Is there interest in retrofocus-optics for 4x5 5x7 Graflex from existing lens parts

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.

This sounds really interesting. Can you post some pics of your experiments, and the various lenses you have constructed?

Interesting concept!

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Originally Posted by ludwig

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.

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What is the flange focal distance for this combination?

The big Graflexes are dead and gone, except for an occasional elderly camera nut (me included). It is a total waste of effort in trying to resurrect them. Find some other toys to play with.

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Originally Posted by Bill_1856

The big Graflexes are dead and gone, except for an occasional elderly camera nut (me included). It is a total waste of effort in trying to resurrect them. Find some other toys to play with.

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I have a feeling that there are plenty of "elderly" camera nuts ( >70 y. o. ) who are still fascinated by large Graflex cameras. I have a number of them in varying states of restoration, decay or whatever and they all pretty much work. I've been looking for a 5x7 for quite a while, haven't been able to get my hands on one in any condition, but I'm sure I will. :) :) :)


m

Oren:

infinity-distance last glas-surface to screen is s'F'
s'F' without converter 142,5mm, flat field, vignetting starts few mm before 5x7''
s'F' with converter 148,5mm, flat field, vignetting through converter starts ca 2 cm before 5x7
probably is a systematic error from measuring on the quick, but identic for the two.

To start for your own, a normal Dagor 150mm is also a good first step in this direction. The no-name adapter: 2 separated, quite thin (?) lenses (Cannot remount them, dont want to kill them), front is nearly flat-convex (long radius), back-surface is concav with a prismatic corner of around 3 mm for to let light to the CDS-Meter of a 35mm-Compactcamera. I have no mechanical adapter for that thing (Ethernal Holy Optical Manifest No. 1 : You have never the adapter, you just need.), backlens must be pushed stright on the Dagor 154-front. A few tenth mm distance helps against rest of residual coma, that means, a possible adapter must have some variables to find right distance. Independent of that is the question, if the adapter can be modified with slight distance-variables, but this now only one I want not to kill.

EdSawyer:

I would not say, that I construct lenses when I arrange lens-parts new. Once I had really construct via Optalix a lens, a Dagor-like wideangle, but only for to know and learn, how lens-design is really. It was around 2001, when I phone to Mr Blechinger, the constructor of Optalix-software. When he noticed, that I was the person who published an article about 1000-time enlargement to show diffraction limited of a lens 1:2.5, he said to me, that this had opened a new field for the lensdesigners. Now they could go to the limits and he gave me the software for free. But I want to have only the student version, not the version, where every calculation-step will get via automatic 500 variables. I want to learn from myself, I want not to depend on the automatic stupidness-gratitude (Zahlenrausch-Dumpfheit) of a computer. After a long time and some long evenings in "mathematical meditation" of a non-mathematican I got in contact to Mr Beltrando, show him the calculation and he was pleased. You can ask him, how he found this. I must mention, this work was only for to learn, not for production. My starting idea was orientated by the Perigraphe from Berthiot, I learn a lot and comes quite near, but not full. Because I have several Perigraphes 60-250mm, I noticed, that the early ones have more angle of view than newer (the beginner-fortune of a constructor). It seems to be a glas problem in production over 50-60 years.

By now you probably already know the answer to your question.
Would 2015 $ be enough to acquire such a converter from you?

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Originally Posted by ludwig

infinity-distance last glas-surface to screen is s'F'
s'F' without converter 142,5mm, flat field, vignetting starts few mm before 5x7''
s'F' with converter 148,5mm, flat field, vignetting through converter starts ca 2 cm before 5x7
probably is a systematic error from measuring on the quick, but identic for the two.

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Something here seems not to compute. According to the bible, 10th edition, the Graflex SLRs with the shortest flange-focal distance are the RB Ser. D and Super D, both at 6 3/4". It isn't clear that either's mirror will clear a lens with 148.5 mm back focus. It is less clear that a 5x7 Graflex SLR's mirror will clear a lens with such a short back focus.

The difference between back focus of 142.5 mm and 148.5 mm isn't large. The gain doesn't seem to be worth the gymnastics.

If the OP is thinking of Graphic press cameras -- many people use Graflex, which, properly speaking refers only to Graflex SLRs, when speaking of Graphics -- then the exercise makes no sense at all. I don't have specs for any 5 x7 Graphic, but the shortest 4x5er's minimum extension -- back focus will be shorter -- is 2 9/16".

Nodda Duma wrote on 10-Feb-2015, 22:09 here in this forum :
edited the thread title to clarify this is a build-your-own-lens project.

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Originally Posted by Dan Fromm

Something here seems not to compute. According to the bible, 10th edition, the Graflex SLRs with the shortest flange-focal distance are the RB Ser. D and Super D, both at 6 3/4". It isn't clear that either's mirror will clear a lens with 148.5 mm back focus. It is less clear that a 5x7 Graflex SLR's mirror will clear a lens with such a short back focus.

The difference between back focus of 142.5 mm and 148.5 mm isn't large. The gain doesn't seem to be worth the gymnastics.

Dan Fromm :
Thanks for that info. I just grab my Reflex-Primar 9x12, take the lens from the other camera, go outside for infinity (its night and weather is clear for the skyline). I hold the lens for infinity into the camera and the mirror works. That Graflex cameras need longer focus, I didnt know.
6 3/4 inch seems to be 171,45mm - the next focal length is a 168mm Dagor. I had never had a Grafelx reflex in my hands, please inform me about the normal used minimal focal length.


If the OP is thinking of Graphic press cameras -- many people use Graflex, which, properly speaking refers only to Graflex SLRs, when speaking of Graphics -- then the exercise makes no sense at all. I don't have specs for any 5 x7 Graphic, but the shortest 4x5er's minimum extension -- back focus will be shorter -- is 2 9/16".

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