What true zoom for Pentax video?

eurostar · 02-29-2012, 12:16 AM

I am starting to make video with my k-5, and I have found one problem with my lenses (DA* 16-50 and 60-250): they are variofocal lenses that when you zoom, focus is not kept, and you have too refocus. This make impossimple to zoom during shooting. What options exists among older lenses for Pentax? In the past I had A35-105 and F70-210, but don't remember if they kept focus during zooming.

Alizarine · 02-29-2012, 01:57 AM

I think the K-5 doesn't allow focus tracking while in video mode... it's all manual

metaphiston · 02-29-2012, 02:54 AM

In my experience, the older manual focus lenses are parfocal (they keep same focus throughout zoom range) and the newer autofocus lenses are varifocal (they have variable focus throughout the zoom range). I have several old A and M zoom lenses and they are all parfocal, because they were designed so that you could zoom in to focus then zoom out to compose. I don't know if this is true for all A and M zooms, but I suspect so.

Lenses designed for video cameras are parfocal, but autofocus lenses intended primarily for stills are not as an optical compromise that allows the lens designers to maximise quality and lightness by ditching the need to keep focus throughout the zoom.

Relatedly, I find the older lenses have much smoother manual focus rings than modern lenses which makes manual focus during a video recording (which is of course the ONLY way to focus during a video recording on k-5) easier and better looking.

Hope that's helpful!

eurostar · 02-29-2012, 02:59 AM

Originally posted by Alizarine

I think the K-5 doesn't allow focus tracking while in video mode... it's all manual

Yes, that's why I asked what zooms (if any) keep the focus during zooming. With AF, it's the camera to correct focus for you during zooming. Without AF you need a zoom that keep focus.

eurostar · 02-29-2012, 03:02 AM

Originally posted by metaphiston

In my experience, the older manual focus lenses are parfocal (they keep same focus throughout zoom range) and the newer autofocus lenses are varifocal (they have variable focus throughout the zoom range). I have several old A and M zoom lenses and they are all parfocal, because they were designed so that you could zoom in to focus then zoom out to compose. I don't know if this is true for all A and M zooms, but I suspect so.

Lenses designed for video cameras are parfocal, but autofocus lenses intended primarily for stills are not as an optical compromise that allows the lens designers to maximise quality and lightness by ditching the need to keep focus throughout the zoom.

Relatedly, I find the older lenses have much smoother manual focus rings than modern lenses which makes manual focus during a video recording (which is of course the ONLY way to focus during a video recording on k-5) easier and better looking.

Hope that's helpful!

That's helpful indeed. Now I just have to be sure of what zoom to chose. Maybe A 28-135... normal to medium tele.

cmohr · 02-29-2012, 04:02 AM

I'm unsure if it works in video, but the Pentax Powerzooms keep focus when zooming. I'll fish mine out and see if it works.

cmohr · 02-29-2012, 04:22 AM

No... sorry, I tracks focus up until you press the record button, then. it stops focusing. worth a try. But my 50-135 seems to keep focus when zooming, I focus at 135, and then when zooming out it remains infocus

liukaitc · 02-29-2012, 12:12 PM

...I think k-5 does not allow tracking focus in video.
for that you need GH2..but that is not 100% accurate, sometimes it will miss the focus and refocus.
that is why pro rely on manual focus with large montior and follow focus. that is the best way to go with HDSLR.

eurostar · 02-29-2012, 10:49 PM

Originally posted by liukaitc

...I think k-5 does not allow tracking focus in video.
for that you need GH2..but that is not 100% accurate, sometimes it will miss the focus and refocus.
that is why pro rely on manual focus with large montior and follow focus. that is the best way to go with HDSLR.

Sure, but we are speaking of zooming, not focusing. I have no problem at focusing manually, but if zooming the focus change, I can't manually zooming and focusing at the same time. I need a zoom that doesn't change focus when zooming during recording.

Anvh · 03-01-2012, 01:19 AM

It's hard reading some times... XD

But older lenses sound indeed good, you can also take out the click in the aperture ring as well when you buy a lens specially for filming. =]
ps. not sure you should look at the cheaper zoom lenses or zoom lenses with a big range if you want to focus to stay, be sure to test those first but i fear the worst...

altopiet · 03-01-2012, 01:51 AM

I modified an old Vivitar 70-150mm by removing the aperture ball and lever, giving it sound free aperture control while taking video clips in AV, and as it is a push-pull zoom, focus stays the same when zooming while filming

metaphiston · 03-01-2012, 02:50 AM

Quote:

That's helpful indeed. Now I just have to be sure of what zoom to chose. Maybe A 28-135... normal to medium tele.

I haven't used the A18-135 though the few reviews in the lens database suggests it's not the best optically. I have used the A28-50 f4, and it would work very well for video due to the smooth focus and zoom. Similarly the A35-70 f4 has a robust, smooth feel to the mechanism. The optical quality looks good to me too. They both have modest f4 max aperture but at least it's constant throughout the range.

I own the M75-150 f4, and am very impressed with the optical quality. It is of the push-pull zoom type, though I've found with my copy that the zoom can drift if pointing up or down, this may be an issue with other zoom lenses of this design. I've not used the M35-70 2.8-3.5 but reviewsd are postive, and it's also of the push-pull type for smooth zoom while recording.

The best thing to do would be try before you buy, to double-check it IS parfocal and that the zoom doesn't drift! Not always possible if buying online though.

eurostar · 03-01-2012, 01:05 PM

Many interesting suggestions, thanks very much to you all.

jogiba · 03-04-2012, 06:32 AM

You Tube

reivax · 05-06-2012, 09:35 AM

Hope no one minds that I'm reviving an old thread. It seems like the consensus is to use parfocal lenses for video? I've been searching through older lenses and most don't list if they are parfocal or varifocal (or I'm missing something?). How can one know? Did lens makers stop using parfocal after a particular series? Or does it depend on the lens itself? Is it safe to assume that A series zoom lenses are all parfocal? Or only some? Are there any F series zoom lenses that are parfocal?

I'm really interested in getting a zoom lens that I can use with my Kr for video. I've been using my da 55-300 and while the results are decent, as soon as I need to refocus, I just pretty much have to accept that it's not going to happen (especially with a lot of movement).

02-29-2012, 12:16 AM	#1
eurostar Veteran Member Join Date: Dec 2006 Location: Albareto, Italy Photos: Gallery Posts: 819	What true zoom for Pentax video? I am starting to make video with my k-5, and I have found one problem with my lenses (DA* 16-50 and 60-250): they are variofocal lenses that when you zoom, focus is not kept, and you have too refocus. This make impossimple to zoom during shooting. What options exists among older lenses for Pentax? In the past I had A35-105 and F70-210, but don't remember if they kept focus during zooming.

02-29-2012, 12:12 PM	#8
liukaitc Veteran Member Join Date: Jul 2010 Location: New York Photos: Albums Posts: 1,008	...I think k-5 does not allow tracking focus in video. for that you need GH2..but that is not 100% accurate, sometimes it will miss the focus and refocus. that is why pro rely on manual focus with large montior and follow focus. that is the best way to go with HDSLR. Last edited by liukaitc; 02-29-2012 at 12:19 PM.

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02-29-2012, 01:57 AM	#2
Alizarine Veteran Member Join Date: Dec 2010 Location: Manila Photos: Gallery \| Albums Posts: 2,185	I think the K-5 doesn't allow focus tracking while in video mode... it's all manual

02-29-2012, 02:54 AM	#3
metaphiston Forum Member Join Date: Aug 2010 Location: Edinburgh Posts: 91	In my experience, the older manual focus lenses are parfocal (they keep same focus throughout zoom range) and the newer autofocus lenses are varifocal (they have variable focus throughout the zoom range). I have several old A and M zoom lenses and they are all parfocal, because they were designed so that you could zoom in to focus then zoom out to compose. I don't know if this is true for all A and M zooms, but I suspect so. Lenses designed for video cameras are parfocal, but autofocus lenses intended primarily for stills are not as an optical compromise that allows the lens designers to maximise quality and lightness by ditching the need to keep focus throughout the zoom. Relatedly, I find the older lenses have much smoother manual focus rings than modern lenses which makes manual focus during a video recording (which is of course the ONLY way to focus during a video recording on k-5) easier and better looking. Hope that's helpful!

02-29-2012, 02:59 AM	#4
eurostar Veteran Member Join Date: Dec 2006 Location: Albareto, Italy Photos: Gallery Posts: 819 Original Poster	Originally posted by Alizarine I think the K-5 doesn't allow focus tracking while in video mode... it's all manual Yes, that's why I asked what zooms (if any) keep the focus during zooming. With AF, it's the camera to correct focus for you during zooming. Without AF you need a zoom that keep focus.

02-29-2012, 03:02 AM	#5
eurostar Veteran Member Join Date: Dec 2006 Location: Albareto, Italy Photos: Gallery Posts: 819 Original Poster	Originally posted by metaphiston In my experience, the older manual focus lenses are parfocal (they keep same focus throughout zoom range) and the newer autofocus lenses are varifocal (they have variable focus throughout the zoom range). I have several old A and M zoom lenses and they are all parfocal, because they were designed so that you could zoom in to focus then zoom out to compose. I don't know if this is true for all A and M zooms, but I suspect so. Lenses designed for video cameras are parfocal, but autofocus lenses intended primarily for stills are not as an optical compromise that allows the lens designers to maximise quality and lightness by ditching the need to keep focus throughout the zoom. Relatedly, I find the older lenses have much smoother manual focus rings than modern lenses which makes manual focus during a video recording (which is of course the ONLY way to focus during a video recording on k-5) easier and better looking. Hope that's helpful! That's helpful indeed. Now I just have to be sure of what zoom to chose. Maybe A 28-135... normal to medium tele.

02-29-2012, 04:02 AM	#6
cmohr Pentaxian Join Date: Apr 2011 Location: Brisbane. Australia Photos: Gallery Posts: 1,824	I'm unsure if it works in video, but the Pentax Powerzooms keep focus when zooming. I'll fish mine out and see if it works.

02-29-2012, 04:22 AM	#7
cmohr Pentaxian Join Date: Apr 2011 Location: Brisbane. Australia Photos: Gallery Posts: 1,824	No... sorry, I tracks focus up until you press the record button, then. it stops focusing. worth a try. But my 50-135 seems to keep focus when zooming, I focus at 135, and then when zooming out it remains infocus

02-29-2012, 10:49 PM	#9
eurostar Veteran Member Join Date: Dec 2006 Location: Albareto, Italy Photos: Gallery Posts: 819 Original Poster	Originally posted by liukaitc ...I think k-5 does not allow tracking focus in video. for that you need GH2..but that is not 100% accurate, sometimes it will miss the focus and refocus. that is why pro rely on manual focus with large montior and follow focus. that is the best way to go with HDSLR. Sure, but we are speaking of zooming, not focusing. I have no problem at focusing manually, but if zooming the focus change, I can't manually zooming and focusing at the same time. I need a zoom that doesn't change focus when zooming during recording.

03-01-2012, 01:19 AM	#10
Anvh Veteran Member Join Date: Sep 2011 Posts: 4,616	It's hard reading some times... XD But older lenses sound indeed good, you can also take out the click in the aperture ring as well when you buy a lens specially for filming. =] ps. not sure you should look at the cheaper zoom lenses or zoom lenses with a big range if you want to focus to stay, be sure to test those first but i fear the worst...

03-01-2012, 01:51 AM	#11
altopiet Veteran Member Join Date: Sep 2010 Location: The Gem of the Karoo, South Africa Photos: Gallery \| Albums Posts: 2,307	I modified an old Vivitar 70-150mm by removing the aperture ball and lever, giving it sound free aperture control while taking video clips in AV, and as it is a push-pull zoom, focus stays the same when zooming while filming

03-01-2012, 02:50 AM	#12
metaphiston Forum Member Join Date: Aug 2010 Location: Edinburgh Posts: 91	Quote: That's helpful indeed. Now I just have to be sure of what zoom to chose. Maybe A 28-135... normal to medium tele. I haven't used the A18-135 though the few reviews in the lens database suggests it's not the best optically. I have used the A28-50 f4, and it would work very well for video due to the smooth focus and zoom. Similarly the A35-70 f4 has a robust, smooth feel to the mechanism. The optical quality looks good to me too. They both have modest f4 max aperture but at least it's constant throughout the range. I own the M75-150 f4, and am very impressed with the optical quality. It is of the push-pull zoom type, though I've found with my copy that the zoom can drift if pointing up or down, this may be an issue with other zoom lenses of this design. I've not used the M35-70 2.8-3.5 but reviewsd are postive, and it's also of the push-pull type for smooth zoom while recording. The best thing to do would be try before you buy, to double-check it IS parfocal and that the zoom doesn't drift! Not always possible if buying online though.

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03-01-2012, 01:05 PM	#13
eurostar Veteran Member Join Date: Dec 2006 Location: Albareto, Italy Photos: Gallery Posts: 819 Original Poster	Many interesting suggestions, thanks very much to you all.

05-06-2012, 09:35 AM	#15
reivax Veteran Member Join Date: Jun 2011 Location: California Posts: 826	Hope no one minds that I'm reviving an old thread. It seems like the consensus is to use parfocal lenses for video? I've been searching through older lenses and most don't list if they are parfocal or varifocal (or I'm missing something?). How can one know? Did lens makers stop using parfocal after a particular series? Or does it depend on the lens itself? Is it safe to assume that A series zoom lenses are all parfocal? Or only some? Are there any F series zoom lenses that are parfocal? I'm really interested in getting a zoom lens that I can use with my Kr for video. I've been using my da 55-300 and while the results are decent, as soon as I need to refocus, I just pretty much have to accept that it's not going to happen (especially with a lot of movement).