Separate camera lens/body

 

<p>Hi all. I have a Canon 7D camera and a Tamron 17-50mm lens. I am working on a project that requires me to separate the Tamron lens from the camera body by approximately 3 inches and still be able to capture in-focus photos.</p>

<p>My question is as follows: is there a way to focus the light coming out of the back of the separated lens so that the image produced by the Canon 7D is as in-focus as an image produced when the lens is attached normally to the camera?</p>

<p>Thanks for your help.</p>

 

 

<p>I assume you've never used a bellows-mounted lens or extension tubes, or you would already know the answer to your question. Read up on the use of extension tubes for macro photography and I think you'll figure it all out. Since this sounds like a homework project, I don't think it would be a good idea to tell you more than that.</p>

<p>Thank you for your response Craig.</p>

<p>This is not a homework project. This is something that I am working on in my spare time in collaboration with several other photographers. We have of course looked into using bellows and extensions tubes as part of our rig, however, it is not our goal to take macro photographs. Rather, we would like to capture exactly the same image (zoom, focus, DoF) as if the lens was attached to the camera body normally.</p>

<p>Does this make sense?</p>

<p>Again, thanks for your help.</p>

<p>Thanks for the clarification. If you simply move a 17-50mm lens three inches (76mm) away from the camera body, I think you would need corrective optics to get <em>anything</em> in focus. I should have realized that problem when I first read your post -- that's a long, long way out for a lens of such short focal lengths.</p>

<p>If you care to explain more about what you're trying to do, perhaps someone will be able to suggest a different approach.</p>

<p>I unfortunately cannot be more specific about what we are trying to accomplish outside of moving the lens away from the camera body by approximately 3 inches.<br /><br />Do you have any suggestions for where I could find more information about corrective optics that may suit our purposes?</p>

<p>Unfortunately, no. I've never been in a situation where I had to put additional optics (other than a telecoverter, which isn't what you want here) between the camera and the lens. Perhaps someone else will have some ideas on this?</p>

<p>What you are looking for is effectively a 1X tele-converter. Try looking at some optical setups of tele-converters for what type of lenses you need, comparing 1.4 and 2x ones will give you an idea of what you need, you will just require less magnification.</p>

<p> </p>

 

<blockquote>

<p>I unfortunately cannot be more specific about what we are trying to accomplish outside of moving the lens away from the camera body by approximately 3 inches.</p>

</blockquote>

<p>The laws of optics, not just some technicality or 'power of the will,' are what you are up against here.<br>

It would be possible to take the lens out 3 inches, and then optically correct the image so it would be the same as with the lens on the camera. But why? What else are you planning to put into the 3" gap?</p>

<p>JDM von Weinberg,<br>

I cannot be more specific as to why we are doing this. I am sorry. Do you have any suggestions on how to optically correct the image?</p>

<p>Unless all you have between the lens, the correcting optics and the existing image plane is air, you will have to correct for that as well. A 0.15mm thick optical flat glass plate will affect the focusing.</p>

<p>Sure, toss away that lens and get an old 100mm long focus (not telephoto) lens. Then the lens will be far enough from the sensor but an image will still form. Use longer optics if you want an image to form.</p>

<p>Better yet, why not take your first shot and then Photoshop the 2nd image you want into the sensor. Or, as we did in the old days, sandwich the negatives together to put two images in the same photo.</p>

<p>I am totally baffled by the statement that reads " I cannot be more specific but the lens has to be<br>

removed 3" from the body.<br>

1) when the lens is 3" from the body, it will only focus much closer than<br>

normal. the diaphram will not open and close and if the camera is auto focus as that is not connetec.<br>

what you will have is a manual lens and since it is a many element zoom lens it will not work as well and a much simpler lens.<br>

best suggestion is to get a folding camera or enlarger lens with a 50 or 75 or 100 mm focal length and attach it to a bellows<br>

this will give you a sharp clear image and enable you to take all kinds of close-ups.<br>

the longer focal lenths will be better and easier to deal with.<br>

many years ago 35mm cameras had REAL macro lenses that mounted on the body and allowed 1:1 ( life sized) or2:1 half life sized. with a lens and bellows on the front of the camera you may be able to do 2:1 twice life size or more.<br>

I cannot understand the fixation on the 3" spacing.</p>

 

 

<p>Bob Sunley: For all intents and purposes, you can assume that the space between the lens, corrective optics and camera sensor is filled with air.</p>

<p>Tom Cheshire: We would like to be able to shoot fairly wide with this rig. 50mm or wider is our goal. I do not understand your statement about Photoshopping an image onto the sensor. Could you please explain?</p>

<p>Walter Degroot: The 3" spacing is an established technical limit for this project. The spacing could be more than 3" but it cannot be less. I am aware that the auto focus and diaphragm will not function normally. As I explained before, the goal of our project is not to capture macro images. Rather we want to capture the exact same images that the camera would get if the lens was attached to the body normally.</p>

 

 

<p>I appreciate all of these good questions. Does anyone know where I could find more information about corrective optics that might work for this project? Is what I am asking even possible?</p>

<p>If the only tools you have are camera and lens then I can't see a solution.<br>

However you could try experimenting with a pinhole on the camera body:<br>

Make pinhole in lens cap using usual methods; mount lens 3" away and see what you can capture.<br>

Additionally you could insert (in gap) a piece of ground glass, focus the image from the lens on that and capture the image.<br>

Haven't a clue if it would work. But it might.<br>

~Laurence</p>

 

<p>Yes its possible, and if you have a decent budget to cover the cost of a one off optical assembly, these folks may be able to help. http://www.rolyn.com/</p>

<p>Your image will be somewhat degraded due to any added mirrors and/or optics, there is a reason why most high quality teleconverters are mostly glass inside the housing. If you need a 3" clear space in this system, you might need two groups of optical elements.</p>

 

<p>I don't think it's even possible to do this with "air" between the lens and camera. Your 3" probably needs to be taken up with a really complicated optical assembly to capture, refocus and reduce the image. The light coming out of the back of a lens is expanding. And all of those corrective optics are going to wind up with a terrible image, low contrast, bad corner sharpness, all kinds of bizarre optical abberations etc. <br>

I don't think it's worth using your lens. If you really need the space then you really NEED a lens designed for a camera that has that space. That means you need to invest cash into a wide angle lens for a medium format camera. You need to look for lenses for 6x6 or 6x7 cameras... the 6x7 cameras would give you more room. Maybe look into Pentax 67 lenses?</p>

<p>http://en.wikipedia.org/wiki/List_of_lens_mounts</p>

<p>Here's the 45mm f/4 at the STEAL price of $500:</p>

<p>http://www.google.com/products/catalog?hl=en&expIds=17259,18167,20782,24472,27147,27491,27556,27642&sugexp=ldymls&xhr=t&q=Pentax+67+wide+lens&cp=19&um=1&biw=1103&bih=624&ie=UTF-8&cid=16655809107762740110&ei=U6IOTdq_M4O78gaoiLXrDQ&sa=X&oi=product_catalog_result&ct=result&resnum=4&ved=0CFkQ8wIwAw#</p>

<p>Nick,<br>

You will need to do some reading and experimentation, I think.<br>

I have a similar need for correcting optics for a project and I found that there isn't much easily digested info on optics on the net, but I think sometimes the practical approach is as good as a theoretical one.<br>

There's a great source for lenses here - <a href="http://www.surplusshed.com/lens.cfm">http://www.surplusshed.com/lens.cfm</a><br>

Sounds like you might be able to use a Barlow lens to increase the focal length of your lens:<br>

<a href="http://en.wikipedia.org/wiki/Barlow_lens">http://en.wikipedia.org/wiki/Barlow_lens</a></p>

 

<p>The rest of you remind me of the three shoe-repairers that outright refused to modify my boots to fit under skinny jeans. I lost my patience, went home and did it myself.<br>

;P</p>

<p>Laurence Olver: We have tried using the pinhole technique and have been unsatisfied with the results. The problem inherent to pinhole cameras is that the light loss is extreme. Using longer exposures to correct for the light loss is not an option. The idea of using ground glass to produce an intermediate image is an interesting one that we may look into more.</p>

<p>Bob Sunley: Thanks for the information and the link. The idea of using two optical elements combined with Laurence's ground glass idea might work. The less glass the better though. I would like to be able to do this with as few elements between the camera and lens as possible.</p>

<p>Patrick Dempsey: Using a medium format camera for our project would take us way over budget. Even if the image coming out of the corrective optics is terrible, I would still like to know how to achieve that terrible image that has close to the same zoom level and focus. I am skeptical that we will be able to get this to work, but we think it is worth trying our best to make it happen.</p>

<p>Seth: We too have been frustrated with the amount of information on the Internet about this topic. We have read through academic articles, physics books, and consulted with an optics professor who gave us some lenses to work with. The lenses he gave us were Barlow lenses, though he did not refer to them as such. Your links are quite useful. Thanks!</p>

<p>Nick,<br>

The telephoto page on wikipedia is useful too. Perhaps something like a retrofocus lens (halfway down the page) is closer to what you want.</p>

<p>One last link and I'm done:<br>

<a href="http://www.rondexter.com/library/retro_focus_and_tele.htm">http://www.rondexter.com/library/retro_focus_and_tele.htm</a></p>

<p>Seth: This appears to be exactly what we want! Do you have any information about where we could purchase a retrofocus lens with a back focal distance of 3 or more inches? Thank you so, so much for your help.</p>

<p>Look at the bottom of this page.</p>

<p>http://en.wikipedia.org/wiki/Lens_mount</p>

<p> </p>

<p>The problem with any of those is you still won't get 3 inches between your camera flange and the back of the lens.</p>

<p>Retrofocus lenses are only made when they have to be used, ie, like a 21mm lens on a 35mm SLR with a flange to image plane distance of 45mm or so. They are an order of magnitude more difficult to design and manufacture than a normal lens. </p>

<p> </p>

<p>Nick,<br>

I'm not sure you will find something off-the-shelf but if you do some figuring on paper and get some kind of ballpark figure for what you want, then you can probably come up with something.<br>

Have a look at the description of wide angle lenses on wikipedia, especially the wide-angle/retrofocus info.<br>

I'm starting suspect might find a wide angle lens you can mount onto the front of your Tamron.<br>

If it was my task, I'd make my mount or lens tube so the Tamrom is mounted that extra 3 inches away, then try and get a feel for what you need by experimenting with various lenses. Get an old pair of binoculars, for example, or a damaged zoom/wide-angle lens that you can pull the elements from.<br>

(And try to ignore the people that tell you that you can't do it ;)</p>