35mm F Stop numbers

[PaPa]

Just a quick question.

The difference between a nikon 50mm lens at F 1.4 and a nikon 50mm lens at F 1.8, is it worth a potential 200 dollars more for the 1.4 ?

im considering picking up one of the ifocus adapters and am juggling between the two,

the F 1.8, with the adapter can vary anywher ein price between 400-550 where as the F 1.4 with the adapter can vary in price between 500-650?

what do you guys think?

[PDX_DVX]

I think that with a 35mm adapter it's good to have options, as they tend to lose light. With a 1.4 though the DOF is SO shallow that you don't have a whole lot of breathing room. I would say you would be fine with a 1.8 if you know you're going to be able to light things well.

[bklyndv]

A 50mm 1.4 Nikon shouldn't even cost $200 to begin with, so I can't imagine how much you'd be ripped off if it's $200 more than the cost of another lens. A great quality/condition used 50mm 1.4 should go for at most $100-120. A good shopper should have no problems finding one in the $50-75 range.

[PDX_DVX]

I didn't think about that, but you're right. I guess I had the newer 1.4's in my head.

[scharky]

There is more than an f stop difference between those two lenses. Elelement numbers and aperature leaf count play a big roll in that as well.

[PaPa]

well put it this way. i dont awnt something with Super super short depth of field.

within a few feet to a few yards would be good, but not a few cm. but at the same time it has to allow enough light in so i can use my 500 watt lights indoors without problem.

please guys, best bet for an F stpo thatwill give me this would be what? I dont like some of the adapter footage i see out there becuase moving your subject literaly a few inches forward or back puts them completely out of focus, i want something in between the dvx and THAT in my lens. Which would it be? Thanks

[khmuse]

Since both lenses are using an f-stop designation (as opposed to t-stop) they only reference the ratio of the aperture to the focal length (this effects the DOF).

The actual "speed" of the lens (light transmission) is unknown. The more expensive (f 1.4 lens) may be faster (more light) at the same aperture and may well be worth the difference in price when working with a focus screen adapter (they can exhibit several stops of light loss).

[snodart]

please guys, best bet for an F stpo thatwill give me this would be what? I dont like some of the adapter footage i see out there becuase moving your subject literaly a few inches forward or back puts them completely out of focus, i want something in between the dvx and THAT in my lens. Which would it be? Thanks

The main drawbacks of a 35mm adapter is light loss and too narrow of a DOF. I'm not too sure it can be avoided. Closing down the f-stop on the 35mm lens will of course give you a more deep DOF, but it will also begin to cause problems notable on the GG.

With the static GG adapter that I built, I could only close down the f-stop to around f/2.8 before the grain on my Nikon D screen (GG) started showing up. I have since built a vibrating GG adapter which has given me a little more room to play with. With the vibrating GG I can sometimes close down as far as f/8 with no problems. Keep in mind that this is with a canon 50mm 1.4 lense that I bought off of ebay for around $50.

Are you looking at auto focus lenses? It seems you might if they are priced that high. All you should need is an older manual focus 50mm lens ($50-120). Just make sure that the mount type is compatable with whichever adapter you decide to buy.

[PaPa]

so in terms of not getting a lens that has toooo shallow a dpeth of field, preferably so that my subject can move several inches and or feet before going out of focus. which fstop lens would that be without sacrificin too much light loss for interior shots. so the best of both worlds, not too much light loss, not too hsallow depth of field.

[snodart]

I would go with a 1.4. It seems to be pretty much the standard for adapters.

There are great deals on ebay. Just make sure you get a lens with the mount that you want.

ebay example- canon FD 50mm 1.4:
http://cgi.ebay.com/CANON-FD-50mm-Lens-1-1-4-f1-4-PERFECT-GLASS-MINT-BLADES_W0QQitemZ7611909789QQcategoryZ48552QQrdZ1QQ cmdZViewItem

I'm not up with Nikon or some of the other lenses, but I would assume that you can find good prices as well.

Just keep this in mind:


Since both lenses are using an f-stop designation (as opposed to t-stop) they only reference the ratio of the aperture to the focal length (this effects the DOF).

The actual "speed" of the lens (light transmission) is unknown. The more expensive (f 1.4 lens) may be faster (more light) at the same aperture and may well be worth the difference in price when working with a focus screen adapter (they can exhibit several stops of light loss).

[PaPa]

ya but the problem i have with the 1.4 is that the depth of field is wayyyyyyyyyy to shallow, in fact i hate the way it looks.

unless with the 1.4, you can close the fstop down a few notches with the actual lens to deepend the depth of field? Becaues lets say i got a F2.8, more light would be lost but i would have a bit deeper depth of field correct? but does it work like this: if i buya 1.4, can i close it down t oa 2.8 retaining th same light loss and depth of field that buying a lens already at F 2.8 would give me?

[snodart]

unless with the 1.4, you can close the fstop down a few notches with the actual lens to deepend the depth of field? Becaues lets say i got a F2.8, more light would be lost but i would have a bit deeper depth of field correct? but does it work like this: if i buya 1.4, can i close it down t oa 2.8 retaining th same light loss and depth of field that buying a lens already at F 2.8 would give me?

Yes, you can close down the 1.4 lens to deepen your DOF. The 1.4 lens set at f/2.8 should mimic a 2.8 lens set at f/2.8. The f-stop is directly related to the size of the aperture. So, f/2.8 will have the same size aperture on any of the 50mm lenses.

The equation to find the aperture size for a 50mm lens is:

50(mm) divided by the current f/stop setting.

So a 1.4 lens set at f/2.8 will have an aperture size of 17.9mm (50/2.8=17.9)
The same equation would apply to the 2.8 lens and it also would have an aperture size of 17.9mm when set to f/2.8.

That being said... The aperture size is directly related to the DOF. The smaller the aperture, the deeper the DOF will be . The larger the aperture, the more shallow the DOF will be.

So,
low f-stop > larger diameter aperture > shallow DOF (and more light to the GG)
high f-stop > smaller diameter aperture > deeper DOF (and less light to the GG)

Here is the deal with the adapter:

With any of the lenses, closing down the f-stop will deepen the DOF (make a larger in-focus range).

The problem with this, as you said, is light loss. This is a problem for adapters because that means there is less light getting to the Ground Glass. When there is less light on the GG, grain on the GG starts to show up in your images.

With the static GG adapter that I built from Edwierdo's design, I could close the f-stop down to f/2.8 and sometimes get away without the grain of the GG showing up. Closing the f-stop any more the 2.8 (f/4 for example) caused the grain of the GG to show up. The amount of grain that will show up also depends on what GG you are using. I have been using the Nikon D screen, which has been known to preform pretty well. Still, no matter what static GG you use, I would say that you will probably not be able to close down the f-stop much more that f/2.8 or f/4 max.

One way to allow the f-stop to be closed down more is to move the GG (ie: spin or vibrate). This helps because the pits in the glass which cause the grain do not stay in one spot, thus better hiding them from the DV/HD camera.

With my vibrating DIY adapter, I am able to crank down the f-stop as far as f/8 at times without seeing the grain. f/8 is about the max though. Closing it down more than that causes patterns of the moving grain to show up.

The bottom line is that DOF 35mm adapters are limited by a shallow DOF. You can close down the f-stop to make the DOF less shallow and more deep, but too far will show the grain of the GG.

Having the 1.4 lens will just give you a little more room to play with. Yes it will give you a very shallow DOF, but you may find that you want that at some point while shooting.

Hope that helps. It took me a while to make sense of it all.

[Noel Evans]

Snodart nice post ... clear and informative. Personally I wouldnt buy any lense from ebay. Why? Because I cant insepct it. Used lense quality varies a lot.

[PaPa]

So is the only way to get a more deep depth of field to close down the F stop?

Is it also then safe to say that alot more light is required to get a shot with a deeper depth of field as the f stop has to be closed more and more to achieve this/. are there no such lenses that are made ready to have a deeper depth of field or it relies solely on the f stop?

sucks/// dang , didnt know this

[snodart]

So is the only way to get a more deep depth of field to close down the F stop?

Correct.


Is it also then safe to say that alot more light is required to get a shot with a deeper depth of field as the f stop has to be closed more and more to achieve this/.

Correct.


are there no such lenses that are made ready to have a deeper depth of field or it relies solely on the f stop?

Relies on f/stop and aperture. No lenses that I know of. I am not an expert in this area. ncje might know more.


sucks/// dang , didnt know this

Yes, it is a bummer.

Keep in mind that you can get a limited DOF with just a DV cam. Back the cam away from the subject and zoom in. Set a low f-stop (open aperture) and a fast shutter speed. Doesn't do much and you can't utilize much camera movement since it is zoomed in, but it gives a little.