Wide angle video vs focal length of still

[everymansaved 0]

I have a question about determining the aproximate focal length of a video camera with a wide angle lens. AFAIK, the focal length of normal sight is 50mm, correct? Does that mean that a video camera with a .45x wide angle lens equate to an aproximate focal length of 22.5mm (50mm x 0.45)? Is there some error in my reasoning? If this be the case, would setting the focal length on a still camera @ 22.5mm produce the same field of view as the camcorder with the .45x? Thanks.

God made firefighters so paramedics would have heroes...and someone can put out the trailer fires.

[dragon2 2]

Forget exact measuring which video lens goes with which still lens, it totally depends on which brand video lens on which camera with or without a step ring, and which still camera brand (for DSLRs: generally canon x1.6 nikon x1.5 so a sigma 15mm is 24mm on a canon but 22,5mm on a nikon).

I've had a .6 lens that was wider than my current .45 And not all still lenses are created equal either - I had a 28-200 lens that at 200mm had the same aov as my 150mm macro lens
Using the same .45 lens gives a slightly different aov on my TRV25 as on my PC2.

On my nikon, my 16mm is wider than my trv25/pc2 with hama .45, my 20mm is narrower, so 18mm or so would probably be a perfect match.

Just take a guess at it, try to borrow the lenses if you can. It doesn't have to be a perfect match anyway

ciel bleu,
Saskia

[indyz 1]

In theory, the focal length of your video camera with a lens is equal to the base focal length of the camera multiplied by the conversion factor of the lens. So a camera with a 50mm base focal length and a .45x lens would be equivalent to 22.5mm. In theory.

Unfortunately, it isn't that simple. First, he focal length of the built-in lens is probably not 50mm. You have to check your camera's manual to be sure (it might also be printed on the camera body somewhere). Second, and most important, is that there is no standard for conversion lenses. For example, a Sony .6x lens is wider than many .5x lenses. Adding step-up or -down rings also affect the conversion factor.

[monkycndo 0]

My Sony .6x is about equal to a Kenco .45x.

50 donations so far. Give it a try.

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Jump an Infinity

[everymansaved 0]

Cool, thanks for e info guys, I'll just have to play around with it!

God made firefighters so paramedics would have heroes...and someone can put out the trailer fires.

[PharmerPhil 0]

Quote

AFAIK, the focal length of normal sight is 50mm, correct?

Well,...not exactly. You cannot look at focal length alone without looking at the size of the image sensor. The common thought that a 50mm focal length equals "normal sight" is based on 35mm film (or an image sensor with similar dimensions, 24mm x 35mm). For a larger format camera, a longer focal length would be considered "normal." For a smaller format, a shorter focal length would be considered "normal."

When it comes to small consumer camcorders, (or even larger pro camcorders) the image sensor is much, much smaller than 35mm. Typically at least a third smaller or more.Therefore, a lens with an equally smaller focal length would be considered "normal." Most camcorders have their focal length range written right on the front of their lenses, often a number like 5.1-51mm with 5mm being the wide end of the range. But they don't say what size the sensor is.

To do the math (which I haven't) you would need to know the size of your imager, the focal length of your lens (presumably at it's widest setting because most camcorders have an optical zoom), and know the real multiplier for the wide-angle lens adapter. Searching previous threads will show that the simple multipliers (0.5x, o.45x, etc.) are misleading. Aditionally, using a filter thread adapter (i.e. 37mm-30mm) changes the wide-angle conversion of the lens adapter.

Never bothered to do the math because anequedotal evidence tends to be easier to work with (for me). Would love it if someone with time and inclination would post real formulas (including what effect those filter adapters have). But it probably wouldn't change my current choices in lenses and lens adapters.

...my too sense...

Phil Roberson

[everymansaved 0]

Wow, that's a lot of info, thanks Phil! What is a good way to find out the real multiplier of a lens?

God made firefighters so paramedics would have heroes...and someone can put out the trailer fires.

[everymansaved 0]

Okay, time to re-hash this. I did some math and I want to know if it's correct. My still cam lens (Pentax DA 18-55) says that it's 18mm setting is comparable to 27.5mm in 35mm format, and my video camera (PC120) says that it's widest angle is 48mm at 35mm equivilant. Now, with the wide angle on the video cam, it frames the exact same amount as the still cam @ ~25mm as indicated on the lens. So from this, I can calculate that the 25mm written on the lens corresppnds to 38mm @ 35mm equivilant. So if a 48mm video lens with a wide angle captures the same image as a 38mm still lens, that means that the wide angle's actual multiplier is 0.8 (38mm / 48mm)right?

God made firefighters so paramedics would have heroes...and someone can put out the trailer fires.

[PharmerPhil 0]

That sounds about right. A 0.8x adapter give you a focal lenght wchi is 0.8x the existing lens it is put over. I don't really know the Pentax DSLRs. The last time I looked into these things, most consumer DSLRs had a crop factor of 1.5x. That is, an 18mm lens gave you the same field of view as a 27mm lens on a full-size (35mm) SLR. Canon's worked out to about 1.6x (When I looked into this, Canon was making their own sensors, and Nikon was using a Sony sensor, but I don't know about the other manufacturers).

Again, the numbers on many W/A lens adapters just aren't accurate. (I worked in consumer electronics for many years, and this is just a case of specs being "measured" by the marketing dept.) Also, putting a step-up ring in between the camera and the lens changes the math by moving the lens adapter away from the stock lens and sensor.

And another thing to remember is that video cameras have a different aspect ratio than most still cameas so they will NEVER be exactly the same field of view. i.e., my Canon shoots a 3:2 image, while video cameras are either 4:3 for SD or 16:9 for HD.

Which brings me back to the last point in my previous post, I wouldn't get too concerned with the math for anything other than curiosity. Put a tripod up, roll some video tape with and without the lens adapters in question, put your still camera on the tripod and do the same, and then compare the results. One great thing about digital is immediate feedback. Pick what works for you. (If you do this at a DZ, you may be able to borrow lots of other lens adapters to compare.) I actually did this not too long ago and output a contact sheet of the results somewhere. I'll see if I can dig it out and send it to you.

[PharmerPhil 0]

I found some photos I took with various lenses and cameras, all from the same spot and pointed in close to the same dirction. I just posted them here:

http://www.philroberson.com/lenscomparison/index.htm

I shot these using a Sony TRV-38, a Sony HVR-A1U (like the HC-1), and a Canon 20D. The photo titles should tell you which camera/lens combo was used. The last images (12-16) are using the HVR-A1U in memory stick mode which yields images with different sizes and aspect ratios, but the video ones (photos 04-07) should give you an idea of what you wiil see while shooting video.

Your mileage may vary.

[everymansaved 0]

Thanks. I'm just a little ticked, as the lens I just worked out to a .8 is suposed to be a .45. It hardly widens the view at all!

God made firefighters so paramedics would have heroes...and someone can put out the trailer fires.