Jump to content

Parfocal lens for Speedbooster XL


Recommended Posts

Hello everyone,

I'm using GH4/G7 with Speedbooster XL an looking for a lens that won't lose focus when i zoom in. Basically i'm trying to achieve this zoom effect:

https://vimeo.com/141729555

What would be the best EF lens for that? Or even a panasonic lens that can do it? I've seen a lot of arguing about 24-105 f4 lens that some people mention works well some say it loses focus.

Also, i heard that speedboster ruins it while the lens may keep focus on full frame. 

Please help. Thank you

Link to post
Share on other sites

I don't think there are many still lenses that are really parfocal but some are better than others. Still lens mounts are not accurate enough for them to be anyway. In order for a lens to be parfocal the flange focal distance must be correct and the lens needs to be designed to do so. The reason why some say the canon lens is and some say it isn't is due to the in-accuracy of the lens mount. Basically some are closer to the correct distance than others so results vary. The speed booster is actually a positive because it can be used to adjust the back focus of the lens. If you adjust the booster until infinity hits its mark then you will have better results than you might otherwise. You may find that the canon lens is parfocal enough if you do that. No guarentees I have never tried it.

 

I don't recall which but some of the rumored parfocal canon zooms are only parfocal when zooming tele to wide.

Link to post
Share on other sites

I'm 99% sure that the 70-200 f/2.8 Non-IS is parfocal, i used to have one back when i shot canon. Tarantinos crash zoom often end with a very long focal length so 200mm (300mm FF equiv.) will be perfect for what you are doing.

yeah, but on GH4 this will be only good to film the moon in details. i'm looking into 24-70, 24-105 focal length to shoot portraits almost like in the reference i attached.

Link to post
Share on other sites

yeah, but on GH4 this will be only good to film the moon in details. i'm looking into 24-70, 24-105 focal length to shoot portraits almost like in the reference i attached.

Well the thread title states Speed Booster and Tarantino Crash zooms. If you look at that video again you will see that most go around 60-250mm (s35)

Link to post
Share on other sites

yeah, but on GH4 this will be only good to film the moon in details. i'm looking into 24-70, 24-105 focal length to shoot portraits almost like in the reference i attached.

based by the video you linked it looks like it zooms in to around 200-300mm from around 80. so a 70-200 will probably be good but you are the one to choose.

Link to post
Share on other sites

Hello everyone,

I'm using GH4/G7 with Speedbooster XL an looking for a lens that won't lose focus when i zoom in. Basically i'm trying to achieve this zoom effect:

https://vimeo.com/141729555

What would be the best EF lens for that? Or even a panasonic lens that can do it? I've seen a lot of arguing about 24-105 f4 lens that some people mention works well some say it loses focus.

Also, i heard that speedboster ruins it while the lens may keep focus on full frame. 

Please help. Thank you

3 scenarios here:

1)  Your zoom lens is perfectly parfocal, meaning the two endpoints and all points in-between focus to the same plane.  Adding a properly adjusted Speed Booster to such a lens will have no effect on its parfocality.  If the Speed Booster has a small adjustment error you can loosen the set-screw on the side of the lens mount and then thread the optical cell in or out to achieve perfect parfocality.

2)  Your zoom lens is parfocal at the end points (wide and tele), but drifts in-between.  This is a non-linear condition that is normally cured by re-machining the cam in really expensive cine zooms.  If your lens cost less than ~$20k then this non-linear error is ignored.  A Speed Booster has no effect on it.

3) Your zoom is not quite parfocal at the end points.  The Speed Booster can be used just like a set of precision shims to fix this condition.  However, the Speed Booster will likely not be properly adjusted for your other lenses.  So either you need a dedicated Speed Booster for this particular lens, or else consider the parfocality adjustment to be temporary.

Link to post
Share on other sites

3 scenarios here:

1)  Your zoom lens is perfectly parfocal, meaning the two endpoints and all points in-between focus to the same plane.  Adding a properly adjusted Speed Booster to such a lens will have no effect on its parfocality.  If the Speed Booster has a small adjustment error you can loosen the set-screw on the side of the lens mount and then thread the optical cell in or out to achieve perfect parfocality.

2)  Your zoom lens is parfocal at the end points (wide and tele), but drifts in-between.  This is a non-linear condition that is normally cured by re-machining the cam in really expensive cine zooms.  If your lens cost less than ~$20k then this non-linear error is ignored.  A Speed Booster has no effect on it.

3) Your zoom is not quite parfocal at the end points.  The Speed Booster can be used just like a set of precision shims to fix this condition.  However, the Speed Booster will likely not be properly adjusted for your other lenses.  So either you need a dedicated Speed Booster for this particular lens, or else consider the parfocality adjustment to be temporary.

Thank you Brian. This is a helpful info. I think before adjusting my speedbooster i'd need to decide on the more or less parfocal lens to rent. I don't own anything but canon ef 24-105 3.5-5.6 stm so would need to rent some.

Link to post
Share on other sites

I have the old Tokina/Angineux ATX Pro 28-70 f/2.6-2.8 and its parfocal. Even though it's an AF lens, you pull the focus ring toward the camera to engage MF and it has hard stops, so pulls are repeatable. Best part - it's an amazing lens and I paid $300. It's even usable wide open, best bargain in a zoom IMO. There are a few different versions, Google the lens for a rundown on which version to look for, they pop up on eBay all the time. 

Link to post
Share on other sites

I have the old Tokina/Angineux ATX Pro 28-70 f/2.6-2.8 and its parfocal. Even though it's an AF lens, you pull the focus ring toward the camera to engage MF and it has hard stops, so pulls are repeatable. Best part - it's an amazing lens and I paid $300. It's even usable wide open, best bargain in a zoom IMO. There are a few different versions, Google the lens for a rundown on which version to look for, they pop up on eBay all the time. 

this is very useful. i might buy it. not expensive and since it's parfocal sounds like a option for me. Thank you

Does it have to be used on speedbooster? I'm under the strong impression that the angenieux 17-68 2.2 is parfocal and it almost covers the gh4 4k crop. With minimal cropping in post it should be roughly 50-200 FF equivalent.

doesn't have to. thank you

I have the old Tokina/Angineux ATX Pro 28-70 f/2.6-2.8 and its parfocal. Even though it's an AF lens, you pull the focus ring toward the camera to engage MF and it has hard stops, so pulls are repeatable. Best part - it's an amazing lens and I paid $300. It's even usable wide open, best bargain in a zoom IMO. There are a few different versions, Google the lens for a rundown on which version to look for, they pop up on eBay all the time. 

do you mean hard stops for zoom? how is that? i'd need to pull the zoom smoothly from 28 to 70 and keep the focus? will this lens do it?

Link to post
Share on other sites

Agreed. Fantastic lens!

n8A51C8.jpg

The focus ring itself has a certain travel between its hard stops, it makes pulling focus from subject A to subject B easy, should you need to. It's just additional information for you. Hasn't got to do with zoom. If want to zoom in on subject A, and want subject A to be in focus during the zoom, with a parfocal lens you don't need any focus pulling of course. So yes, should work exactly like you want.

Link to post
Share on other sites

Agreed. Fantastic lens!

n8A51C8.jpg

The focus ring itself has a certain travel between its hard stops, it makes pulling focus from subject A to subject B easy, should you need to. It's just additional information for you. Hasn't got to do with zoom. If want to zoom in on subject A, and want subject A to be in focus during the zoom, with a parfocal lens you don't need any focus pulling of course. So yes, should work exactly like you want.

I can only find constant 2.8 lens not 2.6-2.8. do you know if it has the same characteristics?

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...