Someone mentioned on here a way of using a ground glass held at the gate to check focus….so
I was thinking of a s8 cartage that checked focus using a mini video camera that films a ground glass….this could be used to test if lenses that look correct in the view finder is actually in focus at the gate….what made me think of this is when i put a canon c8 wide-angle lens on a 5008/6-70 schneider lens it looks in focus but is often out….but at one stage it had perfect focus….when it was gaffa tapped on the front of the lens.
So I'm thinking a ground glass that sits where the film would be…..with a little security camera behind it that shoots a zoomed in version of the gate projected image…so you could see a video output to see if its in focus. I'm thinking of 3d printing one up to see if it would work.
what do you guys reckon? Can you get a ground glass super8 gate magnifier already?
I've used adhesive tape as a temp focusing screen on Bolex 16mm cameras. Works pretty good. The video camera idea is pretty neat. They're certainly small enough now to do it.
Years ago, I had a Canon 1014E, which I loved because the Super 8 carts loaded from the rear. But, like even the best Super 8 cameras, you simply could not trust the accuracy of framing on the view finder for title work. So I tore open a cart and put a small light bulb in place that would project down through the lens. The power cord came out the back of the cart. You couldn't use it for focusing but it was deadly reliable for framing. You just put the camera on a copy stand pointed down at your titles target area, turn off the room lights, turn on the inserted cart with the light in it, then move your artwork around within the projected gate area on the copy stand. You could make sure that your titles were both perfectly centered and level. Worked great. Made a few for friends that had the same camera. I also made one that had the power cable out the side for a friend that had a regular Super 8 camera with the typical side loading compartment. I've seriously thought of making and selling a few just for fun.
Hi Roger..thats a cool way of getting the framing right for titles. 8)
I like the adhesive tape idea. I remember years ago you suggested using tracing paper for a depth of field adaptor idea i was experimenting with….that would work for this to probably. I have some silicon carbide powder which works great for grinding a ground glass with …i will give that a go and see if that works the hardest thing will be cutting the glass neatly.
I have a hd webcam that is already half pulled apart that might work for the video part…i will try and test.
Yeah another camera that was out of focus last time was our litre eumig Nautica…it to has the wide angle attachment to that seams to do weird stuff sometimes
Hi Mana…yep i was underwater, but everything was an even 10% out of focus. :oops: But good point ,i guess that would be impossible to test with the focus adaptor …if it focus could only be tested underwater he he. :oops:
If you build a focus checker you'll need a way of checking the focus checker.
A focus checker checker?
One way is to ensure the camera and a test chart are locked in position with respect to each other, and then using something other than the focus checker, determine which lens position has the image in the film plane in focus (for example exposing film for different lens settings). Once the film plane image is known to be in focus one then inserts the focus checker and adjusts the position of it's ground glass screen (or substitute) until it has the image in focus. The screen of the focus checker is then locked into place. From then on the focus checker can be used.
In other words, when you build the focus checker build it in such a way that allows you to adjust it's screen position, ie. to calibrate the focus checker.
I imagine the viewfinder optics are probably adjustable for the same reason. So that could be the alternative - re-calibrating the viewfinder optics.
Hi Carl..I figured the ground glass would be pressed against the gate…..then you would focus the video camera lens through the clean glass side through to the frosted side of the glass onto which the super8 cameras lens would project the image that would normaly fall on the film. So you would just focus the video lens till the frosted glass was sharp.
If you have a camera that you KNOW gives good focus at infinity, you don't actually need the ground glass in order to set up the "focus checker"..... or to use it.
First, set the camera lens to infinity, place it on a tripod and point the camera at a distant object. Then insert the "focus checker" cartridge (no ground glass), start the camera and adujst the CCD camera for best focus . Done!
The ground glass is NOT needed: the camera lens forms a REAL image "in space" at the film plane and the CCD camera lens transfers it to the sensor. The CCD camera lens is actually now part of a lens "system" from object to CCD sensor, in the same way as the viewfinder mirror, eyepiece and your eye's lens are part of a lens "system" from object to Retina. No ground glass is needed there either.
Now, I'll bet that a lot of you will tell me I'm wrong........ but those that know their Optics will know that I'm right. Let battle commence!
granfer wrote:If you have a camera that you KNOW gives good focus at infinity, you don't actually need the ground glass in order to set up the "focus checker"..... or to use it.
First, set the camera lens to infinity, place it on a tripod and point the camera at a distant object. Then insert the "focus checker" cartridge (no ground glass), start the camera and adujst the CCD camera for best focus . Done!
The ground glass is NOT needed: the camera lens forms a REAL image "in space" at the film plane and the CCD camera lens transfers it to the sensor. The CCD camera lens is actually now part of a lens "system" from object to CCD sensor, in the same way as the viewfinder mirror, eyepiece and your eye's lens are part of a lens "system" from object to Retina. No ground glass is needed there either.
Now, I'll bet that a lot of you will tell me I'm wrong........ but those that know their Optics will know that I'm right. Let battle commence!
Yes. That will work....
....IF the rear element of the Super 8 camera lens is the right size and IF the lens diameter of the CCD lens is the right size and IF the CCD camera lens is the right focal length and IF the CCD camera/lens assembly is the right distance and IF the CCD is the right size. In my experience, this alignment of planets rarely happens that easily, which is why the 35mm film-look adapters all used a spinning ground glass instead of aerial imaging. Theoretically, you could pick out the aerial image without the spinning ground glass but matching the necessary optics for aerial image focus is not a casual affair and would change from one camera set up to the next. That "unknown" is what would create potential problems for the focus checker application. In fact, it would be far easier to just remove the lens of the CCD board camera and focus the Super 8 lens directly on the CCD chip. If you know the Super 8 camera lens is focused properly, then all you have to do is move the CCD chip toward the gate until the image is crisp and then lock it down. No aerial image required. Even if the COI of the Super 8 lens is too big or too small, all you really care about is focus; not size.
Hi guys... i had a crack at this the other day….one thing the ground glass does compensate for is if the video camera is at a slight angle because of its size…it can still see if the image projected on the ground glass is in focus…at east in the centre of it….but i will rip the end off and try gong directly to the sensor…and see it that works….but i think i need a smaller camera to get in close enough….the one I'm using is a hd webcam its board is slightly wider than what i need maybe one of those inspection cameras would work?…..i will have another go with this though.
Also was thinking of piece of reversal film shot and processed of something white would work well instead of the ground glass and would be perfect size ?
Just put a tiny first surface mirror at a 45 degree angle and let the video camera view the ground glass that way. Then it doesn't matter how small the video camera is. For that matter, just use your eye with a close up lens to see the ground glass via the mirror.
milesandjules wrote:
Also was thinking of piece of reversal film shot and processed of something white would work well instead of the ground glass and would be perfect size ?
Go to the art supply store and get a sheet of frosted drafting mylar. It's a perfect rear screen material and is the same thickness as film. You can cut it to any size easily.
