Achromats- What are the best performing for 35mm Adapters
 

It is clear to me that the quality of image I get out of my DIY 35mm will depend on the quality of the achromat I use as well as the ground glass system used.

I have built a Micro 35, based on plans from Redrock. I've also built a static adapater. I used 1970 vintage stacked 35mm close up lenses in the relay system for both to allow close focusing, with lousy results. I also tried by a 10 diopter close up lens from BH Photo that was supposed to be 58 mm, but it turned out to be maybe 37 mm lens mounted in a 58mm ring. Both result in blurred images, and lack of sharpness.

I just am reluctant to put out the $400 for an achromat from Redrock for HD -- especially when I am not seeing a lot of stuff done with the FX1 yet, and I am wondering if there is an issue there. So I ask these questions of those that have gone before me:

1. Is there any thing about that FX1 that creates a special problem with these adapters and the achromats.

2. Has any one tried and used the 72 mm closeup lens sets available from BH, and other places, and if so, what effect.

3. With the Redrock M2, what is your experience with the FX1.

4. Has anyone tried the Redrock achromat on other adapters, and if so, to what success.

Shipped with my Brevis adapter. Flawless quality.

Chris.

I can't speak for the M2 as I don't know if it uses added optics in the path, namely condensers.

I have used both (separately) a 4+ and a 7+ achromatic dioptre for an approx 24mm x 16mm 16:9 image into an FX1 via a home made device.

The FX1 zoom has to be all the way at 54mm to frame 24mm x 16mm with the 4+ and at about 40mm to frame 24mm x 16mm with the 7+. This was with no added optics in the path.

The achromatic dioptres are both Century Optics 58mm filter thread mounts for PD150 with a 58mm - 72mm adaptor - just a brass ring with 58mm diam thread on inside and 72mm diam thread on outside. Because you are zoomed in most of the way with the FX1, the 58mm dioptres work adequately because you don't pick up the edge.

Unfortunately, my 4+ test with a number of SLR lenses posted at filefactory has timed out unused and gone to heaven. There is a lesser example with the +7 as a Divx version of a fisheye lens test at this address which will give you some hint of what happens to a FX1 with a 7+.

http://www.filefactory.com/file/c6a42d/

When you stacked your close-up lenses, disregarding the sharpness in the outer areas of the image, were you able to get centre sharpness in the image and the correct framing of the groundglass image with the stacked lenses?

My original testing was with stacked HOYA single element close-up lenses. They were a 1+, 2+ and 4+ which gave me 4+, to 7+. Stacked they were not very good but gave a general indication of what lens powers worked.

With the 7+, the lens to GG distance will be about 5" or about 125mm. With the 4+, the lens to GG distance will be about 8" or about 200mm. If you are not using a flip path which shortens the distance, then a stronger achromat might be desirable to keep the length of the device within practical reason.

As I understand things, there are no or few achromats of say +10 or stronger in the 58mm or 72mm filter mount size which is why the M2 people and others have been getting their own made up in powers best suited for their non flip (non erecting) adaptors. I don't know the power of their lenses.

I have rambled a little. Don't pay too much heed to my comments.

Chris, we no longer supply the RRM achromats (long story). We now have our own 72mm HD achromats which are manufactured exactly to our specifications. The achromats are fully coated, HD quality, and have refreshingly thorough quality controls. I did some tests with the new achromats, using one as a "close up filter" with my 8Mp digital SLR. I now understand why pro's use macro stands, focusing bellows etc. The DOF when the achromat is used in this manner is incredibly shallow, making image alignment to the lens super critical.

As Bob alludes, there are no achromats out there in the +7 to +10 range at 72mm...which is why we originally undertook our prototype program last May.

Its true, a high quality commercial achromat comes at a high price, and even the century optics +7 is not quite perfect diameter or strength. This is why adapter builders like myself and Dennis have gone to the trouble of designing our own and getting them custom made.

The SGpro's achromat is designed for the purpose. Its fully anti reflection coated and has been tested with the FX1, HVX200 and HD100.

Bob:

Exactly what I was looking for, actually. Thanks a lot.

The + 10 was just okay at center, and quickly fell off as you moved off to edges. It was $50 lens at BH, from B&W, and I was a little disturbed that the glass only covered about 40mm.

Actually looks like Cinevate (see post below) has a reasonably priced achromat.

Edit: I just l downloaded your Perth footage. Good job. I note a little darkness in corner, that I associate with fisheye vignetting issues. Is that with FX1 or what ?

Ben:

What camera are you using to shoot with the Brevis ?

The FX1. Works great.

Chris.

RE: "" Edit: I just l downloaded your Perth footage. Good job. I note a little darkness in corner, that I associate with fisheye vignetting issues. Is that with FX1 or what ? "".

The cam used for that test was a HVRZ1P, same optics as the FX1. I have been jumping from one to another in a borrow environment and forget which one sometimes.

The vignette you observed is the SLR lens mount being about 0.7mm off the centre axis. I hang my gadget straight off the front of the camcorder lens hood bayonet fitting and have the achromat mounted separately and not mechanically loaded in the 72mm threaded filter mount.

This means that there need only be a degree or so of angular misalignment from mounting and dismounting the appliance to throw the centre axis off a little.

For the GG work it is not so critical but it does become an issue when shooting the aerial image with long lenses of f4 or tighter aperture with the GG removed.

It is the way I have designed the thing to try and preserve the agile portability of the original camera and someting I have chosen to live with.

With the normal lenses you would rarely spot it except for the ultra-wides which stretch the corners but the Peleng projects a smaller diameter image and on the fullsize 36mm x 24mm still-camera frame lays down a true vignetted fisheye circular image.

My diametric framing on the GG is about 22mm - 24mm and I was just picking up the edge of the circle on a corner. What amazes me about that lens is the light gathering capacity of the thing. I have yet to see how it does with indoors artificial lighting.

I suspect flare might become an issue but whatever the lens coating is, it seems to work well and also seems to colour correct the Sony image in a good way.

It is f3.5 yet it does not provoke groundglass artifacts and I could actually tighten the aperture a little to sharpen things up a little. It would be interesting to try a Nikon fisheye. I seem to recall, either Dennis or Wayne has done so.

Thanks Ben and Bob.

Bob:

Were these shots made with the Letus type or Agus type of device ? Seems like I saw you talking about both in another thread.

Chris.

The Peleng tests were with a modified home-made AGUS35 with a full CD-R sized optical glass disk finished to an AO5 grade.

APVE is my acronym for Australian Plumber's Version Erecting* (AKA *Flip) because it is made from sewer pipe, matching end-caps, a piece of soft polypropolene whiteboard and some store-bought bits and pieces.

One of these days I get you a picture of my California Plumbers Micro35 version. I don't even know where to start with a flip version, but I am mastering the use of Black sewer pipe and fittings :)

I decided to order the Cinevate HD Achromat. With the cost of the Century, the $240 USD plus shipping and handling was not so bad. I will let you know how that works out.

I also have a Costco Kirkland trash can liner bag vibrating GG design in the works to work eliminate the spinning disk aspect. I take a two inch to 1.5 inch reduce fitting, and stretch the liner bag to make a decent ground glass. Still needs to be vibrated because of imperfections, but the screen is easily replaced...

Chris.

Black pipe?? Do they use polypropolene for resistance to seismic damage or is the black plastic PVC? Ours is white out here.

A "flip" arrangement is not as hard as it seems and there are variations, all which are workable. My own "flip" arrangement is fairly simple, two right angled prisms in ninety degree opposition, one's half-hypotenuse face across the half-hypotenuse face of the other. - Think binocular prisms and you have it, only binocular prisms are smaller.

I wanted a close couple to the camera for handholding so had to keep the size fairly small and use a 7+ dioptre which through the current prism path only just yields a 24mm wide image on a good day. Fortunately this is adequate but borderline for HDV with the AO5 groundglass.

There is a jpg of the current version. The image crops a little off the groundglass enclsure. The image can be found here:-

http://www.dvinfo.net/media/hart/agusmto8.JPG

In an ideal and cost free world, instead of an identical prism pair, I would use a longer and narrower transverse prism and a shorter and wider one for the vertical as a closer match to the 16:9 frame and able to fit within my existing case design.

My arrangement does not maintain the camcorder and SLR optical centres in vertical alignment like Quyen Le's Letus flip but causes my camcorder centre to be offset to the right side by about one 24mm frame width plus about 4mm clearance.

I have yet to reverse draw my current arrangement into the computer. When I get it done, I'll post it as a .pdf.

You might get a better result with your plastic bags bags by stretching them over an oxy welding goggles replacement clear round glass or maybe between two glass rounds. I think the path labs may have round microscope slides as well as the long rectangular ones.

Once you have a decent acromat on the job, plastic bag material will likely fall short of your expectations especially where high contrast sharp edges occur in the image.