DIY spinning 35mm adapter discussion

[Bob Hart]

I knew I was missing something when I got that lens mount.. It looked alittle bare.. I will go back in there and try to get the circular sping you are talking about. Do you think it will be hard to get that spring mechinism to to function the same way? I understand what you are saying about not smashing the spring flat to the body of the box when I screw the mount on. So what I will have to do if I understand this correctly is build an extension that I can mount the lens mount and circular spring to so that it raises it away from the box. Like how Shoot35 are selling them (which btw are almost $100!!??).



If you mount straight to the project box, cut the lens mount hole only just wide enough to allow the lugs on the lens to be able to turn - just. You will find on the spring, three little inward sectors which the lugs of the lens engage with. You will also find on the spring, reliefs cut for the screws to clear through and the lock pin also. In back of the mount there is a channel cut to accommodate this spring. The bulges the lens lugs ride upon rise rearwards.

When you place the spring against the plastic of the box around the hole you have cut, then place the mount over it, you will observe the mount rides about 0.7mm high because the bulges in the spring lift it up. Where these bulges go is where you mill out a clearance with a Dremel or hot soldering iron. If the spring is a bit of a sloppy fit in there that is okay, as long as it is not holding the mount away anu longer and you still have enough meat in the plastic for your screw threads to be cut in or your through-bolts to be supported against rocking and working loose.


Quote:
You then file out the pilot hole wider in one direction until you get it optically centred for the camera view, then ream this centre out for a hole-saw centre or use it for a centre hole for a dividers or compass if you are makring the outline of the larger hole for cutting out by other means.

Ok so in other words, zoom in about 80% then boar out the center untill all of it is out of sight. Correct?


No. - You are only using the centre [ + ] of the camcorder frame marker view to accurately place the centre of Nikon lens, relative to the camcorder image centre before you install your groundglass. A small pilot hole is about the only way for a mug like me to do this. I do it this way because the camcorders I have dealt with all had their centre of sensor not co-incident with the lens optical centre. You can check for this by fixing your camera on a tripod, zooming in, marking a target at centre on the wall or whatver, then zooming back and checking to see if it is still in centre. Chances are in most instances, the image will walk to the right as you zoom out. If you mount your achromat separate from the camera, don't offset the acrhomat but make sure it is centred to the camcorder optial axis. This is important but a trap for beginners. So you don't zoom back to establish an optical clearance for the hole. There is no point as you are using the groundglass image. If your camcorder zoom-in walks the image, then you need to first check with your achromat installed to the camera and test target drawn on a piece of paper, just how far you have to be zoomed in to obtain your chosen frame size. For home-build purposes to keep things fairly simple, don't aim for more than 28mm frame width on the groundglass at most. Once you have established this frame width and the zoom position needed to achieve it, you can then make up the mount for the camera lens filter thread fitting. To establish the distance from groundglass to camera, the preference varies. P+S seem to have preferred to set the MINI35 up with the camcorder focus towards the infinity end, probably to minimise distortion, however your build accuracy has to be spot-on to do this, well within their engineering abilities as many of them used to build ARRI cameras but not so mine with hacksaw files and breadknife. I set mine up so that focus was closer to about 4M or about 16 feet. This is more central of the available range of focus movment instead of confined towards the infinity end like the MINI35.

It is entirely up to you whether you want to fix your Nikon mount directly to the front of the project box or bring it forward on a tubular extension. Be mindful that your box has to support the odd heavy lens and the furthur outboard of the structure it is on a tube extension, the more leverage the weight of the lens, handling and the occasional thump will have on the front case structure and things may be more easily bent. If you have to add length, then it is best added in the section between the rear of the project box and the camcorder because you can brace to the camera baseplate. It is not always convenient to brace forward under a heavy lens when homebuilding. You may find that you need to re-inforce the front face of your project box. Sometimes after the mold has been released the plastic will try to bow inwards in an attempt to return that which it once was, a blob. If it has done this, the axial alignment of the lens mount will be off angularly. You may need to add a 2mm piece of aluminium to the inner face of the case to force it straight.



To get the distance from the lens to the GG, like Marcel said, go out side with the lens, hold it to the sunlight and back the GG up until the image is focused on it. There is how far apart I want the two.



For the Nikon lens, distance from flange face of the lens mount to ground surface of groundglass is 46.5mm.

For your 8+ achromat or whichever one you choose, you will need to determine the front-of-camcorder to ground-surface-of-groundglass distance by measuring from a reference point on your camera to the groundglass surface when you have achieved your preferred frame size and zoom position at about 4M or 16 feet focus setting on the camcorder. From front of achromat when mounted to the camera is may be in the ballpark of about 4".

It is desirable to provide backfocus adjustment. You can do it with fixed shims under your nikon lens mount, but it is awkard and consumer level plastic project boxes change shape with time, so the adjusmtnet may not hold. It is easier to move the groundglass by making a wide mount plate for the motor and make the three or four corner fixing points adjustable. My personal preference was to put springs over long studs, then pull the mount plate down against these springs with adjusting nuts. This enables both a linear backfocus movement and angular adjustment to deal with any axial misalignment of the lens mount. There is no x-y adjustment of the camcorder view or angular optical axis correction for the camera unless you design this in with a sliding plate mount and a similar angular adjustment ayatem. It is best to get the front and rear faces dead parallel and the problem goes away leaving you with only centres to get accurate.



Marcel - I emailed Wayne, he said he has A Achromat for 20 Euro... A achromat means just some random achromat doesn't it.. not the same from the SGpro..


If Wayne is quoting you an achromat, it will likely work. Just ask him what power it is. He might even be able tell you the groundglass-to-camcorder distance for that achromat if your camcorder is not the latest and greatest. His current product is for flip adaptors and these require a less powerful achromat.


I think i'm starting to understand this now..

Honestly, i feel bad I made you guys sit there and type all that stuff out. I honestly appreciate you explaining all this.


Don't feel bad, just pay some favour forward some day.

[Marcel D. Van Someren]

Terry,

as Bob said, if Wayne is quoating you for an Achromat, I'm sure it's one that he's manufactured. If you're unsure, just ask him. What you want to do is make sure you get the Achromat for a non-flipped version of his adapter. That's essentially what you are building.

-M

[Terry Lee]

Hey everyone,

Alright.. alot of information to take in here. Good to know I am talking to people who know what they are doing. That is certainly proven.

I emailed Wayne and asked him what power the achromat is along with the distance from ground glass to camera for that paticular achromat. I hope to hear from him tomorrow. I haven't been able to get back to the camera shop and retrieve the circular spring but hopefully tomorrow.

I found quite a selection of project boxes on ebay but don't really know the dimensions yet since I don't know the dimensions of the GG disk. Do you think Wayne also has a GG disks?

As soon as I get all of the parts I will start trial and erroring all of the information that you have both given me.

My list thus far is - project box (size depending on GG), circular spring for lens mount, tube to fit achromat in (What size?), ground glass disk, CD player motor (nothing over 3Vdc), Toggle switch, wire and battery.

When I fit the achromat to the camera, Do I use a step up ring that attaches to the tube that the achromat goes in?

Again, thank you all!
Terry.

[Bob Hart]

Wayne is an obliging fellow and am sure he will help you out with advice as he started off in these from way back right here on dvinfo.

Being now a manufacturer and vendor, he may now be in the situation of having to pull back personal interaction with home-build enthusiasts otherwise nothing will get done if there are too many requests.

I understand he had a UK supplier of both glass and acrylic disks when he was still in R&D of his first commercial device.

To be fair though, do not get heart-broken if he cannot supply, or declines to supply a disk for your application.

The fact that you have to hack a fitment to your own design carries with it the potential for a dissatisfied customer issue even if all bets are off related to performance and warranties.

CD player motor. These cope with a range of DC voltages. 3v max was my recommendation. There are CD player motors and CD player motors. You may find that DVD transports are being used in CD players.

Some newer motors are brushless DC which require an electronic circuit to drive them. Just soldering on a couple of wires won't get you anywhere with them.

The older "can" style motors are what you want if you are hacking kitchen table style. However, if you are up to designing and building brushless DC motor control circuits, you give yourself a few more options for speed control, maybe even syncing up to camera frame rate to eliminiate any flickering artifacts from pushing the shutter speed and lens aperture envelope.

The wall for adaptors is generally accepted as 1/100th sec shutter and f5.6 but there are a few exceptions with some lenses.

His disks may now be a custom fitting to a special spindle hub to a different motor. You may be able to get his swap-in disk as a part and make your own custom spindle hub to suit your chosen motor.

Regarding the spring, take your mount with you as there are two styles, a four-screw and five-screw. The springs I think are different.

[Marcel D. Van Someren]

Remember that if you're thinking about getting a GG from Wayne, the GG he uses currently is a much smaller diameter than what Bob or I built. In fact, the RotoRazor as it is branded, is only about 73mm in diameter (2.874"). The cool thing about the RotoRazor is that it comes with a motor installed. Also, they make 3 different flavors of the RotoRazor.

take a look at this comparison chart:

Untitled Document

Depending on which RR you choose, you can use shutter speeds up to 1/500 and up to f22.

I have personally pushed RR2 to f8 which is more than advertised, pointed at a bright blue sky with no grain visible.

I guess you could just purchase a RR and mount that in your project box. The problem is that the optics used with the RR are very custom. The image projected on the GG is smaller than on your typical DIY adapter ( it has to be to fit such a small GG) so your optics need to be pure to achieve good results.

That said, if you can get a hold of the older (and larger) SGPro GG, then it will be more in line with what you're building.

-M

[Terry Lee]

Wayne emailed me back and told me the distance from ground glass to camera should be 100mm.

I'll email Wayne and ask him if he has a SGpro GG.


Off to get the spring part for the mount and a stop at a couple hardware stores to see if they have project boxes!

[Bob Hart]

Now how's that for guesstimate, 4" = about 100mm.


It seems that what you are going to end up with is a Q-ship SGPro?SGBlade hybrid.

My personal preference would be to hold on getting that project box until you have the dimensions of your working components locked down. The box itself is basically to keep the light, rain and your dandruff out and need not be a loadbearing element if you use a carry-though structure to bridge between the Nikon lens and camera.

The AGUS35 version I built used plumber's pipe, mainly because it was handy not for practical reasons except one.

In common with some of the non-flip and fixed groundglass adaptors I have used a tube as a carry-through structure, entire from front to back. This helps to ensure maintenance of the optical axes of the Nikon lens and camcorder plus dioptre on a common axis.

It also eliminates bending loads on the front and rear panels of whatever you enclose the groundglass in, my case being two sewer caps.

Wayne's smaller diameter rotorazor disk, if that is what you are getting, offers you the possibiity of a smaller case and the possibility of passing a support rods structure beneath the case from the camera. This is why I suggest you don't buy in the case until you have the bits and pieces gathered.

A bigger groundglass diameter rules this out because the case gets in the way of either the path of the rods if you offset down or gets blocked by overhanging handles or on-camera mikes if you offset up. Offsetting sideways is not an option as your useable area of the groundglass becomes an upright rectangle.

In my version, the whole structure was too big. Any bridgeing structure to carry rails around to the front was huge, heavy and impractical.

The carry-through tube was slotted so that the disk and motor could enter the tube from below. I glued the whole thing together once I had it worked out and left one pipe cap unglued as a detachable cover.

I also used smaller pipe caps for the Nikon mount to fasten to on front and for the camera on the rear.

Because plastic caps and my holes cut in them are of less precision than a machined tube, I skewed them on the tube for the last bit of axial alignment, taking care to make sure the front face of the lens mount was parallel to the camera mount face.

My case arrangement was a bayonet to the lens hood mount on the camera. The caps were internally tapered which permitted me to do this.

I mounted the achromat to the camera via the filter thread separately and the rest of the adaptor mounted around it onto the lens hood mount. This eliminated loading the threads but did not eliminate loading the case structure of the camera.

I got away with this because my casework and parts were relatively light but the outboard loading caused by a heavy metal lens was always a worry.

[Terry Lee]

Alright so I was able to stop by Chuck's finally to get the rest of the lens mount. He just gave me the rest of the camera and told me to bring it back. I explained to him that everyone is saying that I need also the circular spring that allows the lens to lock into place. He was confused as to what I was talking about. He showed me the camera he got the flange off of and I too am confused. Pictures below.

By the way, Wayne is giving me the Achromat and Ground glass from the SGpro for 45 Euro. Decent?


Hmmm. Its not letting me upload anything..Keeps saying 503 service unavailable. I'll try again soon.

[Terry Lee]

Wierd. Worked instantly.

[Marcel D. Van Someren]

That is a decent price (although I would think it would be British Pounds Sterling, not Euros) at the current exchage rate for BPS to USD it's about $74 which is a lot less than what the current SGBlade GG is going for.

I'll let Bob answer the questions about the lens mount.

[Terry Lee]

You're right! BPS. In Portugal its Euros and I keep getting the symbols mixed up eventhough they look totally different.

$74 sounds like a great price. Now lets see if I can build the rest for $26!

[Bob Hart]

Terry.


That has me a little bit perplexed. That appears to be an FM2 there in the image, therefore there should have been a spring unless it had already been ratted to fix another camera and the mount put back on.

There should have been a spring which looks like a corrugated big flat washer, about 0.3mm thick, as wide as the hole the mount fits over, with chunks cut out of it to allow it to fit around the pillars in the castwork. The broadness of the spring from outer circumference to inner circumference is only about 5mm - 6mm.

If you look at the 12-30 clock position, you can see one of the clearance cut outs, there should be others at about 5-00 o'clock and at 8-00 o'clock.

[Terry Lee]

It has probably already been stripped. Either that or it fell off when he took the flange off. I'll have to go back in there and see if he has another FM2 that he doesn't mind parting out.

Ok so I think I have the clearance cuts highlighted in the image below, however I think I might have highlighted to much so I took red and highlighted a slot between what appears to be a lip that runs around the edge. Are these what you are talking about?

[Bob Hart]

Terry.


That is pretty much where they are.

The rearwards raised "bow shapes" in the spring are only about 1cm long each and about 2mm broad I think and they stick out into the path where the lens lugs will arrive as you twist the lens into its mount.

There are reliefs cut out of the spring to clear the support pillars where the screws go in and a bit of a zig-zag when the latchpin comes through. The cutouts stop the spring which almost floats in the space from turning when the lens is twisted.

If you look close inside, you may see a 0.3mm shiny flat mark against the clockwise face of one or more of the pillars where the edge has born against the side of the pillar.

As long as your lens focus mechanism is not stiff - most old ones will be because the lube will have dried out - the lens will stay put in the mount, certainly the modern AF lenses will as there is not resistance in the focus movement.

[Terry Lee]

I see the areas where the flat leaf like springs will fit and on mine thats the only place I see where the lens will connect with the spring system. After looking in my D40, I see exactly how these things will connect.

It wouldn't be to hard to make this box out of metal althought that is added weight to the front and I would want to use thin metal. But if I do that I won't have enough depth to drimmel out the slots for the springs, or does it matter if there is no material behind the springs?

I just paied for the Achromat and GG. Should be on its way tomorrow.