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D2x+105mm+2xTC+Woody's diopter


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#21 herbko

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Posted 01 September 2005 - 02:30 PM

Rand, I think you've got it! Could you move the crop up a little for the fringe thing. It'd be interesting to see that detail. I have shots with similar features I can compair to when I get home.
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#22 randapex

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Posted 01 September 2005 - 02:36 PM

Here it is:

Posted Image

Herb, I found a little better one as far as sharpness goes:

Posted Image
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#23 james

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Posted 01 September 2005 - 03:03 PM

Wow! Thanks for the clarification and explanation Herb - that's the ticket.

That second crop of the fringe looks like it has some blue chromattic aberration. Otherwise, the sharpness looks (in my qualitative opinion) about the same as my shot using the diopters and f22.

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#24 randapex

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Posted 01 September 2005 - 03:19 PM

Guess when someone produces a camera that keeps that 100% crop tack sharp, I'll think of making a change. Until then.... ;)
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#25 herbko

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Posted 01 September 2005 - 09:27 PM

Here's a comparision with one of my shots taken with the Sigma 105 and an 1.4x TC shot at F/16 effective F/22.

The whole frame scaled down:
Posted Image

100% crop
Posted Image

smaller 100% crop
Posted Image

smaller 100% crop scaled up 1.5x for comparison to 12Mpixel shot
Posted Image

I made the last one to compare with a 12MPixel shot by upsampling my shot to the resolution of 12M Pixels.

Rand, I think the extream aperture you were using is costing you resolution.
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#26 yahsemtough

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Posted 02 September 2005 - 06:42 AM

Are you sure it is the aperature and not the shutter speed potentially taking away the resolution?

Remember he was shooting at 1/25 I think whereas I guess your shot to be about 1/100 to 1/160. Maybe a little shake on firing the trigger and the slow shutter is capturing that?
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#27 Rocha

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Posted 02 September 2005 - 06:51 AM

I also think that the apparent lack of sharpness was caused by slow shutter speed. I just looked at the exif of Rand's pictures, and the first was at a shutter speed of 1/25, the second was at 1/20, I think this is too slow for a 100+mm lens. Herb's was at 1/200.

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#28 segal3

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Posted 02 September 2005 - 08:12 AM

Remember too, that the only reason that the entire frame is not blurry is because with those settings (F/29 or whatever translated is, F45?), when the flash fires in 1/400s or 1/500s or whatever it is, that that's where the majority of your light is coming from, 'freezing' the subject.

But yes, I agree that a higher shutter speed is necessary regardless, and I merely theorize on why it worked period.

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#29 randapex

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Posted 02 September 2005 - 08:41 AM

Herb, thanks for the comparison and the pics.

The main difference between yours and mine, besides the the fact you were using a 1.4 instead of the 2x, which we can put aside for now, (Some say the 1.4 is sharper) is that the Woody's diopter, was also attached. As to what affect it has/had on overall sharpness, I'm not sure. Enough people complain that by it'self, the Woody's isn't all that sharp.

I'd like to thank everyone who's contributed as it's given me some ideas, answers and more questions. So, very productive.

What I'll try next time:

Shutter speed needs to be pushed up.

Open up the aperture a bit. Maybe trying around f18-f20. The Mosshead Warbonnets in Port Hardy are larger than the blennies but have the same fringes on top so DOF will still be an issue. I'd love to fill the frame with one of those guys. They're about the size of your little finger.

Perhaps push the ISO up a little. See how that affects the exposures. And find out if the overall image quality is still acceptable.

Look at strobe positioning and see if it's possible to move them forward a bit
farther.

Rand
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#30 herbko

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Posted 02 September 2005 - 09:27 AM

Are you sure it is the aperature and not the shutter speed potentially taking away the resolution?

Remember he was shooting at 1/25 I think whereas I guess your shot to be about 1/100 to 1/160. Maybe a little shake on firing the trigger and the slow shutter is capturing that?

<{POST_SNAPBACK}>


That may be part of it. If the light is mostly coming from the strobe, then the slow shutter speed should not blur the image. As I commented on before, in Rand's case a significant part of the light is probably coming from the spotting light, so slow shutter can affect the image. I think at 1/25 motion blur should be directional, that is the lens is panning in some direction, but I don't see that in Rand's shot. I still think the very small aperture, F/58, is the primary cause of lost resolution.
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#31 james

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Posted 02 September 2005 - 10:30 AM

Rand,

His aperture is set on the lens at f22 or whatever he used. It's the aperture that results in the diffraction I think, due to light passing through a small hole.

The aperture and focal length are also what affect depth of field.

Effective f-stop is influenced by the teleconverter and the bellows effect.

Does that sound right gang?

What I'm trying to say is that setting the aperture on the lens below the cut-off for diffraction spreading light between two pixels may be all that's necessary, and perhaps that's not affected by the TC or diopters.

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#32 segal3

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Posted 02 September 2005 - 11:05 AM

To clear up some ideas being thrown around here...

Given a perfect optical lens, a camera captures the most resolution (resolving power) when the aperture is wide-open, and the least resolution (losing inherent sharpness and ability to see detail) when stopped down, due to diffraction and the fact that you're taking a picture of a scene through a tiny hole (as compared to a larger one that will allow more light through, etc).

Now, when given a real-world lens, the same applies, but you are limited by the lens at the widest apertures (look at MTF charts for the variances). This is why it is usually taught to stop down 1 or 2 stops to get the best balanced resolution (resolving power, ability to see detail) from any given lens and camera.

When shooting at extremely tiny apertures, no matter what you do, even though you gain DOF, the amount of the image in focus will not be as sharp as that taken at a lower aperture.

On a separate note, in response to Rand's comment about the Woody's diopter, I have seen no reports from any individual that the addition of Woody's diopter leads to any noticeable (real-world) loss of sharpness (resolution).

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#33 randapex

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Posted 02 September 2005 - 11:24 AM

Herb, I've been meaning to ask if you have any idea of reproduction ratio achieved with the combonation of 105mm, 2xTC and the Woody's??

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#34 scorpio_fish

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Posted 02 September 2005 - 12:02 PM

Given a perfect optical lens, a camera captures the most resolution (resolving power) when the aperture is wide-open


Not true

I believe Rand must have hit the limit of the strobes in order to require a slower shutter speed. It may be solved by positioning (remember that icky inverse squares thing).

He didn't have the problem with just the diopter. That extra 2-stops is a killer.

Assuming that f/29 is the actual f-stop then one can easily assume a loss of sharpness due to diffraction. As a matter of fact, it looks that way to me just based on my own experience.

In the old film days, we would physically adjust the camera aperture. The LED in the viewfinder would give the effective aperture on Nikons, not the actual. It varied by camera as to actual vs. effective being displayed. It was weird seeing the readout f45. It is the actual aperture that causes diffraction (i.e. the physical opening), not the effective aperture.

Anyway, time to get some manly strobes instead of those boy toys. ;)
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#35 james

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Posted 02 September 2005 - 12:08 PM

Some stronger Inon strobes would be nice, eh? Watch this space.

FWIW, I was able to shoot 5:1 (35mm equivalent) with the Z220's set at -1 when I had my strobes pointed correctly. I had my lens set at f22

I don't know the exact number/math, but I'm guessing they could do effective f32

Cheers
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#36 herbko

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Posted 02 September 2005 - 01:12 PM

I go off to a meeting and come back to find all this confusion. ;)

Some of it is I think caused by my careless use of the word "effictive", so I'll try to clear it up.

The aperture is the ratio of the lens diaphram opening to the focal length. Adding a TC increases the focal length, so if the opening is unchanged the aperture is reduced (larger F number). I 've read that some camera and TC combination will adjust for this automatically: if you add a TC and set the same aperture the opening will be bigger to compensate. You should find out if your's does by the simple test I described on my first post. I know that mine does not. The shot I posted had aperture set to F/16 by it is REALLY F/22, and I wrote F/22 for the aperture even though the camera setting was F/16 as you can see in the EXIF.

Becasue of diffraction small apertures will limit resolution even for an ideal lens. Lens imperfection will limit resolution for large apertures. That's why most of the resolution tests you see for cameras at sites like dpreview is shot around F/8. For the 1.6x cropped 6Mpixel sensor 300D, at around F/16 diffraction starts to eat into the resolution and becomes the limiting factor not the number of pixels. I do not expect the 12Mpixel sensor on the D2x to have much better resolution than the 300D at this REAL aperture and smaller. That's the theory. I asked Rand for the 100% crops to see if it's consistant.

Rand, your lens by itself has maximum magnification 1:1, with a 2x TC it should be 2:1. You can just fit an 11mm subject in the frame at max magnification. I'm not sure what your diopter will do as I have not tried that one.

James, Mark has given hints about a higher powered Inon strobe. Have you any details you can share. Brighter strobes are on my list just ahead of the 5D.
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#37 james

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Posted 02 September 2005 - 01:20 PM

Hi Herb,

I'm confused. I thought an aperture was a mechanical opening (a small hole) and small holes (as well as slits, like we used in physics class) creat diffraction.

I though a F-stop depends on the size of the aperture and the focal length.

But I could be wrong.

RE the Inon's. I'm just making hopeful guesses based on what Mark has posted on various message boards.

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#38 randapex

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Posted 02 September 2005 - 01:29 PM

Thanks for the explaination Herb. I'll test that out tonight and see how the camera responds. I do seem to recall getting some high f stop readings, ie f45.

Also at one point, of having the camera read with a strange symbol: <f7 and it wouldn't change with the aperture wheel being turned. Some of my shots read f0 so I'm not sure if I've got a faulty connection with the TC or some other issue. After the dive, I removed the TC put the 105mm back on and the f stops read correctly.

As for the Woody's. I'd taken some shots with and without the diopter and I'd say that with it, the subject was roughly 50% bigger than without. Perhaps getting me in the area of 3-1. Thanks for the calculation.

Rand
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#39 herbko

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Posted 02 September 2005 - 01:31 PM

Hi Herb,

I'm confused.  I thought an aperture was a mechanical opening (a small hole) and small holes (as well as slits, like we used in physics class) creat diffraction.

I though a F-stop depends on the size of the aperture and the focal length.

But I could be wrong.

Cheers
James

<{POST_SNAPBACK}>


I think technically you are right. But I think in photography the term has come to mean F-stop. When someone asks you what aperture you set on a shot, you never respond with 5mm. It may be fun to do to see the reaction. ;)
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#40 acroporas

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Posted 02 September 2005 - 02:10 PM

I am confident that the lack of sharpness is from using both teleconverter and diopter and it is not just because woody's is a low quality diopter.

I have experimented with using both with my Canon 1.4X and Canon 500D diopter on the following lenses: canon 300/4, canon 100/2.8 and sigma 150/2.8 (I had to use an extension tube to make the macros compatible with the 1.4x)

I found that with all the lenses at any aperature, more detail was captured by using teleconver or diopter than with both.

Can anyone post an example of a sharp 100% crop that utilized both a diopter and a teleconverter?
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