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Same focal lengthes and so different.
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PostPosted: Mon Sep 27, 2010 9:07 pm    Post subject: Same focal lengthes and so different. Reply with quote
I was wondering why such differences between these 3 50mm and what characteristics are the best.
I understand that all 3 have the rear lens at a distance from the sensor of 50mm. Am I true ?
Left : a M42 will westlar vastar 2.8/50. Very very small.
Center : a M42 CZJ Tessar 2.8/50 either but bigger.
Right : a P6 CZJ Flektogon 4/50. So huge...

I was wondering what are the optical rules explaining those so different designs. Anybody can explain ? Smile







Thank you.


PostPosted: Mon Sep 27, 2010 9:22 pm    Post subject: Re: Same focal lengthes and so different. Reply with quote
Olivier wrote:

Left : a M42 will westlar vastar 2.8/50. Very very small.
Center : a M42 CZJ Tessar 2.8/50 either but bigger.
Right : a P6 CZJ Flektogon 4/50. So huge...


Left: enlarger lens
Centre: format 135 lens
Right: medium format lens

A "normal" photo lens normally needs more space for the mechanical parts than an enlarger lens. And the bigger the image circle needs to be the bigger the lens will be.


PostPosted: Mon Sep 27, 2010 9:22 pm    Post subject: Reply with quote
I think P6 is a larger format, so 50mm lens must be a wideangle design.

I think they could have made the Tessar 50/2.8 smaller, but wanted it to be in balance with the body.

Never seen the third lens before...


PostPosted: Mon Sep 27, 2010 11:49 pm    Post subject: Reply with quote
Riku wrote:
I think P6 is a larger format, so 50mm lens must be a wideangle design.


That's right. However, I have a Mamiya M645 55/2.8, and that lens is much smaller and lighter than the Flektogon. (Much sharper, too, but not that sharp anyway as it is just that - a retrofocus wideangle for medium-format cameras).


PostPosted: Tue Sep 28, 2010 3:46 am    Post subject: Reply with quote
I bet the Mamiya M645 55/2.8 front element is larger than the Flektogon -- it has to have larger diameter front element to let in the additional light necessary to illuminate the larger 645 surface to f/2.8 brightness. Smaller lighter body material too.


PostPosted: Tue Sep 28, 2010 8:31 am    Post subject: Reply with quote
Thank you for your answers. Smile

So, Carsten, the Will. Westlar Vastar is an enlarger lens ?
I didn't know they were built like camera lenses : aperture ring from 2.8 to 22, focusing distance 3 ft to infinite, 12 blades diaph.

That's a very well built tiny lens and some kinf of engineer perormance.


PostPosted: Tue Sep 28, 2010 12:48 pm    Post subject: Reply with quote
Hi,

I don't believe the Vastar is an enlarger lens (although it's certainly as small as an enlarger lens!); it has a conventional focusing mount and M42 fitting.

I don't own one, but I've handled and used the lens. If memory serves, it's about the same size as the Ludwig Victar/Practicar 50/2.9.

Cheers,

Jon


PostPosted: Tue Sep 28, 2010 1:56 pm    Post subject: Reply with quote
Olivier wrote:
Thank you for your answers. Smile

So, Carsten, the Will. Westlar Vastar is an enlarger lens ?
I didn't know they were built like camera lenses : aperture ring from 2.8 to 22, focusing distance 3 ft to infinite, 12 blades diaph.

That's a very well built tiny lens and some kinf of engineer perormance.


Ah, OK. Perhaps it is not. The size and the fact that I have a Will enlarger lens made me think so. Wink


PostPosted: Tue Sep 28, 2010 2:28 pm    Post subject: Reply with quote
Hi,

You're absolutely right - so far as I know, the Wilon company was much better known for enlarger lenses than camera lenses. (Wasn't the "Gnome" one of their brands?) It may be, in fact, that the Vastar was their only camera lens - or at least the only one in M42 mount.

Cheers,

Jon


PostPosted: Tue Sep 28, 2010 10:06 pm    Post subject: Reply with quote
Maybe the only one in M42 mount ?
That makes some interest to me to have it.

It's very tiny and subtle.
I'll made some trials with it.
When I received it, I just checked with the 40D at f2.8 and it was soft.


PostPosted: Tue Sep 28, 2010 10:13 pm    Post subject: Reply with quote
visualopsins wrote:
I bet the Mamiya M645 55/2.8 front element is larger than the Flektogon -- it has to have larger diameter front element to let in the additional light necessary to illuminate the larger 645 surface to f/2.8 brightness. Smaller lighter body material too.

Diameter of front lens element isn't directly proportional to lens speed. It's also related to the optical formula.

example (two retrofocal wide-angle lenses):
Asahi Takumar S-M-C 35/2: 36.5mm
Meyer Primagon V 35/4.5: 37.5mm


PostPosted: Tue Sep 28, 2010 10:15 pm    Post subject: Reply with quote
visualopsins wrote:
I bet the Mamiya M645 55/2.8 front element is larger than the Flektogon -- it has to have larger diameter front element to let in the additional light necessary to illuminate the larger 645 surface to f/2.8 brightness. Smaller lighter body material too.


Nope, it has a very small front element - about 40mm in diameter. Here's a picture:



Considering that the front thread is just 58mm, you can get the idea how small is the front element.


PostPosted: Wed Sep 29, 2010 7:38 am    Post subject: Reply with quote
no-X wrote:

Diameter of front lens element isn't directly proportional to lens speed. It's also related to the optical formula.


That's true... but... lens speed is connected to the maximum aperture of the visual diaphragm and a small front element can be a limiting factor in this sense. (This is hardly the case, though.)


PostPosted: Fri Oct 15, 2010 6:54 am    Post subject: Reply with quote
aoleg wrote:
visualopsins wrote:
I bet the Mamiya M645 55/2.8 front element is larger than the Flektogon -- it has to have larger diameter front element to let in the additional light necessary to illuminate the larger 645 surface to f/2.8 brightness. Smaller lighter body material too.


Nope, it has a very small front element - about 40mm in diameter. Here's a picture:



Considering that the front thread is just 58mm, you can get the idea how small is the front element.


Laughing Embarassed I meant to compare Mamiya with Tessar not Flektogon, above. Then the part about larger image circle makes sense.

Wow the Mamiya is tiny compared to Flek!

I see the Flek has much larger front element but is slower lens. Shocked Why? Different optical formulas, the Flek has more elements, is longer; the front is larger to let in more light to replace what is lost to more elements and more distance traveled, almost twice the focal length compared to Mamiya. Light lost by longer travel is similar to light lost with extension tubes or bellows, the exposure factor. The Mamiya is short.


PostPosted: Fri Oct 15, 2010 7:19 am    Post subject: Reply with quote
visualopsins wrote:
I see the Flek has much larger front element but is slower lens. Shocked Why? Different optical formulas, the Flek has more elements, is longer; the front is larger to let in more light to replace what is lost to more elements and more distance traveled, almost twice the focal length compared to Mamiya. Light lost by longer travel is similar to light lost with extension tubes or bellows, the exposure factor. The Mamiya is short.

I understand clearly. Smile
Explained like this, it's obvious.
Thank you.


PostPosted: Fri Oct 15, 2010 8:27 am    Post subject: Re: Same focal lengthes and so different. Reply with quote
Olivier wrote:
...
I understand that all 3 have the rear lens at a distance from the sensor of 50mm. Am I true ?
...


If the lenses are ideal thin lenses, the one and only lens will have a distance of 50 mm to the image at infinity.

But this are not ideal thin lenses. This optical constructions are depending on different lenses in a system. And so the last lens lens element surface is in most cases not in focal length distance from the image.

To get the last lens element far away from the image, is a aim of the retrofocus construction
http://en.wikipedia.org/wiki/Angenieux_retrofocus
Without this construction a 17 mm lens would need lens elements prodtruding deply into the camera mirror box - and so only SLR cameras with looked up mirror could work with such a lens.
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