I apologize for my deep ignorance of optics, but...

So, unlike in an SLR camera where you might have a fresnel or condenser before the ground glass, you are saying that a better choice, in this instance, is the field lens after the ground glass. Why is that?

It looks like we are on the same page here because your basically saying the same thing I just wrote. Its too bad gg reacts that way. BTW the 2" prisms exist. Im going to have to hunt down where I last saw them. I wonder though how DVX100 users will ever get ANY type of prism(s) in the shallow gap between the camera's lens and the ground glass. With one +10 diopter the minimum focus is 10cm which, if Im not mistaken, becomes 5cm with the use of a second +10 diopter to make a total +20. The DVX is going to need the help of a +16 or greater power diopter to beable to focus on the intended target on the ground glass. With the P+S Technik being used on the DVX100 already we known that it is possible...but how?

Because the Fresnel is so thin, it forms a single unit with the GG. You can put the Fresnel either before or after the GG, although I still think that putting Fresnel after the ground glass is better: you're collecting diffused off-axis light rays & make them follow the optical path of your system, thus increasing image brightness. AFAIK, most SLRs have a GG in front of the Fresnel. Have a look at this link, it'll help:

http://topcontechnotes.home.att.net/viewingsystem/page4.html

The article also goes on to describe chromatic aberrations and pincushion correction, and the use of a Fresnel.

2 Brett: I'm totally confident that you'll find those 2" suckers, judging by tons of useful reference material you've dug up so far! If 2" porro is not available, how do you feel about a 2" 45degree diagonal prism? I think that's what MovieTube is using, but having your camcorder at 45 degrees feels awkward to me.

Brett, please disregard this paragraph, I misread your post...
[I haven't given much thought to the prism placement, but I'd say it has to go after the GG, not before. You just don't have the room between the objective lens & GG. The additional path through the prism should also be considered when selecting the macro. The distance added is equal to the light path through the prism times prism's refraction index.]

Okay, but does this solution correct chromatic aberrration?

So let me get this straight, we don't need any achromats, but instead it would go:

(SLR) - (GG-Fresnel-Condenser) - (Macro) - (DV Cam)

So if this is the case please explain the specifics of the fresnel and condenser required, ie. do they need to have differing values depending on what SLR lense used? Any good source to buy these?

It does if your field lens is an achromat. Or, if your field lens is a thin plano-convex, but I'm not 100% sure on that.

<<<-- Originally posted by Tavis Shaver : Okay, but does this solution correct chromatic aberrration?

So let me get this straight, we don't need any achromats, but instead it would go:

(SLR) - (GG-Fresnel-Condenser) - (Macro) - (DV Cam)

So if this is the case please explain the specifics of the fresnel and condenser required, ie. do they need to have differing values depending on what SLR lense used? Any good source to buy these? -->>>

Any 'good' lens is an achromat lens. Brett covered this very thoroughly in his posts. Your macro should be an achromat. Is there a suitable acromat for a field lens? I don't know, sorry. You don't want Fresnel for the field lens because of it's inferior quality.

There is no dependency: SLR lens projects onto the GG. This image becomes an object for the second part of your system. Both parts can be treated independently.

Another consideration: if you have a really good diffuser (like a holographic one), you may not need a field lens at all.

Roman you keep using fresnel in your examples. They work fine in SLR's but you need to replace them with a achromatic condenser (field lens) for our purpose here because the ridges of a fresnel lens are visable to the camera's lens.

Also, as I understand it, SLR viewfinders use both a fresnel AND a condenser with one on one side of the GG and the other one on the other side. The reason for both is the same reason that achromats need two lenses to correct for chroma abberation.

So if this is all true you would need two condensers (field lenses) so they can work together on this problem.

"Can you dig it?"

When you say a holographic diffuser I guessing you mean the ones found at EdmundOptics.com. What has your experience been with them? Sounds like your saying they have a much wider viewable angle than normal ground glass but even if thats true I would think they would be brighter if viewed straight on. Besides if they have the characteristics of being viewable at the same brightness at very wide angles that mean they have incredibly high diffusing properties. The more something diffuses a light source the more light you need to pump thru it. In other words they would suck up a hell of alot of f/stops worth of light.

Seems we need to figure out the proper focal length for our two element achromat condenser. What I cant seem to figure out is what distance to measure for it.

A)The distance between the gg and the CCD of the camera

or

B)The distance between the gg and the front element of the achromat macro lens in front of our camera

or

C)?

doesn't the power of the achromat correspond to the focal length of the primary lense (the SLR)?

As I understand it there is a relationship between the focal length of the SLR lens and the condenser because the angle of light coming from the SLR lens changes as you zoom in and out with your lens. This is why the hot spot on the ground glass might be even worse when you use one SLR lens verses another. Apparently though there is a bit of wiggle room for the condenser otherwise we would be seeing hot spots in our still camera viewfinders as we zoom in and out. So lets say for example we want to use a Nikon 28-135mm lens most of the time with our adapter...what would be the ideal focal length of our achromat condenser?

that is a very good question that i am in absolutely no way qualified to answer...

Ah... this is getting fun. (And extremely addictive... I stayed up until 8am reading about optics). Anyone else feel like starting an 'Aldu35 Anonymous' group?

[jonathon] "Hi, I'm Jonathon"

[group] "Hi Jonathon"

Anyways... I'm just going to try some things... too much reading and narrative speculation for me. Need some hands-on so I have a better feel for it.

For any interested, http://www.sciplus.com is an interesting resource for really inexpensive optics. I'm not looking at these things as my final optics - but as a means of practical experimentation.

I ordered 6 2x2 ground glass squares, about 20 various sized lenses, a set of 3 various achromats, 3 credit card fresnels for like $18.00 including shipping. (!). They also have prisms, etc... I just wanted to start with the optics first and worry about inversion later.

They acknowledge that the quality isn't great, but I'm not all that interested yet. For <$20 I'll have lots of things to experiment with and once I feel like I know what the (explitive deleted) I'm doing, I'll invest in better optics.

The holographic diffusers are interesting - $100 for a 2" square - but it would replace the ground glass while keeping 85% of the incoming light. The only question is the image on the diffuser good? Hard to know without seeing and hard to just drop $100 to check it out.

Nothing like a good old trial and error but I wonder, are the lenses in that kit labeled? I hope so otherwise when you find a element that works you wont know what it is and what you need to go out and buy.

That would be a real shame.

Roman,

Louis Feng was researching using holographic diffusers for this purpose on the other Static35 thread, but the middle of last month, he sort of disappeared...

Maybe he was on to something and they found out.

Sorry, too many conspiracy theory books.

Anyway, so you also think that a holographic diffuser would probably remove the need for some type of condenser/fresnel lens?

When I did my original post yesterday, I didn't mean to stir up a contraversy, I simply felt that the discussion was getting off track when achromats started appearing before and after GG. I did follow this thread from its inception when Alain introduced his amazing results. Let's just get back to reality here: Alain had created a simple, elegant system that works. He took time with his GG, and got excellent results with just one additional macro lens. Jonathon is right on the money: we have to experiment more, and then report our results. Thanks for the link, Jonathon, just lay off those Fresnels :), they're no good for imaging applications. I only used the word Fresnel as an example of a field lens, I didn't mean to use them as part of our system.

I have no real experience with holographic diffusers. All I know is that circular diffusers are available with angle of diffusion from 5 to 80 degrees. Lower angles mean brighter image and (potentially) a hotspot. True, at $100 a pop it's an unkown commodity.

What is the focal length of an achromat condenser? I'm gonna stick my neck out and say: in theory, it doesn't matter. As I said before, if that lens is positioned in the focal plane of the SLR lens, i.e. right after the GG, it does not introduce changes to the focal length of the system. Take any thin lens you have, put it flat on a page of text. You should see no magnification.

Since you're discussing the SLR lens / condenser lens relationship, let me say this again: any optical system can be broken into its sequential elements to analyze it. In our case, the element 1 (SLR lens) makes an image I1 of the object O1 (whatever you're filming). The I1 is visible on the GG, but the GG is not necessary for the analysis: knowing the object distance & focal length of the SLR lens, you get the image I1 distance from that lens. This I1 becomes the object O2 for the second optical element - the achromat macro. The macro forms an image I2 that becomes an object O3 for camcorder lens. Notice I'm not mentioning the GG itself or the condenser lens, they're not relevant for calculating distances, since both are positioned in the focal plane of the SLR lens.

There certainly won't be fresnels in my final adapter. I also think my kids'll get a bang out of some of this stuff, so I just got a batch of things to mess around with. Yeah - they're likely *not* labeled, but then again, I'm not really looking for that kind of information... I'm more interested in answering simple questions like, "does the focal length of the condenser even matter?"

so no fresnel at all? hmmmm...

No... instead of a Fresnel, I'll have a 'real' lens.

It's been commonplace to use the term 'Fresnel' in this discussion to mean the thing which increases light and reduces distortion behind the GG, because many SLR camera viewfinders actually use a real Fresnel lens to do this. In SLR's there's never a Fresnel in the light path to the film - just in the light path to the viewfinder.

So, witholding more detail, I'd say the diagram has gotten pretty simple recently:

SLR Lens
Ground Glass at correct focal distance
Condenser (not a fresnel - a real lens) as close to GG as possible
Macro (if needed)
DVCam

details, still discussing:

Theoretically the condenser focal length doesn't matter... it should just be large enough to cover the image on the ground glass. It seems like one would want the condenser to be the inverse of the spherical effects of the macro... but now I'm outside of my skills/knowledge.

Best way to 'house' all of this:
Many have successfully used PVC.

There are rumours (Brett) of making the SLR-GG distance adjustable so that various types of SLR lenses/mounts could be used on the same adapter. Haven't seen designs for this yet.

Some talk of a T-Mount extension tube.

Also - in current form the image that reaches the DVCam is still rotated 180 degrees. Makes it a little hard to use - would be nice if there were some way to view the image right-side-up while composing.

Thanks for summing everything up. I still think the condenser lens has to have a particular curvature (focal length) but thats what experimenting is going to have to answer. My adjustable tubes are micro threaded tubes that fit inside one another. As they unscrew they extend and then you lock them in place as you would on a rail system. Im currently looking for some new ones with a flat black finish.

-Brett

------ Also - in current form the image that reaches the DVCam is still rotated 180 degrees. Makes it a little hard to use - would be nice if there were some way to view the image right-side-up while composing.--------

What I did to reverse the image is using a cheap Ambico V-0310 Fish-eye ,around $60, that I put on my lcd and on top of it I use a smal telescope prism that reverse the image. Now I have a view finder on the side of my Vx-2000 so I can put it on my shoulder.

I also have a lcd monitor that I can put on the side but I realy don't like those monitor ,you have to be realy in front of it and it's hard to focus on this.

Here is a example.This is not the final version but not no far.

http://ideaspora.net/aldu35/ALDU35.JPG

Good job on the viewfinder. What kind of prism(s) are you using? I know what you mean about the LCD's. Never the less Im still going to flip or buy a special LCD because Im a steadicam operator as well.

The only thing that troubles me about the add-on LCD is the need for some kind of power for it. If you're walking around with your steadycam, you're going to have more wires and more weight in your batteries, or whatever. I'm sure it will work, but it's starting to be a lot of baggage... I like Alain's prism idea... I guess that old "learn to operate your viewfinder with both eyes open" technique really has its place here :)

As usual, Alain - nice job... looks like a nice rig.

It's call 45 degree erecting prism and it's $39.

Alain

There is some here but more expensive
mine is $39 Can so in Us it should be $2 :-(

http://secure.sciencecompany.com/thesciencecompany/product1.cfm?SID=1&Product_ID=261

Maybe something interesting here.

http://tweaktown.dealtime.com/xPF-Bausch_and_Lomb_Bausch_Lomb_Erecting_Prism_1_25

Alain, that's it, if you're going to put it on the viewfinder, the 1.25" size is OK, and you won't need your fisheye lens anymore. I was hoping to find this in the 2" size, to make the camcorder see correct image. Brett, have you had any luck finding the 2" porro?

This seems like such an elegant solution. Throw one of these onto the existing eyepiece... here's some more of the same, but lower prices:

http://www.scopestuff.com/ss_diag7.htm

http://www.scopestuff.com/ss_diag6.htm

It's not that easy.
It cannot just be put on the viewfinder.We have to put another
magnification lens on top of it to replace the one already on the viewfinder, and the focal of this is a problem ,You cannot just put the actual magnifier from the camera.Because the prism change the focal lenght neede'd.


I have see some biger but it's around $300.

Alain

<<<-- Also - in current form the image that reaches the DVCam is still rotated 180 degrees. Makes it a little hard to use - would be nice if there were some way to view the image right-side-up while composing. -->>>

Hi everybody (new to this very interesting forum ),
a way to rotate the image is to add an other lens....like the SLR lense rotate the image an additional lense after the condenser will revert the image...

but that makes a lot of glass to go through...and considering that the amount of light is a problem...


but we are forced to add a macro adaptor....i think that the additional lense to re -rotate the image and the macro adaptor can be merged into one single lense that we are going to calculate the front and back focal length.... :)

i don't know if it's really possible but why not...

Malheureusement , ce n'est pas si simple.


Alain

Right, Alain. I wonder if the eyepiece has a built in lens that corrects for the entire added eyepiece's focal length difference.

here is some new motivation for you all, a short made with a static35'ish device.

This short is groundbreaking!
http://www.dvinfo.net/conf/showthread.php?s=&threadid=21567&perpage=15&pagenumber=1

http://www.originalversion.net/temp/makingof01.jpg

What I don't understand, is why he had a hotspot in Marla. Was it the result of taping through the viewfinder.

I will start getting my parts in this week. I have high hopes, wish me luck.

http://www.kauserinternational.com/Photography/Ohner/Copier/Ohnar%20Digital.htm

and

http://www.ephotozine.com/equipment/tests/testdetail.cfm?test_id=124

found on Ebay for 70$, very nice quality, fully dismountable.
tube diameter 52mm with 58mm ring adapter.

so here is the k.i.s.s. (keep it simple stupid) updated version of the Aldu35 for standard DV cams, as i understand it.

http://www.dinoreyes.com/images/lens_standard_dv_simple.jpg

comments, corrections? i just want to get this right...

ideally both connecting tubes cound have an adjustable collar

nice link Giroud, so close...

-D

Dino, isnt the frenel supposed to be on the 35mm side of the GG?

That looks right, Dino. We're pretty sure that there should be nothing between the 35mm lens and the ground glass. The condensor helps more light more evenly reach the dv cam.

The only comment I have is on the macro - the requirements here will vary widely, depending on the needs of the DV cam. Mine has a built-in macro and doesn't even need it. Some need like a +7, some need more...

Conceptually, it breaks down to getting a macro that lets your dv cam focus on something that is only an inch or two away (distance from the dvcam to the ground glass).

Easy to test out: just take your plain ol' camcorder and put a photograph/newspaper about two inches in front of the lens. If you can sharply focus on it, you don't need a macro - if you can't... then you do :)

why not to make de front part side of the fresnel sanded in way
to have de gg and the condenser lens in one piece ?

if by any chance you already have dismantled an LCD screen (particularly on laptop) you will find many intersting layers made of plastic material that are ultra thin and looks either like gg or fresnel or even both.
cannot give a sample there, but it worth to give a try.

if you got a sony VX2000 (no macro feature) , you can have a correct focus very close to the front lens on the camera, but unfortunately the zooming range to fill the screen is very short before you loose focus.
The trick would be to have the gg image bigger than the 24x36 size.
Is this a problem with a 35mm lens

as always it would be nice to keep it simple, but could we have these scenarios?

1) if you use a fresnel lens, in order to avoid the appearance of the concentric circles, it would be placed IN FRONT of the gg

2a) if you have a condensor lens, you would place it IN BACK of the gg

2b) i also believe that a condensor lens may(?) have a indented back, but if it has a flat back you could possibly sand that also like a gg (a more radical approach to 2a)... and yet another question, would the curved part face the ccds or face the primary lens?

would the observations be correct for 1 or 2, anyone have an idea?

Of course, the coolest thing about any built-it-yourself project is, you're free to do whatever you'd like. I'd recommend not using a fresnel anywhere because of the visible rings.

I believe it was Roman who correctly spoke of trying to keep the relationship between the SLR lens and the ground glass pristine. As he said, this is already a perfect relationship, and its unlikely that we will improve it. This is the reason for not having anything between the SLR lens and the gg.

I think that at least some of the condensers I've seen are flat on the 'intake' side - and could theoretically be turned into a ground glass... but it's a pretty radical step, especially considering that you can just place a normal ground glass right up against it for the same effect. I'm not sure what you'd gain by directly making the back of the condenser a diffusion surface.

I'm 99% sure that the curved side of the condenser is on the camcorder side... the flat side rests right against the back side of the ground glass.

we should just rent a mini35 for a day- take it apart- take pictures- then put it back together

or become friends with an optics major

John: Ha ha ha! That would be very helpful.

I took my GL2 and mini 35 static homebrew system out this weekend and played around with it a bit. I discovered that if I attached the ground glass directly to the front of my GL2 (it's a ground 58mm uv filter), the camera was able to focus on it. I shot some footage like this for a while and then removed the ground glass and put a spacer inbetween. With the later approach, I had to zoom in a bit.

This is all I had:

35mm lens (50mm) -> spacer -> ground glass -> spacer -> GL2

Overall, I really liked the look with the shallow DOF.
I have discovered how hard it is to keep ground glass free from dust and other bits of stuff. These things really show up in the image. Also, I think I need to grind the glass even more. Sometimes the grain isn't noticeable, depending on the light, but it should probably be more fine for the resolution. The picture looks low-rez / soft, overall. (I got used to looking through the adapter, and when I took it off and saw the regular camera image through the viewfinder, I thought it was HD. Not really, but I'm just saying how much sharper the regular image is. :-) )

It looks like I don't need an achromatic diopter, but I am still looking for a condenser from an old SLR camera. I think this will help out a lot. I don't see why an extra condenser is needed for the other side, though.

Forgive my ignorance to optical theory and explanation, but it seems that by having a single condenser between the 35mm lens and the ground glass (the flat side of the condenser being against the ground glass), the condenser is 'channeling' the incoming image in a more flat/uniform manner onto the ground glass, at which point the camera would pick up that image - which should have no hotspots or vignetting, but an even distribution across the ground glass. However, I then think about how SLR cameras basically have a mirror that lifts to expose the film in the back of the camera, which (to my knowledge) has nothing inbetween it (the film) and the lens out front. Is that correct?

btw, I did all my shooting in Frame Mode, which made it easier to flip in post without having to mess with the field order. Thought I'd mention that as an incentive for you guys with this feature.

Thanks for all the posting. This has been the most enjoyable thread.


,Frank

Okay, are you guys 100% sure that the condenser or fresnel or whatever lense you use to distribute the light more evenly goes behind the GG?

Doesn't the hotspotting and chromatic aberration come from light hitting the GG unevenly? If this is the case wouldn't you want to put the fresnel, or whatever in front of the GG?

The GG becomes your Object to shoot with your macro adapter on your DV cam right? So shouldn't the image be colour and light corrected before it becomes the object on the GG?

SLR > Spacer > Condenser > GG > Spacer > Macro > DV

Please correct me if i'm wrong as i'm just trying to figure out what would work the best.

We thought that for a while :)

But if you think about it... if you just had a plain old 35mm SLR camera, the light coming into the lens gets focused onto the film, which reacts to the incoming light, making a purty picture. There's no fresnel or condenser in the middle of that interaction.

Our ground glass is right where the film would be, so it gets exactly the same light as film would get.

The hotspotting comes from how we then consequently view the ground glass... from behind with a macro, which is basically an intense wide-angle lens. Have you ever noticed that whenever you use a wide-angle lens (fisheye, for example) there is some pretty serious distortion around the edges? Our macro puts us in a similar situation.

<<<-- But if you think about it... if you just had a plain old 35mm SLR camera, the light coming into the lens gets focused onto the film, which reacts to the incoming light, making a purty picture. There's no fresnel or condenser in the middle of that interaction. -->>>

Yes but we can't compare a ground glass to a film... the ground glass is much more efficient with a light coming perpendicularly...but the risk is to ruin an optical system (the slr lens) with a poor lens ...the film is not really sensitive to direction of the light comming to it because it's near to 100% absorbing the light....


correct me if i'm wrong

2 Giroud Francois: you can make the GG image bigger, but the brightness will be lower: you only have so much light coming through the SLR lens. Also, try to think of a qualty lens for the condenser, Fresnels are no good. Thanks for the LCD screen tip, I'm going to take my old IBM screen apart & see what I find!

2 Dino Reyes: diffused light is scattered in a cone pattern; say, a 20 degree diffuser makes a 20 degree cone of light out of every incident ray that hits it. The periferal part of the diffuser will appear darker than the centre because some fo the diffused light will not hit the next optical element (macro or DV lens). That's why you want the condenser lens to follow the diffuser, not the other way around. The curved part should face the CCD, just like Jonathon Wilson said. As for grounding the flat part of the condensor: if it's a quality lens, it would be multi-coated to increase light transmission. If you grind that coating away, you may not like the results :D.

2 Frank Ladner: I'm with you 100% on the film analogy. What kind of condenser can you get from an SLR? Wouldn't that be a Fresnel? Also, what software do you use for flipping & left-right correction in post?

2 Tavis Shaver: Yes, pretty sure ;)... BTW, chromatic aberration is non-existent in reflective or diffusive components, it affects only lenses (prisms too, I believe), because the index of refraction of the lens material depends on the wavelength of light going through that lens. Au contrare, the hotspotting is found only in diffusers. Yes, GG (together with the condenser!) is your object, so if the condenser is an achromat lens, you're OK. So, my order would be:
SLR lens -> spacer -> GG -> Condenser -> spacer -> Macro (if needed) -> DV

2 Jonathon Wilson: the higher the power of your macro lens, the more barrelling (sp?) you'll observe. I'd say, go with the macro of lowest power taht allows you to focus on the image with your DV.

Last night, I finished fabricating & painting my 'adapter', and now trying to find a suitable condensor lens. Also, I'm going to Efston Science store, to play with diagonal and porro erecting attachements they may have. I also need to think about the support (bridge plate, support rods, etc.) to put the whole thing together. Unfortunately, a router and a Dremel are the most high-tech tools I have. I may try to rout the baseplate out of a phenolic sheet. Anyone got ideas (or links?) for an adjustable support?