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Exotic Macro Beyond 1:1


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#21 Ryan

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Posted 13 January 2005 - 09:00 AM

UWPN, in your ikelite port, adding the diopter will likely cause the front of the lens to bump the front of the port, not letting your lens extend to 1:1, and negating much of its benefit. An external wetmate diopter might be a better solution in this case.

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#22 frogfish

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Posted 13 January 2005 - 06:02 PM

Re: (Viz?) Viz'art's point about multiple-element diopters for wide-angle lenses above, I used to use the 5T and 6T diopters with the fixed focal length 20 mm lens on my film set-up. There's no question in my mind that the images were better than those taken with single-element diopters i tried. However, the larger size (depth) of these diopters meant that there was very noticeable vignetting. Edge/corner sharpness wasn't great either, but that was probably due to the smaller Subal dome I used then.

I use a single-element +2 diopter (supplied by Subal) with the 12-24 and 17-35 lenses, and the results are very good. Has anyone tried multiple element diopters (such as the larger diameter Canon products Viz'art mentions) with these lenses and compared results?

I sometimes use 4T with the 105 mm. That's about as much magnifiation as I ever want or need.
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#23 bvanant

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Posted 13 January 2005 - 10:15 PM

If you want to really go super macro look at the Canon 65 mm lens. Unbelievable but I would guess difficult to play with UW.
Bill

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#24 craig

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Posted 14 January 2005 - 05:09 AM

The Canon 65mm is impractical to house underwater and has no working distance.
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#25 Viz'art

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Posted 14 January 2005 - 06:34 AM

Re:  Edge/corner sharpness wasn't great either, but that was probably due to the smaller Subal dome I used then.  

I use a single-element +2 diopter (supplied by Subal) with the 12-24 and 17-35 lenses, and the results are very good..


The diameter of your Dome should be matched to the diopter and Subal most likely did the calculation for their dome and came up with this strenght of +2, but just for fun check it out by yourself, I recall an article by Julian on Wetpixel about dome theory and finding the right diopter, so take your trusty old calculator and check it out,

http://www.wetpixel....-1-pid-57.phtml
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#26 bvanant

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Posted 14 January 2005 - 08:26 AM

Craig:
I agree, but it really takes some very cool pictures.
Bill

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#27 richgarrett

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Posted 15 January 2005 - 08:36 PM

I have used this lens to shoot Flag Blennies in St Vincent.
it was VERY difficult to use, but did work.
The lens has a fixed focus distance for any magnification.
I racked the lens out to the max for my 100mm port and was shooting at about 3X magnification. the focus was VERY close to the port which made lighting VERY difficult!

As with other methods of high mag macro, finding the subject and getting good focus was a real challenge, but I did get some shots.

would love to try Pygmy Seahorses with this lens.

rich

#28 bvanant

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Posted 16 January 2005 - 10:04 PM

I never had the nerve to try to take it underwater, topside, I love it.
Bill

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#29 divegypsy

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Posted 31 January 2007 - 06:42 AM

Hello Wetpixelites,

A few thoughts and experiences with shooting really little subjects – meaning shooting at larger than 1:1 magnifications. As always my basic testing and shooting experiences are with film, on the Nikon F5.

Starting thoughts. The theory. Any lens is capable of only so high a resolution at a particular magnification. I’ll use some theoretical numbers here to illustrate what I want to convey. Let’s say, for example, you have a Nikon 105mm f2.8. And that at your actual shooting aperture of f16, and at closest focus, 1:1 magnification, the lens is capable of resolving 200 lines per millimeter at the center of the picture. If you extend the lens out farther from the camera body using extension tubes or a bellows attachment to reach a 2:1 (2x) magnification, you are spreading that resolution of 200 lpm over twice the frame length and therefore your actual resolution, everything else being equal, is going to be only 100 lpm.

The recording medium also has an effect. If your film or digital sensor has a lower resolving capability than the lens, it then becomes the limiting factor on the resolution of the image. Taking the above lens as a starting point. If your sensor or film can only resolve 150 lpm, at 1:1 the best you can get is the 150 lpm. But when you go to 2x, the lens becomes the limiting factor and the best you can get is 100 lpm. And at 4x the best is only 50 lpm.

The whole point of this theory is that magnification ALONE will reduce the sharpness. And at a certain point, depending on your own standards and the use you want to make of the image, magnification alone can make the image unusable.

Magnification can be gained by other than just lens extension alone. And the reality is that any optical elements you add to that perfectly designed macro lens will cost you some sharpness above and beyond that which you lose to magnification alone. The more practical “additional optics" are usually either close-up lenses which fit on the front of your prime optic. Or tele-converters which go between the prime lens and the camera body.

In my experience the dual element, or achromatic type, close-up lenses cost you less sharpness than the single element simple diopters. And are particularly sharper near the edges of the picture. The dual element close-up lenses achieve at least some (or all) of their magnifying effect by narrowing the angle of the lens itself in addition to allowing the lens to focus closer. This makes the dual element close-up lenses a bit less suitableto use with wide-angle lenses for the purpose of allowing the lens to focus closer in order to use it in a dome port. How do I know this. Years ago I had an opticial company cut a dual element Canon close-up lens in half with the idea that it would be even better for the “under” half of over/under shots than a split diopter. The split dual element lens was sharper, but the two halves of the image didn’t line up. The underwater portion of the image was less wide-angle. With a single element diopter the above and below halves of an image do line up.

For actual close-up small subject shooting, typically done with a flat port, the greatest magnification I have been able to get using a dual element close-up lens, Nikon’s T4, is about 1.5x. Not a really great gain. Since the dual element close-up lens or an extension tube both limit the total focusing range of the resulting optic, I prefer to use extension tubes because they cost no sharpness beyond that lost to the actual magnification.

Kenko makes a nice set of auto-extension tubes for Nikon (and also for Canon I think). The three tube set has individual lengths of 12, 20, and 36mm. And up to three or four tubes can be stacked and still maintain the lens diaphragm operation. However, when the total tube length becomes too long, the coupling of the electrical contacts for electronic aperture setting and light metering can be compromised by the weight of the lens pulling downward. To prevent from happenng I have incorporated a plastic ring onto the 105 that just barely touches the inside of the housing extension ring and thereby keeps the front of the 105mm centered and thus maintains the electrical contact. The 105mm Micro-Nikkor used with both the 20mm and 36mm kenko tubes together allows a FILM shooting magnification range of about .5x (half lifesize) to about 1.75x. I use this combination quite often when I expect to be shooting things like smaller sized nudibranchs. If I use only the 36mm tube withthe 105mm I have a range of about one-third lifesize to 1.5x, which is a very similar magnification range to that provided by the Nikon T4 close-up lens on the 105mm. But a bit sharper. Two 36mm tubes and two 20mm tubes, a total of 112mm of extension, give you a shooting magnification range of about 1:1 to 2.5x.

This amount of extension tubes gets to be a quite long bit of gear to house. And quite limited in its use. So before I get to that point, I usually add a tele-converter to the rig.

But any tele-converter costs additional sharpness. Last year, before I sold my D2X, I reran some tests I had done a few years prior to try to get some idea of how much sharpness was being lost to the teleconverter. Using an Australian $10 note (I was in Australia at the time) which has a lot of very fine detail on it, as my subject, I shot the same framing of a small portion of the note using three different optical combinations. First I used enough extension tubes plus the 105 Micro-Nikkor to shoot the note at about 2.25x. Then I shot the very same portion of the $10 note using the Nikon 1.4x AF-S teleconverter and less extension tubes with the 105mm lens. And finally the same framing again with Nikon’s 2x AF-S converter combined with a 20mm kenko tube, and the 105mm lens. The AF-S converters do not allow the older style 105mm Micro-nikkor lens to be mounted directly onto them. But it is possible to mount a slightly modified 20mm Kenko extension tube onto the tele-converter. And then mount the 105mm lens onto the extension ring. All optical combinations were shot at a variety of apertures using a strobe for lighting to reduce the possibility that camera shake would affect the results. I use the Nikon AF-S converters because in my earlier tests I had felt they had given me sharper results and I didn’t have the Kenko converters with me to retest at that time. The reason for keeping the total magnification and framing consistent was to make the presence of the converters the only variable in the image's creatiom.

The results were consistent. The shots with extension tubes alone were the sharpest. The shots with the 1.4x converter were only very slightly less sharp, and were still sharp enough that I am quite willing to use the 1.4x converter. The 2x converter was noticeably less sharp and as a result of this test, I will use it ONLY when I really want magnifications that I cannot practically attain with the 1.4x and extension tubes, or tubes alone. Since I find diaphragm operation begins to fail if I put more that four components between the 105mm and the camera body, the final really satisfactory combination is the camera body, then the 1.4x converter, then 92mm of extension tubes, and finally the 105mm lens.

This combination gives a shooting magnification range of about 1.2x to 3x. Replacing the 1.4x converter with the 2x allows me to attain just over 4.4x magnification, but with a little less sharpness that I would really like to settle for. Either combination is quite unwieldy and also requires that I mount a fair sized light on the rig to have enough brightness for accurate focusing. Holding it all steady enough to shoot also becomes quite difficult.

My most pleasing results with the 4.4x rig so far have been of a set of amenonefish eggs during a four day incubation. I had passed the anemone the day before when there were not eggs, and then noticed fresh red eggs the following day. So each day about noon, I shot the eggs. They were gone on the fifth day, meaning they had either hatched or someone had eaten them. Last year I reshot the series again using a better means of keeping the distance between the port front and the subject more constant. I haven’t scanned those yet, but visually it seemed as though the sharpness wasn’t significantly better than the previous try, but the percentage of sharp shots was far higher as a result of my being steadier.

If I can, I’ll try to attach the four shot series of the egg incubation to this post.

divegypsy

Attached Images

  • eggs_day_1.jpg
  • eggs_day_2.jpg
  • eggs_day_3.jpg
  • eggs_day_4.jpg


#30 james

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Posted 31 January 2007 - 07:21 AM

Fred:

Thanks for posting this detailed message. It's almost an article in itself!

My preferred "typical" macro setup for FF shooting is a Sigma 150mm lens with the Canon 500D diopter.

Sincerely,
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#31 divegypsy

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Posted 31 January 2007 - 12:46 PM

Hi James,

Glad you felt what I wrote was worthwhile. I would think that using the Canon close-up lens on your ful-frame digital camera would give you just about the same magnification (about 1.5x maximum) as using the Nikon T4 on the 105 Micro-Nikkor, but with about 50% more working distance from the front of the lens to the subject. Both are a nice easy way to go in that there is usually a bit of "extra space" in the macro port into which you can fit the CU-lens. And thus not have to carry an additional port. It also keeps things a bit simpler as using one of the CU-lenses usually doesn't require manual focusing as there is no "extension factor" that with the kenko tubes might increase the apparent f-stop of the lens at maximim aperture to a darker image that requires manual focusing because auto-focus no longer works.

I've built my macro system a bit differently and have very short length of tubing with either the flat macro glass or the macro dome. And then add to that from a selection of extension tube lengths and a manual focusing tube. At 4.4x. the magnification of the anemonefish egg pix, there is a light loss due to the extension tubes and 2x tele-converter of about 6 f-stops. This means that the effective maximum aperture, the aperture you view and focus at is somewhere about f22. Really dark! And thus the need for the quite bright focusing light. And the quite long nose on the housing which is composed of 155mm of regular Seacam extension ring, a manual focusing ring which is 75mm long, and then the flat glass tube which adds about 40mm more. So a total housing "nose" about eleven inches long. It's not something I use very often, but is the only way I can get images that are sufficiently sharp enough for magazine publication at that magnification.

The 105 with 56mm of kenko extension tubes, which I mentioned gives me a really sharp image range of .5x to 1.75x has a mose composed simply of a 60mm extension tube, plus the manual focusing tube, and then the flat glass port front and is only a couple inches longer that the 105mm port alone. This rig could work most of the time on auto-focus, but particularly at the higher magnification end of the range I am more satisfied with the results I get with manual focus. But that's just my personal preference. There is no right or wrong way to do any of it. Just do what pleases yourself.

Fred

#32 james

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Posted 31 January 2007 - 01:07 PM

Hi Fred,

I'd like to learn more about the Seacam macro port system. For Nikon they have the nice port system that you use which is made up of 3 or 4 pieces, the back extension ring, the focusing ring, the front extension, and the flat glass end.

I want something similar for Canon, that has a focus knob or zoom knob on the port.

Would you mind posting a photo of your port - what does it look like? Thanks.

James
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#33 divegypsy

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Posted 31 January 2007 - 08:01 PM

Hi James,

Unfortunately I no longer have a digital camera of any sort to take a quick picture for posting. Do feel the need for one, though, and will probably pick-up some smaller digital camera, such as the recently announced Olympus SP-550 UZ as a general snapshot and digital image "note taker". But unless Nikon introduces a full-frame D-SLR body I'm probably out of that part of the digital market for a while.

SeaCam makes an extension tube with a manual focus knob right on it. Which then couples to a lens gear that is about 2mm smaller in diameter than their normal zoom gears that couple with the housing body knobs. Its a bit fatter that the normal extension tube and mine are 75mm long. I seem to recall that Harald later told me that they had decided to shorten the length of this manual focus tube tube by 5 or 10mm. I'm sure Steve Frink can give you the details on its current dimensions.

I bought several of the 75mm manual focus tubes when I bought my F5 housings and have felt no need to buy any more just to get a different length. In addition to these tubes with their manual focus knobs, I bought about a dozen regular extension rings in various lengths from 65mm down to 25mm. And recently added one of his new 20mm tubes. This allows me to add extensions of virtually any length to every Seacam glass port I have. These ports include the 9" Superdome, the 6" fisheye dome. the 6" wideport, the smaller diameter macro dome, and flat glass macro ports. The idea was to make my whole system completely modular so that as I added or changed my lenses, I could simply change the length of the straight tubes in a particular set-up to adapt any glass port to any lens. The usefulness of this idea became evident when Sigma introduced their new and improved 14mm lens, which was physically longer. I simply used a 30mm tube between the housng body and the SuperDome in place of the 25mm tube I had been using.

As my lens selection changed, (17-35 f.2.8 replaced the 20-35 andthe 24-85 replaced the 28-85), I have found I can now use one particular length of straight extension tube with the four lenses I use the most.
A 60mm tube. It also means I have some extra tubes, 65mm, which I can sell cheap to anyone who might want one of that length.

With the 17-35mm f2.8 I have the housing body, then one 60mm tube, and then the superdome.

With the 24-85mm F2.8~f4 D I again have the housing body, then a 60mm tube, and lastly the 6" wideport. I use the wideport with this lens because it is more compact and the lens focuses so close.

With the 70-180mm Micro-nikkor I again start with the housing body and a 60mm tube, then I have the tube with the manual focus knob, and then a short 25mm tube followed by either a flat macro glass or a macro dome.

With the 105mm Micro-nikkor alone I use the 60mm tube, a 20mm tube, and then the flat glass

With the 105mm plus 56mm of of Kenko auto-extension tubes (my .5x~1.75x rig) I again start with the housing and the 60mm tube followed by the Seacam focusing tube, and finally the flat glass port

And on the extreme 4.4x rig I have the housing body, two 60mm tubes, a 35mm tube, and finally the focusing tube and the flat glass port.

The modular philosophy also works well with my packing for travels. My photogear goes into two Coleman 68 coolers lined with a nice closed-cell foam for padding. Each cooler gets one housing body, two strobes, a pair of strobe arms and some sync cables. Each box gets at least one of the three dome ports I travel with, a flat macro glass, a macro dome, and about half of the regular extension rings. I pack this way, as I mentioned before, so that if the airline loses one of the two camera boxes, it does hurt, but it doesn't disable me completely. I can still put together a shooting rig that will work with any of the lenses I use most.

I was hoping Wetpixel would have a booth at DEMA this year at Orlando. And that I'd get to meet you and Eric. But I didn't see one while I was there during the last two days of the show.

I hope this verbal description has helped you understand how I am using the gear. In this case I agre that a picture might be worth a thousand words and I will eventually pick up some little digital camera for snapshot uses that would help with this kind of exchange.

Fred

#34 james

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Posted 01 February 2007 - 07:57 AM

Hi Fred,

Thanks for the description. If you can borrow a snapshot camera and make some digital pixs taht would be great but I understand if you don't have time.

What I'm interested in seeing is a general photo and also a photo of some of the manual focus gears that mesh w/ the focusing tube. I've never seen those before.

Right now I use a long extension ring and a very long manual focus gear w/ my Sigma 150mm. The focus ring goes all the way back to the housing body. I'd like to try shooting a zoom lens w/ manual focus - something similar to the 70-180 would be good.

Cheers
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#35 herbko

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Posted 01 February 2007 - 11:25 AM

Fred. Thanks for taking the time to share your experience. I agree with James. That post is an interesting article in itself.

I've been using a Canon 100mm + 1.4x teleconverter and a Canon 500D (+2 diopter) in combinations for most of my shots so far. I think I'll get a set of extensions and try them out in the future.


Starting thoughts. The theory. Any lens is capable of only so high a resolution at a particular magnification. I’ll use some theoretical numbers here to illustrate what I want to convey. Let’s say, for example, you have a Nikon 105mm f2.8. And that at your actual shooting aperture of f16, and at closest focus, 1:1 magnification, the lens is capable of resolving 200 lines per millimeter at the center of the picture. If you extend the lens out farther from the camera body using extension tubes or a bellows attachment to reach a 2:1 (2x) magnification, you are spreading that resolution of 200 lpm over twice the frame length and therefore your actual resolution, everything else being equal, is going to be only 100 lpm.

divegypsy


It's true that there are optical limits that will limit resolution at high magnification, but I don't think the above is a good example of how that works. Taken to the other extreme your example would imply that a lens focused at 5 meters would only have half the resolution of the same lens focused at 10 meters.

I came across this extensive test chart for Canon lenses used with diopters and tubes by Bob Atkins at photo.net awhile ago. It's very handy.

http://www.bobatkins...faq/closeup.htm
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#36 divegypsy

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Posted 01 February 2007 - 01:28 PM

Hi guys,

I will try to see if someone I know has a little digital camera I can borrow and make some shots.

Additional background. I am VERY serious about having very good gears on my lenses. End especially about having good, smooth manual focus gears on every lens I use if possible. Serious to the extent that I work with a machine shop to make my lens gears just the way I like then.

I bought some cylinders of delrin plastic, about a foot in length, and then took them to a shot that cuts gears and asked them to match both of the sizes that Seacam uses. Now, when I want a new gear, I have my machine shop guy make most of it out of aluminum and then cut a slice off my giant delrin gear to attach where it needs to mate with the Seacam housing gear. Sounds expensive, huh? If you were doing only one or two gears it would be prohibitive. But since I want manual focus gears on as many lenses as possible. In the long run I have reached the break-even point vs buying the gears Seacam makes. And I feel mine work much more smoothly. AND even more to the point, I have manual focus gears for lenses that Seacam doesn't make gears for at all!

I have also modified my F5 housings with an "automatic transmission" that engages or disengages the manual focus gear right when I switch the MSC lever on the housing. No longer need to pull out the plastic knob to disengage a manual focus gear when the camera is in one of the auto-focus modes and you don't want the AF motor straining to turn all the manual focus gear train. I showed the auto-transmission design to Harald at a recent DEMA and thought it was a nice design. BUT he also said that virtually no one asks for manual focus any more and that over the previous year he had had only ONE order for a manual focus gear.

So it would seem, that like film cameras, manual focus is commercially dead. Except to a Filmosaurus like myself.

The gear situation in some ways mirrors my whole attitude concerning underwater gear. It is too often designed, for commercial reason, in way or without features that I consider far less than ideal. So when I do need to buy something, like a housing, I don't just look for the one that is closest to what I want. I also look to see if there is some way I can have it changed to be even better. I believe that the placement and smoothness of the controls is one of the most critical considerations when buying a housing.

The controls for the features of the camera you need to use the most often need to be easily accessable. And ideally accessable when your hand are on the handgrips of the housing and the housing is held at your eye for shooting.

As an example - If you have to take the housing down from your eye and push little buttons to change the auto-focus point, it is almost useless. How can you use this feature when the fish noves to a different position in the frame, or changes direction? By the time you take the camera down from your eye and push little buttons to make the change, the fish may be gone or have changed direction again.

Another example - Why should you have to take the camera down from your eye to change the compensation amount. IF you use this control to bracket your TTL (sorry Filmsaurus technique again) flash, lowering the camera to fiddle with controls for this takes too much time and will cost you shots when things are happening quickly.

These are two camera functions that I use constantly, and are especially vital to have easy when things are moving and happening. And I can do both of them, in only a second or two, WITH the housing held to my eye so that I can maintain visual contact with the subject. And I wish more housing makers would pay attention to these things. And the might, except that the "market" doesn't really care enough about them to be willing to pay a little more for them.

One of the things I have liked best about using Seacam is that Harald does pay more attention to this king of thing more than most manufacturers. And that by paying a bit extra for a few more extension tube, which Harald will make for you in virtually any length you want, you can have a more versatile and responsive tool to use underwater.

Fred

#37 divegypsy

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Posted 01 February 2007 - 02:18 PM

Herbko,

In your post you said the following.

"It's true that there are optical limits that will limit resolution at high magnification, but I don't think the above is a good example of how that works. Taken to the other extreme your example would imply that a lens focused at 5 meters would only have half the resolution of the same lens focused at 10 meters."

There is a big difference in your example using 5m vs 10 m. shooting distances. And that is that the lens is at anear infinity working distance in both cases and therefore the optical image brought to the sensor (or film) varies very little in its actual size. And the distance of the rear element of the lens to film or sensor is also almost the same. So the lens resolution also varies very little. When you get very close, you are using a smaller and smaller portion of what the lens sees, of the lens's designed angle of coverage, and making it bigger and bigger.

As a slight analogy. Take a photo with your camera, and a fixed focal length lens, from 10m. Then shoot the same subject, a "cropped" view from 5m. Take that "cropped" view and make a 20-30" print of it. Then take the center section (equal to the 5m view) of the more distant view (about 50% of either the length or width) and also blow that center section up to a 20-30" print. Or some similar large magnification for both. I believe you will have no difficulty seeing that the image that has been magnified double the amount of the other has less sharpness and detail.

Yes, there are other factors that come into play. These include the working distance the lens was designed for, which is why I use the the 105mm micro-nikkor for this "high magnification" shooting. It is a lens designed to perform well in close shooting, not just a lens that focuses closely. Diffraction can also play a part, which is why, when I made my tests of the different converters, I shoot three or four apertures, and compared equivalent mechanical and equivalent effective aperures. But I really believe that the most significant factor in the reduced resolution I see in images shot at 1:1 vs 2:1 and even more so at 3:1 or 4:1 is simply the magnification factor and the spreading of the lenses resolution over a larger and larger area.

This is why I am interested in the new macro lens Zeiss will soon be offering in the Nikon mount. IF there really is a significant difference in resolution, as Zeiss claims, I believe it will show up more clearly at higher magnifications. And this is also a type of photography where the fact that the Zeiss lens doesn't have auto-focus will make the least difference.

When I try to test something, like a lens, I do everything I can to eliminate variables other than the thing I want to test for. And try to make the test under the conditions I hope to use the lens in most. Therefore, because water distance also diminishes resolution, I generally ONLY use a lens like the 105mm a closer distances. And try to use a wider lens whenever possilbe. That is one of the reasons I like the 70-180 Micro-nikkor so much. And when I finally get to see and test the new Zeiss 100 f2 Makro-planar, I will do it on an extension bellows at about 3:1 and shoot the identical shot with the Nikon Micro-nikkor. And ONLY if I can see a clear difference in the actual results, will I spend the money on the Zeiss lens, which by early information looks like it will cost about $2000!

Fred

#38 herbko

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Posted 01 February 2007 - 04:17 PM

Hi Fred,

I was not disputing your conclusions about loss of resolution with magnification, and your example is probably technically correct. The reason that moving the lens twice the distance from image plane halves the resolution is that the aperture is moved twice as far away. The lens is stopped downed two stops, and the diffraction fringes are twice as big. If you open that up 2 stops you'll get back the resolution but your depth of field will be much worst. You're right that my example of focusing at 10m is not that good either.


This is why I am interested in the new macro lens Zeiss will soon be offering in the Nikon mount. IF there really is a significant difference in resolution, as Zeiss claims, I believe it will show up more clearly at higher magnifications. And this is also a type of photography where the fact that the Zeiss lens doesn't have auto-focus will make the least difference.

Fred


Please let us know your findings. From what I learned about optics in the classroom, at small enough aperture, ~ F/22 for film and sensors like the ones in the Canon 5D and 1DsII, you'll be diffraction limited and better glass won't help much. I really like to see a careful test of this.
Herb Ko http://herbko.net
Canon 5D; Aquatica housing; 2 Inon Z220 strobes; Canon 100mm macro, 17-40mm ; Sigma 15mm FE, 24mm macro, 50mm macro

#39 divegypsy

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Posted 01 February 2007 - 10:25 PM

Hello again Herb,

I agree that diffraction CAN be a limiting factor. And my shooting experience has indicated, at least to me, that shooting the 105 Micro-nikkor, at 1:1, at an aperture below 22 results in a loss of sharpness I am not willing to accept. And unless depth-of-field is really crucial I try to shoot somewhere between f16 & f22.

As I tried to work at larger than !:1 with the 200 Micro-nikkor I found that I was not happy with that lens closed down beyond a third of an aperture past f16.

These numbers are the narked aperture on the aperture ring. With the F5 which give its aperture read-out in effective apertures as you focus closer with the lens (but does not account for extension tubes in this read-out) I accomplish the equivalent by closing the lens down as far as it will go with the electronic aperture control (front input dial) and then counting the 1/3 aperture clicks as I open the lens.

My tests have NOT shown that I can regain equal sharpness at 2:1 as I get at 1:1 by simply opening the aperture two stops. It might get slightly better, but not really close to equal. Any really close shooting puts you in the position of having to make value judgements pitting sharpness against depth-of-field. Almost every lens test I have seen and most things I have read seem to indicate that a lens's greatest resolution usually occurs about 2-3 apertures stopped down from wide open. This would suggest that the 105mm would be sharpest around f5.6 or f8. And lenses can be designed to give better resolution closed down a bit further, which is supposed to be one of the considerations in the design of a lens intended for true close photography. My recollection of the photo magazine lens test I saw quite some years ago on the 105mm Micro-nikkor I use (not the image-stabilized newest one) was that it achieved its highest resolution between f8 and f11. So, without question, there is some sharpness loss by even f16. And almost certainly this is due to diffraction.

It is interesting to note that the newer Sigma 150 macro lens and the announced Zeiss lenses do not even have a physical f32 on their aperture ring.

The fact that diffraction may reduce both the sharpness of the Micro-nikkor and the Zeiss lens by the time I would be shooting at f16 or f22 does not mean that both would then give the same resolution. Both may have their sharpness reduced. But both may not have their sharpness reduced to the same absolute degree. And if the Zeiss starts out with 30% or 40% higher resolution, it still may deliver better resolution. And that is why I would want to do my own tests that mirror the types of uses I would hope to use the lens under.

Theory is great. And I do try to use it as a starting point in my tests and my shooting. But I also beleive there is no substitute for Real World application. And as I did say initially, I would spend the big bucks Zeiss is putting on the lens ONLY if I could see a significant difference under the conditions I want to use the lens.

I did similar tests comparing my older 105mm Micro-nikkor and the new image-stabilized version, at 1:1 and 2:1, and at all apertures from f8-f32. And could not see any real difference in sharpness using the D2X. And for that reason did not buy the new lens at that time. However, it was a fairly quick test and not under as perfect conditions as I would like. So I will repeat the test, and on film, when I get the chance.

But thanks for your thoughts on this whole subject.

Fred