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Old Sep 27, 2003, 3:35 PM   #11
kex
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Quote:
Originally Posted by richardh
I have been leed to believe that +1 or +2 gives very little magnification on prosumer digital cameras due to the smallers lens systems and ccd's. It might be beter to get a +10 or a +7/+10 set. I would try to find some example pics on a digital before I made a decision if I were you.
Just as an example, I have a slr lens that I reverse on my a70. I have been told that is either equivalent to a +20 or +27. Take the amount of magnification that you see here ant take 1/20 of that for a +1 filter. It does not seem like much improvment to me.
The 2 wide angle shots were with the a70 with no add on lens. The other 2 are with the reversed slr lens.
http://www.pbase.com/richardh/slr_macro

thanks for your answer, richard.
can you explain me what a "slr lense" is?
Your pictures look very good with that lense!
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Old Sep 27, 2003, 4:13 PM   #12
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Single lens reflex. In other words it is a lens for a slr film camera mounted backwards using a macro coupler. If you are not farmiliar with slr cameras, they are the high end of cameras. The do not have any lens on them. You switch lenses to the type you want to use. As film slr cameras are not new like digital cameras (been around for a long time), There are lots of used lenses out there. I am not sure about avalability or pricing there but in the US macro coupler rings are under 10$US and you can get an appropriate slr lens for 20-40$US used. They are avalable here in used camera shops, pawn shops etc., and of course there are plenty on ebay. There are at least a half dozen low priced slr lenses of the appropriate type on ebay at any given time.
If you are farmiliar with slr's at all, you want a lens that is f1.2 (harder to find) or f1.4(more comon). The pic I posted was with a f1.8 lens but I have to go to full optical zoom to avoid vinyetting. I would suspect some f1.8 lenses might vinyette some. You want a lens that is 50mm (that is the focal length, not a thread size). You mount the lens backwards from what it was originally intended using the filter threads on the front so you want appropriate filter threads on the lens.They make macro coupler rings to go fro 52mm to many diffrent sizes so you could probably use several filter thread sizes (49mm, 52mm, 55mm, 57mm etc.). I would imagind some may be to small to work or too big to be practical but anything close to 52 should work.
Do a search on reversed slr and you will probably find info or I can try to answer some questions after work if no one else answers them first.
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Old Sep 27, 2003, 4:21 PM   #13
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thanks for your very good explaination!
I'll search some forums about "reversed slr lenses" and I'll probably consider to buy such a lense instead of a macro lense set.
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Old Sep 28, 2003, 1:46 AM   #14
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Quote:
Originally Posted by kex
I'll search some forums about "reversed slr lenses" and I'll probably consider to buy such a lense instead of a macro lense set.
Reversing a SLR lens, in theory, means the SLR lens becomes a high diopter close-up lens. Here is the most basic concept. If your on-camera lens has longest focal length of X and the SLR lens to be reversed has a focal length of Y, then the magnification of the combo is X/Y. For example, the Canon A60 has maximum focal length 16.2mm (use the actual focal length rather than its 35mm equivalent) and a 50mm SLR lens is mounted reversely, the magnification is 16.2/50=0.324X, which is not so great. In fact, a set of better close-up lenses can easily achieve this magnification. Another drawback in using reverse-mounted SLR lens is that if the SLR lens is not flat-field, you will likely only get the center portion sharp and the edge portion blurred. One may stop-down the reverse-mounted SLR lens to improve this situation, but light-loss may be a significant problem. Moreover, if the focal length of the camera lens is too short (like the Canon A60 example above), vignetting will occur. Normally, for good results, one choose a long focal length good quality on-camera lens, and a good flat-field SLR lens reversely mounted. Thus, those long zooms will definitely have an advantage, and I suspect your A60 with a 50mm SLR lens is very likely to vignette. Moreover, since good flat-field SLR lenses are not cheap, I would really suggest to go with close-up lenses. Note that higher diopter close-up lenses share the same problems when using reverse-mounted SLR lens minus vignetting.

This link gives you some initial thought of the reverse-mounting idea, although the magnification estimates are not very accurate because actual image sensor sizes are not used. However, the error rate is not significant.
http://forums.dpreview.com/forums/re...essage=4967574
The "TC-E2 for Close-Up?" page in the "Odd Stuffs" section of my Coolpix 990 user guide shows you the vignetting problem when a 50mm lens is mounted on a Nikon Coolpix 990 (max. focal length = 115mm - 35mm equivalent) plus a 2X teleconverter (to increase the focal length of the on-camera lens to 300mm+).


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Old Sep 28, 2003, 11:06 AM   #15
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I don't mean to argue with you here so please don't take it that way. You seem to be more knoledgable about this than I am. A couple of points though (and perhaps a few questions). I use a reversed slr lens with my a70 which shares the same lens system as the a60 so this should directlly translate. First of all, this is how much extra magnification you would get (I know the focus isn't that great, I just took these shots quick to demonstrate the magnification to someone in the past and it's a pain to upload new shots with dialup).
http://www.pbase.com/richardh/slr_macro
I have had a hard time finding a definative answer on how this translates to a diopter value. I have heard from diffrent sources that it is either +20 or +27. As you seem to know that math behind it, could you please help me out here?
As far as vinyeting goes, I have been leed to believe that it is a function of the apature of the slr lens. The larger the apature, the less vinyetting. The distance from the filter threads to the lens also plays a smaller part. The shots I linked to were taken with an f1.8 lens. I always recomend a f1.4 or f1.2 lens to be safe. Does that sound about right or is their a flaw in my logic?
You mention diffrences in slr lenses. I have very little knoledge about slr lenses. The lens I have is an olympus om-system f.zuiko auto-s 1:1.8 f=50mm 730019. Is this a decent lens (I paid 20$)? The only way I would sugest that this would be cost effective is if you got a good price on a used lens. there are tons on ebay cheap. I have the advantage of living near one of wolf/ritz's two national clearance centers that gets everything from all the other stores. One good one I saw recentlly when looking at them on ebay was a nikon nikkor f1.4 50mm (I don't remember the rest of the details). It had a problem with the apature sticking but would stay wide open just fine and the glass was in good condition. It sold for 33$. Obviouslly this lens was a lot more expensive new. How do I tell if it is a flat field lens by the way?
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Old Sep 28, 2003, 10:21 PM   #16
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Kex, I ran across an exelent comparison (power wise) between the lower power macro lenses and a reversed slr lens.
http://www.pbase.com/jmovich/macro_comparison
These were taken with an a60.
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Old Sep 29, 2003, 5:28 AM   #17
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Quote:
Originally Posted by richardh
I have had a hard time finding a definative answer on how this translates to a diopter value. I have heard from diffrent sources that it is either +20 or +27. As you seem to know that math behind it, could you please help me out here?
Adding a diopter X close-up lens in front of a camera lens of focal length F yields magnification M as follows:

M = X * (F/1000)

Thus, adding a +3 and +10 diopter to the A60, which has a maximum focal length 16.2mm, yield magnification of M=3*(16.2/1000)=0.05X and M=10*(16.2/1000)=0.16X. Thus, when using close-up lenses, the longer the focal length a camera has, the higher magnification we can get. The reversed SLR lens of focal length X becomes a close-up lens of diopter 1000/X. Thus, the reversed 50mm and 24mm lenses become close-up lenses of diopter values +20 and +42. Thus, the shorter the focal length of SLR lens, the higher the magnification you can get.

However, keep in mind that the above formulas are intended for "theoretical" study because it is based on the assumption that all lenses are calibrated at infinity and the gap of the close-up lens and the on-camera lens is very small that can be ignored. In reality, we do not do close-up by setting the lens to infinity, and the gap between the close-up lens and the camera lens is normally much larger than this theoretical assumption.

Quote:
Originally Posted by richardh
As far as vinyeting goes, I have been leed to believe that it is a function of the apature of the slr lens. The larger the apature, the less vinyetting. The distance from the filter threads to the lens also plays a smaller part. The shots I linked to were taken with an f1.8 lens. I always recomend a f1.4 or f1.2 lens to be safe. Does that sound about right or is their a flaw in my logic?
You are partially right. Vignetting indeed depends on the aperture; but, we normally shoot wide open to gain more light. Vignetting actually comes from the view angles of the reversed lens and the on-camera lens, and the gap between them. The reversed lens projects an image for the camera lens to pick up. Thus, if the gap is too large, the projected image may be smaller than the view angle of the camera lens, and vignetting occurs. Most SLR normal lenses, especially those micro/macro lenses, may have their front glass elements recessed or even deeply recessed. This will increase the gap and cause vignetting. Of course, when the reversed lens is stepped down, the projected image becomes smaller, which also causes vignetting. As mentioned above, most people set the reversed lens wide open to gain more incoming light intensity.

The F1.2 or F1.4 lenses may not be as good as a F1.8 len, because the former, when shooting wide open, are not as good as a smaller aperture lenses. In Nikon world, people like to reverse-mounting a 24MM F2,8 to a 200MM F4 to get a 200/24=8X magnification. The F1.4 and F1.2 lenses may be too soft when shooting wide open.

Quote:
Originally Posted by richardh
The lens I have is an olympus om-system f.zuiko auto-s 1:1.8 f=50mm 730019. Is this a decent lens (I paid 20$)?
I have no knowledge whatsoever about the Zuiko lenses. However, a flat-field lens is preferred. Simply speaking, a flat-field lens is a lens that projects a flat subject (e.g., a planar subject) that is perpendicular to the lens axis onto the film plane completely. Normally, this is a required optic condition for good normal to wide angle lenses. The lens document should have this stated clearly. As for Nikon system, the 20mm F2.8, 24mm F2.8 and 28mm F2.8 all have the flat-field feature (Nikon calls it CRC-close-range correction), and this is the reason that many people prefer to reversely mount the 24mm on a 200mm. The 50mm F1.8 is another good choice for digital because the on-camera lens of a typical digital camera is not long enough to use the 24mm. The 50mm F1.8 is cheap and costs about $100.00 for an important version. Thus, if you can find a Nikon 50mm F1.8, give it a try.

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Old Sep 29, 2003, 11:56 PM   #18
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Thanks for the information.
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Old Sep 30, 2003, 12:25 PM   #19
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thank you all for your posts and explainations on reversed slr lenses, macro lenses and so on.
I decided to wait with buying a macro lense.

Two days ago I found my old field glasses.
I screwed the lenses down and taped them together.
when I hold them in front of the cam. it makes really good pics, but I'm still trying some things out. it's not that bad at all.
the pic tooth pic picture in the close-up forum for example was taken this way..

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