Rodenstock TV-Heligon 50mm f/0.75 for Nikon (with focusing and aperture) - part 2

[dalex_257]

Hi All,

This is a continuation of my DYI thread started here to modify Rodenstock TV-Heligon 50mm f/0.75 for Nikon. But this time I made it focus and added AIS aperture (for those non Nikon folks - AIS allows keeping aperture fully open during framing but then stops it down to selected one when shooting).

Having acquired a new Rodenstock TV-Heligon 50mm F/0.75 lens (which incidentally is brand new - never been used whict in itself seems to be rarity) I now made the initial modifications to allow it to be mounted on Nikon F mount with limited focusing and full aperture control. As the first time, the lens came from the same source (Adam Bexley at Abex UK) and I would recommend to use Adam's help if you are after the lens like this one.

The focusing part is removable and the lens can be used in the same way as my first conversion as well. To achieve this, the basis of conversion was to attach the 72mm to 52mm step down ring to the base of the lens which then makes it possible to mount various 52mm threded attachments.



The BR-2A reverse mounting ring (next to lens on the photo above) can then be screwed in to give the same type of convesrion as my first lens (only making it slightly shallower which increases the working distance for the lens a bit). The photo below shows this configuration:



The stepdown ring was glued to the lens backside the same way as before with Araldite epoxy for metals. I will reinforce it with screws in a future when I find the right sized tap. And a closeup of this (step down ring is black one in the middle):



To allow the limited focusing and aperture control, I used an old Nikon E-Series 50mm F/1.8 lens which is relatively flat (nearly a pancake lens). Using something like 45mm GN Nikkor (a proper pancake lens) would have been better since it would allow closer mounting to the lens rear element but those lenses nowadays are ridiculously expensive so it is out of the question for me.

The Nikon lens had all the glass and some frontal parts removed. I left the diaphragm assembly, lens mountg and helicoid intact. For the first implementation (proof of concept), I also left the filter thread there and use a 52mm reverse coupling ring to attach that to the Rodenstock lens. This is how the modified Nikon E-Series looks with the coupling ring and fully extended helicoid:



And a view from the top:



The beauty of having the full lens to play with is that the diaphragm part is working as it is on a normal lens - i.e. it is fully opened when composing but pressing the shutter closes it down to the selected aperture value. This also makes DOF possible which is nice to have feature with this lens. The aperture selected by the aperture ring and for this lens ranges from F/1.8 to F/22. Considering that the lens is mounted further from its optimal position those values are just about right. This is how the whole lens looks when assembled:



And on a D200 camera:





I still have a problem with this design, the diaphragm is a bit further from the lens back element so it is not in its optimal position. I will eventually reconstruct the mounting 52mm thread and get rid of the filter ring and coupling adapter altogether. This though will be in a future as I am still wating on some parts and will need to experiment.

For sample images please see followup message - due to limit it was not fitting in one message.

Any comments, questions - please do ask.

[dalex_257]

To show the difference it makes using the diaphragm, I have taken a few quick and dirty photos this morning (had to use high iso as it was done in a hurry so sorry for the grainy images).

The two below are taken with widest aperture (lens used as before without extra focussing/aperture attachment):





The same two taken with focussing/aperture attachment at f/8:

[Boynielaad]

I am at risk of being shot down in flames but here goes...

I am confused as to why you are doing this. It seems to me that the images are very poor and unuseable.

I am no expert and am happy to be corrected if I am missing the point.

[dalex_257]

Originally Posted by Boynielaad

I am at risk of being shot down in flames but here goes...

I am confused as to why you are doing this. It seems to me that the images are very poor and unuseable.

I am no expert and am happy to be corrected if I am missing the point.

This to me indicates that you have not read the message in the post with the sample images. I said that I taken them quick and dirty to show the difference when using the diaphragm.

To see what you can really do with the lens - look at my other thread here.

[Messiah Khan]

Still keeping a close eye on these threads. But adding an aperture so you can stop down.... sacrilege! Surely the point of the Ultra fast lenses is to shoot wide open. If you are going to stop down to f8 etc, then you would just use a nifty fifty. Althugh getting focusing would be very usefull. How far back would you need to go to get infinity focus? Good job on getting a brand new one btw. One day I might have to pick one of these up.

[dalex_257]

Originally Posted by Messiah Khan

Still keeping a close eye on these threads. But adding an aperture so you can stop down.... sacrilege! Surely the point of the Ultra fast lenses is to shoot wide open.

I know, I know - it's blasphemy

It was just an experiment. However to my eyes it shows that stopped down this lens is very sharp. And according to some other stuff I read on a net, it is very sharp wide open if placed in optimal position (i.e. close to it's infinity focus). And even stopped down it has that nice way of washing away out of focus parts of the image.

The focusing part is easy though, you can always use the conversion method I used for this lens (step down ring) and then buy one of those M42 focusing helicoids (the 16-30mm seems to be fitting perfectly). When I'll fed up playing with the aperture, I'll get rid of the iris and shorten the helicoid so it will focus with back element as much protruded back as possible.

Originally Posted by Messiah Khan

Althugh getting focusing would be very usefull. How far back would you need to go to get infinity focus?

Well way too far I'm afraid. According to spec it should be 8mm from focal plane. Nikon has 46mm in its lenses and you can play safely till about 40. To have these lense focusing on more useful range than macro you'd need either to get a larger lens (75mm ish - but those are enormous) or add some glass at the back of the lens to refocus at a longer distance (but this will compromise the optics). I am so far happy with it as it is and treating is as a speciality lens. Despite all the focusing and aperture mods I am still using it mainly the same way as before - with a simple config where it mounted in a fixed way (this gives me a best possible range singe the lens back element in this position is as far back as possible).

[dalex_257]

Following the criticism of my samples being unusable, I have went out during last weekend (after my holidays) and taken a few more shots. Thanks to springtime - it is now a heaven for floral photography. Most of them are on my site in this gallery but here are a few samples (just to keep them referenced in this DIY lens thread).

Sweet cherry blossom:



Yellow daisy:



In a dandelion world:



Sweet violet:



Tiny flower:

[yodasz]

Hi Charles,

You probably should post this in my Rodenstock thread - so people can find the answers as well ;-)

I'll try to answer inline.


---Quote (Originally by yodasz)---
I found your topic discussing the adaptation of Rodenstock lenses since I'm trying to build a similar system.
---End Quote---
I had 2 conversions done (there were 2 threads on TP) and both were done slightly differently.


---Quote (Originally by yodasz)---
I have not so much technical knowledge about lenses though, and since I want to use it on an EOS system, I wanted to ask you how I could do that.
---End Quote---
The same way I did for Nikon. In my first mod I just bought a cheap extension ring set from eBay (oine of those chinese ones) and glued the end part of it where you mount a lens to the Rodenstock with industry strength epoxy (I used Araldite for metals bought in Robert Dyas but also available everywhere like B&Q). The epoxy after it fixes (about 8 hours) will be as string as a rock. I then attached the other end from that extension tubes set (the camera mont end) directly to the glued lens end without any extension tubes in between (this gave the shortest adapter height).

This setup is fairly limited though because the screw thread on those extension rings is very non-standard (Chinese made - heh) so you would struggle to attach anything else to this apart from those extension rings you get and the camera mount adapter. So I went and did an improved version of it in my second mod.

For the second mod, I got myself a 72 to 52 mm step down ring (the widest available on eBay) and glued it to the lens base with the same epoxy. This will give you a very shallow addition to the lens base and will actually make 72mm (male) and 52mm (female) threads available on the base of your Rodenstock. From there the possibilities are endless really. There are plenty 52mm to anything else adapters including M42 (which enables you to have any M42 attachments). The simplest way for me to attach that construction to the camera was by using the reversing adapter. Those do exist practically for any camera brand and allow to mount the lens in reverse on your camera. Majority of them do have 52mm male thread to attach to the reversed lens filter thread. This will actually give you the furthest possible protrusion of the Rodenstock into your camera mirror chamber (be careful to check that it is not too far) so the working distance for the macro can be increased to the maximum.


---Quote (Originally by yodasz)---
The problem is that I did not really understand which mount the Rodenstock is in.
---End Quote---
Rodenstocks do not come in any mount - they are not mounted on a camera - they usually mounted in massive industrial plate in front of a sensor so most of them will have the thread on the lens barrel itself for that.

Hope it does clarifies it a bit.

Good luck with the conversion,

Thanks

So if I get this right you could do the same thing with an EOS focusing helicoid of the same range, I should be able to create a focusable version?

[yodasz]

BTW do you know the flange-to-focal-plane distance of the Rodenstock? This would allow the use of an optical adaptor

[dalex_257]

Originally Posted by yodasz

So if I get this right you could do the same thing with an EOS focusing helicoid of the same range, I should be able to create a focusable version?

Focussing is possible by attaching this lens to any moving helicoid - you can scavenge this from any older or broken lens for example. However, you should be aware that it will only be a limited focussing since the lens will be pushed away from its optimal position - you can only be able to do macros with it.

Originally Posted by yodasz

BTW do you know the flange-to-focal-plane distance of the Rodenstock? This would allow the use of an optical adaptor

This depends on a kind of Rodenstock you have. This page (in italian) has details and drawings of some Rodenstock construction with back focal distance. For TV-Heligon you have 6.1 mm and for XR-Heligon 7.1mm.

The Canon EOS has 44mm flange-to-focal-plane distance which means that it is significantly larger than any Heligon has. No matter how you mount it, you won't be able to achieve that short distance on EOS hence the reason you will only be limited to macro with this lens. This is also a reason why I for example use a conversion which is modular where I can use it with remnants of old lens (with added focussing and aperture) but still can take that off and use it with reverse mounting adapter. The latter case gived me the tightest possible mount on Nikon with rear lens element as deep as possible into the mirror chamber. Using any kind of helicoid will add to the lens back focal distance and hence push it out even more which in turn shortens your working range (you need to get closer to the tsubject to be able to focus).

You are probably right and it is possible to fix it with an optical adapter - something like reversed telephoto construction (back part of the very wide-angle length say Sigma 10-20mm) which do similar thing. However, my limited knowledge in optics will say that this is also going to reduce the amount of light reaching the sensor. So by doing so you would effectively turn your lens into F/2.8 or whatever the new max aperture will be - there is no point of doing it really since there are plenty of lenses around that do it already . This is basically the reason why F/0.75 is not easily achievable - with relatively simple element construction you need to have focal plane really close to the lens to get the amount of light for F/0.75. To move it further away would require humongously sized optics and this lens is already way too large for 50mm...

You can have a look at the Rodenstock original designs: TV-Heligon is a US patent #3454326 and XR-Heligon is a US patent #3300267 (you can freely access them here). If you look carefully at the lens design you will see that it is designed with a large optical front group that consequtively reduces size of the area as it progresses down to wards the lens end. This in effect concentrates the light in tiny exit area which is projected to a small sensor not far from the lens exit. And this is what allows to achieve F/0.75. Adding the optical element to expand this area and take the light to the sensor further away is going to reduce the intensity of it so it won't be F/0.75 anymore.

[yodasz]

Thanks again for your help... just finished my first adapted lens with an xr heligon 68mm... it is enourmously fun to play with