DIY spinning 35mm adapter discussion

[Bob Hart]

Terry.


I think from memory, the thicknes of the flat areas of the spring fit inside the back of the mount ring itself. The reliefs only have to be cut to allow the three "bows" in the spring to not be squashed. The hole behind could probably be wider so they are in the clear.

The problem you will have will be having enough material where those four screws thread in unless you cut the hole as small a diameter as you can and yet still clear the lugs on the back of the lens when it is inserted.

YouTube has gone bellyup as I write this so I can't refer you to the agus35 dismantled clip but I think it is listed back a page or two on this thread. You will see the mount is not let down inside of the plastic at all, just screwed down onto the face.

The mount was screwed down directly into the PVC plastic or the pipe cap I used fro front of case. The wall thickness of the Iplex caps is about 3mm and the plastic is tough. Other plastic caps have a 2mm wall thickess.

You may find that you only need to Dremel out clearances for the spring bows about 1mm deep as the flat portion of the spring will rest up inside the back of the mount ring. The little sharp ridge around the outside of the mount ring will sit high about 0.5mm. That's okay.

[Terry Lee]

Haven't given up Bob, still waiting on the achromat and ground glass. Have yet been able to stop back by the camera store. This Thursday is my birthday so i'll be heading to Fort Lauderdale and Miami beach. By the time I get back i'll have everything and I can get down to business on building this thing.

Thanks again,
Terry.

[Terry Lee]

Alright so I now have in my posession the achromatic glass and the ground glass disk. What I have yet to obtain is the lens mount, which I will hopefully find soon.

Alright so now to set this achromat into place with my lens... What do I use?

[Marcel D. Van Someren]

For testing to get the proper distances or for your final connection to the camera?


By the way, as far as the lens mount goes, if you don't find one soon, there's always the one from shoot35.

[Terry Lee]

Yea sorry I was kind of vague with that question..

By lens I meant the camera lens, not the 35mm lens. What should be the distance of the achromat from the camera?

Do I find some sort of tube that this large piece of glass will fit into thus attaching it by a step up ring?

Thanks!
Terry.

[Marcel D. Van Someren]

The achromat should actually screw right into the filter threads of the A1. If it's from an old SGPro than it should be 72mm filter thread which is exactly the size on the A1. So, basically, the achromat should be as close to the A1 lens as possible.

[Bob Hart]

I endorse Marcel's suggestion.

[Terry Lee]

What Wayne sent me was a bare piece of glass. My camera is an HV30 though...therefore I will have to use a step up ring.

[Bob Hart]

What you have is an unmounted achromat, a wrinkle in the process but not an insoluble problem.

To do properly would require mounting in a machined metal or plastic barrel of some kind with 72mm filter thread on the camera end and a suitable internal thread on the other end to mate up with a tube at the adaptor end if that is the way you are going.

A method of mounting a lens in a barrel and to have front internal thread is to have a threaded retainer ring going in from the front and sharing the common thread.

Depending on how much you are willing to spend on this thing you could make a custom tube going from front to back with a clearance slot for a disk and motor. The Nikon mount would go on the front as with extention tube.

The achromat could fit facing forward in the rear of the tube against a machined shoulder and a threaded hollow plug go in from the back as retainer ring with the camera thread machined onto the back of it.

An appliance made of plastic and glue will have to be supported from the camera baseplate with no loads on the camera filter thread at all.

Unless you have the machine shop and skillset to use it, that option is going to be beyond you unless you can go into the photographic equivalent of a wreckers yard and mine through all their bits and pieces.

You could do it on the cheap by using plastic water pipe, glue and a 72mm filter ring. The achromat would be retained in the plastic tube by two rings of smaller diameter tube or thin cuts of the same tube with a piece cut out and squeezed in to fit the inner diameter then glued into place with the lens in between them.

Getting the optical axis correct with the elcheapo method will be extremely difficult but it can be done. Best would be to have the faces of all tubes and rings cut on a lathe or use one to score accurate reference marks for hand cutting and filing.

One of the internal retaining rings should be cut at least 3/4" long so that it tends to fit accurately in the tube without skewing the optical axis sideways. This would be the fixed shoulder in a metal arrangement.

To make the tube fit in the lathe chuck without deforming and falling out would require a tight plug to be made to fit inside the tube to resist the crush of the chuck jaws.

I can't emphasise enough that the achromat optical centre axis must be centred to the camera optical centre axis and that there is no angular deviation of the achromat centre axis. The rest of the appliance can be out and you will still get a workable image.

Wayne may be able to sell you a barrel for the achromat with 72mm filter thread but it may be that the mounting of the achromat was integral with the rear body of the SGPro in which case the only other separate part might be a threaded retention ring.

The lens, if it is made of optical glass will be very brittle, easily chipped and sensitive to sudden temperature changes if they are localised to an area of the lens glass. You will have to be careful when trying it into any mounting system you design until you get it securely mounted.

Any metal barrels or retaining rings should have a fine finish on the contact faces. My personal preference would be to make up thin washers of fine paper or plastic shim material to cushion these surfaces. Retention of the lens in a metal barrel should be lightly snug, sufficient to prevent movement but not tight.

[Terry Lee]

Originally Posted by Bob Hart

To do properly would require mounting in a machined metal or plastic barrel of some kind with 72mm filter thread on the camera end and a suitable internal thread on the other end to mate up with a tube at the adaptor end if that is the way you are going.

Luckily I have a friend who has a lathe and uses it all the time. All I would have to do is bring him a 72mm UV filter and have him match the threads on the camera side.

A method of mounting a lens in a barrel and to have front internal thread is to have a threaded retainer ring going in from the front and sharing the common thread.

In other words I will be screwing something with the function of a washer/retainer in on the internal thread to hold the achromat in place? Thus shimming it tight (but not to tight) in from the other side.

I can't emphasise enough that the achromat optical centre axis must be centred to the camera optical centre axis and that there is no angular deviation of the achromat centre axis. The rest of the appliance can be out and you will still get a workable image.

Well noted. I will certaintly pay attention to this. What could I do to ensure that it is truely set at the camera's optical centre axis?



Terry.

[Marcel D. Van Someren]

Originally Posted by Terry Lee

Well noted. I will certaintly pay attention to this. What could I do to ensure that it is truely set at the camera's optical centre axis?

Terry.

Seems to me that if your friend is making something to hold the achromat that has a 72mm thread on it, as long as the achromat fits snugly into this "tube" and the wall thickness of the tube doesn't vary around it's circumference, the achromat is automatically centered on the camera's optical center axis. The trick will be to make sure that the achromat in this tube is parallel to the lens on the A1.

[Bob Hart]

I endorse Marcel's comment.

To retain the achromat in the tube it is not necessary to use a threaded collar. I have seen some appliances which use an internal wire circlip and a thick soft shim between circlip and the edge of the lens. If you use this method it is better to insert the lens into the tube from the camera side so that the circlip is not buried deep where you cant get at it.

When you offer your achromat up to the camera lens for the first time, cut a thin piece of writing paper into a circle shape about 10mm smaller diameter than the front glass in your camera lens. Put it into the space between camera lens and achromat so that there occurs no direct contact between the two glass surfaces if they would otherwise clash.

Tip the assembled achromat/camera side to side and check to see if the paper is free to slip about inside. If it is not movimg. chances are it is trapped between the two surfaces. Therefore the achromat will touch the camera lens and damage it if you assemble it. You should shim the achromat forward or take out a little more metal from the shoulder of the barrel you have made up for the achromat so that it sits furthur forward in the barrel and the paper moves freely.

It seems best to have the achromat as close to the camera lens as you can safely place it, however there may be ideal positions for different zoom settings. To cater for this possibility it might be best to cut the shoulder about 2mm deeper and then cut several shims you can place between achromat and shoulder and between achromat and retainer to move the achromat back and forth in testing.

[Terry Lee]

Alright awesome. Now all I need to do is aquire the tube.

So I am looking for a 72mm tube but how long? Just a tad longer than the achromat?


About the lens mount - It doesn't necessarily have to be from the FM2 correct? I am looking on ebay just to find an old parts camera but I am expecting to pay on average $50. I found the lens mount and the circular spring by itself but they want $30 for it.. What other cameras could I get the lens mount from?

Terry.

[Bob Hart]

Terry.


This is the point where you probably need to sit down with a pen and paper or AutoCAD, TurboCAD or some other if you into computers and design software.

My personal preference is to use a common tube right through the project case. This helps keep things centred and aligned to a common axis almost automatically. Once the tube is established in the case, you can cut a clearance slot out of one side for the disk and maybe the motor as I had to to.

I would be inclined to use some cardboard to roll up a tube or even some tube out of a butcher's roll. use another cardboard roll inside it to position your achromat. Pringles chip cans are handy for test jigs. A piece of groundglassed microcope slide shoved through a slot makes an adequate test groundglass if you dont want to risk your thorlabs screen.

Get your distance right in the cardboard tube, then measure off the separations between components and draw up your machining diagram for your machinist.

If your friend is willing to make up a lens barrel for your achromat, it might be easier to make the barrel a separate component with the 72mm filter thread for the camera on one end.

If he is clever enough to cut an internal matching thread in the front-end for the rear end thread of a storebought extention tube, you might have him make the achromat barrel long enough that combined with a extention tube with Nikon mount on front of it, that the combined assembly will be the correct length.

A warning. I don't like cutting internal threads, I detest them to perdition. Maybe your machinist is more generous or accomplished than I and he wont fret about it.

Cutting the 0.7mm pitch thread to fit into the front-end of the camera is going to be a real bitch, no matter how clever he is because the plastic threads on these cams are very easily damaged if you use them for the fit up process and things are not quite right.

With metal to metal, as long as you are careful and lube the initial fit up, the fit can be a bit tight or loose but with plastic camera casework, tightness or looseness will do harm. A loose fit will bruise the tops off the plastic threads when metal might just hang on.

The best bet is if you can find an old metal bodied lens with a good 72mm front filter thread that has not been dented inwards from being bumped or dropped.

Use that to offer up to the turned thread on the achromat barrel whilst it is still in the lathe chuck and the thread cutter is still synchronised to the thread. That way your operator can incrementally dress the thread deeper until the fit is good.

When offering up the lens front to the newly cut thread, rotate the chuck anticlockwise by hand with the lens offered up until the end of the thread clicks, then attempt to screw the lens on by turning the lathe chuck in the clockwise direction.

Your machinist may know a better way but it might be worth him knowing that my method method of cutting the threads, especially the internal ones with the crappy lathe I have is to rotate the chuck by hand for the cut and the backoff.

I back off far enough that for the next cut, the slack in the transport will take up, keep the travelling drive engaged at all times and locked against any creep of the engagement lever out of mesh. He will know all this stuff, may have access to some really good gear, and come back with a "relaaaax, I know what I am doing."

Alternative to cutting an internal thread in the front of your lens barrel might be to make it a bit longer with an internal diameter to fit snugly over or external diameter to fit inside your storebought metal extention tube. Your machinist could drill and tap for you three clamping screw threads into the outermost tube on 120degree radial centres.

This would allow you some wriggle room if you don't get your lengths right or add a condensor down the track.

[Terry Lee]

Wow.. This is turning out to be alot of work. I have been running around like crazy trying to aquire parts to build this adapter, finish my crane and construct my dolly. Tonight i'll try to re-design my steadicam plans with time left to go to a movie and dinner :)!

Unfortunately I don't have AutoCAD or TurboCAD and even if I did it'd be like putting a monkey infront of a typwriter. So the old fassion pencel and paper has suited me for the time being. I've been drawing a rough sketch of how these parts will come together. Interestingly though the drawing looks like a comic book.. I'll post a picture of my progress as soon as I get more progress done.

The common tube suggestion is the design i'll go with. I'll be able to match camera to achromat, and achromat to the lens center axis alot easier.

I have found a place that will make the lens barrel for the achromat but it might cost me a bit. Turns out my friend can't cut threads yet on his lathe.

I would be inclined to use some cardboard to roll up a tube or even some tube out of a butcher's roll. use another cardboard roll inside it to position your achromat. Pringles chip cans are handy for test jigs. A piece of groundglassed microcope slide shoved through a slot makes an adequate test groundglass if you dont want to risk your thorlabs screen.

Get your distance right in the cardboard tube, then measure off the separations between components and draw up your machining diagram for your machinist.

If your friend is willing to make up a lens barrel for your achromat, it might be easier to make the barrel a separate component with the 72mm filter thread for the camera on one end.

Ok so let me see if I understand this. What I am trying to do here is match up the achromat with the GG. The distance from the GG to the Camera should be 100mm so therefore I have to adjust the achromat so that the camera can focus on the exact point where the image coming throught the Nikon lens meets the GG. So like you said, a pringles can with the lens in one end, the GG slid up through a slot in the pringles can and my achromat on the other end. The distance from the Nikon mount to the GG should be 46.5mm. So first i'll set into place my Nikon lens, measure out 46.5mm back and cut a slot then measure 100mm from that point to the camera and I should have my distances for all my components. Then test and fine tune.

I tend to simplify things where as things are alot more complicated.. Some other factors I will have to consider are making sure the components aren't shifted off axis. It will be difficult trying to center the achromat that doesn't have the threads yet. I can probably wrap the edge with a piece of paper then tape around until it fits sung in the pringles can? That doesn't guarentee that its center though...

Sence my camera is the HV30 and has a 43mm thread I will need to use a 43-72mm step up ring that I should probably go ahead and purchase.

I want to make the barrel of the achromat a stand alone part by itself with a male end toward the camera where I will screw on a step-up ring and on the other end, will be a female end where I can screw on a tube that makes up the remaining length to the box.

I do like your suggestion about adding the extension tube... Although from what I understand, The extension tube will make up the rest of the tube that goes through the box. Therefore I will have to cut the area for the GG in the extension tube? Going this rout will allow me to by-pass cutting the right size hole for the lens mount and grinding out clearance for the spring. that'll save some time..