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11-10-2010, 05:56 PM   #16
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QuoteOriginally posted by Damian Quote
Your link isn't working. Can you try and re-post please.
never mind. I guess my computer was having an issue.

11-10-2010, 07:41 PM   #17
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i've just spent my evening trying out combinations of lenses to get the best compromise- I think a 135mm prime with a reversed 28mm gave me a good magnification with an acceptable working distance

only trouble is the 135mm is m42, so manual stop down- maybe this is a good opertunity to pick up a 75-150mm f4 to use with the reversed 28mm


all of a sudden 1:1 doesn't look so 'macro' any more
11-11-2010, 05:07 AM   #18
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QuoteOriginally posted by clark Quote
if money was no object (canon mpe-65 not withstanding), what's the best way to get high magnification with decent light getting into the viewfinder and retaining full or at least partial control over aperture

and giving a decent (i.e. more than 1") working distance with suitable depth of field at f16...

I have the tamron 90mm macro, used a reversed 28mm on it, but mag was only about 3.5:1 and the working distance was about an inch, viewfinder was very bright still. So what combination of extension tube, teleconverters and reversed lenses will give the most magnification with decent optical quality?
(1) Regarding image brightness, simple theory says (and practice confirms):
(1.1) Stacking a large aperture close-up or reversed camera lens in front of a primary lens to get higher magnification has no effect on image brightness.

(1.2) If the added lens has a smaller aperture than the primary lens, image brightness will decrease (the lens with smallest aperture controls brightness.)

(1.3) A teleconverter behind the primary lens decreases image brightness with the square of the teleconverter's power (in effect the TC moves the primary lens away from the camera.)

(1.4) Increasing the distance between lens and camera with tubes, bellows, etc., causes image brightness to fall with the square of distance.

(2) Regarding image quality as measured by diffraction spot size for perfect lenses:
(2.1) Stacking lenses to increase magnification has little effect on resolution (because absolute aperture and distance to the image plane don't change).

(2.2) Increasing the distance between lens and camera with tubes, bellows, etc., decreases resolution in proportion to distance.

The above considerations indicate that with perfect lenses, stacking to achieve magnification is preferable to extension as far as brightness and resolution are concerned (although diffraction resolution is seldom a practical macro problem.)

Unfortunately, perfect lenses are hard to find, so you'll have to experiment with the lenses you have.

Dave

PS Depth of field at constant macro magnification depends only on f-stop. For long working distances you are best off using extension with long focal length lenses.
11-11-2010, 05:22 AM   #19
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QuoteOriginally posted by clark Quote
i've just spent my evening trying out combinations of lenses to get the best compromise- I think a 135mm prime with a reversed 28mm gave me a good magnification with an acceptable working distance

only trouble is the 135mm is m42, so manual stop down- maybe this is a good opertunity to pick up a 75-150mm f4 to use with the reversed 28mm


all of a sudden 1:1 doesn't look so 'macro' any more
With stacked lenses the effective working distance is about the focal length of the added lens, so you should expect about an inch working distance with the 28mm stacked lens. wrong - see below!

if you stacked a 56mm lens on a 270mm lens you'd have the same magnification (4.8X) and twice the working distance. wrong - see below! Also the same brightness if the f-stops are the same.

You'd have to extend the 135mm lens by about 650mm to get the same magnification. The working distance would be around 170mm and the image would be 33 times dimmer.

Dave

EDIT: above I said the working distance for a 28mm lens reversed on a primary lens would be about 28mm; this is wrong. It would be true for reversing a simple lens like an enlarger lens, but a camera lens is designed so the distance from the rear of the lens to its focal point is equal to the camera's registration distance. For Pentax cameras this distance (from the lens mount to the image plane) is 45.46mm, 1.78".

Hence any Pentax lens reversed on another primary lens will have a working distance a little more than 1.5" or about 40mm when the aperture lever etc is considered.

Sorry if I misled anyone,
Dave



Last edited by newarts; 11-13-2010 at 05:21 AM.
11-11-2010, 07:05 AM   #20
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There is another option. I just posted a thread about it a couple of days ago, I've used it all summer.

Binocular Lens Macro Rig

All you need is a lens with 49mm filter ring and a junk pair of 10x50 binoculars. I find them for under $5 in resale shops and yard sales pretty frequently. Picture quality? Take a look at the link. Working distance 4-6 inches. I can't see a noticeable difference in brightness.
11-11-2010, 12:16 PM   #21
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New to Macro

I have just recently put my simple macro kit together. Reversing adaptor 52mm with a 49mm stepdown ring. Bought on fleabay a 50mm f1.9 Chinon. This fixed focus system focusses at about 75mm. The DOF at f1.9 is small, needs to be shut down to f8 for anything usable. magnification ratio about 1:1.

Just started to play, hand held is just about possible, but tripod will be needed in most cases.
11-11-2010, 08:06 PM   #22
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QuoteOriginally posted by newarts Quote
The above considerations indicate that with perfect lenses, stacking to achieve magnification is preferable to extension as far as brightness and resolution are concerned (although diffraction resolution is seldom a practical macro problem.)

Unfortunately, perfect lenses are hard to find, so you'll have to experiment with the lenses you have.

Dave

PS Depth of field at constant macro magnification depends only on f-stop. For long working distances you are best off using extension with long focal length lenses.
thank you, I think i'm slowly getting my head around that

QuoteOriginally posted by newarts Quote
With stacked lenses the effective working distance is about the focal length of the added lens, so you should expect about an inch working distance with the 28mm stacked lens.

if you stacked a 56mm lens on a 270mm lens you'd have the same magnification (4.8X) and twice the working distance. Also the same brightness if the f-stops are the same.

You'd have to extend the 135mm lens by about 650mm to get the same magnification. The working distance would be around 170mm and the image would be 33 times dimmer.

Dave
thank you, that clears a lot up.

I'm running a canon and a pentax system, the 90mm macro I use is canon mount- but i'm thinking of taking it back to the shop for a refund.
A pentax 70-210 with a reversed 28 would be a good macro setup I think- but optical quality might not be as high as the tamron macro. I'm thinking that a 2x tc on the tamron will give me 2:1 at the same WD as I get now (i.e. 5"), and then a reversed 50 on the front? The 28mm reversed in front of the tamron gives me more working distance than a 50mm, but the 28 doesn't fill the whole frame, i thought it might be because it's f2.8, but I tried a 28mm f1.8 and that didn't fill the frame either
11-11-2010, 10:03 PM   #23
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I used an M 28/3.5 reversed on a 52 > 49 step down ring and a 52mm lens mount reversing adapter to get 2.1:1. The working distance is the registration distance of the camera (43 + mm), which sure isn't much, and the depth of field is tiny. The quality of the image is superb.

The rig won a court case for a friend of mine who had an expensive ring ruined by a jeweler resizing it. I took the picture with the reversed kit on Fuji 100, and she enlarged the negative to get an 8x10 print. The file gouges that were the problem looked like plow furrows. She showed up, made her complaint, showed the snap and the jeweler folded.

11-12-2010, 08:02 AM - 2 Likes   #24
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Here's my suggestion for a reversed "stacked" setup. Get yourself an old parfocal slide zoom (with the 'a' on the aperture ring) and reverse and old fast prime in front of it.

The slide zoom needs to be the type that does not change in length as it is zoomed. Like an old Kiron or Vivitar series one, but there are plenty of other brands out there that will work as well. The reason I mention Kiron or Vivitar is that they are known to be decent lenses from that time period. It has to be a parfocal (a lens that stays in focus while the focal length - zoom - is changed) for this to work properly. Preferably something with a zoom lock so it doesn't creep on you when you get everything just right.

The prime doesn't even have to be one you can or would use on your camera. I have and old non-Ai Nikkor 50 f2 that I use for reversing. It doesn't have to be a 50, you could use any of the myriad of 28 f2.8's out there if you can find one cheap enough. Just something that is sharp, fast and considered to be 'good glass'. It could be an old Tak, or M42 mount or another lens brand or mount all together.

Now here's the why behind all this. The beauty of this setup is that you can set up your reverse macro, zoom all the way in and get the focus just right, then pull the zoom back (widen) to get the composition you are looking for and still have everything perfectly in focus. Basically, if you find that you are too close, and there is not enough interest at 4:1 or whatever, you can back out to 3.5:1 or 2:1 or anywhere in between. All the while keeping the subject in focus. Since it's a non-extending zoom, you can zoom in and out all day long without having to move your rig back and forth. Once you nail the focus, you are set to try multiple magnifications all you wish.

Don't forget the reversing filter thread adapter and any step up or down filter rings you might need to make this work.
11-12-2010, 04:19 PM   #25
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QuoteOriginally posted by Clark:
A pentax 70-210 with a reversed 28 would be a good macro setup I think.
You'll find it difficult to use; the minimum magnification will be about 70/28=2.5 and the max mag above 7.5. Such magnifications are very difficult to work with - you'll need good focusing rails and precision sample stages.

I recommend you get more experience with something like the 50-135mm with reversed 50mm before going to higher magnifications and shorter working distances.

To get an idea of the difficulties, at 5X mag and F10 aperture you can expect a depth of field of around 1/10mm. That's why microscopes are used at such magnifications - they can be reliably moved in such small increments.

Dave
11-13-2010, 05:07 AM   #26
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Earlier I said the working distance for a 28mm lens reversed on a primary lens would be about 28mm; this is wrong. It would be true for a simple lens like an enlarger lens, but a camera lens is designed so the distance from the rear of the lens to its focal point is equal to the camera's registration distance. For Pentax cameras this distance (from the lens mount to the image plane) is 45.46mm, 1.78".

Hence any Pentax lens reversed on another primary lens will have a working distance a little more than 1.5" or about 40mm when the aperture lever etc is considered.

Sorry if I misled anyone,
Dave

PS this may be reason to prefer using a good close-up lens rather than a reversed camera lens. For example, the Raynox 250's focal length is 125mm, so has a working distance about 125mm, while a reversed Pentax 135mm lens has a working distance of about 40mm, even though both lenses have a similar effect on magnification.

From a working distance standpoint, a close-up lens will have a greater working distance than a reversed camera lens on a primary lens for close-up lens focal length greater than about 45mm (Dipoter strength less than ~22).

Last edited by newarts; 11-13-2010 at 06:29 AM.
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