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-   -   Two achromats and still getting vignetting (https://www.dvinfo.net/forum/alternative-imaging-methods/46584-two-achromats-still-getting-vignetting.html)

Leo Mandy June 21st, 2005 08:02 PM

Two achromats and still getting vignetting
Boy, you would have thought I would give up after all the failures, stops and starts with this thing! Now, I have two achromats on this thing, and still I am getting vignetting and I don't know why. With my eye, looks great, with the camera, again darkness around the edges. I don't know if it is my stupid camera at this point because it seems that others have gotten around this quite easily. Any ideas?

Cody Dulock June 22nd, 2005 12:04 AM

are you zooming in past the vingetting?

Daves Spi June 22nd, 2005 01:34 AM

If you increase discance between GG and you camera, what happen ?

Leo Mandy June 22nd, 2005 05:45 AM

Done it both ways - not sure about the achromat that much anymore though - when I am too close, they don't seem to do anything - but when far away, they really make the image bigger (no blurring on the edges though, so I think they are not macros). So when I get far away, I see the problem - moving in close doesn't really increase the picture size with the achromat because of what I had stated above. Any ideas?

Bob Hart June 22nd, 2005 07:33 AM

Two achromatic diopters are likely to give you problems. One may be seeing the edges of the other in combination with the lenses in camcorder.

The achromatic diopter may have to be as absolutely close to the camcorder lens as you can get it.

The achromatic diopter will desirably be wider than the front lens of your camcorder.

With my SW5042 lens set, I barely got away with it at 52mm front camcorder lens diameter and 44mm front diameter on the lens set, zoom through at about 70% and focus only 12 - 18mm in front of the lens set. This was a very powerful lens. With a less powerful lens and the groundglass furthur away, the inside diameter of the achromatic lens on you case is oping to have to be much more like the diameter of your camcorder front lens. The separation between the front glass of my camcorder lens and rear glass of the lens set was only 0.5mm. Much too close for comfort but necessary in my case to avoid the vignetting.

If you can get a single 7+ achromatic diopter which is wider diameter than your front camcorder lens diameter, I think you will be much better served than with two smaller ones. Unless it is closely engineered by experts, more unplanned pieces of glass in the path may work against image clarity

Cody Dulock June 22nd, 2005 11:27 AM

the achromat isnt supposed to enlarge the image, its supposed to allow you to focus on objects that are close to the lens. some times you have to move your camera further away from the GG to gain the proper focus. as bob said, 2 achromats are probably trouble.

Leo Mandy June 22nd, 2005 03:33 PM

Well, most of the trouble comes, not the edges of the lens, but the blackness that creeps in because of the DV camera. When looking at it with the naked eye, it is a full shot, nice image, no hotspot, but once the camera gets put in front, I get the graduated image turning from bright in the center to dark as it get towards the outside. Maybe it is my camera that is acting up, not sure. But Bob is right, my dioptre is not big enough - it is smaller and probably not making the image big enough. I have had it close and far and so far, still getting the vignetting. I guess I am going to have to find the condensers to see if this solves the problem - or a better achromat.
BTW, I wonder if going the surplusshed.com route would work better than the achromat I have - they seem to have a big diameter.

Leo Mandy June 25th, 2005 05:18 PM

I tried a new lens (f1.2) and hotspot problem gone, no more vignetting! What a difference it makes. I still have some new FL adjusting to do, but I am much happier now that I can see without the vignetting what is happening. The image looks good, only shot at night(about 7:30pm) so far, so want to see what the day hold and the night (after 9:00pm) holds as well. I am hoping that a condenser is not needed at this point and I can go on to my final Spinning adapter which I would be able to bring out of the house without someone yelling - "hey, is that a birdhouse in front of your camera?"

Wayne Kinney June 25th, 2005 05:58 PM

Mandy thats great news. Can you tell us the specs of the lens? was an F1.2 expensive?? Also, what lens were you using before?

Im currently running tests with a 58mm F2 lens and i get vignetting, (no condensor yet) i guess jumping from an F2 to a F1.2, ill also see a big improvement?

Thanks, look foward to seeing some test footage, Mandy.


Oscar Spierenburg June 25th, 2005 06:04 PM

For me the difference between a 1.7 and a 1.4 I use now was enormous. The whole image is much richer and brighter. Leo, congratulations with the new lens.

Leo Mandy June 25th, 2005 06:05 PM


I will have to tell you, it is the strangest thing - but maybe if I had some optics background, I wouldn't have gotten alot farther then I am today!

I was using a MIRAGE 135mm f:1:2:8 (HUGE front lens - I mean BIG and nice size back lens on it). The image on the GG was amazingly big, which I thought would be benefitial! BUT hotspot galore and loads of vignetting even when really really close (zoomed in or close to the GG).

Now, I am using, and get this, a 50mm SEARS f:1.2.0 (SMALL front end, and nice size back lens), but NO HOTSPOT (or minimized so it is not seeable). I am very happy with it so far. Going to post some shots when I have time. I still need to see how it is in the daylight and at night (right now, just 7:30pm shots taken). The good thing about it is, I am stepping down to about f3.2-f0 on my MiniDV and still getting lots of image and little light loss (which helps with the hotspotting, I am guessing).

Wayne Kinney June 26th, 2005 05:20 AM

Oscar & Mandy,
This is great news. I think its going to be too expensive to pick up an F1.2 lens, but i see some f1.4 50mm lenses on ebay going for cheap. I have also been trying to find some wide angle lenses, like 28mm, but can only find them at F2.8 and no lower? is F2.8 the lowest for a 28mm lens?

Mandy, are you happy enough with your setup to say your not going to buy a condenser lens?


Leo Mandy June 26th, 2005 08:10 AM

Well, here is the posting of my newest shot at night with the window open, curly bulb 100watts (using 23Watts) and a small 11 inch TV to illuminate. Pretty dark, but not too bad (this was using a Sears 1:2.0 lens with my mini DV Iris open allllllll the way). I have a Canon 1:1.8 lens I am going to next.
As for the condenser, yes I am still going to get one - probably at www.anchoroptics.com or something. Oscar is getting great results with a slower lens and his wax GG with two condensers, so maybe that has alot to do with it (besides the fact that Oscar is a genius - give him a day and he will figure out Cold Fusion next!).


I know it sucks because you want the lens right away, but I have been looking for lenses for about 6 months and you do come across them at charity shops and the like - so if you don't want to spend alot of money, patience is the key. I got a Canon EOS 750 camera with 50mm 1:1.8 lens for about $20.00 at a charity shop.

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