PaulNg 寫:I agree that the proof is pretty convincing... but I've been looking at some images, like this... taken by TMB130 with flattener, 6X7 E200. It shows no dark banding like that...anguslau 寫:The problem should not be directly related with a specific design, such as Petzval. It should be directly related to the amount of vignetting inherited in the design.PaulNg 寫:講下講下, 突然間覺得好似同個光學系統既設計有關
A: 有問題既設計--> Petzval 既折射鏡 (再加reducer一樣有問題), 相機鏡頭
B: 冇問題既設計--> 普通折射鏡+flattener
結論: 會唔會係同個"flattener"既設計有關?
A類設計flattener係內置, 即不能隨對焦既動作移動, 同sensor距離可以變.
B類設計flattener外加, 同sensor距離固定.
1) we know that an olived-shaped aperture will produce dark bands
2) we also actually see the olived-shaped aperture shadow in Sing Chai's experiment, directly correlating with the dark bands
3) for any system with vignetting, part of its aperture is blocked; the question is what is the shape of the partially blocked aperture? I believe it is generally olive-shaped for most optical designs; if so, this will produce dark bands similar to the FSQ85
4) if you agree with 3) above, it means most optical systems which exhibits vignetting should have dark band problems; in fact, unless you believe the partially blocked aperture shape is not olive, the characteristic dark band should result
This can only explain TMB130 can be no problem .
It may not represent the general feature just counting the lens matter .
Besides , the design may be different .
May be it has certain particular design .
Once design matter is involved , it can be any reason is related . And may not be just what you can have a conclution base on 2/3/4 lens matter .