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25mm c-mount vignetting shootout

madmaxmedia

New member
Since most all lenses are softest wide open, I wonder how lens makers arbitrarily draw the line at what the max. aperture is for a lens.

For example, in C-mount there are a few lenses that come in f/1.5 and f/1.9 apertures (or other numbers, but half to one stop apart.) Is there that much difference in the lens designs, or is it mainly just that the blades on one lens opens a little more than the other?

Or perhaps 2 different such lenses could have the same basic design, but the tolerance for the glass elements and overall manufacturing is tighter for the faster lens. Because of this the wide open fast lens is similar in image quality to the wide open slower lens.
 

madmaxmedia

New member
Re: Is "fast" really worth it?

People who buy fast for things like night shots should do an experiment. Shoot with the lens wide open at a set ISO. Then, close the lens down two stops and shoot at an ISO two stops higher. Run the second shot through noise reduction software and then decide which shot is better. Sometimes, the wide open shots are so soft, lacking in contrast that the higher ISO shot turns out better. Therefore, the faster lens speed is not worth using in such a case.
This is a good suggestion, though for real low light shooters I think they will always take whatever extra stops they can get.

I actually have both a Wollensak 1.5 and 1.9 coming, and will try to do a comparison. I guess that's about 2/3 stop difference.
 
M

milapse

Guest
Great comparison. Thanks for the effort!

The 25s are all over the place for sure. I have a wollensak 1.9 which continues to grow on me despite the tiny factor.

At the end of the day, like others here... I'm totally in love with the 26/1.1:
 
R

RandySmith

Guest
I am brand new to this web site, but have been selling c mount lenses on eBay for a few months. I just got a G1 body and have just started to use it with some of the lenses I am selling (they mostly go to Hong Kong).I have posted some photos of a cooke ivotal anastigmat 1" f1.4 on photobucket, along with some others. I will post some photos here as soon as I get a chance. I am an old nikon guy and really only got the G1 for marketing, but it's starting to grow on me. Randy
http://s478.photobucket.com/albums/rr145/RandySmith_photo/Lumix G1 with C Mount Lenses/Ivotal/
 

MRfanny

New member
I am brand new to this web site, but have been selling c mount lenses on eBay for a few months. I just got a G1 body and have just started to use it with some of the lenses I am selling (they mostly go to Hong Kong).I have posted some photos of a cooke ivotal anastigmat 1" f1.4 on photobucket, along with some others. I will post some photos here as soon as I get a chance. I am an old nikon guy and really only got the G1 for marketing, but it's starting to grow on me. Randy
http://s478.photobucket.com/albums/rr145/RandySmith_photo/Lumix G1 with C Mount Lenses/Ivotal/
some fine lens examples. at the risk of giving away your trade secret, where does one generally go to source old c-mount lenses? I notice the ebay sellers seem to have a never ending supply, they must be sourcing from somewhere? I just only want a few for myself without paying through the nose...lol You can PM me if you like =)
 

apicius9

New member
some fine lens examples. at the risk of giving away your trade secret, where does one generally go to source old c-mount lenses? I notice the ebay sellers seem to have a never ending supply, they must be sourcing from somewhere? I just only want a few for myself without paying through the nose...lol You can PM me if you like =)
No, No, we all want to know! :)

Stefan
 

laptoprob

New member
Well, I have a Pentax 25 coming to me from CCDWorld and an adapter from China.
So then I will have a few fast primes besides the slower Panny zoom.
 

MRfanny

New member
Give us a heads up on the condition of the "used" lens as I'd like to pick one up too. its the $45 one yeah?
 

laptoprob

New member
Yep. Probably will do some vignetting, smeared or unsharp corners wide open. Maybe I will restrict the use to squares...
 

ggibson

Well-known member
Looks to me like the Pentax is the winner wide open.

I'm curious what the appeal of a c-mount 25mm lens is over the Panasonic 20mm? It seems like such a minimal change in length. I'm more curious about fast legacy lenses in the 35-50mm range. My father owns a 40mm Summicron-C f2 which I've been eager to test out, but don't have the adapter yet.
 

madmaxmedia

New member
The biggest difference is price, at least compared to the Pentax.

Other c-mounts can of course be even more expensive than the Pana 20mm.
 

ggibson

Well-known member
Yes, price I figured is a good incentive =)

One thing that appeals to me is the unique bokeh from some of these lenses. Like apicius and milapse's images above. Very cool.
 

MRfanny

New member
i notice some c mounts have that radial blur like above. is it a general common characteristic of a c mount or is it lens/brand specific. It makes me dizzy sometimes looking at images like that so id like to avoid it if possible when buying.
 
T

thearne3

Guest
i notice some c mounts have that radial blur like above. is it a general common characteristic of a c mount or is it lens/brand specific. It makes me dizzy sometimes looking at images like that so id like to avoid it if possible when buying.
Not sure I'm seeing what you are seeing...it looks like the dog is in focus in the foreground, all else less so. It IS true that frame edges for some c-mounts are less sharp, but I don't have the impression that's what you're talking about.

Best,
Tom
 

MRfanny

New member
Not sure I'm seeing what you are seeing...it looks like the dog is in focus in the foreground, all else less so. It IS true that frame edges for some c-mounts are less sharp, but I don't have the impression that's what you're talking about.

Best,
Tom
Really? I get a very distinct vision of radial blur/bokeh where the centre is in focus but it looks like the pics been spun the more you go out. It is very different to something just being in or out of focus to me. Sebs examples the first pic is fine but the other two i see it. It could just be the characteristic of the bokeh that creates this illusion. then again it could just be me but I have seen alot of c mount pics that show this characteristic.

I also see it strongly in Apicus's flower example too. All the other pics look normal to me which leads me to believe it could be brand/lens specific characteristic.

You really don't see it?
 
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madmaxmedia

New member
I believe it is due to angle of light hitting the edge of the sensor, due to the short distance between back of lens and sensor. This is not an issue with film, but digital sensors are sensitive to this. The same issue happens with wide angle Leica rangefinder lenses on M 4/3.

The Leica M9 corrects for this with offset microlenses on the sensor.
 

Jonas

Active member
(...)
I also see it strongly in Apicus's flower example too. All the other pics look normal to me which leads me to believe it could be brand/lens specific characteristic.

You really don't see it?
"Swirling bokeh" You see it in many lenses wide open, stopped down things go back to normal again.
The effect is caused by optical vignetting (and can so bee seen as the known Cat's Eye effect).

Here you have it in post #6 and several in post #7. Another example is here and you can follow the discussion about it.

So, it is not specific to the mount, but to the lens. Many fast lenses show it ised wide open or near wide open. To not do it they would need larger elements right through the whole lens and then have the largest ooening locked down to a smaller than maximum value.

I believe it is due to angle of light hitting the edge of the sensor, due to the short distance between back of lens and sensor. This is not an issue with film, but digital sensors are sensitive to this. The same issue happens with wide angle Leica rangefinder lenses on M 4/3.

The Leica M9 corrects for this with offset microlenses on the sensor.
This is something else and simply called border smear, or corner smear. Smeared corners can be a problem for many images, and doesn't nother at all in other situations.

Now if I got everything wrong it is because I didn't read Vivek's book vlose enough. Please correct me!
 

madmaxmedia

New member
I think you got both right. The swirling bokeh can also be seen on the Noctilux, right? Now you can get that look with C-Mount for 1/100 of the cost! :)

I think it is not necessarily bad, depending of course on what you are going for.

What is Vivek's book?
 

Jonas

Active member
(...)
What is Vivek's book?
Vivek recommended a book in a thread discussing f and T values here.
I remember it as I have been close to buy it a couple of times. But the price... In the meanwhile I sometimes go toothwalker's site here instead (earlier known as Vanwalree's site). OK, I'm now officially a cheapskate obviously not striving to know it all, a dangerous sort.

/Jonas
 
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