Author Topic: Let's talk LENSES!  (Read 921 times)

Taofledermaus

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Let's talk LENSES!
« on: July 13, 2017, 10:08:41 PM »
I admit I know very little about lenses.  When people have suggested certain lenses and adaptors,   it has just confused me even more!   It would be interesting to know
what people have used,  what has worked,   and what lenses work best for different applications like macro to zoom.   Trying to find the perfect lens can get very expensive,  so I hope
we can all learn from each other.   

Johnny

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Re: Let's talk LENSES!
« Reply #1 on: July 14, 2017, 09:55:25 AM »
My lenses so far:

Angenieux 10mm f1,8 Retrofocus
Kern Paillard Switar 25mm f1.4 (needs some modification)
Angenieux 15-150mm 1.9

All three of them have a native c-mount.

The 25mm Switar is the only one that needs some sawing of the outer frame to fit. It is because of the c to cs-mount adapter that has to be used. I think that if the camera would have a native c-mount it would not need the modification.
It is fairly easy modification to do, if you know how to use a saw or file.

All of them work fine after adjusting the back focus.
« Last Edit: July 14, 2017, 09:58:16 AM by Johnny »

ExaltedDuck

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Re: Let's talk LENSES!
« Reply #2 on: July 15, 2017, 10:46:53 AM »
Hi TFM, I've been enjoying your content for years. 

I'm in kind of the same boat, never owned a camera before that didn't come with its only lens attached.  Well technically, I still don't (and probably wouldn't for stills unless/until my trusty WB850F dies).  I was likely the very last kickstarter and am still a few weeks away from receiving my Chronos, from the sound of things.  That hasn't stopped me from researching and shopping though.  I've taken the plunge on a Schneider Variogon 18-90mm f/2 from ebay and have already received a Belle & Howe Angenieux 25mm f/0.95 from Victoria Camera Traders (great guys and fast service there, btw).  Neither broke the bank, with both priced about the same as a new sample of the computar 12.5-75mm.  I'll hope the CS-C adapter I plan to get with my Chronos backsaces them properly, but we'll have to wait and see.

I was aiming to find lenses meant for 16mm and super-16.  The frame size of 16mm film is almost a match to the 2/3" sensor on the Chronos so there should be no vignetting and only a minimal cropping factor (a 50mm focal length lens for 16mm film frame should produce an image like a 58mm focal length lens on a 2/3" sensor).  Super-16 is pretty reasonable as well (a 50mm would behave like a 66mm).  Some good info is here and here.  I've been trying to think about the physics of it and while I think I kind of understand how the mismatch alters the field depth to behave like a different f-stop, I am inclined to believe this wouldn't have much impact on the light gathering performance. (if a 4/3" 50 mm f/2 lens is on a 2/3" sensor, we can expect it produce an image framed like 100 mm lens with the field depth of an f/4 aperture but I *think* it would provide the same contrast and brightness as though it were still on a 4/3" sensor at f/2. If anyone knows better, please, by all means, correct me. :) )  I've also noticed there's quite a bit of interest for vintage lenses in the Blackmagic Pocket Cinema Camera communities... its sensor is between 16mm and super-16 so their findings are quite valuable to us, as well.

Anyway, thanks for all the entertainment over the years.  That headspinning Chakotay still has my mind reeling like a block of clay after a silly putty slug. Once my camera is in, if you ever want a second angle, I'd be willing to make the drive from OC up your neck of the woods. Might give me the impetus to finally get my BFR45-70 fixed (or just say screw it and haul up the 460 instead)

nik282000

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Re: Let's talk LENSES!
« Reply #3 on: July 15, 2017, 04:55:06 PM »
C and CS mount lenses are an easy way to go but I have found that unless you pay "real" lens prices you are going to get quality somewhere between security camera and VHS, you get what you pay for.

I have been using a pair of C-mounts, an 8mm f1.3 and a 16mm f1.4 which are both good for a normal field of view, catching what you might expect to see when looking an an object within a few meters of the camera, the 8mm allowing you to fit an ~1m object in view at a distance of 1m.

For close cropped shots I have been using manual focus SLR lenses with a C-mount adapter, lenses like a 50mm f1.4 are great for catching outdoor subjects (birds or squirrels in a park). With the 50mm an object ~1m wide will fill the screen at a distance of 6m.

If the 50mm lens lets you focus at distances of 1m or less you can use it for macro shots of large insects, with an 80mm+ lens you can capture fairly small insects. If your lens wont let you focus at very short distances you have a couple of options, first is to buy a macro filter, these fit on most SLR lenses and make it so you can focus very close (almost touching the lens). If you don't want to use a macro filter you can use macro-rings/extension rings, these move the lens slightly farther away from the camera which makes the lens focus closer, they are made specifically for each lens mount BUT if you want to just hack it you might be able to get away with stacking 1 or 2 CS to C mount adapters. This will have the same effect as macro rings but may cut off the corners of your image.

For insanely high magnification I have used a 400mm f8 lens on the Chronos, it let me see a golfer teeing off from nearly 1km away and still have the ball visible. An ~1m object would have to be 50m away in order to fit on the screen at that point.

Finally, all of the "will fit on your screen" numbers only apply when you shoot at 1280px image width, when you increase the frame rate and shrink the resolution you will need to use lenses with shorter focal lengths to get a wider field of view. For example if I can see my whole shot with the 16mm lens at 1280x720 I will have to switch to the 8mm lens if I want to film at 640x360.

Hope this was helpful.

Simon

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Re: Let's talk LENSES!
« Reply #4 on: July 15, 2017, 07:40:36 PM »
I'm hoping to get away with my Canon lenses - a 17-35/2.8L, 70-200/2.8L. 

Bought a Fotodiox C to EF adapter - nice quality. All I need now is the camera.

Also have a 17-85 Macro that was chucked in for free with a 2nd hand body I once bought because its electronics would fail and lock the body - glad I kept it.

I will be mainly analysing the strike of a golf ball and prelim calcs showed me the 17-35 will be good. The minimum focusing distance of 0.42m shouldn't change because of the crop, but the crop factor magnification is a godsend in making that golf ball occupy more pixels, so more accurate measurements can be taken.

Like ExaltedDuck, I believe the light gathering performance won't be affected by the crop - sure less total light will hit the sensor but each sensor pixel will still get the same exposure as it would have if the sensor was full frame.

I have done macro work before taping the 17-35 backwards to the 70-200, but depth of field is just too small for anything moving. I had the center of a fly's eye in focus, the outer parts way out of focus it is that small.

Electra

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Re: Let's talk LENSES!
« Reply #5 on: July 17, 2017, 02:49:42 AM »
My collection is the 2/3"  12mm, F/1,6 Prime that David offered with the kickstarter. (This will be the lens that will stay on the camera when it's packed away.)
* A Secondhand Cosmicar 22-66mm, F/1.8 Zoom 'TV Lens' that should be at least full 2/3" or better frame.
* AU$75 8-50mm F1.4  1/2"  Lens from Aliexpress that is our 'cheap lens' test.
* And currently at a friend's place but promised to me, a "Zenit Photosniper" with a Tair-3AS 300mm f/4.5 lens that I have no idea what it'll be like to use but at least in full sunlight looks like it might work up to about 4000fps.

In 2-3 weeks I should have test footage with the first three up. The last one, I have no idea when I'll actually get it.  I'll update when I have info.
I'm very interested in what other's experiences are too.

akeeh

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Re: Let's talk LENSES!
« Reply #6 on: July 17, 2017, 03:23:14 AM »
My collection of C-mount lenses is as follows, I will post some test results with these (normal use and macro use with extension tubes) after I finally receive my camera, hopefully in the next coming weeks:
- VT Lens 12.5mm f/1.3
- Canon TV Lens VF 25mm f/1.4
- Tamron 25mm f/1.6
- Canon TV Lens PHF 35mm f/1.2
- VT TV Lens 50mm f/1.3
- Canon TV Lens VF 50mm f/1.8
- Two somewhat identical lenses with different manufacturer engraving: VT TV Lens 75mm f/1.3 and eneo TV Lens 75mm f/1.3
- Collection of extensions tubes and a 2x extender for C-mount
- Different microscope lenses and a C-mount adapter for them

I also have a Nikon F to C-mount adapter and I'll do more tests at least with these Nikon lenses: 35mm f/2.0D, 50mm f/1.4D, 55mm f/2.8 macro and a 180mm f/2.8

Dan Kanes

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Re: Let's talk LENSES!
« Reply #7 on: July 20, 2017, 04:44:23 PM »
(a 50mm focal length lens for 16mm film frame should produce an image like a 58mm focal length lens on a 2/3" sensor).  Super-16 is pretty reasonable as well (a 50mm would behave like a 66mm).  Some good info is here and here.  I've been trying to think about the physics of it and while I think I kind of understand how the mismatch alters the field depth to behave like a different f-stop, I am inclined to believe this wouldn't have much impact on the light gathering performance. (if a 4/3" 50 mm f/2 lens is on a 2/3" sensor, we can expect it produce an image framed like 100 mm lens with the field depth of an f/4 aperture but I *think* it would provide the same contrast and brightness as though it were still on a 4/3" sensor at f/2. If anyone knows better, please, by all means, correct me. :) )

A lens's focal length is a different way of describing its Magnification effect.

A 50mm lens made for a 35mm camera will offer the same field of view as a 50mm lens made for 2/3" or 16mm.l [FOR A GIVEN SENSOR SIZE]

The angle of view is sensor dependent.

There are other factors that affect usability / quality of image - such as vignetting if the elements or element holders are not appropriatelt sized for the format.

This should help you understand :

http://blog.abelcine.com/2010/05/14/a-lens-is-a-lens-is-a-lens/


https://youtu.be/ZF4GSMw1CeQ

Personally I'm interested in applying a Focal Reducer to the Chronos to see what we can get out of it.
« Last Edit: July 21, 2017, 07:22:38 PM by Dan Kanes »

BiduleOhm

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Re: Let's talk LENSES!
« Reply #8 on: July 21, 2017, 04:04:43 AM »
A 50mm lens made for a 35mm camera will offer the same field of view as a 50mm lens made for 2/3" or 16mm.

Actually, no, the "A lens is a lens is a lens, and it doesn’t know what size sensor or film gate is placed behind it." is exactly why we have the crop factor. Please see https://photographylife.com/what-is-crop-factor and https://www.bhphotovideo.com/explora/photography/tips-and-solutions/understanding-crop-factor and https://en.wikipedia.org/wiki/Crop_factor

This means that for our 2/3" sensor the crop factor is almost 4, so a 50 mm lens on 2/3" sensor will have the same effect as a 200 mm lens on a 35 mm sensor, and what ExaltedDuck said is spot on (except the reference sensor isn't 4/3" but 35 mm).
« Last Edit: July 21, 2017, 04:06:39 AM by BiduleOhm »

John DeLonghi

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Re: Let's talk LENSES!
« Reply #9 on: July 21, 2017, 06:51:21 AM »
A good focal reducer would make a lot of sense for the Chronos. Especially if, like me, you've got some decent 35mm glass and want to use it instead of investing in C mount lenses.

Has anyone tried one yet?

BiduleOhm

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Re: Let's talk LENSES!
« Reply #10 on: July 21, 2017, 12:08:13 PM »
Even without a reducer you can still use it without any problem, you just need to put the camera farther away and/or use lens with a smaller focal length ;)

Dan Kanes

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Re: Let's talk LENSES!
« Reply #11 on: July 21, 2017, 07:35:11 PM »
Sorry , no.

Crop factor is a bad idea that confuses people about how lenses work.

What he was saying is you need a 50mm lens made for a 2/3" sensor, and that a 50mm lens for a 2/3" sensor would have a different field of view than a 50mm lens made for a 35mm sensor.

Go get a 50mm 16mm format lens, a 50mm 35mm lens, and a 50mm 2/3" lens - they will all provide the same field of view on the Chronos - because they are ALL 50MM LENSES.

Now, your understanding of effective crop factor is sort of an okay way to translate concepts - but you get into a real shitstorm when you realize there are a lot of 35mm formats and you start making decisions about a shot size on incorrect understandings of how lenses function.

It's better to think in "wide, normal, and telephoto" terms if you're just starting out.

A wide on the Chronos could be anywhere from 6mm to 12mm pretty much.

A medium on the Chronos would be 16 , 25 or 35 (with 35 being pretty long actually)

Telephoto could be a 50 and above on Chronos.

On a 36x24 film format a 50mm is a "medium"

And on a super-35mm motion format a 35 is pretty much "medium"

You could try learning with this whole crop factor BS that photogs often lean heavily on, but if you want to learn the more scientific way that won't leave you with incorrect assumptions - watch the Abelcine video with mitch gross that I posted.

I hate crop factor because it always confuses people new to motion imaging and is akin to trying to translate every word in a foreign language before learning a native language.


A 50mm lens made for a 35mm camera will offer the same field of view as a 50mm lens made for 2/3" or 16mm.

Actually, no, the "A lens is a lens is a lens, and it doesn’t know what size sensor or film gate is placed behind it." is exactly why we have the crop factor. Please see https://photographylife.com/what-is-crop-factor and https://www.bhphotovideo.com/explora/photography/tips-and-solutions/understanding-crop-factor and https://en.wikipedia.org/wiki/Crop_factor

This means that for our 2/3" sensor the crop factor is almost 4, so a 50 mm lens on 2/3" sensor will have the same effect as a 200 mm lens on a 35 mm sensor, and what ExaltedDuck said is spot on (except the reference sensor isn't 4/3" but 35 mm).

ExaltedDuck

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Re: Let's talk LENSES!
« Reply #12 on: July 22, 2017, 12:07:19 AM »
FWIW, The way I think of it is in terms of the resolved image circle's diameter and whether that is relatively similar to the sensor's widest dimension (diagonal).  If the circle is smaller, there will be vignetting, if it's similar, the lens should work as expected, and if it's larger then the edges of the resolved image are not captured, reducing the field of view.  I tried to keep the language similar to how photographers describe things because that is what we will find if we look into photo/videography forums for ideas as to what might work on our cameras as well as being consistent with how the topics were approached in the links I offered. 

Anyhow, I don't want to jack the thread from its original intent: discussion of which lenses we've chosen for our cameras, and why.  I wanted to try a prime and a zoom, I wanted something native C-mount to (hopefully) minimize hassle, I wanted it to be intended for at least a 16mm film size to minimize likelihood of vignetting but no bigger than super-16 to ensure that as much as possible of the objective lens's light gather capability is focused on the sensor. I wanted to find something not much more expensive than the Computar 12.5-75 and I was willing to settle for maximum aperture around 1.8-2.0 as long as it was from a notable name in optics.  I looked at many possibilities on ebay, bhphotovideo, and a few other sites. I preferred to buy second-hand so that if I am unhappy with the results, I should be able to recoup my costs and redirect the money to something else. Those models I chose met all of my criteria.  I have high hopes for both and anxious to try them out when my camera gets here in a few weeks.

BiduleOhm

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Re: Let's talk LENSES!
« Reply #13 on: July 22, 2017, 03:45:22 AM »
@Dan Kanes I'll not argue more on the subject and I'll wait to have the camera and some F-mount lenses (already bought a F to C mount adapter) to compare to some real C-mount lenses (actually the Computar 12.5-75 mm and some other small lenses for CCTV) so I'll see by myself who is right.

@ExaltedDuck As said I have the Computar 12.5-75 mm f1.2 which should be perfect for most shots (excepted macro maybe) and I have some small CCTV lenses I was using for CCTV but maybe one of them will do good on the Chronos (or maybe they're all too crappy...) :)

Electra

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Re: Let's talk LENSES!
« Reply #14 on: July 23, 2017, 03:15:33 AM »
I'd have thought that the focal reducer/speed booster would have been more useful because it gives you another F/stop?  Are there such things for C mount or is this going to be Krontech's next custom made accessory? :)
That's why I was looking at them. If you take a lens for a 4/3 or full frame sensor and focus all that light on the 3/4" sensor the Chronos has, it'll give you much better light gathering capabilities, the one thing that your always fighting for with high speed cameras.
Getting second hand glass for much larger sensors is fairly easy due to the SLR market, but a lot of the light is lost using it with the smaller sensor size. It would be nice to get some of it back even if it means quite drastically changing the lens focus length.