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Alt Lens FAQ

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p.1 #1 · p.1 #1 · Alt Lens FAQ

I noticed this post by AhamB suggesting that we need some alt lens "sticky" posts to answer common questions. That seems like a good idea to me, but since no one else has posted one yet, here is my attempt at a FAQ outline mainly focused on alt lens usage on DSLRs. Please post your comments/criticisms/suggestions below, and I will attempt to edit/revise this post to incorporate them. Each item in this FAQ could be (and often has been) the topic of a long and complex thread; however, for an introductory FAQ, one needs to balance the merits of brevity against encyclopedic completeness; please keep this in mind when complaining about whatever fine details and unusual exceptions I have left out. Links that I can include to other informative threads on the alt lenses board to better describe the details would probably be most useful. Apologies in advance for typos, inconsistencies, and major missing sections. Perhaps if we can collectively edit this into a sufficiently useful and informative post, it can get "stickied" by some higher power on the board and save several of us the time of re-typing these answers every few weeks.


This FAQ is meant to address common questions and issues about using "alt lenses" on DSLRs.

What are "alt lenses"?
"Alt lenses" mean alternatives to the major Original Equipment Manufacturers' ("OEMs", e.g. Canon, Nikon, Sony Alpha) current lens lineups. This can range from third-party autofocus zooms to pinhole cameras. Most of the activity here on the alt lens board revolves around manual focus lenses, many from older and discontinued lens lines, but also a few new manual-focus designs (from, e.g., Zeiss, Cosina/Voigtlander, and Samyang). Even new Nikon lenses can be considered "alt" if used on Canon bodies.

Why use an alt lens?
Alt lenses greatly expand the range of photographic possibilities beyond what the OEMs offer in their own lens lineups. Alt lenses can be less expensive, offer better image quality, or produce images with a unique rendering character that OEM lenses do not. Manual focus lenses are often smaller and lighter than their OEM autofocus counterparts. Some people are also attracted to the history and fine craftsmanship embodied in classic lenses, or like the precise control and smooth handling of a manual-focus-specific lens.

How do I use an alt lens?
For third-party autofocus lenses, operation is identical to native mount lenses. You will likely find more discussion of these lenses on the appropriate Canon/Nikon gear boards.
The "alt" lenses mostly discussed here are manual focus lenses, so you will need to focus the lens by hand. See the sections below on chipped adapters and focusing issues for more discussion. Some currently produced lenses have the electronic contacts needed to allow the camera to automatically control the aperture of the lens (e.g. Zeiss ZE/ZF/ZA lenses for Canon/Nikon/Sony Alpha, or Cosina/Voigtlander SLI/II lenses), so aperture and exposure setting works just like the OEM lenses.

However, many alt lenses require manual operation of the aperture by turning the aperture ring on the lens to the appropriate aperture before hitting the shutter button. The camera metering system also doesn't know what aperture you are using, so you either need to meter once the lens is already stopped down to the intended working aperture, or correct in your head for the correct metering. An easy way to get fairly-automatic metering is to use "aperture priority" metering mode on your camera, where you choose the aperture on the lens and the camera chooses the appropriate shutter speed for the scene right before taking the picture.

What alt lenses can I use on my camera?
A few current alt-lens manufacturers, such as Zeiss, Voigtlander, and Samyang, offer lenses that can be directly attached to popular Nikon/Canon/Sony Alpha/Pentax/etc DSLRs with no additional work. However, many lenses originally designed for other camera mounts may also be usable on your DSLR with minor (or major) additions or alterations.

The most important factor in determining whether you can use a lens on your camera is the "register distance," the distance between the lens mount and the film or sensor plane for the lens' native mount. You can find a fairly comprehensive list of mount register distances here; some of the interesting ones are:

  1. Leica M (rangefinder): 27.95mm
  2. Canon FD: 42mm
  3. Minolta MD: 43.72mm
  4. Canon EOS: 44mm
  5. Sony Alpha: 44.6mm
  6. M42 (Pentax Screwmount): 45.46mm
  7. Pentax K: 45.46mm
  8. Contax/Yashica (CY): 45.5mm
  9. Olympus OM: 46mm
  10. Nikon F : 46.5mm
  11. Leica R (SLR): 47mm
  12. Contax N: 48mm
  13. Mamiya 645: 63.3mm

This sampling explains the popularity of Canon EOS cameras (and the emerging popularity of Sony Alpha) with many alt lens users; with one of the shorter register distances, every mount after Canon EOS on the list can be easily adapted. For lenses with a longer register distance than your camera, there are usually easily available adapters (see section below on adapters) from the lens mount to your camera. For lenses with slightly shorter register distances, it is sometimes possible to convert the lens mount by removing and replacing parts of the original mount (see section below on conversions). For lenses with much shorter register distances, e.g. Leica M on Canon, you're out of luck --- though you can likely use them on one of the increasingly popular mirrorless "electronic viewfinder interchangeable lens" ("EVIL") smaller format cameras.

Even for lens mounts that will fit your DSLR according to register distance, there still may be other protruding parts that can interfere with your camera's mirror. For example, some Contax lenses have a "fin" used to transmit aperture information to Contax camera bodies that might collide with some DSLR mirrors (and may need to be slightly filed down or removed). A few Leica R lenses also have rear elements that extend unusually far back into the camera. The smaller mirror in a crop-format camera is much less likely to cause problems than the full-sized mirror on a full-frame cameras. FM member John Black's Pebble Place review site hosts a database of user reports on camera compatibility for Leica-R and Contax lenses. In order to use a few exceptional lenses that cause problems on full-frame DSLRs, a few dedicated alt lens users even go so far as to grind down their camera mirror to provide greater lens clearance.

What lens adapter should I use?
There are many off-brand adapters available on eBay in the $5-$15 range for a variety of lens types. Such adapters are often "good enough" for most purposes, though adapter thickness and precise fit can be a bit sloppy. Having a variety of cheap adapters around can be handy for initially evaluating a lens before committing to a more expensive, dedicated adapter.

EBay seller Big_IS is a popular source for more reliably accurate adapters; these adapters are also offered in "chipped" versions (see below).

Fotodiox offers a large variety of adapters; their "Pro" adapters are very nicely made.

Cameraquest and Novoflex offer extremely high quality, but also highly expensive, adapters.

Some lenses are pickier about adapters than others. For "unit focusing" lenses, where all the lens elements move together as a group to focus the lens, adapter precision tends to be less important --- variations in adapter thickness will at most effect whether infinity focus occurs at the correct mark on the lens (too thin an adapter and the lens will focus past infinity; too thick, and the lens won't quite reach infinity). For more complicated optical designs, where different lens groups move relative to each other during focusing, having the correct lens-to-sensor spacing can be critical to getting proper performance from the lens. Such lenses might have notably degraded performance on a shoddy adapter (which is sometimes incorrectly blamed on the lens).

What is a "chipped adapter," and do I need one?
Lenses originally intended for other camera mounts do not have the electronic contacts that modern DSLRs use to determine what lens is mounted. This means that the pictures you take will not contain the focal length or aperture of the lens used, and some in-camera functions (such as the focus confirmation beep and viewfinder light on Canon bodies) will not work. Some adapters come with electronic chips (or you can buy glue-on chips) that provide the missing information to the camera body, informing it that a lens is attached with a particular focal length and max aperture. The chips have limited functionality compared to built-in electronics in modern lenses; for example, the chip cannot tell what focal length you are zoomed to on a zoom lens, or what aperture you are stopped down to (although some newer chips allow you to set aperture information manually for each shot, if you remember to do so). The biggest advantage of chips on Canon cameras is enabling the camera's focus confirmation sensor. While you are focusing by hand with the shutter button half-pressed, the camera will beep and flash the viewfinder focus confirm points as it would for an autofocus lens in manual focus mode, which can be very helpful when it is hard to judge focus "by eye" from the focus screen.

What about adapters with glass elements?
Some manufacturers offer adapters with a built in lens element to allow lenses with a shorter register distance than the camera to be mounted and focus to infinity. These adapters act like a weak teleconverter, typically multiplying the lens focal length (and aperture f-number) by ~1.3x. Unfortunately, they tend to be disastrous for image quality. The very cheap and simple optical designs used (often only a single lens element, or at best a cemented doublet) cannot be highly corrected, and typically add heaps of chromatic and spherical aberration. The lens surfaces are often uncoated or poorly coated, contributing to flare and general low contrast. The small size of the lens element acts as a limiting aperture, making fast aperture lenses (with a rear element larger than the adapter lens) fairly useless. Though these adapters are often quite cheap, they are simply not worth it.

What about "macro" adapters?
One final way to adapt lenses with too short a register distance is to go ahead and use a reasonably thick adapter that positions the lens farther from the sensor plane than it was designed for. Such adapters may be sold labeled as "macro" adapters, or can be made by removing the lens from a glass-element adapter. Just like using an extension tube, this prevents the lens from focusing all the way to infinity and decreases the minimum focus distance (hence the "macro" labeling); the extent of this effect depends on the lens' focal length (with wider angle / shorter focal lengths being more strongly affected). How well this works depends on the details of the design of the lens; some lenses (especially those with simple, unit-focusing designs) work excellently on a slight extension, while others do not.

How do I convert an alt lens to use with my camera?
Conversions involve removing the original lens mount and replacing it with one correctly shaped for your DSLR.

Leitax offers a variety of lens conversion kits, including Leica, Olympus, and Zeiss Contax to Nikon and Sony Alpha. Leitax also offers adapters to Canon EOS that screw on over the original mount, which creates a more rigid and precise mount than typical detachable adapters.

FM Forums member Jim Buchanan offers excellent professional lens conversions to Canon EOS mount, including custom adjustment of the adapter for precise infinity focus on each lens.

Contax N lenses (from the short-lived Zeiss autofocusing Contax N system) can be converted to Canon EOS with fully functioning autofocus by FM member Conurus' lens conversions.

If you are mechanically talented, you can also perform lens conversions yourself (there are several threads here on the Alt Lenses forum, along with google-locatable information elsewhere on the internet, where people share their experiences and techniques for home-made conversions).

Why am I missing focus with my alt lens?
First, check that your viewfinder diopter adjustment is correctly set. Most cameras will have a small dial near the viewfinder which you can fiddle back and forth to make the viewfinder focus points/markings appear most sharp. If your viewfinder is always blurry, you will have trouble finding where the image is sharp.

If focus is still off, check the viewfinder using another autofocus lens or live view. When using an autofocus lens, does the viewfinder image look most sharp where the camera thinks the lens is in focus, or can you still improve the viewfinder image sharpness by adjusting the manual focus ring? Does the focused image in the viewfinder have the same focus point as you see in live view or when you take a picture? If the viewfinder image does not agree with the autofocus or images taken, then you may need to have the spacing between your focus screen and the camera mirror adjusted. This can be done by a camera repair technician, or by mechanically-adept home users by adding/removing the thin shims that fine-tune the focus screen position.

Why am I missing focus with my fast aperture alt lens?
Fast aperture (f2 and wider) lenses offer additional challenges for manual focusing. One common reason for frequent missed focus with wide-aperture manual lenses is the focusing screen typically shipped with your camera. The surface of your camera's focusing screen consists of hundreds of thousands of microlenses, each directing light from particular regions on the back of the lens towards your eye. The microlenses on the screen that probably came with your camera are all directed towards parts of the lens that let light through at f2.8 or slower apertures; however, light from the farther out sections of the lens that corresponds to faster apertures is not directed to your eye. This design choice is to provide a maximally clear and bright image for slower lenses, but with faster lenses what you see in the viewfinder is as if the lens is already stopped down to f2.8. Because you can't see the real, extra-thin plane of focus of your fast lens, you are likely to miss focus even though the viewfinder image looks sharp.

Many cameras allow you to replace the focus screen with a different one that makes use of the faster-aperture light (at the expense of a slightly dimmer image for slower lenses), such as the Canon E*-s "precision matte" focus screen series. The manufacturers' replacement focus screens are usually inexpensive (~$30), and are an indispensable upgrade if you want to manually focus fast glass (and also useful for checking precise autofocus placement in the viewfinder). There are also third-party screens that may offer additional focus aids (e.g. split prisms, microprism rings) and a brighter image, but they also tend to be rather expensive (often $200 or more).

If you are having focus issues only when stopping down a fast lens (i.e. the image is properly focused when the lens is wide open but misses focus when you stop down right before shooting), you might be experiencing the effects of "focus shift." Focus shift is an annoyance present in some lens designs, where the plane of best focus moves significantly as the lens is stopped down (rather than simply broadening around the same point). Searching here and on Google for "focus shift" plus the name of your lens should turn up if this is a known issue with the lens. The surest way to avoid focus shift issues on problematic lenses is to focus with the lens already stopped down to the final aperture; otherwise, you just have to learn how much to correct for the particular lens and aperture combinations.

What alt lens should I get?
This is a very personal question that will depend on your own needs, wants, taste, and budget. I would recommend browsing through several of the images threads on this board to see what catches your eye. Several specific alt lens brands (even individual lenses) and camera types have their own image threads, which are an excellent way to get a feel for the particular drawing style and characteristics of a wide variety of alt lenses. A few of the major threads are:

  1. General alt images thread --- a mix of everything
  2. Leica R lens images
  3. Leica M8, M9, X1 (digital rangefinder cameras) images
  4. Olympus OM lens images
  5. Sony NEX (compact, mirrorless interchangeable lens cameras) with many alt lenses
  6. Takumar lens images
  7. Zeiss Z* lens images
  8. Zeiss Contax lens images
  9. Zeiss Contax N lens images
  10. Canon lenses alt images

Where do I get alt lenses from?
The Buy and Sell board here on FM forums is a great place to find a wide variety of good deals on good alt lenses.

New, currently produced alt lenses, like Zeiss Z*, Cosina/Voigtlander SLII, and Samyang/Rokinon/Bower, are available from several of the "usual" big online camera dealers (e.g. Adorama and B&H), or possibly even from your local brick-and-mortar store. Cameraquest specializes in new Cosina/Voigtlander lenses.

Used alt lenses can be found wherever used lenses are sold --- garage sales, flea markets, local camera and camera repair stores, online auction sites. Most online camera dealers also have a moderate used lens selection. Much larger selections can be found from dealers that specialize in used camera gear, such as KEH in the US or FFordes in the UK. If you are after a particular used alt lens, you may have to be patient and keep checking many sources until one comes up (in a condition/price you are happy with).

How much money is this alt lens worth?
Forum member JColwell maintains a handy database tracking lens sale prices for a wide variety of lenses (both alt and non-alt), which will tell you recent sale price ranges. If the lens isn't on the list, you will have to do the detective work yourself --- see if you can find recent forum sales, completed auction prices, or used lens retailer prices for the lens. For uncommon lenses with few sales, the "correct" price is not well defined (and may vary greatly between sales).

If you're hoping to sell your alt lens, one way to boost the price is to post a bunch of awesome photos taken with the lens on the Alt board (and pretend the awesomeness is due more to the lens than the photographer's skill).

What focal length will this 85mm medium format lens be on my Canon 50D?
Focal length is a property of the lens, not the lens/sensor combination, so an 85mm lens is always an 85mm lens no matter what camera it is used on (and will have the same field of view as any other 85mm lens on that camera). What changes between sensor sizes is the field of view that a particular focal length provides. An 85mm lens on 6x4.5cm medium format has the same horizontal field of view as a 50mm lens on 35mm "full frame"; when used on the 1.6x "crop frame" 50D sensor, it will have the field of view of a 85x1.6=135mm lens on 35mm full frame.

Why is my important question unanswered?
My machine for reading your mind in the future is out for repairs, along with my Canon 5DM Leica-M compatible full frame digital rangefinder. Based on the initial estimate, I won't have it back until next February 30th. I suggest you use the forum search feature to see if someone else has had the foresight to answer your question for you.

Alt Jargon Glossary
There are many jargon terms and opaque acronyms that occur frequently in Alt Lens board discussions. Here's a brief glossary of the most likely meanings of commonly used terms:

  1. CA: Chromatic aberration, a family of lens aberrations caused by different wavelengths of light being focused differently by a lens (see also LCA, LoCA).
  2. CPol: circular polarizer
  3. 'Cron: see Summicron
  4. CV: Cosina Voigtlander, lenses and cameras manufactured by Cosina and sold under the Voigtlander brand.
  5. CY, C/Y: Contax/Yashica, a line of cameras and lenses produced in cooperation between Zeiss and Kyocera.
  6. CZ: Carl Zeiss
  7. CZJ: Carl Zeiss Jena, the original factory location of Carl Zeiss, which was split off into a separate East German optics company in the partitioning of Germany after World War II.
  8. Distagon: Zeiss' name for wide angle, retrofocus design lenses
  9. Elmarit: Leica's naming scheme for an f2.8 lens; often followed by "-R" or "-M" to indicate SLR or rangefinder mount
  10. FF: Full-frame, typically used to describe a digital camera sensor the same size as a traditional 35mm film frame (24mm x 36mm).
  11. LCA, LaCA: Lateral chromatic aberration, results in color fringes along image edges that increase farther from the center of the frame.
  12. LoCA: Longitudinal chromatic aberration: adds spurious color tints to edges in front and behind the plane of focus (commonly magenta in front and greenish behind); may also contribute to "purple haze" around bright highlights.
  13. MC: multicoated
  14. MD: Minolta lens mount
  15. MF: Manual Focus or Medium Format depending on context
  16. Mirex: a brand of tilt/shift lens adapter for mounting medium format lenses on 35mm cameras.
  17. MP: Makro-Planar, a Zeiss Z* 50mm/f2 or 100/f2 macro lens
  18. M645: Mamiya 645 (6cm x 4.5cm) medium-format film cameras and lenses
  19. OM: Olympus OM mount (SLR cameras and lenses)
  20. PC: Perspective Control, label on a lens indicating shift movements
  21. Planar: Zeiss' name for a family of standard to short-telephoto focal length, fast aperture lenses with near-symmetric designs
  22. PP: Post-processing, tweaking and editing done to an image, often to prepare it for printing or web display
  23. Rokinon: one of the many labels Samyang lenses are sold under
  24. Rokkor: a line of lenses produced by Minolta (MD mount)
  25. SMC, S-M-C: "Super Multi Coated" or "Super-Multi-Coated," a label on Takumar lenses
  26. Samyang: a Korean lens manufacturer who has recently released some impressive and well-regarded lenses
  27. Summicron: Leica's naming scheme for an f2.0 lens; often followed by "-R" or "-M" to indicate SLR or rangefinder mount
  28. Summilux: Leica's naming scheme for an f1.4lens
  29. Super-Tak: "Super-Takumar," a single-coated Takumar lens (from before the introduction of SMC coatings)
  30. Tak: Takumar lenses, produced by Asahi Optical Co before they changed their lens branding to Pentax
  31. T/S: Tilt/Shift, additional movements giving a lens view-camera like capabilities for controlling perspective distortion and focal plane placement.
  32. T*: Zeiss' name for their multicoating technology
  33. ZA, ZE, ZF, ZK, ZM, Z*: A recently introduced series of lenses by Carl Zeiss for various contemporary camera mounts. A=Sony Alpha, E=Canon EOS, F=Nikon F, K=Pentax K, M=Leica M, *=any/all of the preceding mounts.
  34. Zuiko: Olympus lenses for OM mount
  35. 3D: an optical illusion discussed in detail here, here, here, here, here, here, here, here, here, and here.

Edited on May 19, 2011 at 10:58 PM · View previous versions

May 16, 2011 at 12:33 AM
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p.1 #2 · p.1 #2 · Alt Lens FAQ

Brilliant idea and excution, Mike!

May 16, 2011 at 12:46 AM
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p.1 #3 · p.1 #3 · Alt Lens FAQ

top idea, mp. My suggestions:

Please add Sony Alpha to the places where one sees Nikon and Canon. Sony Alpha is eminently suitable as a platform for many alt lenses.

NEX, which is now an open source platform as specified by Sony, is about the fastest selling such camera at present and really needs its own alt lens section, perhaps written by douglas13 if he wants to do so. The other small formats need a mention also with similar content.

Leitax have mounts for ZF and Voigtlander lenses for Sony also, and it would be good if this was mentioned. David also does custom work to fit non-standard lenses to several mounts including Alpha.

If you want to be cheeky, call Leica and Zeiss 'high end lenses', and provide a link to denoir's comparison thread of ZE with Canon L lenses, surely enough to get many Canon users interested in the Alt world.

for Search, include the search engine text [site:www.fredmiranda.com 'search terms'] for example:

site:www.fredmiranda.com 'leica 90mm asph'

there is an enormous amount of accumulated high quality material and it would be a shame no tto have access to it in years to come.

cheers, phil.

May 16, 2011 at 01:02 AM
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p.1 #4 · p.1 #4 · Alt Lens FAQ

You might also include the caveat, under "precision matte" that though it enhances manual focus for fast glass, autofocus is, of course, still possible. (you'll word it better than I)

May 16, 2011 at 01:40 AM
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p.1 #5 · p.1 #5 · Alt Lens FAQ

Great idea and execution! Perhaps those of us posting after you can delete our posts when you have addressed our points, to keep the thread clean.

There is a mistake in the Leitax URL code, so it doesn't display correctly.

May 16, 2011 at 02:00 AM
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p.1 #6 · p.1 #6 · Alt Lens FAQ

Thanks for the suggestions so far. I've added a "glossary" of commonly used alt lens jargon (I'd appreciate suggestions for additional terms to include), and I've tried to include Sony Alpha more fairly in the FAQ.

Phil, I'm not sure what you mean about including the text for search terms. I'm also not familiar enough with the various new small-format interchangeable lens cameras, even though I know they are a great way to use virtually any alt lens --- I'll take any help I can get with better describing the non-SLR options than my short passing reference to EVIL cameras.

Carsten: fixed the Leitax typo. Also, you could delete your answered posts, or maybe I could re-post a new "clean" copy in its own thread instead once it's reached sticky-worthy status. I'm not sure which would be better (or what the mechanics of elevating a post to sticky status are).

May 16, 2011 at 02:06 AM
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p.1 #7 · p.1 #7 · Alt Lens FAQ

mpmendenhall wrote:
Thanks for the suggestions so far. I've added a "glossary" of commonly used alt lens jargon (I'd appreciate suggestions for additional terms to include), and I've tried to include Sony Alpha more fairly in the FAQ.

Phil, I'm not sure what you mean about including the text for search terms. I'm also not familiar enough with the various new small-format interchangeable lens cameras, even though I know they are a great way to use virtually any alt lens --- I'll take any help I can get with better describing the non-SLR options than my short passing reference to EVIL cameras.

the search term reference allows you to use the power of google to search all of fredmiranda.com (including archive threads) rather than the anemic built in search engine. for example, if i wanted to find all the threads mentioning the rokkor 58/1.2, i could type the following into google: "site:fredmiranda.com rokkor 58mm"

May 16, 2011 at 02:09 AM
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p.1 #8 · p.1 #8 · Alt Lens FAQ

Hmm, it looks like only the latest poster can delete the post. I wonder if the last posters deletes the post, if the second-last then gets another chance?

May 16, 2011 at 02:19 AM
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p.1 #9 · p.1 #9 · Alt Lens FAQ

Nice work, Michael. Did I stir this up, or did you already have something in the works?
Now it just needs to be stickied.

One nitpick: focusing screens don't have "prisms", but microlenses. The microlenses on the focusing screen just gather light, as opposed to microprisms, which are a focusing aid that refract part of the image in different angles depending on the focus.
Perhaps the explanation you provide is too technical and confusing for beginners though. It may be better to just link to the explanation that theSuede gave, including his illustrations (I'll see if I can dig up the link). Edit: found his post, but unfortunately the images are offline: https://www.fredmiranda.com/forum/topic/989421/3#9399347

May 16, 2011 at 02:41 AM
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p.1 #10 · p.1 #10 · Alt Lens FAQ


Great start! I'll send some specific comments when I get home from my current road trip. For now, I have two quick comments: I think you should add Pentax-K mount to the M42 register entry; and, don't forget to put Summilux in the Glossary.

Cheers, Jim

May 16, 2011 at 08:08 AM

Search in Used Dept. 

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p.1 #11 · p.1 #11 · Alt Lens FAQ

jcolwell wrote:
don't forget to put Summilux in the Glossary.

And Noctilux and Elmar and Summarit...

May 16, 2011 at 08:52 AM
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p.1 #12 · p.1 #12 · Alt Lens FAQ

AhamB, I didn't have any writeup started until I saw your post (and waited a while to see if someone more knowledgeable and prepared already had something to post). I know that my focusing screen section is one of the longer and perhaps overly technical parts of the FAQ; unfortunately, without the images the linked post you give also requires a lot of knowledge to interpret.

I think "tiny prism" may still be an appropriate description of what a focusing screen consists of --- angled facets (much smaller and more varied orientation than the ones in a microprism focusing aid) for redirecting light rays. Old-school focusing screens were ground glass, producing somewhat randomly oriented scratches with a variety of angles; now the process is more controlled with laser cutting, but I believe the principle is the same. I say "prism" instead of "lens" because the focusing screen surface elements aren't aiming to form an image by converging a large bundle of rays to a point, but rather to grossly change the direction of rays coming from a particular angle; given the extremely small aperture that the focus screen elements have, attempting to truly focus in a lens-like way would be futile against diffraction. Do you know whether modern, laser-cut focus screen facets are curved or just flat? Admittedly, a small wedge prism can be though of as an off-axis fragment of a lens (and a lens as a carefully ordered array of prisms).

Jim, I added Summilux and Pentax K to the FAQ.

I also added CA, LCA, LoCA to the glossary (since these turn up in discussion a lot). Is there a good link to a thread that explains these clearly without being buried in too much confused argument? I suppose a link to Toothwalker's site would provide the most thorough and accurate technical description.

May 16, 2011 at 09:19 AM
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p.1 #13 · p.1 #13 · Alt Lens FAQ

carstenw wrote:
And Noctilux and Elmar and Summarit...

And Nokton, Biogon, Sonnar, Tessar, Lanthar....
I think trying to include every lens naming scheme would clutter up the glossary too much (perhaps a separate thread/post with a listing of lens name terminology and origins would be useful). I've tried to get the ones most relevant to adapted-lens DSLR users, that a new forum reader might more frequently see without enough supporting context; I need to put some limit on increasingly arcane terminology for scarcer or non-SLR-relevant lenses. If there are any that you think I've unfairly slighted (that are sufficiently common and useful to know), I'd appreciate the input.

May 16, 2011 at 09:29 AM
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p.1 #14 · p.1 #14 · Alt Lens FAQ

Considering the frequency of Zeiss lens threads and posts, I can't help but think that a Zeiss board might be beneficial.

May 16, 2011 at 09:34 AM
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p.1 #15 · p.1 #15 · Alt Lens FAQ

That's great, Michael. One small correction- Fotodiox also offers chipped adapters, both in the pro and non-pro-lines.

May 16, 2011 at 10:02 AM
wayne seltzer
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p.1 #16 · p.1 #16 · Alt Lens FAQ

Can you add Contax N to the beginning alt list and mention its special ability having AF and very decent MF capability.
Also add our fine FM'r friend Conurus (Cyberstudio) and his incredible Contax N lens conversion service.
And add the Contax N thread to the list.

May 16, 2011 at 11:00 AM
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p.1 #17 · p.1 #17 · Alt Lens FAQ

Amazing, Michael. Kudos!!!

May 16, 2011 at 11:17 AM
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p.1 #18 · p.1 #18 · Alt Lens FAQ

alexandre wrote:
Amazing, Michael. Kudos!!!

+100. Thanks!

May 16, 2011 at 11:45 AM
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p.1 #19 · p.1 #19 · Alt Lens FAQ

mpmendenhall wrote:
I think "tiny prism" may still be an appropriate description of what a focusing screen consists of --- angled facets (much smaller and more varied orientation than the ones in a microprism focusing aid) for redirecting light rays. Old-school focusing screens were ground glass, producing somewhat randomly oriented scratches with a variety of angles; now the process is more controlled with laser cutting, but I believe the principle is the same. I say "prism" instead of "lens" because the focusing screen surface elements aren't aiming to form an image by converging a large bundle of rays to a point, but
...Show more

Have a look at the flickr link at the bottom of this page: http://forums.dpreview.com/forums/read.asp?forum=1019&message=26635036
This is informative as well: http://forums.dpreview.com/forums/read.asp?forum=1019&message=38132287
I didn't find a really conclusive answer here. Perhaps electron microscopy images are needed to find out how the surface elements of *s screens are really shaped.

I also added CA, LCA, LoCA to the glossary
I find LCA and LoCA a bit confusing. LCA could mean both longitudinal and lateral CA. Why not LaCA to be more specific? (Frankly, I don't think I've ever seen "LCA" used outside of your posts.)

Anyway, nice additions. You didn't really have to credit me at the top of the OP.

One thing that could perhaps be changed a bit is to mention the use of adapters and what they are in a single sentence, in the earlier sections (what are alt lenses or how do I use alt lenses). Readers first have to digest the explanation about registry distances now, which seems like the reverse order.
Alt lenses are very much about using lenses that have a different mount than the camera, by a simple mechanical adapter that allows the lens to be attached to the camera, as a rule with fully manual operation of aperture and focus. This could be re-phrased to something better.

Maybe you could make two sub-sections of "How do I use alt lenses", namely for adapting and converting.

Edited on May 16, 2011 at 12:28 PM · View previous versions

May 16, 2011 at 12:05 PM
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p.1 #20 · p.1 #20 · Alt Lens FAQ

Here's what I just sent to Fred. Please, all of you Alt folks, feel free to do the same.

Hi Fred,

Could you please arrange to make the "Alt Lens FAQ" thread a sticky? It's a solid foundation for a wonderful resource. Also, please tell Michael thanks from all of us in the Alternative forum!

Cheers, Jim

Alt Lens FAQ https://www.fredmiranda.com/forum/topic/1009663

May 16, 2011 at 12:15 PM
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