How to mount a DE OUDE DELFT RAYXAR E65/0.75 Revisited

[Bjørn Rørslett]

I removed the entire rear lens cell and now it will be possible to get infinity on a Panasonic or similar camera. However, as I said, image quality suffers.

However, being experimentally inclined, I think we should dare to split the 2-group rear cell as there cannot be much refractive power in the very last element, plus there should be an airspace to effectuate the split line. The two groups are joined by a metal film (to my eye), thus judicious use of a thin chisel or similar should do the trick in prying the groups apart along the air space.

If this strategy works, there should be little problems getting the "Infinity Rayxar" functional on a bespoke m43 camera with a nice high-resolution sensor and good ISO performance.

[BEZ]

You confirmed the make up of the rear cell then  ...I remember mine slipping out when assembling the mount and I thought it was a single element.

I read a blog where the author rearranged the elements of the lens to achieve various focus distances, including infinity. His example images were not convincing so I did not save the link. 
I will try and find it, in case it contains any points of interest.

Personally I would not want (brave enough) to separate the rear element as I enjoy the lens in standard form. I realise your curiosity (bravery) is much stronger than mine.

What would be your main interest in using the lens at infinity?   

[Bjørn Rørslett]

"Because I can" -- natural curiosity. A new twist on familiar scenes. Etc.

[bjornthun]

You might be able to do with a camera without a mechanical shutter. A few m43 models offer a completely electronic shutter, but you will be limited by the rolling shutter effect. Maybe a Nikon 1 model also has a fully electronic shutter. However, I have no idea, if said cameras will even boot up without their mechanical shutter unit.

[Bjørn Rørslett]

By removing (partially or entirely) the rear lens cell, the working distance gets much longer and there will in principle be no problem with a shutter curtain. Except for the [focusing] mount, which has to be a bespoke design, various cameras could be attached and probably these won't need much of a modification, if at all.

[charlie]

I've been doing my own experimenting with X-Ray lenses and infinity focus and while I can not speak to the De Oude Delft Rayxar, the Heligon 100mm f/1.5 and the Kowa 42mm f/0.75 can achieve infinity focus by the removal of certain elements and other means.

I don't want to derail this thread though with those experiments, perhaps a new topic.

[BEZ]

I've been doing my own experimenting with X-Ray lenses and infinity focus and while I can not speak to the De Oude Delft Rayxar, the Heligon 100mm f/1.5 and the Kowa 42mm f/0.75 can achieve infinity focus by the removal of certain elements and other means.

I don't want to derail this thread though with those experiments, perhaps a new topic.

Charlie,
I think it works continuing the conversation here ...but here or on a new thread, I am interested in your experiments

Cheers

[karl]

Hi! Very interesting thread . I'm in the process of adapting my E65 and can't figure out wether I should split the rear element or not as Bjørn was saying.

I'm more interested in using this lens for landscape or night skies than macro/proxy photography so getting rid of the rear element is going to happen but I don't really understand what the last thin layer of glass is supposed to do.

Bjørn, did you do it at the end? If you did, what do you think now?

Plus, has anyone tried to adapt this lens on medium format?

Cheers!

[Bjørn Rørslett]

In order to achieve infinity focus with the 65/0.75, the distance rear element to image plane has to be less than 4 mm. Even on a mirrorless camera this is not possible if there is a shutter curtain present.

Adapting this lens to medium format has only meaning if one shoots close-ups, as the image circle is pretty small and doesn't even cover 24x36 for anything else than close focusing. Be aware the curvature of field is extreme.

[karl]

Ok. So I'll have to redefine my goals a little then, forget about infinity/far focussing. What is the further you could achieve focus?

[Bjørn Rørslett]

If lens is mounted in a light-tight box, without shutter, you can get infinity focus. There are descriptions of such 'deep sky' cameras on the 'net.

[simsurace]

Couldn't one make a relay that takes and puts it further away to not interfere with the mirror? This would be more cost effective than building a custom camera.

[karl]

So Bjørn, if I follow correctly. If I mount the lens on a box with bellows or something, and create a ground glass for it. I could then achieve infinity focus, and I would "simply" have to take a picture of the ground glass, or scan it. Right? (of course scanning for a dark sky isn't practical but for daylight landscape  I think it would work, don't you?)

Cheers!

[Bjørn Rørslett]

In principle, yes, but all advantages of using a superfast lens is lost. In order to show an image, the screen has to break up the aerial image thus it must have grain and this structure - literally - is engrained in your final image. Plus the projected image would be bright on the optical axis and probably dim elsewhere.

Simone's idea of an optical relay circumvents some of these issues, but the overall "speed" drops dramatically.

[karl]

Well, it's not really the speed that I'm looking for with this lens. It's more the extremely shallow depth of field. If it was for the speed, I'm OK with the couple 0.95 lenses I already use. But anyway, I hear you.

If I could find a way to get around these problems, that would be even more interesting.

Is there somewhere an accurate measurement of the "film" coverage one can get from this lens? When I removed the rear element, I got something larger than fullframe but I can tell for sure how large I can get with it.