Have anyone found a prism which is both big enough and is colorcorrected so it could work with the homemade 35mm adaptors(to flip the image)???

For PD150/VX2000,PD170/VX2180, with +7 achomatic diopter, two 40mm x 40mm x 56mm prisms of 40mm thickness across all faces seem to be large enough to relay a 24mm x 18mm standard 4:3 motion picture academy frame. These seem to be fairly commonly available.

When you search, use the search term "rightangle prism" or "right angle" or "right angled" prism. "90 degree prism" should also find it for you.

Will any of these prism work? :

http://www.thorlabs.com/NewGroupPage.cfm?Guide=48&Category_ID=138&ObjectGroup_ID=905

The coated prisms on that web page will not work. They are a special product intended to be very stable, optically precise mirrors.

Also, all the prisms I saw on the list were too small but they may have other prisms listed.

The coating is on the hypotenuse face and is totally reflective.

The hypotenuse face is the one you want to be clear as the image passes in through one half-face and out again through the other half-face.

Reflective surfaces on the small sides would be great.

I did not search the website for other prism products as I am on a very slow landline here. (720 bytes per second on bad days).

Thanks for the quick explanation.

I found another prism which is up to 60mm and with no coating.

http://www.thorlabs.com/NewGroupPage.cfm?Guide=49&Category_ID=140&ObjectGroup_ID=142

Will it work??? If the prism is 6 cm then it will allow for the filmsize to be 8,5cm * 6cm = 36mm - or what?

I just realized how long it has been since I've used math for anything.

Sorry for my absurd math above (I was really tired ;-) ).

The 40mm prism on the page below should work just fine right??? It has a 40mm * 40mm surface which should work perfectly with the 36mm * 24mm frame, right?

http://www.thorlabs.com/NewGroupPage.cfm?Guide=49&Category_ID=140&ObjectGroup_ID=142

I really need help on this. Thanks

I e-mailed the company and will post whatever response they give. I have also asked them what the price will be with the coating on the small sides.

I am sorry I cannot be much help on the above prism mentioned. 40mm? on which face. You really need to ask Thorlabs the dimensions on all faces and the common thickness across all.

As a really rough guide, the longest face on the prism has to be at least 56mm for the 24mm x 18mm frame because the lower half of the upright prism is almost hard against the groundglass if you use a +7 power close up lens.

I am not an optical engineer and I can only vouch for what has worked for me when I have put things together.

The two prisms each overlap each other by only half on the longest face. You also have to give up a bit of area to support the prism face by its edges.

So I would be home-free if I bought the 60mm *60 mm (square part of the prism)???

I have dismantled the "pentaprism" of the Mamya C (medium format twin reflex) stills camera. It is called PORROFLEX and inside there are only 3 mirrors!!! A similar setup with 4 mirrors would inverse the image properly for the video camera.
Isn't there a significant loss of light with the prisms combo?

There is, which is probably why P+S Technik seem to use a combination prism-mirror path.

With mirrors the mounting has to be precise for so many more components, a build quality probably outside of the realm of many here.

Prisms are fixed on two surfaces each in this application which means less complication for mountings to be made, even less if the two prisms are glued together at the common half-face.

So it is just a question of allignment??? If so couldn't you just mount the mirrors individually on some kind of mount so you could adjust them and with a laserpen point to see if the allignment is correct?????

By the way would the light travel as far with four mirrors as with 2 mirrors and a prism????

hi everyone I am sure you could align prism correctly on this system .

http://www.thorlabs.com/NewGroupPage4.cfm?Guide=5&Category_ID=16&ObjectGroup_ID=180

http://www.thorlabs.com/ProductDetail.cfm?DID=6&ObjectGroup_ID=181&Product_ID=11714

http://www.thorlabs.com/ProductDetail.cfm?DID=6&ObjectGroup_ID=213&Product_ID=1481


this is a german site with an exploded view of the $10,000
35mm adapter. I am sure ..... the thorlabs cage and tube system could do this to the same tolerences


http://www.pstechnik.de/sheets/downloads/pp-dec12.pdf

I have a hard time getting an overlook of the different parts - could you perhaps make a quick drawing or explanation which explains exactly how you would put the parts together??

hi everyone :I have a number of these parts on order .
the first stage is to build a static adapter.

these are the componets I plan to use.
http://www.thorlabs.com/ProductDetail.cfm?DID=6&ObjectGroup_ID=213&Product_ID=1481

http://www.thorlabs.com/ProductDetail.cfm?DID=6&ObjectGroup_ID=848&Product_ID=1483

http://www.thorlabs.com/ProductDetail.cfm?&DID=6&ObjectGroup_ID=1132&Product_ID=36109

http://www.optics-online.com/PXP.asp?PN=PXP157

the next stage will be with the following parts.

http://www.thorlabs.com/ProductDetail.cfm?DID=6&ObjectGroup_ID=60&Product_ID=11138

ball bearings and shafts ,pulley system ,dc motor

and the last part will be the prism system with mirrors.

the image will come through the cage and mirror system will either reflect up or down and come out on a cage plate.

http://www.thorlabs.com/ProductDetail.cfm?DID=6&ObjectGroup_ID=181&Product_ID=11714

this is a link to a part notice the tolerence of the part.

http://www.thorlabs.com/ProductDetail.cfm?DID=6&ObjectGroup_ID=60&Product_ID=294

Just noted that the new DSLR Olympus E-300 camera (to be released in Dec 2004) is using instead of a pentaprism a combination of 1+3 mirrors (porro arrangement).
I still want to know what is the loss of light from using the prisms? 60-70%?

The e-mail I sent to Thorlabs was answered today. They said that the best way for me to find out if it fitted the purpose was to buy one and return it again if it didn't!

So I could go ahead and order the 60 mm (the two sqaresides of the prism are 60mm * 60mm) or would the 40mm * 40mm do better???

Can the prism be to big???

Anders.

I am not an optical engineer so you should test anything I suggest with other opinions.

If you only want to relay the 24mm x 18mm 4:3 movie frame, then 40mm x 40mm x 56mm 40mm common thickness will be enough.

If you want the larger still camera frame, then you will need the larger prism.

Too large is not so much the issue as too heavy or too expensive.

If your 60mm prisms are 60mm x 60mm x 84mm and 60mm thick across all faces, there may be a space problem for a 7+ close-up lens path though I think you might just squeeze it all in. However it may not allow you much space to add a condenser lens if it becomes needed, but a lower power close-up lens could be chosen which would lengthen the path. That in turn puts the heavy bits furthur outboard of the front-end of your camcorder but if you are using a studio style set-up with rod mounts, filter box hood etc to support the appliance, then this is not an issue anyway.

There is another issue which has slipped by. The Aldu35 versions mostly use an image tube with the unused area of the groundglass being spread around the outside. The 4:3 frame sits in center which means the rear prism had to be set back from the GG for the front prism to clear the gg.

With the Agus35, it is possible to place both prisms within a safe clearance of the groundglass up to half a millimetre off if you are confident your disk isn't going to move and hit the prisms. This is because you can choose where the image sits on the groundglass and ideally it should be as close to the outer edge as possible for best linear speed for a given disk rpm.

The alternative for the Aldu is to groundglass one half of the hypotenuse face of the rear prism but this burns a lot of bridges :-

Scratch that prism and there is no going back.

You eliminate the option of adding a condenser lens in the part of the relat path that matters.

Hi Bob

I've bought the canon XL-1 relay lens which requires a 12 cm distance to the GG. (P+S technik reduces this distance by using a prism) Do you have any idea of the prism size in the P+S adaptor??? Thanks

Anders.

The relay lens sounds about 7+ at that distance and should frame the movie frame at about 40%-60% zoom. The PD150 will autofocus on the groundglass while the zoom is adjusted but once it finds focus you need to lock it off with the manual switch.

I think P+S Technik also relay an image smaller than the 24mm x 18mm movie frame. I saw reference somewhere a while ago to a 21mm image and I think it may have been 21mm diagonal corner to corner. This may have been how they avoided the hotspot problem by simply shooting the center out of it. Their image frame is certainly much smaller than a 35mm still-camera frame.

I believe they use a mix of prism and mirror in their relay path. There is a site with a breakdown diagram of their system but it is a stylised graphic and not a design drawing.

I think that you are talking about this pdf file:

http://www.pstechnik.de/sheets/downloads/pp-dec12.pdf

I don't get how the image travels from the GG to the camera?? I want to replicate the PRO design.

Since I have already bought the P+S relaylens it is already to late for me to use a bigger GG so I might as well get the 40mm - right???

Anders.

I don't get it either. That diagram might be disinfo to protect the actual design.

If you are going for the small frame size, 24mm x 18mm, the 40mm x 40mm x 56mm by thickness 40mm prisms should work.

If your P+S Technik relay lens crops corners of the groundglass 24mm x 18mm frame and you have to go smaller, then you might even get away with using a pair of smaller prisms.

If you can run this enquiry past others before you commit it would be a good thing to do as I am no engineer. All I can recommend is what has worked for me so far which may not be the best or most effective methods.

So could any optical-expert confirm what Bob is saying???

Anders.

I can't see any hands up in the class so far.

My method with the prisms was to take the rear prism, the vertical one in my arrangement, as close as I could get to the groundglass image.

This gave me less of a problem with lining up the position of the usable area (across a half of the long side) with the part of the groundglass image I wanted, the 4:3 movie frame.

With the spinner version, I have the front prism, the horizontal one in my arrangement sitting above the disk with about 1/2 to 1mm clearance. I used a whiteboard marker pen to draw a 24mm x 18mm target on a spare groundglass which I fixed in temporarily.

I then positioned my prism path which is the two prisms mounted up together in a wooden block. I adjusted the block until I had the frame in the prism image without it being cropped on the edges of the path.

These edges are the sides of the three holes you cut in your prism mounting block. Alternatively you cut a single letter "L" shaped hole which covers the area of all three holes. The prisms each have one half face covering the corner of the "L".

I chose a close-up lens which enabled me to keep the camcorder as close as I could get it to the prism path. With the 40mm prisms it ended up being a +7. Distance from gg to rear prism face which faces frontwards is about 10mm. Distance from front prism face which faces rearwards to the camcorder close-up lens is about 45mm.

With a fixed ALDU35 arrangement inside a tube or stack of filter rings, fixing the gg close to the front face of the rear prism is not going to possible unless a smaller GG with a flat upper edge is made to provide clearance for the prism. Otherwise another 45mm of so has to be allowed for which means a +5 or maybe +6 close-up lens.

The current ALDU arrangements won't conveniently work with prisms unless the tube is made at least 130mm to accommodate them plus the offset SLR lens mount and Camcorder adaptor.

Thanks Bob!

Before I buy the right angle prism could you explain the differerence between the right angle prism and the pentaprism??

Does the pentaprism rotate the image 90 degrees or what (thorlabs also has a pentaprism)?

http://www.thorlabs.com/ProductDetail.cfm?&DID=6&ObjectGroup_ID=143&Product_ID=12205

If so I would rather get the pentaprism and avoid any mirrors!

Anders.

I am not wise relating to pentaprisms. My understanding is that for a relay path into a camcorder the exit face of the prism can not be large enough to be practical. The pupil of the eye is a much smaller apeture and for a SLR viewfinder the pentaprism is fine.

I understand also that the pentaprism requires an added mirror (the shutter mirror in a SLR camera) for the related image to be completely erected.

If one uses image manipulation software speak to describe the Agus35 application, right angled prisms have to be a pair before you can relay and erected image. The first rear (forward facing and upright) prism, flips the image vertically and it exits forward in the direction it came from. The front (rearward facing and horizontal - resting on its side) prism, flips the image horizontally and it exits backward towards the camcorder. Each prism works like a pair of mirrors set around an included angle of 90 degrees.

If the two 90 degree mirror pairs a set 180 degrees opposed, you get a periscope. The image is the same as your eye sees.

If the two 90 degree mirror pairs are set 90 degree opposed, then the image your eye sees has been rotated through 180 degrees.

There was a lot of discussion on pentaprisms, roof prisms and some others. It proved much of a dead-end though one visitor here claimed success with a small domestic camcorder and SLR camera pentaprism viewfinder optics.

For the Agus35 application, a roof prism which would provide an adequate relay path for a camcorder would likely be too long to be of practial use. It is unlikely to be economically available in the size required if available at all.

Find a pentaprism here (http://shop.mellesgriot.com/products/optics/detail.asp?pf_id=01%20PPS%20011&plga=159424&mscssid) or look for one from stills cameras like PentaconSix, or russian medium format SLRs that can give you a cheap option too.

So would that pentaprism work??? Or would it be easier to get a right angle prism and 2 mirrors??

I'm getting more and more confused by the day!

Anders.

The pentaprism on that website seems to be large enough. As you can see from the diagram, the image comes into the prism in a vertical direction and exits rearwards in a direction 90 degrees to the entry direction.

With this I think you have to have a mirror where the camera shutter mirror would normally be in a still-camera. It would sit under the bottom of the pentaprism, be tilted rearward at an angle of 45 degrees so that the image coming from front is reflected up into the bottom face of the pentaprism.

The mirror would have to be a surface-coated type. You could use a broken scrap of ordinary mirror to test with before going to the cost of a surface coated mirror.

With the right-angled prism design, I went with two prisms, not one prism and a pair of mirrors.

I did this to keep inaccuracy out of my build as much as I could. One prism is near to perfect in alignment when used as a pair of mirrors. Two prisms = four mirrors.

If you want to test the principle quick and easy, go to a glass shop and ask them to cut four small pieces each 40mm x 40mm, or the larger 60mm x 60mm you may prefer.

Make two 90 degree mirror pairs by glueing or taping each mirror in a pair to the corner cut out of a breakfast cereal carton. Trim the carton down to the outer edges and ends of the mirror but leave a 45 degree web of carton between the two sides to support them. This should form the long side of a triangle. It should be cut to the edge runs from one mirror end to the end of its pair partner.

You end up with two corners out of a carton, each with two mirrors in it.

Next you need to find a piece of plywood panel to tape your mirror pairs onto.

Rest one corner piece flat on its side so that the "V" point faces towards you. Hold the other corner upright so that the "V" point faces away from you.

Then move it so that the bottom end of one of its mirrors, is against the the edge of the web of carton which connects the two mirrors in the piece which is resting on its side.

The web edge of the upright pair should be vertical. The lower mirror in the upright pair should point toward only one mirror in the horizontal pair. It should not overlap the other mirror because it will block some of the image off.

You can use parcel tape and a matchbox to hold the upright mirror pair in place. Because they are at 45 degrees, the carton corner will not stand up.

You should now have two mirror pairs, one resting on its side, one upright. Each pair is the same as a right angled prism.

Your assembly on the plywood panel should be positioned so your camcorder looks at the center of one of the mirrors of the horizontal pair which is not masked off by the vertical pair. The mirror will be at 45 degrees to the camcorder. With your zoom backed off it will seem you are looking down a tunnel. Line up the tunnel so the camcorder sees centered down it, then zoom in until the edge reflections just run out of the frame.

With furniture mirrors your image will have lots of straight lines running up and across, but it is good enough to test the idea with.

My next step was to use a close-up lens on the camcorder and attempt to focus on the 4:3 24mm x 18mm size movie frame. To make it easier I taped a barcode from a grocery wrapper along one web edge and one mirror edge of the vertical mirror pair and set the camcorder back from the mirror assembly. With 7+ it sits back about 50mm.

I'm sorry if this is confusing but it is the best I can do without demonstrating.

There were two images on www.dvinfo.net/media/hart titled "mirror array" but they seem to have gone faulty as I could not download them. I still have the second mirror assembly I made with pieces of sheetmetal instead of carton corners. I'll make another .jpg image and email that if it is likely to be of any help.

Thanks Bob - I understand it much better now!

I just tested the P+S relaylens for the XL-1 and it allows the GG to be about 20mm x 15mm!!! Which isn't all that big. But this is how the mini35 works so that is good enough for me!

Which has the greatest lightloss (please put them in order with the least stealing lightoption first):

2 rightangled prisms (expensive!)

1 pentaprism and a mirror (expensive!)

4 mirrors

or

1 rightangled prism and 2 mirrors ???

Please do send me a picture of your mirror test.

Anders.

I don't know enough about the subject to make a qualified opinion.

Ranking would be a guess.

Least Loss.

Surface coated mirrors.
One prism with coated side faces + 2 surface coated mirrors.
One prism without coatings + 2 surface coated mirrors.
Two prisms with coated side faces.
Two uncoated prisms.

Given that P+S Technik are scanning a smaller gg image, they have probably arrived at a compromise between bulk and performance and may be using a much smaller prism and a mirror pair to compensate for the crosswise image in the third and fourth stages of the relay. They'd get away with a prism about 22mm thick across all faces and a hypotenuse length of 35mm.

I've wondered for a while why some of our Agus/Aldu images are sharper than the Mini35 and I think the smaller gg image may be the reason. The Mini35 would also avoid the hotspot problem by framing inside the dark corners.

I could not find an email to send the attachment so I might send it to Chris Hurd to post on www.dvinfo.net/media/hart

I don't know why my e-mail suddenly doesn't show but it is:

anders@floe-svenningsen.dk

In some ways I'm glad that I don't have to bother with a condenser. Still it would be nice to be able to use medium format GG but its too late now. Anyways I like the results the mini35 gives so...

I think I'm gonna go with a coated 25 mm right angle prism and 2 coated mirrors (just like the P+S). Do you think that I will loose significant light with 2 coated rightangle prisms compared to one and mirrors????

I am really not qualified to advise on this subject. If P+S Technik went that route and given the time and effort of their R & D, I'd say there was a good reason for it. Minimising light loss and maintaining colour fidelity may have been a consideration.

Two mirrors in the 3rd and 4th reflective stage before the relay lens would allow for building in of some adjustments for slight mismounting of the camcorder. there might even be a little skew adjustment available.

With the gg image being smaller, you will have to move that groundglass somehow but keep your eyes open regarding wax groundglasses. If I could have economically made two dead-flat disks I would have gone for the wax composite disk in a heartbeat. As a spinner it was just so much better, except for the flicker.

I'll send the .jpg to the email address. The filename will be agusmrcp.jpg. It is a composition of four frame grabs from a PD150.

I looks easy, cheap and effective :-)

Doesn't the image reduce in size for each mirror??? So perhaps I will see a much bigger part of the GG than i thought.

Perhaps I should just go with the mirrors instead! But will the image travel as far as with a prism (I need the image to travel 12 cm between the GG and my relaylens). I think it ought to be the same distance right?



Do you have a link to somewhere you can buy coated glass (perhaps a pair premounted in a 90 degrees angle?)

Also which kind of coating are you referring to?

Would these aluminium coated mirrors work?:

25mm x 25mm
http://www.thorlabs.com/ProductDetail.cfm?&DID=6&ObjectGroup_ID=890&Product_ID=26986

38mm x 38mm:
http://www.thorlabs.com/ProductDetail.cfm?&DID=6&ObjectGroup_ID=890&Product_ID=26985

Have a look here for a 4 mirror configuration diagram (http://new.dpnow.com/1160.html) used in the new Olympus digital camera.
For testing, why not using some 90 degree aluminium profiles that can be easily mounted and adjusted.

Anders.

I can't make an opinion on the 4 mirror path in Valeriu's post. My browswer just chases its own tail forever as the reload speed is too slow on this landline.

Given a choice, I would prefer to stay with prisms and live with the light loss as most of the precision work has already been done for you. They will break but they don't deform or crack right across in a primitive mount like a surface coated mirror may if you are not gentle with it.

If you bond two right-angled prisms in 90 degree offset together at the half-hypotenuse faces and this is done precisely, the only alignment issues you have to worry about are that the SLR lens axis and camcorder lens axis are correctly centered and parallel.

With mirrors there is prospect of misalignment and distortion with each one before you even start lining your lenses up.

To get down to my 40mmm prisms I used larger mirrors as a test bed and incrementally masked off the outer edges of the included 90 degree angle between the pairs with black felt tip marker ink until the image became vignetted or crowded at the edges.

You will observe from the .jpg, the axes of the 90 degree bends in each mirror pair (prism corners) co-incide with the inner edges of the mirror pairs so by masking off the outer edges, the inner image edges don't change. You have to bring your camcorder and SLR lens axes in sideways and downwards slightly to recenter in the available frame.

I think your recoverable groundglass image frame will remain small as the relay lens itself is the limiting factor. All the prisms or mirrors do is bounce light which shortens the distance between groundglass plane and camcorder without shortening the distance the light actually travels.

I don't have any supplier info or links.

The mirrors I used for the prototyping were only household grade mirrors. If you look closely you will see the chips where I broke them down to the right size with glass cutter and a pair of pliers.

Optical grade surface coated mirrors.- Subjectively, there seems to be an increased whiteness or perhaps lower contrast with mirrors than with prisms. P+S Technik perhaps chose to blend the benefits and deficits of each reflective method to achieve the best overall outcome.

Bob,
I am sorry for the link. It seems to work from this end.
I got an intriguing piece of glass from one of my clients (a glass designer).
They call it "fused glass" and is imported from Germany. It looks like a VERY THIN piece of glass fused on a 3mm one. There is NO grain looks more like an opal glass.
I will cut it to fit an old medium format camera that I will probably hack and test it for digital capture.
I thought that you might be interested to see it and test it on one of your rigs. Email me outside the list at valeriuAToptushomeDOTcomDOTau to let me know if you want a piece.

I think that the best solution would be to go with a coated mirror and a coated pentaprism. But that solution would be expensive.

I think that each mirror colours the the image. (ie like when you look at 2 mirrors pointing at each other the end of the infinite tunnel becomes quite green - perhaps this is only with cheap uncoated mirrors?)

I think you would loose less light by a pentaprism rather than 2 right angles prisms. Also it would be really easy to allign - even easier than the 2 rightangled prisms. But then again it requires a damn good quality pentaprism.

Valeriu, have you bought the pentaprism you linked to earlier?? If you have then does it distort the colours in the image??? By the way great link it really helps to understand the pentaprism (at least for me!)

Do you have any idea why P+S doesn't use a pentaprism??

I have made two quick drawings of the two rotating image options I'm considering.

Did I understand it right - and which would work the best?

2 rightangled prism version:

http://www.backbonepictures.com/2%20right%20angle%20prism%20version.jpg

Pentaprism version:

http://www.backbonepictures.com/Pentaprism%20version.jpg

Anders.

As far as I can see the right-angle prism version should work. My final arrangement is the rear prism (faces gg) is upright and the front prism (faces camcorder) is horizontal. I did it this way to mount the camcorder high on the appliance rather than low to help with stability when handholding.

If your prisms are same width on the short sides as thickness across, you will need to make sure the corner of the common path of the two prisms is on the inside corner of the 90 degree angle of the prisms' crossover.

I can't verify the pentaprism arrangement as I have no experience with them.

Anders,
The pentaprism will offset the light only on vertical axis. The 2 x mirror / prism arrangement will producean offset both vertical and horizontal. Beware of stability issues arising from this combination.
AFAIK the prisms should have the reflective surfaces metal coated to deliver better light transmission. Have a look on the website I mentioned in my previous post. They say that will incur an extra cost as well.

Bob - how are you going to mount the porro prisms? Are you going to some how merge them or keep them with a little distance?

This confirms your theory:
http://en.wikipedia.org/wiki/Porro_prism

Anders.

As far as I know, porro-prisms are right-angle prisms but they are cut so as not to waste good glass in unused areas like my arrangement does.

I think they are cut so that the thickness across all faces is the same as the half hypotenuse distance but I am not sure of this.

My present mounting is a piece of finegrained particle board. After drawing my design in Turbocad in 1 : 1 scale, I printed it and used the paper to make an exact template. The Lexmark Optra S1250 and other members of that printer family print 1 : 1. So does the Canon BJC-7100. Most of the modern printers should too providing the document page setup is correct for the paper you print to and the printer setup is to the same paper.

The prisms sit in the channels which are exact width and are retained by thin metal strips like binocular prisms.

When playing with the prisms, make sure you do it over a soft carpetted floor as the chances of dropping one are high.

I then cut a channel across the front face of the board with a router, then cut another channel across the back of the board to cross over the first channel at a right angle (90 degrees).

Where they cross over there is only about 3mm of board. I cut a hole which is an "L" shape which provides the three ports for gg >> rear prism / rear prism << front prism / front prism >> camcorder.

Once I have this accurately established, I then cut and trim the board which in my case fits into a PVC tube which has a cap on either end. One cap has a mount for the SLR lens cut into it (or a camera lens mount screwed on, the other has the camcorder mount.

The rotary disk front enclosure is glued onto the tube and the rear enclosure fits to the front with screws and dome nuts.

There is a .jpg of both the non-erecting and erecting AGUS35 Australian Plumbers Versions as I call them on www.dvinfo.net/media/hart

Does anyone know where to get coated colorcorrected mirrors (40mm * 40mm)???

Bob, so are you using a prism or just an array of mirrors? I was looking at your schematic - and before my head exploded, turned away - and now I am thoroughly confused. If you are using an array of mirrors (which is a great idea), then I can understand a little more.

BTW, what part of Australia are you from? I lived there for a spell.

I started off with simple mirrors to test the principle then bought in two prisms which do the same job as the four mirrors.

P+S Technik seem to have a bet each way according to their diagram and seem to use two mirrors and one prism.

Bob, which prism did you buy?

Are they free of colordistortion???

Was getting rid of the mirrors because it was too bulky or other reasons? Do the prisms end up doing the same job, but better?