Tamron Adaptall-2 80-210mm f3.8-4 Model 03A (push-pull)
45. Tamron Adaptall-2 80-210mm f3.8-4 Model 103A (push-pull)
46. Tamron Adaptall-2 70-210mm f3.8-4 Model 46A (push-pull)
47. Tamron Adaptall-2 SP 70-210mm f3.5-4 Model 52A (two touch)
48. Tamron Adaptall SP 60-300mm f4-5.6 Model 23A (Push-pull)
49. Tamron Adaptall-2 SP 70-210mm f/3.5 (19AH)

*= under discussion.
**= nearly parfocal


===============

I can confirm that my DA 18-135, DAL 18-55, and Pentax DAL 55-300 are NOT parfocal.

I can confirm that my F 35-70 is parfocal as is the Tamron SP AF 24-135mm F/3.5-5.6 AD Aspherical [IF].

Some lenses may be hard to determine, especially wide angle ones. My Sigma EX 10-20 f4-5.6 is nearly parfocal. (Since it's so wide, you have lots of room for error, but basically if you focus at 20mm, it will still be good at 10mm. If you focus at 10mm, it may be a bit off at 20mm.)

If anyone is interested, then, it would be helpful to confirm:

• If those older zooms ( K, M, A, F, FA, and FA-J) are indeed all parfocal
• Which of the DA and DA-L zooms are parfocal
• Which other non-Pentax lenses are parfocal

BTW, it might also be helpful to note which ones have push-pull zoom, since those seem to be easier for video.
Thanks!

NOT Parfocal

1. Pentax DA 18-135
2. Pentax DAL 18-55
3. Pentax DAL 55-300
4. Sigma 70-300mm f/4-5.6 DL Macro Super
5. Tamron Adaptall 35-80mm f2.8-3.5 Model QZ-35M
6. Tamron Adaptall 85-210mm f4.5 Model QZ-210M
7. Tamron Adaptall 85-250mm f3.8-4.5 Model QZ-250M
8. Tamron Adaptall-2 75-250mm f3.8-4.5 Model 104A

[Sagitta]

I'm not so sure how easy the push pulls would be, as the very act of zooming can throw the focus off if you twist your hand even the slightest bit.

Both my budget Sears are parfocal push pulls, but I had to retest a number of times because I'd screw the focus up by turning the barrel while zooming. Actually, for video if you want that flarey, washed 70's kind of look, the awful Sears 28-70 may be what one would want. Sometimes the traits one wants to avoid for stills work for video.

[Ex Finn.]

Just to clarify, the SMC-A 70-210 f4 is a push-pull.
I agree on the difficulty of keeping the barrel from rotating while zooming. It is lot easier when the camera is on a tripod and one can keep the focus distance indication lined up with the IR DOF "base-line".

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[Digitalis]

if you want that flarey, washed 70's kind of look, the awful Sears 28-70 may be what one would want. Sometimes the traits one wants to avoid for stills work for video.

...it is probably better to do that in post production that in-camera.

[Sagitta]

...it is probably better to do that in post production that in-camera.

I'm trying to find something redeeming about that lens!

[Rukia2005]

Anyone tried DA* 60-250mm yet? I feel like it's parfocal since the design is close to DA* 50-135mm which is a parfocal lens

[gofour3]

UPDATED 2015.02.19 (w/ latest info)

These K Series zooms are all an "one touch push/pull" design:

K45-125/4
K80-200/4.5
K85-210/3.5
K85-210/4.5
K135-600/6.7

Phil.

[mgvh]

These K Series zooms are all an "one touch push/pull" design:

K45-125/4
K80-200/4.5
K85-210/3.5
K85-210/4.5
K135-600/6.7

Phil.

Hi, Phil. Are you also saying that these are parfocal lenses?

[sholtzma]

Is the FA* 28-70mm f2.8 parfocal? I haven't done tests yet, but someone may have the answer already.

Also, can we get this information on the lens review pages?

[gofour3]

Hi, Phil. Are you also saying that these are parfocal lenses?

Yep, focus then push/pull to zoom.

Phil.

[Bukaj]

Tokina RMC 25 - 50 F4

...after puting it on more resolving camera (24, instead of 10 MPx) I can see a slight focus shift when zooming.