Vignetting and hotspot

U

ufuk aksoy

Active member
I have this vignetting problem, I ve searched the forum but could not find an answer. I use sgpro achromat. I increased the length of tubes but did not work. would a condenser solve the problerm? please help, I dont want to quit it after I came this far!

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Hi,

Yes you will need a condenser lens close to your GG. The most common setup is a PCX (plano convex) lens between the GG and the achromat, close to GG.
 
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Wayne,
Do you use both a condensor lens and an achromat one at each end of the tube? I've been wondering why I have glass at both ends.

- Lenny Levy (who's SGPro tube moves freely now thank you.)
 
Cool, it does the job .
Have you tried it on a 2/3" camera or tried to come up with a mod for 2/3" cameras?
I've always wondered if there is an optical reason why this is never done?
 
Can you tell me where can I buy it on internet? 55mm lenses fit in my tube, so I search for 55mm condenser lens on ebay, but there is no such thing! How should I search it? thank you!
 
I did notice that you are using the FD to EOS converter. This will reduce image quality in a big way, and also contribute to vignetting...
 
I quit the EOS to FD converter, installed the condenser but I still have the vignetting as you'll see below. And in the first picture you can see the fish eye effect of the condenser when not in focus! Should the condenser be much closer to the GG, and maybe the opposite side? Any more suggestions! Maybe this design does not work for 72mm cameras, ha?
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Three questions:

1. What camera are you using?
2. What is the distance between your achromat and GG?
3. What's the focal length of the condenser?

You will need to experiment a bit with the condensor distance from your GG, but start with about 10mm. Edge efficiency as a lens is stopped down is a tough nut to crack for this type of setup, but expect vignetting as you stop down if your collimation distances are off and/or your condenser's focal length is not correct for your setup. Don't feel too bad about these problems...our R&D budget to address issues like these is more than you'd likely spend on a few hundred prototypes!
 
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1/ I use a DVX102b (PAL)
2/ The distance is 57mm
3/ I dont know, it's just a 10X Macro Lens

It is based on Daniel's design in jetsetmodels.info.
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You should try increasing the distance between your achromat and GG, you should notice that the vignetting evens out the more you increase distance.
 
Yea. The problem is that EE-A screen=vignette in 35mm Adapter if u close down the SLR lens aperture below 1.4.
And u shouldn't use condenser with EE-A because there is a fresnel field on it which act as condenser.
You may try to use EE-S screen instead. Which has less vignette problem.
If u use condenser lens. I suggest you could try to grind your own class with a microscope slide and 9-12 micron Aluminium Oxide. Which is a very good choice because it produce nice bokeh and virtually no vignette problem when using a proper condenser. But the grain is more visible than canon screen.
 
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