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 Replies: 528 / Views: 87,234 |
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Pillar of the Community
United States
4132 Posts |
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Pillar of the Community
  United States
4038 Posts |
Contact me for photographic equipment or visit my home page at: http://macrocoins.com |
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Moderator
United States
23522 Posts |
Already gone. I'd have been on that so fast your head would have spun. If I'd seen it in time.  |
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Pillar of the Community
United States
4038 Posts |
So, does that mean you bought it? Good going if you did. I have a couple of these and they're pretty good lenses.
Contact me for photographic equipment or visit my home page at: http://macrocoins.com |
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Moderator
United States
23522 Posts |
No, somebody else got it.
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Pillar of the Community
United States
4132 Posts |
A longer lens would reduce the minimum magnification of my setup, correct? If so, let me know if you spot any el-cheapos in the 105mm range. I can't get whole-coin images of large dollars currently - I just barely can't get my camera on the bellows without the extension. I could remove the bellows entirely, but that's not ideal either. I see El-Nikkors pretty often, but they go for more than I currently want to spend on something I'm going to be using pretty infrequently.
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Pillar of the Community
United States
627 Posts |
Captain, is this limitation the amount of height you are able to get above the coin? With the Pentax autobellows built in focus rail extended together with your microscope stand that Ray built, you should be able to get high enough to fit a Morgan dollar on the T2i sensor using the 75ARD1. Are you extending the focus rail of the pentax bellows? |
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Pillar of the Community
United States
4038 Posts |
For the Pentax Auto Bellows, you will likely need to remove all extensions to get full Dollar shots with the 75mm lens. This causes two problems:
1) You will only be able to mount the camera in "normal" orientation, ie with bottom of camera facing the bellows
2) You won't be able to rotate the camera on the bayonet mount for mounting/dismounting. Remove the bellows lens mount, mount to the camera, then attach entire assembly to the bellows
I do look for longer lenses to put in this El-Cheapo thread, though I must admit I'm biased toward 75-80mm due to ease of application on the B&L Stands. 105mm lenses greatly increase the height of the camera mount since they require a longer extension plus longer working distance, both of which force the camera to rise.
A good alternative for longer working distance but with similar quality to the 75ARD1 is the 90ACHM (90mm Schneider-Kreuznach Apo-Componon HM) but this one will cost you around $400. It's not a duplicating lens, but is optimized well for 1:2 and thus is good for Dollars. Definitely not El-Cheapo though.
Potentially in the El-Cheapo category is the Vivitar 80mm VHE lens. Even that extra 5mm focal length can make a big difference in magnification and yet not push the camera up too high. I've seen 80VHE's go for <$30 so are a good one to look out for. They often have bad haze, though and are not that easy to clean.
Contact me for photographic equipment or visit my home page at: http://macrocoins.com |
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Pillar of the Community
United States
4132 Posts |
I can extend it plenty high enough to focus (and well beyond) - the problem is actually a difference in the shape of the camera body between the T2i and the T3i. One of the spots where the T3i is slightly thicker happens to bump into the frame of the bellows unless the extension is in there, even in "normal" orientation. If I had a T2i it would fit. It's actually a matter of about 1-2mm, so I could actually probably shave that much off the bellows with a Dremel. Maybe I could get away with a really short extension tube, or even putting some sort of big washer between the adapter and the bellows. Here's a side-by-side comparison of the two cameras. See the extra 2mm in height below the bottom of the lens? That's what's killing me. Anyhow, the result is that I have to leave the extension tube in, which means the minimum magnification I can achieve won't frame a dollar. The reason I was thinking 105mm, is because I want to maximize my range. I might want to image American silver eagles, and they're a bit bigger than dollars. Do you think a 80-90mm would work for coins that big? I get a lot of extra focus range because of the focus rail on the bellows, so 105mm should still work I think. Edited by CaptainFwiffo
08/06/2012 2:42 pm
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Pillar of the Community
United States
627 Posts |
As Ray mentioned, the 105mm really puts your camera way up in the air. I use an 80mm EL-Nikkor lens that I like a lot when I need just a tinge more diameter flexibility than the 75ARD1 will give me. I wasn't aware of that very small difference in the T2i and T3i...that's a bummer. Another method I have had to resort to was taking multiple images and then using the stitch software that comes with Adobe Photoshop to combine them in the "Panorama" mode. For example, the medal below (60mm diameter) is a combination of 4 images of each the obverse and the reverse (8 total images) taken with my 75ARD1 and stitched together in Adobe Photoshop. This is not a method I would recommend as a sustainable processing workflow, but it was sufficient for the occasional large medal I want to image.  |
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Pillar of the Community
United States
4038 Posts |
Interesting, I thought they were the same...
90mm should work fine, and I'd bet on 80mm being OK as well. 105mm should allow you to go to a much larger field, like slab size or larger.
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Pillar of the Community
United States
4132 Posts |
It's a pretty small difference between the cameras, it's actually sort of an amazing accident that it is even a problem. Another bellows, or even a different M42 to EOS adapter could give enough clearance. I found a really cheap set of M42 extension tubes, and maybe one of them is short enough to let me fit a dollar while giving me the extra hair of spacing that I need. I might even get away with some sort of crude shim.
Is there a formula I can use to get the field of view for a given focal length if I know the FOV for my 75mm lens at my minimum extension?
How do you avoid getting seams in the panorama of the medal? Since you have to move the coin about, isn't it going to be moving relative to the light source, thereby having different highlights and shadows in each image? Or do you somehow move the lights and the medal together?
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Pillar of the Community
United States
4038 Posts |
The formula for magnification is: M = (TE - FL) / FL TE = LE + BE + CRD Where: M is the magnification TE is the total extension LE is the lens extension, which can be positive or negative BE is the bellows extension CRD is the camera register distance FL is the focal length of the lens For Canon cameras, the CRD is 44mm. Here is a link to CRDs for about all cameras ever made: http://www.graphics.cornell.edu/~we...egister.htmlFor the 75ARD1 the LE is 13.3mm. You can deduce this from the data sheet: http://www.rodenstock-photo.com/med...62__8230.pdfNote that infinity focus is a magnification of zero and happens when the total extension is equal to the focal length. So for infinity focus, you need a TE = 75mm. The BE for this is then 75 - 44 - 13.3 = 17.7mm, impossible to achieve with any bellows. To fill the sensor with a Dollar, you will need a magnification of 14.9 / 38 = 0.392, so your TE needs to be 104.4mm, thus BE should be 47.1mm. |
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Pillar of the Community
United States
4132 Posts |
OK, measuring my magnification based on taking a picture of some graph paper at minimum extension, I get about 0.45x. Doing the math backwards gives me a TE of about 109mm. The extension tube seems to be 14mm. A 9mm tube instead would get me to a dollar.
A magnification of 0.367 (14.9 / 40.6) would let me get in a silver eagle, which is a TE of about 102.5mm. I should manage that with a 7mm extension tube, which is in the set of tubes I have coming. Google suggests that 5mm M42 extension tubes exist.
I only have about 2-3mm clearance between the camera grip and the bellows rail, so I won't have a choice of orientation with the shorter tube, but I'd only need to use it for the largest coins, which is going to be the minority of what I'm shooting.
Where did you find the lens extension in that PDF?
Edited by CaptainFwiffo
08/06/2012 8:32 pm
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Pillar of the Community
United States
4038 Posts |
On page 60, the "flange focal length" (which is equivalent to CRD + BE) is given as 136.7mm for M=1. Knowing the TE must be 150mm for M=1 gives 13.3mm for LE.
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Posted 07/25/2012 10:13 am
