The lens-collectors here and lens-designer will know the old wideangle-aplanats or other aplanats with their heavy astigmatism, so much koma sometimes (I mean the older before 1890, not those, which have new glasses, these newer have extrem high curvature of field, more than the brave Angulon) that any picture is not possible, even with stop 256.

With a simple method you can let just this astigmatism dissapear (the curvature of field could not be allways tested), its like magic. You know the wide-angle converter for normal amateur of the last 30 years, I have never them collected as collectable, sometimes I get them as gift from the seller on the markets, because I was the only one, who has had interesse in optic things. The only one, I bought specific, has been the Olympus A-28 wide angle converter 0.8 for to use in combination with my Olympus OM 1:1,2 - 50mm with open stop for my highresolutionfilm. The other, I collected thanks an advice from Mr Haber, once working by Schneider, he gave me the tip, "Look at that here, buy this Canon C-8 wide angle converter 0.65, its the best of its class." The Olympus is from around 1995, is very light, probably only plastic, the Canon is from around 1965, very heavy. The two high-quality lenses (1) are very different in their results.

How I come to this result?

My research started with reflecting on the kind of bookeh for large-format-lenses by using the Olympus A-28 wide angle converter 0.8, because I had the little hope, that this modern thing has an asphaeric element (reflecting on the modern Cooke-version of Pinkham Smith). By what I was doing I was wondering about the kind of quality. And step by step in the last week I go in an other direction because I noticed, that there is more in a kind of fundamental optic. In my collection I have also other very simple converters of the low-budget-versions (2), which I need now for the first time in my life for enhanced testing.

Simpliefied summary of the tests:
1-1 : Is the basic optic a well corrected lens, and is the converter well corrected (1), than is the resulting with open stop much spheric softness, this will be reduced by stop down. That is normal knowledge for all of us users.

2-1 : Is the basic optic low or not corrected for astigmatism, like aplanat, low-class-triplet or Petzval for projection, and is the suited converter well corrected (1), than is the resulting reduced astigmatism, not or reduced spheric softness, can be reduced by stop down. This is not known.

2-2 : Is the basic optic low or not corrected (2) for astigmatism and is the suited converter low-budget corrected (2), than is the resulting reduced astigmatism, normal contrast, not or reduced spheric softness, can be reduced by stop down. This is not known.

If you have some experience in lens-calculating, you smell the ratt - you need a specific error in your lens to the specific error in your converter, parallel to that will the focus reduced - and with that focus-reducing additionally as a surplus some errors. I have no datas from wide angle converters for to calculate, with my Optalix I can only calculate in geometric, not for the wave theorie.

My questions are : Are I am right in the opinion, that wide angle converters (two lenses cemented or not) could be build in the time 1840-1880 with the existing optical glass-type of that time by reducing the necessary wavelength only in 380-420 nm (collodiumplates are only blue-sensitiv). If this is the case, some parts of history of optic must revised. It could be just the same case as with the Omnar, an anastigmat built from old glasses.

Perhaps exist in this time from 1840-1870 "a child play thing", a kind of looking through glas, where the world can be seen some more little, probably with high chromatic effects.

If thuch existed once, than this kind of optic was probably not sold, only lent; or only sold with secrecy-aggrement.

I go here to you in largeformatphotograpy.info, because your forum is for do-it-yourself (optic), and some use Zeemax. From existing parts, I have now an around 120 mm retrofocus with just sufficient sharpness (so so la la, its not an Apo-Sironar)) in the edges (!) for 4x5 by stop 22. Front is Dagor 6.8-154mm Nr around 103xxx, back is Hermagis Aplanastigmat 6.8/160mm Nr around 170xxx, the wide angle converter is a very lightwight no-name "STAR-D Aux. wideangle Focus distance Japan", build in 2 separat lenses with filterscrew 46 for rangefindercameras. The Goerz-Hermagis-combination is from older studies of mine, to enhance the symmetric ones like Dagor, Satz-Protar or Plasmat with slightly assymetrical modifications for more open stop or minimizing curvature of field.

I do not know, in which plentity of their different forms wide angle converters exist and since which date they exist - my questions to you in this forum. This had been all the time for us users a low-tec-thing (The Photomasters told us: Be a brave boy, do not touch such thing, its for simple-minded amateurs).

Perhaps this will motivate the users of 4x5 inch reflexes, to construct from existing new and old optics parts (a lot of work for selecting and testing) a retrofocus, because for industrie this is not a market.

By the way, you can use 2 different wide angle converter together, it works. Than is 08 x 0.8 a resulting 0.65.