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Old May 30th, 2008, 05:06 PM   #1
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Yet another DoF update

Well, I can't seem to get past the focus issue where focus is sharp in the center and falls off towards the sides. I thought it was my camera based on the following:

HC1
http://i120.photobucket.com/albums/o.../HD_zoomed.jpg

compared with:

D8
http://i120.photobucket.com/albums/o.../D8_zoomed.jpg

I also thought the achromat might be causing problems, but I'm not sure as I've tried a fair number of different combinations and none seem to help with the focus issue. In fact I did a test without any achromat or focus screen, just the DoF tube with a 35mm lens attached:

http://i120.photobucket.com/albums/o...35mm_no_fc.jpg
This was shot with the focus screen removed - essentially it is shooting through the 35mm lens (50mm f/1.8)

Compare to this:
http://i120.photobucket.com/albums/o...m_attached.jpg
This is with all the DoF stuff removed - this is just the camera. Sharp focus across the entire view.

And to this:
http://i120.photobucket.com/albums/o...200mm_lens.jpg
This is using a Vivitar 200mm f/3.5 lens with the focus screen in place (and slightly rotated). To me it looks like the effect is less but still present. The "infinite focus" element was also removed for this shot (thus the focus screen was closer to the lens).

I'm embarrassed at how little I seem to know regarding optics, but the description of a DoF adapter seemed very straight foward - 35mm lens focuses image onto focus screen, camcorder records from focus screen. Calibrate the distance from the lens to the focus screen to match the markings on the lens (I'm using a Vivitar self-contained autofocus lens as a check) and you should be good to go as long as you can maintain focus while zooming in on the focus screen to completely fill the view.

My HC1 has a 37mm thread. To this I've added a 37mm-52mm step up which screws into a 52mm filter (removed) that fits onto the bayonet blades of the Canon EOS tube extension. This is secured with JB Weld. I can attach 37mm macro lenses between this and the camera (I have two, Lensbaby +4 and Lensbaby +10), or I can install a 39.8mm Achromat inside this "end piece", or I can install a Kenko 0.5x WA lens inside this "end piece", or I can add a #3 tube extension and add the two 50mm binocular lenses arranged as per Daniel's tutorial.

My distance between the macro/achromat and the focus screen can vary between about 2" to about 4", depending on which achromat/macro I'm using and how many of what kind of extension tubes I add. Some combinations result in barrel distortion, some don't.

The distance between the focus screen and 35mm lens is not exact to the tenth of a millimeter, but I've found (right or wrong) that this seems to be only critical for using a zoom lens or for changing to a different lens. I'm probably wrong.

For some additional info on what I've been building:
http://members.cox.net/pnixon18/new_...oject_DOF.html

Am I trying to use this rig incorrectly? It seems to do quite well for close-up work where there is a single object in the field of view, but I think this is going to bite me if I have two people sitting either side of a table, so one person will be on each side of the shot - both of them are going to be out of focus, or else whatever is in between them will be out of focus. No?

Last edited by Paul Nixon; May 30th, 2008 at 07:50 PM. Reason: additional info
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Old May 30th, 2008, 11:00 PM   #2
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i think you need a different achromat.
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Old May 31st, 2008, 12:50 PM   #3
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Quote:
Originally Posted by Rich Hibner View Post
i think you need a different achromat.
Hi Rich,

Dennis Wood (Brevis35 fame) suggested the issue might be the amount of zoom I needed and that a 72mm achromat could resolve the problem. It sounded logical (which is why I experimented with so many configurations myself). However, I see that the problem exists even when NO achromat is installed.

A couple of days ago I took a serious of photos with the camera through the DoF adapter using various zooms to see the effect. Basically I pulled the zoom all the way back, took a pic, zoomed in a notch, tool a pic, and so on:

http://i120.photobucket.com/albums/o...obar/zoom1.jpg
http://i120.photobucket.com/albums/o...obar/zoom3.jpg
http://i120.photobucket.com/albums/o...obar/zoom5.jpg
http://i120.photobucket.com/albums/o...obar/zoom7.jpg
http://i120.photobucket.com/albums/o...obar/zoom9.jpg
http://i120.photobucket.com/albums/o...bar/zoom11.jpg

Looking at this picture:
http://i120.photobucket.com/albums/o...35mm_no_fc.jpg

Plus this one:
http://i120.photobucket.com/albums/o.../HD_zoomed.jpg
(just the HC1 - there is no other lens or adapter attached)

Seemed to suggest the issue was with the HC1. However, I then compared to this pic:
http://i120.photobucket.com/albums/o...m_attached.jpg

I don't see any appreciable distortion in that last pic.

There is one major difference between the pics I can think of - the pic using the HC1 by itself with zoom is focused on a distant object. All other pics showing the focus "issue" are "close" focused. Hmmm...
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Old May 31st, 2008, 11:35 PM   #4
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More testing!

Okay, I replaced the 38mm achromat with a 45mm achromat and took some video earlier this evening. Here are a couple of shots:

http://i120.photobucket.com/albums/o...ar/angela1.jpg

http://i120.photobucket.com/albums/o...bar/fubar2.jpg

Compare to:

http://i120.photobucket.com/albums/o...bar/fubar1.jpg
This used the old Canon AE-1 screen and, probably, the 39mm achromat.

I wish I knew more about optics, but it seems to me that one can't throw just any achromat into the mix - it seems it has to be tuned to the camera itself. Thus the Surplushed achromat commonly used with the Canon HV20 may not actually work for the Sony HC1.

To date I've experimented with a variety of lenses:

50mm x1 binocular objective (achromat)
50mm x2 binocular objective (achromat)

38mm x1 achromat
38mm x2 achromat

Lensbabies +4 macro
Lensbabies +10 macro
Lenbabies +4 and +10 macro

Kenko 0.5x WA
Kenko 2x Tele

45mm x1 achromat
45mm x2 achromat

The latest results were obtained using the 45mm x1 achromat and would probably have been better except the lenses were in average shape (scratched) (http://www.surplusshed.com/pages/item/l3989.html)
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Old June 1st, 2008, 01:10 AM   #5
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fubar2 the pic of the dog was much better than the rest.

here's a lot that you have to factor into sharpness. the diffusion of your screen. the thicker the less sharp it'll be be, but deeper dof and better bokeh.

achromat FL. do you know what yours are?

try to move your achromat further or closer to the screen.

also, the type of lens you're using will increase or decrease sharpness.

i'm guessin you're using both achromats from the binocular. how are you stacking them together? flat sides together or the round side? i used two before and i put the flat sides together and had great results.

you said Dennis made the comment to zoom in closer. I can't argue with him and say that's a bad or good idea, but from my experience, the closer I got, the worse off i was.

i have an achromat you can have. it's 10x at 40mm diameter. to mount it i used step up rings and electrical tape. it's from a good supplier from Italy.
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Old June 1st, 2008, 11:53 AM   #6
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Quote:
Originally Posted by Rich Hibner View Post
fubar2 the pic of the dog was much better than the rest.

here's a lot that you have to factor into sharpness. the diffusion of your screen. the thicker the less sharp it'll be be, but deeper dof and better bokeh.

achromat FL. do you know what yours are?

try to move your achromat further or closer to the screen.

also, the type of lens you're using will increase or decrease sharpness.

i'm guessin you're using both achromats from the binocular. how are you stacking them together? flat sides together or the round side? i used two before and i put the flat sides together and had great results.

you said Dennis made the comment to zoom in closer. I can't argue with him and say that's a bad or good idea, but from my experience, the closer I got, the worse off i was.

i have an achromat you can have. it's 10x at 40mm diameter. to mount it i used step up rings and electrical tape. it's from a good supplier from Italy.
Hi and thank you!

The FL of the achromat is 77mm. My focus screen is a Canon Ee-A.

I experimented with placement of the achromat and was intrigued at the differences I saw.

Dennis suggested that if I used a recommended 72mm achromat, I would require *less* zoom and thus the distortion might be less. I've been working on that idea with my collection of lenses to try to get an handle on what effect each of them has. My EOS tubes are only about, what, 60mm in diameter, so I can't use a 72mm achromat.

The binocular achromats - yes, I have tried them one at a time and both together. When used together I've had them round side facing based on Daniel's tutorial. Again I had to learn this from this group - I didn't actually know it made a difference such was the state of my knowledge. The binocular lenses seemed to provide the flattest image, but it was overly soft. I believe this to be caused by the very poor state of these lenses. I've been thinking of buying a new pair but decided it would be a better idea to try to understand the nature of the problem.

I very much appreciate the offer for your achromat, but right now I'd be very happy with information. Why is the image out of focus away from center? Why is it this way whether an achromat is present or not? And since it is present with and without an achromat, why does changing the achromat make such a big difference (and I have seen some very substantial differences in my experimentation)?
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Old June 4th, 2008, 10:03 PM   #7
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judging from the size of your camera, a 72mm achromat is overkill. your lens diameter is like 40something mm's. so no, you'd waste your money on a 72mm achromat.

are you positive the fl is 77mm? that's a high powered achromat.
thats' called barrel distortion when the outer edges are all blury. that's just the type of achromat being used. you can have cheaply made glass as well making it difficult to focus.

i wouldn't use an achromat bigger than 50mm for you camera. stick with something around that size. to determine the best distance from you achromat to your GG is some math. for instance.

some of your problems sound like it could boil down to a bad lens. lens can create trouble as well.

An achromat at 77mm focal length would be 1000/77 equals power. Divide your Fl by 25.4. Having a 77fl achromat would equal to you having it at or around 3inches away.

1000/Focal length=Power
Focal length/25.4=equals distance.
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Old June 12th, 2008, 11:02 AM   #8
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Quote:
Originally Posted by Rich Hibner View Post
judging from the size of your camera, a 72mm achromat is overkill. your lens diameter is like 40something mm's. so no, you'd waste your money on a 72mm achromat.

are you positive the fl is 77mm? that's a high powered achromat.
thats' called barrel distortion when the outer edges are all blury. that's just the type of achromat being used. you can have cheaply made glass as well making it difficult to focus.

i wouldn't use an achromat bigger than 50mm for you camera. stick with something around that size. to determine the best distance from you achromat to your GG is some math. for instance.

some of your problems sound like it could boil down to a bad lens. lens can create trouble as well.

An achromat at 77mm focal length would be 1000/77 equals power. Divide your Fl by 25.4. Having a 77fl achromat would equal to you having it at or around 3inches away.

1000/Focal length=Power
Focal length/25.4=equals distance.
Hi Rich,

The lens diameter on my cams is 37mm, so you were just about spot on.

Am I positive about the FL of the achromat? That's the number quoted from the surplushsed website for this particular lens. I can't guarantee that's what the FL is, but that's what they claim.

The achromat setup I am currently using is a single 45mm with a 77mm FL, and it had been 2 inches from the GG. Since reading your reply I moved it out to as close to 3 inches as I have tubing for. I am anxious to see what difference that might make.

And the 45mm achromats are in relatively poor condition - very different from the smaller lenses I received in the same shipment. Oh well...

Paul
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