Canon Serenar 135

[gb hill]

Can a Canon Serenar 135 lens be hacked or modified to work on a camera with a short base length such as a Bessa R. If so would the lens then become a 85mm ofr shorter? I know almost nothing really of how a lens works as far as camera base length to lens ratio. I'm guessing this has to do with the distance of the rear element to front element, but then some lenses have a inner glass element, I don't know about the Serenar, so it is a bit confusing! Then again my thinking might be totally off base! I doubt I will ever hack my Canon lens but it would be nice if I could use it with my Bessa R. I'm mainly interested in your thoughts on this! The J-3 you helped me with a couple of years ago works great! Thanks!

 

[payasam]

Greg, as range-finder base length decreases and lens focal length increases, focussing becomes more difficult and potentially less accurate. You might get a CV 75mm instead of trying to modify a Serenar 135mm.

 

[gb hill]

Greg, as range-finder base length decreases and lens focal length increases, focussing becomes more difficult and potentially less accurate. You might get a CV 75mm instead of trying to modify a Serenar 135mm.

I have a CV 75/2.5 in my sights! I'm mainly wondering if it could be done & perhaps gain some insight on how a lens to camera ratio as far as baselenght works! I can use the Canon on the Fed 2 but once on the Fed I have to dedicate it to the body until the film is used up because of the cam.

 

[Sonnar Brian]

You can tweek the focal length of a lens by moving the elements around, but something so dramatic as converting a 135 to an 85 would undo all of the optical corrections in it. The piece that translates the 135 focal length to motion for a 51.6mm lens would have to be redone. Best to leave the 135 as is and buy a Canon Serenar 85/2.

The other way around this is to use an eyepiece magnifier to use the 135 on the Bessa. I've used a 135/4.5 Hektor on a CL- just to do it.

 

[gb hill]

You can tweek the focal length of a lens by moving the elements around, but something so dramatic as converting a 135 to an 85 would undo all of the optical corrections in it. The piece that translates the 135 focal length to motion for a 51.6mm lens would have to be redone. Best to leave the 135 as is and buy a Canon Serenar 85/2.

The other way around this is to use an eyepiece magnifier to use the 135 on the Bessa. I've used a 135/4.5 Hektor on a CL- just to do it.

I was guessing if adjusting the lens would actually change the focal length. Is it the distance of the front to rear elements that determines the focal length of a lens? I'm assuming not, because different brands are not all the same size in lenght. I'll have to do a google search & read up on the basic functions of a lens, Lens 101!

As for a lens magnifier! I haven't a clue what that is or how it would even work on a RF!

 

[batterytypehah!]

I'm not sure you guys are all on the same page...

I think Greg really has a very basic question -- will the 135 work on the Bessa R?

The answer is yes, but...

The depth of field with any 135 lens can be very shallow. (Long lens, wide aperture, close distance to subject all reduce DOF; inversely, short lens, small aperture, long distance to subject all increase DOF)

So, with the given 135 on the given Bessa you're fine at all apertures at infinity. As you focus in closer and open up, it becomes more difficult to focus correctly. This is where the precision of the RF mechanism comes into play. When you're using the 135 at close focus in low light (e.g. for a portrait), you need to be really precise.

I don't think we need to go into the "why" here but the precision of an RF depends on its baselength, to the point that artillery rangefinders were built with baselengths of several yards. Hence it's desirable to build them as long as practical (the Contax is an extreme example).

Up to a point, simply magnifying the RF view helps; this doesn't make the mechanism any better (it magnifies inaccuracies just as well) but facilitates accurate "reading" of the coincident image.

So, as always, it all depends on what you're planning to do with the lens. Landscapes in daylight won't be a problem, but then nobody (I hope) needs a rangefinder in the first place to know that you should adjust your lens to infinity for a shot of yon mountains over there.

Indoor portrait sessions are a different kettle of fish. You may want to determine the distance with a measuring tape rather than the RF. Or use fast film and stop down.

 

[Sonnar Brian]

By the magnifier, I mean a magbnifier that fits over the eyepiece.

Most complex lenses are made of groups. The front and rear sections of a lens will form an image independantly. The placement of the front and rear sections controls the overall focal length of the complex lens. The distance of the complex lens from the image plane determines focus. Basically, how a zoom lens works.

I used a Canon 50/1.5 without a rear group as an 80mm lens on a Nikon F to see what it would do. Soft until closed down to F8.

 

[Sonnar Brian]

Can a Canon Serenar 135 lens be hacked or modified to work on a camera with a short base length such as a Bessa R. If so would the lens then become a 85mm ofr shorter? !

By "hacked or modified", and would the lens become 85mm or shorter- I took this to be a question of changing the actual focal length of the lens. In the past, I've posted instructions for changing focal length of a lens. I've also made some lenses out of parts, such as 1/2 J-8 and 1/2 Retina Xenon. By setting the spacing between the modules, and the main shim- the result was an RF coupled 50mm F2 lens.

 

[gb hill]

I'm not sure you guys are all on the same page...

I think Greg really has a very basic question -- will the 135 work on the Bessa R?

The answer is yes, but...

The depth of field with any 135 lens can be very shallow. (Long lens, wide aperture, close distance to subject all reduce DOF; inversely, short lens, small aperture, long distance to subject all increase DOF)

So, with the given 135 on the given Bessa you're fine at all apertures at infinity. As you focus in closer and open up, it becomes more difficult to focus correctly. This is where the precision of the RF mechanism comes into play. When you're using the 135 at close focus in low light (e.g. for a portrait), you need to be really precise.

I don't think we need to go into the "why" here but the precision of an RF depends on its baselength, to the point that artillery rangefinders were built with baselengths of several yards. Hence it's desirable to build them as long as practical (the Contax is an extreme example).

Up to a point, simply magnifying the RF view helps; this doesn't make the mechanism any better (it magnifies inaccuracies just as well) but facilitates accurate "reading" of the coincident image.

So, as always, it all depends on what you're planning to do with the lens. Landscapes in daylight won't be a problem, but then nobody (I hope) needs a rangefinder in the first place to know that you should adjust your lens to infinity for a shot of yon mountains over there.

Indoor portrait sessions are a different kettle of fish. You may want to determine the distance with a measuring tape rather than the RF. Or use fast film and stop down.

Thanks, you cleared up a lot of questions. I will try the lens on the Bessa at infinity.

 

[gb hill]

By the magnifier, I mean a magbnifier that fits over the eyepiece.

Most complex lenses are made of groups. The front and rear sections of a lens will form an image independantly. The placement of the front and rear sections controls the overall focal length of the complex lens. The distance of the complex lens from the image plane determines focus. Basically, how a zoom lens works.

I used a Canon 50/1.5 without a rear group as an 80mm lens on a Nikon F to see what it would do. Soft until closed down to F8.

This answers my question! Apparently I don't know enough about lenses to know the right questions to ask...sorry! I'm courious to know what formula you would use to determine how a 50/1.5 would become an 80 mm lens without the rear group of lenses. Do you measure the distance from the film plane to front element to get your figures? Then what about the circumference of the front glass itself?...this can be confusing because it seems trying to solve one question brings up another question! Somehow I get the feeling I'm making it more complex than it really is.

 

[Sonnar Brian]

On the Canon, I used it on an SLR so the magnification equated to a "about" 80mm.

Focal length of single-element lenses is easy to determine, it is the distance from the lens that an object at infinity comes into focus. Complex lens- not as easy to measure, it is the net result of all the optics. I find the easiest way to determine the focal length is by comparison.