Lens with Perfect Circular Diaphragm stop down

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bene

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Hi I plan to do night scapes with alot of street lamp and lights... so I have a problem of starbursts...

I found the SLR Magic 28mm2.8 for Nex has a Rotating Diaphragm and so perfect circular Iris @ at all apertures...

I was wondering if there is any alternative as I wonder if the lens is sharp enough....

I use mostly M lenses on the Nex
 
Nothing M/LTM out there that will avoid stars. With an even number x of aperture blades, your stars will have x rays, with an odd number y, your stars will have 2 * y rays.

Get a lens that you can use wide open, for example CV 28/3.5, Leica 24/3.8 ASPH, etc. Or, to avoid color fringing, something longer ? L-Hex 50/2.4, or 50/3.5 Heliar, a modern Summicron, etc.
 
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In LTM, Summaron 28/5.6 or Hektor 28/6.3 ?

EDIT: What about pin-hole ? It should work well ...
 
Any lens you use wide open will have a round aperture. Presumably you plan to work from tripod, and are planning to stop down to increase DOF. Perhaps a slower wide lens will perform well at full aperture and not have a too shallow focus.
 
Since you are shooting on NEX. You could always get an inexpensive reflex lens and put your own perfectly round diaphragm in it. A Yashica ML28mm or Zuiko or whatever adapter you have on hand. Making a paper/plastic disc iris is pretty easy. Once installed you are committed to that one f stop. Calculating the diameter for f5.6 f8 is also quite a simple thing to do then, just drill a clean hole in black plastic or stiff cardboard.. I'm guessing diffraction would become an issue stopped down further than that. Nearly any manual focus reflex lens is going to give you great results by f5.6 or so. Since it is retro-focus you may get a bit more distortion but less fringing. Personally I agree with Roland about going to a 50mm or maybe even a 35mm.
 
some options

some options

The original Elmar 50/2.8, heavy brass, and lots of aperture blades gets very close to circular. I've not had any stars with that lens on a Nex.

Same with a J3 stopped down.

However, for 28, your only alternative might be something like this rotating disc lo fi lens.

One thing that helped with the longer lens in getting the bokeh and stars to smoosh to ovals/circles was by using live view and taking advantage of the above lens infinite stepless aperture turning, so if you can find that, it might help, along with live view.

Also, wide open is not always circular. I have an SLR Hexanon 40/1.8 that wide open is hexagonal, as is my Canon 28/2.8 ltm.


bene said:
Hi I plan to do night scapes with alot of street lamp and lights... so I have a problem of starbursts...

I found the SLR Magic 28mm2.8 for Nex has a Rotating Diaphragm and so perfect circular Iris @ at all apertures...

I was wondering if there is any alternative as I wonder if the lens is sharp enough....

I use mostly M lenses on the Nex
Click to expand...
 
I seem to recall that Nikon's old 45mm GN-Nikkor goes circular. But of course, it has a narrower field of view than your 28.
 
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Thanks for the information helps very much! I'll stick with my Zm 25mm and shoot wide open + F8 and photoshop the star bursts.
 
What about a Helios 44 58mm lens? or a Helios 40 , I use them a lot and they have curved blades for aperture, but thats only at f1.5 to about 2.8
 
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