Im having some trouble building a 35mm adapter. I have spent over $100 now and have not yet had any success. I was hoping someone could help me out

I first tried building a plastic CD spinning adapter but i had a very large hot spot. I tried different forms of ground glass, but the hot spot remained. I used a Fresnel and condensers but was unable to get better results.

Recently i bought a F3 Nikon D focus screen. It appears to be joined with a condenser lens. I threw together a PVC assembly to hold it together and block out light, but when i connected it to the camera, there was that hotspot again!

Minolta 50mm 1:1.7 -> (| -> || -> Panasonic PV-GS150

The only thing i have not tried is a macro, but i can zoom in fine.

Is there something wrong with my Minolta lens? I can point the camera through an SLR viewfinder with this same lens and get perfect results with absolutely no hot spot.

If anyone has any advice i would really appreciate it.

Thanks for your time.

It could be the lens or your GG, if the GG is too thin, your hotspot is going to be there - try a different lens. I built my adapter over 1 year ago and I am still tweaking it and it is not right. It just takes time I am afraid. Try different combinations. Even with the Letus35 I had to put a condenser in front of my DV lens to get rid of vignetting, so there is no 'perfect' solution. It is not the answer you wanted, I am afraid.

Playing around with the distance between the gg and the camera sometimes helps, but only if you're using a condenser.

Daniel.

How large is the image you are taking off the groundglass.

The 35mm 4:3 movie frame is 24m x 18mm. Use this size and you should not have a hotspot issue with f1.8 camera lenses wide-open. This choice however is only viable with moving groundglass designs.

Some builders are using a larger area about the size of a 35mm still-camera frame. It seems a condenser arrangement is needed for the larger image to appear best.

The Mini35 as I understand it uses a smaller frame off the groundglass. I understand it to be 21mm corner to corner which makes it more like the digital SLR size frame. My imagining of this choice is that it effectively deals with the hotspot issue and enables a compact device.

In a larger image off groundglasses of equal surface quality, the camcorder will see in larger image frame a finer groundglass texture. In a smaller image, the camcorder will see a coarser groundglass texture. This affects the apparent resolution of the groundglass image.

Static solutions need as much groundglass area as they can get to reduce the scale of that groundglass texture.

As I understand it, this area includes edge areas of the groundglass image where the brightness begins to fall away.

Condensers deal with this problem but they are too high a science for my feeble brain to comprehend so I can't explain why.

I suspect you may be taking a lager image off the groundglass than even the static solutions are using.

You may have to use an add-on close-up lens (macro) to get your camera close enough to be able to zoom in on a smaller frame on the groundglass.


There are better brains than mine at work on these projects so take that advice over mine.

Thank you everyone for your contributions.

If i measured correctly, the Nikon focus screen im using is 35mm x 20mm. I don't want to have to zoom in much into it because it would make the grain a lot more visible. Here is an example of what the hot spot looks like:

http://www.buysmartpc.com/gg.jpg

I would probably have to use a microscope to zoom in enough on the gg to avoid the hot spot.

The ground glass has a condenser lens attached to it. I read on this forum about other people that use this same setup and get great results without having to use a macro. I have tried to contact them and waiting on a reply.

I have tried different distances and other side of the gg with no luck.

Tomorrow im going to visit a camera store and try out some macro lenses, and anything else they have. If something works i guess ill have to spend more money.

That vignette is huge.

I have a Nikon screen and it looks evenly lit all across. So I am guessing your minolta lens is the issue here. Are you closing the apperture much? What's the diameter of the back lens on your Minolta prime?

My screen measures 36x24 mm btw.

Also, the PCX curvature needs to face your camcorder, not the minolta lens. (judging from your diagram you got it backwards)

That is a very small image area for a 50mm f1.7 lens.

Is that lens from a full 35mm still camera or a "half-frame" still camera?

I think Olympus made one and called it the "Pen". The image frame for these was smaller and was widest across the film, not along it, closer to the 35mm motion picture image frame in area.

The only other thing I can think of is that the Minolta lens aperture is set at f11 or smaller.

If it is an automatic lens with a manual aperture ring, you may have a lens which remains closed unless the actuation device in back of the lens, usually a small lever or a pushrod which sticks out a little, is moved to open the aperture up to the manual selection chosen on the aperture ring.

I am only wildly guessing here as I don't know Minolta. Whatever, It definitely does not seem quite right.

the screen is probably 36x24, i did not want to risk damaging it so i measured it from about 1 inch in the enclosure.

Well the lens works perfectly when attached to a SLR film camera when i point the gs150 through the viewfinder.

The lens is open wide, i can see the iris if its closed.

I have tried flipping the focus screen so the lens curves to the camera without any change. Ill try again.


I just had a thought... The SLR camera is a Minolta, with a Minolta focus screen, and a Minolta SLR lens. This focus screen i bought is a Nikon F3. Is it possible that the Minolta SLR is not compatible with the Nikon focus screen?

When i go to the camera store today ill try a Nikon lens on it.

What kind of Minolta lens are you using? Off the SLR and with aperture wide open, if you look through it, do you see a wide open aperture?

Min focus distance on the GS150 is likely 1.6 inches. If you are not using a macro you must have the cam this close, and only in 4:3 mode.

Is that picture you sent actually from the adapter? Try taping a 24x36 rectangle over your GG (not touching it) and take a shot through that. If you have the barrel dimensions I can post up a jpg from Visio for you...you can just cut it out.

The lens reads

MD 50mm 1:1.7 JAPAN o49mm
MINOLTA

Here are a few pictures i took:

http://www.buysmartpc.com/slr/front.JPG
http://www.buysmartpc.com/slr/back.JPG
http://www.buysmartpc.com/slr/side-back.JPG
http://www.buysmartpc.com/slr/top.JPG

The original hot spot image i made in photoshop because i dont think i have a memory stick that will work in this camera. I just had to show an example of what it looks like through the gs150.

The gg is about 1.4 or so inches away from the gs150 lens. I think i can zoom in fine because i get an image in focus (overlooking the blinding hot spot).

The shots were taken as

Minolta lens -> || -> |) -> (not mounted)

I found a memory stick compatible with gs150. Here is a shot with the adapter on:

http://www.buysmartpc.com/slr/gs150.JPG

The hot spot remains the same at any distance between the gg and camera.

*edit*

the camera is zoomed in on the gg looking at a plain evenly lit textured wall, although a bit out of focus. I can focus on objects and get a clear view in the middle.

Daniel. Something seems wrong.

For comparison here is a shot of my Slide-viewer adapter.

http://mentemagica.com/35mmAdapter/Frame2a.jpg

The whole frame is 40mm wide on either side (yes, the actual apperture of the diffusion screen frame) and as you can see it fills the entire frame. I think I can even go wider but I would have to remove the slide mount on the slide-viewer. You can only see vignetting on the bottom corners, and that's because my Nikon lens is mounted a bit off center. I can record a 36x24mm image perfectly with no vignetting.

The setup is like this:

Nikon 1.4 lens || |) |) GL2 camcorder

Even without the second PCX lens the vignetting is pretty much gone after the condenser.

Daniel, what does the zoom level on the LCD say? I can't tell, but are you zoomed in so the nikon D screen fills the frame? Also, make sure you have at least 500 watts illuminating that wall.

What is the distance between the back of your SLR lens and the GG?
I take it is gg facing the SLR lens.

regards

Dave

the zoom level should be about 2x or less. If i go 3x the camera cant focus on the gg.

The frame was completely filled with the gg. If i zoomed out just a hair i could see the edges. I should of taken a picture of that as well.

that wall was lit by the sun, behind me were 4 large windows. Even looking outside on a bright day that hot spot is still there, just a little brighter.

Even without filling the frame with the focus screen, i think it still should be bright and evenly lit.

I flipped the focus screen so the optics are in between the camera and the gg with no change.

Condensers work on either side of the GG ...

Maybe the gg and SLR lens are too close.

Im thinking from that picture, your probally gonna have to take it all apart, and work with it out of the adapter. just experiment the distance between your SLR lens and your GG. from the screen, it looks almost like there is no GG even inbetween your setup. which is odd. i would have to say take it apart. and then put it together again after you find out whats wrong. Good luck on it.

and for the heck of it, try a complety new prime lens. that might be the problem, but i can't see why.

I've just had a look at the Nikon D -type screen outside of any adapter housing.

Image can be viewed here.
http://www.maths.ox.ac.uk/~smithdm/nikondscreen.html
Certainly the hotspotting isn't as evident here.

Dennis,
A potential reason for having the condenser not on the SLR lens side is that if the slr-gg distance is set for that specific lens, once the lens is changed, the distance might not correspond correctly for focusing.
Whereas, if it is identically set to that as it would be in an slr (no condenser between slr lens and gg), then the setup will still hold for all lenses.
I.e, the adition of a condenser on the slr len side will affect the optical properties that side. (maybe)

I.e, the adition of a condenser on the slr len side will affect the optical properties that side. (maybe)

This is correct.

Well im back from the store. I painted the pvc interior black, tried a new Nikon lens, threw on different close ups and macros, changed the distances, put on a Minolta prime, and nothing helped.

*sigh* i think iv been beat

tomorrow ill follow Davids advice and try to put something together outside the adapter. If i cant get a better picture ill just wait till i can fork over the $300 for the letus35

dont give up. follows David's setup, and you should get results.

i think iv found the problem.

"Type D: Overall fine-ground matte field. For specialized close-up photography and for use with long lenses."

<Marco Polimeni> I never tested a D screen but, from a Nikon F manual, I know that using lenses shorter then 135mm the edges of the frame starts to became darker and darker so more the lenses are shorter. </Marco Polimeni>
http://www.dvinfo.net/conf/showpost.php?p=410328&postcount=41

All this time iv been using a 50mm lens.

Turns out this focusing screen is not compatible with my lens.
135mm, thats telephoto isnt it? I was looking forward to using my 28mm and 50mm

I followed Davids instruction. The hot spot did get smaller and i could see a little better on the edges but the camera had to be 12+ inches away from the gg.

I haven't used a D screen either, but that seems pretty odd, because I know quite a few people around here use it, and a 50mm prime is pretty much the standard lens, so I can't imagine it would be so common if it always produced this kind of vignetting on a 50mm.

Yeah i dont understand how. I read about people getting good results with a 1.8 50mm, and a 55mm.

this is directly from the Nikon website:
"Each screen offers unobtructed viewing and easy focusing over the entire matte surface. Type D is especially for telephoto lenses"
http://www.nikon.com.au/productitem.php?pid=699-7a83f575c6


Im not sure if i measured this right but i think the focal length of the nikon screen+condenser is about ~1000mm, which is way out of range for the 60-125mm recommended condensers focal length

type D apparently should not work with any SLR lens under 135mm

just a shot in the dark.. maybe this nikon screen is working for other people because they are using cameras with large diameter lenses that are able to absorb more light at a greater angle from the ground glass? like the GL2(58mm) and dvx100(72mm)... My camera is a gs150 with a ~24mm lens?

That makes sense right?

i think every working adapter i have seen so far that uses this nikon screen is a pro camera.

just a shot in the dark.. maybe this nikon screen is working for other people because they are using cameras with large diameter lenses that are able to absorb more light at a greater angle from the ground glass? like the GL2(58mm) and dvx100(72mm)... My camera is a gs150 with a ~24mm lens?




I have found that from the same distance from the ground glass, the smaller the cams lens the more the vigneting. For example, 40mm away would produce no vignetting with a dvx100, however, at the same distance an XM2 would start to vignett slightly, my 43mm cam a bit more, and a small 37mm cam much more. I have found that you need to increase the distance between the cam and the ground glass the smaller the cam is, more distance.

i think you have to take back from scratch and understand the theory of the adapter. it seems you are just assembling stuff without really understanding how each parameters influence the adapter.
In the beginning we all spend a lot of trials and errors to understand this, and today, new comers can be happy to find lots of informations to not repeat our mistakes. Unfortunately, taking the best part listed in each project and blindly assemble them will probably not produce the expected results.

if you want some rules here they are:

choose a fast lens (between 1.2 and 1.7) with big aperture at the back (this will help minimize hot spot and vignetting).
Respect exactly the distance between back of lens and GG.
use big diameter tubes, and at first, do not try to make a short adapter.
It will probably look longer than you wish, but you can try to shorten later.
Make a prototype with disposable materials like balsa wood and carton to get
the right dimension.
Start with lens/gg/macro lens setup, it is simple and should give pretty good result. Add a condenser and other additional lenses after you really master your prototype.
do not count on the condenser to solve heavy problems, it only improves general quality.
Good track is to replace the GG by a plano convex lens that act as GG and condenser. you gain light, wheigt and a simpler setup.
use large diameter thin lenses (ideally between 55-60 mm), the thicker, the more you will get artifacts and using a lens on the edge is never good.
yo udo not need a camera to produce a good adapter. just looking at the picture on the GG should give you an indication of the result.
condenser, macro lens are just here to adapt the picture to your camera, depending the ability to zoom and focus, but will not change the quality.

i think you have to take back from scratch and understand the theory of the adapter. it seems you are just assembling stuff without really understanding how each parameters influence the adapter.
In the beginning we all spend a lot of trials and errors to understand this, and today, new comers can be happy to find lots of informations to not repeat our mistakes. Unfortunately, taking the best part listed in each project and blindly assemble them will probably not produce the expected results.

if you want some rules here they are:

choose a fast lens (between 1.2 and 1.7) with big aperture at the back (this will help minimize hot spot and vignetting).
Respect exactly the distance between back of lens and GG.
use big diameter tubes, and at first, do not try to make a short adapter.
It will probably look longer than you wish, but you can try to shorten later.
Make a prototype with disposable materials like balsa wood and carton to get
the right dimension.
Start with lens/gg/macro lens setup, it is simple and should give pretty good result. Add a condenser and other additional lenses after you really master your prototype.
do not count on the condenser to solve heavy problems, it only improves general quality.
Good track is to replace the GG by a plano convex lens that act as GG and condenser. you gain light, wheigth and a simpler setup.
use large diameter thin lenses (ideally between 55-60 mm), the thicker, the more you will get artifacts and using a lens on the edge is never good.
yo do not need a camera to produce a good adapter. just looking at the picture on the GG should give you an indication of the result.
condenser, macro lens are just here to adapt the picture to your camera, depending the ability to zoom and focus, but will not change the quality.

Wayne, that sounds exactly like whats happening. The Vignetting is much less when the gs150 is about 12 inches away from the nikon focus screen. Unfortunately i don't have access to a camera with a larger diameter lens.

I removed the Fresnel focus screen from my Minolta camera and it has a much shorter focal length. I set it all up on the table and it almost works! I think it would just need an enclosure. Unfortunately it has a visible focus aid and i cannot use it.

Giroud, i appreciate you taking the time to help but i dont think your giving me enough credit. First of all This is the third adapter i am building. I took two months to read through 3 forums before i started spending money. You should not have to reinvent the wheel every time someone sets out to build an adapter, the knowledge is all here. For the last 3 weeks "trial and error" is exactly what iv been doing.

OK,
Im thinking the answer to your problem is going to be a mix between a slightly shorter focal length PCX and moving the camera away from the focusing screen,

I think i have read others (Ben Winter?) managing to remove the PCX lens off the Nikon D screen, so that you can use another.

yeah thats exactly what i thought. It looks like the assembly is held together with 4 screws. Im contemplating whether or not i want to attack the screws or just return the screen and maybe get my $30 back before its too late.

I just thought I'd mention that I also have a gs150 and a static adapter made of pvc using the nikon d as a ground glass. I use a pentax lens and I realize that I get some vignetting I can completely rid of it by zooming in to about 2.5x. I actually see no noticeable hot spot just looking at it. I think it might be your lens. Can you maybe post pics of your setup?

I just thought I'd mention that I also have a gs150 and a static adapter made of pvc using the nikon d as a ground glass. I use a pentax lens and I realize that I get some vignetting I can completely rid of it by zooming in to about 2.5x. I actually see no noticeable hot spot just looking at it. I think it might be your lens. Can you maybe post pics of your setup?


Could you confirm, your using the Nikon D as ground glass with the original condenser correct?

Exactly what do you mean by "some" vignetting? Here is a shot taken from the gs150 zoomed into the focus screen to fill the frame.
http://www.buysmartpc.com/slr/gs150.JPG

Are you using a lens longer then 50mm?

here are some shots i posted earlier of my setup:
http://www.buysmartpc.com/slr/front.JPG
http://www.buysmartpc.com/slr/back.JPG
http://www.buysmartpc.com/slr/side-back.JPG
http://www.buysmartpc.com/slr/top.JPG

the lens and the focus screen are not glued, and i am able to make fine adjustments.

my minolta lens is a 50mm 1:1.7

Please tell me more about your setup

Based in the fact the Jeff is using the same camcorder and Nikon Screen, it could well be your SLR lens. Might be worth trying a different SLR.

Also, this image: http://www.buysmartpc.com/slr/back.JPG

Was this taken with a still cam?

Based in the fact the Jeff is using the same camcorder and Nikon Screen, it could well be your SLR lens. Might be worth trying a different SLR.

Also, this image: http://www.buysmartpc.com/slr/back.JPG

Was this taken with a still cam?

yes it was taken with a still camera. i did my best to get a visible picture... well i think its clear enough to know whats going on. At the time i did not have a memory stick compatible with the gs150.

i tried two new slr lenses at the store yesterday. I think one was a Nikon 50mm, and the other was some sort of Minolta prime that fit onto my Minolta that would increase the focal length. I got a slightly better picture with the prime but it was not really noticeable.

I also have another Minolta 28mm i tried but the hotspot is much worse then with the 50mm. I imagine this is because of its shorter focal length. Although when i put this 28mm on the Minolta film camera and put the gs150 to the viewfinder i get a perfect image with no vignetting at all without having to zoom in.

I just looked through Jeff's posts and sure enough:
http://www.dvinfo.net/conf/showpost.php?p=356350&postcount=27

He has some great pictures taken with the gs150 and the Nikon D focus screen. Im really looking forward to hearing from him with more info on his setup.

After looking at http://www.buysmartpc.com/slr/back.JPG im starting to think the the type of Nikon screen is no good. It does not seem to be diffusing the light much at all. You said before it was intended for a certain type of lens?

Yes. The Nikon D focus screen is made for long lenses (~135mm)

"Type D: Overall fine-ground matte field. For specialized close-up photography and for use with long lenses."

<Marco Polimeni> I never tested a D screen but, from a Nikon F manual, I know that using lenses shorter then 135mm the edges of the frame starts to became darker and darker so more the lenses are shorter. </Marco Polimeni>
http://www.dvinfo.net/conf/showpost....8&postcount=41

This is directly from the Nikon website:
"Each screen offers unobtructed viewing and easy focusing over the entire matte surface. Type D is especially for telephoto lenses"

Its working for Jeff though and i really want to look into that.

While fixing an adapter I sold, I put in the Nikon D screen I had ordered for it and tested it with an FD 50mm 1.8, on my GL2. Worked perfectly, no vignetting. I think this "bigger camcorder lens means less vignetting" theory might be true.

Im going to take some pictures of my setup so you can see exactly how mine is so maybe it can help you get yours working.

Im going to take some pictures of my setup so you can see exactly how mine is so maybe it can help you get yours working.

Thanks a lot Jeff, I really appreciate it!

Here you are:
http://img456.imageshack.us/img456/7774/gg9qn.jpg (http://imageshack.us)

As you can see what I meant by slight vignetting is the bit you can see in the corners. Its easily avoidable by zooming in a bit. I was surprised to see you had such an extreme hotspot from yours. Here is a pic of my setup:

http://img456.imageshack.us/img456/8840/setup2ub.jpg (http://imageshack.us)

Right now I don't have a set way to hold the lens on so its just taped. And the picture taken of the ground glass were without the macro that you can now see(kind of) in this picture. Here is my lens:

http://img493.imageshack.us/img493/2130/lensfront0qe.jpg (http://imageshack.us)

If you have any other questions just post and I'll be reading this thread. Hopefully I can be of help.

Thanks Jeff.

I have some ideas, ill try them out tomorrow. Ill report back with my results.

I got some good results with the focus screen from my Minolta slr with the focus aid:
(12:22 AM, room lit only by 80 watt light)
http://www.buysmartpc.com/slr/minolta.JPG

its bright enough to see on my monitor, hopefully everyone else can

I know its blurry, i had some tissue paper hold the screen in place and i could not get the lens to focus because the screen was not at a correct distance.

This is on the same adapter and on the same camera. As you can see the image is evenly lit.The hot spot is barely noticeable, would be invisible with 200 watts.

This proves 3 things:
1) The slr lens is fine
2) Adapter works
3) Camera is able to focus and i dont need any macros.

I still cant get anything better then this with my Nikon focusing screen:
http://www.buysmartpc.com/slr/gs150.JPG

im still trying to salvage the Nikon D screen. I ordered another pcx lens from surplus shed, maybe i can replace the one on the screen.

Too bad the Minolta screen has a focus aid..

I wonder if the Nikon ground glass is a Fresnel...

*update*
I was able to add an additional 80 watts = 160 watts

http://www.buysmartpc.com/slr/gs150minolta.JPG
zoomed out
http://www.buysmartpc.com/slr/gs150minoltazoom.JPG
zoomed in