Article, pages and photos are © Mauro Placido - All rights reserved - About the Author
In this section we will review the technical details behind this new solution with the aim to demonstrate how we can transform a Canon DSLR in a DSLR that can accept the Minolta MC/MD Rokkor manual focus lens using an only mechanical "adapter" that allow us to focus to infinity maintaining the original optical quality.
The possibility to use a lens (with X mount) on a DSLR (with a different Y mount) is tied essentially to the concept of optical register ("tiraggio" in Italian).
But what does the "register" mean ? Optical register is the distance (in millimeters) between the focal plane (CMOS sensor plane or film plane) and the flange's top plane (this is a simple definition, I do not want to speak about optical physic and in particular about nodal point for a lens....too difficult for many people).
A simplified schema of mirabox inside a generic DSLR
If the lens register is greater than that of the DSLR (i.e. X>Y), the adaption is easy to make and we can use a simply adapter ring "on" the DSLR's original flange. I this case the adapter ring's thickness (i.e. H=X-Y) will be equal to the difference between the register (X mount) and the register (Y mount). We can see next schema to understand what happens if X>Y.
But what happens if the lens's register is shorter than the DSLR's one (i.e. X<Y) ? This is the situation that occours for Minolta MC/MD lens (X = 43.5mm) when it is mounted on a CANON EOS body (Y = 44mm).
If we want to preserve correct focus operation (in particular about the possibility to reach the infinity distance) it is necessary to modify the flange. So, the only possible solution that allowes to reach the correct infinity focus on bodies like a CANON EOS, without using optical elements inside (therefore operating with an adapter that is only mechanical), is an EOS-MD flange. The adaption is possibile thanks to the wider CANON EF's geometric diameter mount.
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In fact few people know that the register on a DSLR/SLR can be not only increased (for example using the macro extensions tubes) but also decreased. Obviously that flange has to guarantee the Minolta lens to fit and block rigth on it and on the CANON EOS body too. From the digital sensor's optical coverage point of view, we can say that, when mounted on the EOS-MD flange, Minolta MC/MD lens's behavior is "the same" than Canon EF lens. For example, if we use a Minolta MD lens on a CANON EOS with APS-C sensor it is affected by a 1.6X crop factor. |
The EOS-MD flange in rear (on the left) and front (on the right) view. |
The following figure schematically illustrates the concept previously expressed. In brief, the EOS-MD flange descreases the EOS DSLR's register from 44mm to 43.5mm (the Minolta MC/MD's register !).
My personal thanks to the Staff of Minolta Sony Club - Italy (Cejes) for this schema.
So we discovered that the EOS-MD flange is the only possible technical solution (remember: only mechanical !) that allowes to mount the (ALL) 35mm Minolta Manual Focus lens (from 1958 Auto Rokkor to MC/MD Rokkor and last MD) on the Canon EOS DSLR maintaining both the infinity focus and original optical quality.
IMPORTANT: the EOS-MD flange is not the common adapter ring that mounted on the EOS body restricts the use ONLY to the short distance (macrophotography) and is not the common adapter ring with internal optical elements that mounted on the EOS body allowes you to reach infinity focus BUT WITH POOR PERFORMANCE on the final digital images. The EOS-MD flange is a NEW CUSTOMIZED flange that changes EOS DSLR's register from 44mm to 43.5mm value (the Minolta MD's register !).
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IMPORTANT: the EOS-MD flange is a replacement of the original CANON EOS EF flange and allowes to use on it only the following lens:
The EOS-MD flange do not introduce any modification on the electronic circuits inside the CANON DSLR. It is a REVERSIBLE and NOT INVASIVE solution. To return to the original CANON EF mount it is necessary to remove the EOS-MD flange and refit again the CANON EF flange on the CANON DSLR body. |
On the left the EOS-MD flanges ready to mount on a EOS DSLR body, on the right the versions under construction. |
MAIN FEATURES AND COMPATIBILITY ISSUES
- the EOS-MD flange changes EOS DSLR's register from 44mm to 43.5mm value so it allowes infinity focus WITHOUT any inside optical elements and WITHOUT ANY optical image degradation. Infinity focus is obtained ALSO with wide angle lens set at maximum aperture
- the EOS-MD flange has mechanical lock for Minolta MC/MD lens (without the security pin)
- COMPATIBILITY ISSUES WITH EOS DSLR CAMERA: the EOS-MD flange is fully compatible with several EOS DSLR as showed in the following TABLE. There are two options for install the EOS-MD flange on the CANON EOS DSLR. Either shave 0.5mm off the lens aperture pin (the type 1 installation) or remove the electrical contact's support on the CANON EOS body (the type 2 installation). To remove the electric contact's support some skills are required. It is interesting to note that the CANON EOS 300D (with the type 1 flange) does not require ANY modification (the type 1 flange fits perfectly on the 300D body and the Minolta Rokkor lens does not require any modification on the aperture pin !). The following table shows all the options for the most CANON DSLR cameras.
- COMPATIBILITY ISSUES with other lens: the EOS-MD flange is fully compatible with 42x1 or M42 lens (Pentax Takumar, Zeiss Jena, Russian lens, ect). Obviously it is necessary to use the "M-42/Minolta MD adapter" on the EOS-MD flange.
- REVERSIBILITY: you can simply remove the EOS-MD FLANGE, remount the ORIGINAL EOS FLANGE and restore all original functionalities on the EOS DSLR body
- the EOS-MD flange has a "dynamic structure". What does this mean ? The ring below the EOS-MD flange can be rotated, so Minolta MD lens (and the aperture pin...) can be rotated without effect on the lens optical behavior. This is true thanks to "circular optical coverage" for ALL photographic lens. Thanks to this property the EOS-MD flange can be adapted on different EOS DSLR (note that EOS Body's internal mirabox changes when EOS bodies change), so it is possible to reuse it in the future when you will change EOS body
- the EOS-MD flange can be mount easily on your EOS camera and you can do this by yourself (it take about 20 minutes of your time)
- lens focusing is obviously ONLY MANUAL and aperture values can be set in stop-down only
- the distances scale on the MC/MD Rokkor lens matches to the real distances of the subject in focus, so it is possible to use the hyperfocal distances with wideangle lens
- the CANON EOS DSLR camera operates properly only in "M (Manual) mode or "AV (Aperture Value) mode
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1.6X crop factor for Minolta Lens when used on a DSLR EOS with APS-C
sensorAnd what about focus operations ? It is possible to achieve
precise focus operations using this flange ? The answer is yes.
And what about focus operations ? It is possible to achieve precise focus operations using this flange with manual focus lens like the MC/MD Rokkor ? The answer is yes.
Because of the original EOS focus screens are not accurate to use with manual focus lens, two options exists to perform precise focus operations:
1- SPLIT SCREEN - we change the original focus screen with a split screen (easily available new on ebay by searching with "EOS split screen"). The split screens are in general accurate and precise but sometime I have found that they can introduce a slight back focus in (all) photos. Obviously the backfocus (and also frontfocus) are not related to the optical register modification introduced by the EOS-MD flange but only to the thickness of the split screens that can be different in respect to the original ones.
We can see next schema to understand what happens inside a DSLR.
In order to get perfect focus the path P1 must be equal to path P2, so P1 = P2.
If P1 > P2 then we have back focus. This is a situation that can occur using a "non original" focus screen (i.e. split screen).
If P1 < P2 we have front focus.
Obviously it is possible to correct the back focus by making an appropriate adjustment adding thickness between the split screen and the pentaprism in order to obtain P1 = P2. At operational level, simply type the outer perimeter (only !) of the split screen, on the side facing the pentaprism itself, using a thin strip of width equal to 1 mm (max 1.5 mm) of adhesive tape (Scotch Magic 3, thickness = 0.05mm). The calibration consist to find the correct thickness (usually is necessary just 1 or 2 layers of tape, with thickness equal to about 0.1mm) to get the focus correctly by using the scale at 45 ° in the following article (see page 18). Note that this thickness will not be visible in the viewfinder because it is covered by thin metal frame that still the same split screen below the pentaprism.
A split screen (on the left without thickness, on the right with small thickness to the outer perimeter).
2- LIVE VIEW - the Live View is a great feature that allows to focus directly using the focal plane (CMOS sensor). The focus operations are performed on the real 100% image's view directly on the camera's LCD. This is expecially useful for macro and astrophotography works where precise focus is very critical. The Live View also acts as a TTL (directly on the CMOS sensor !) light meter and is it possibile to use the matrix/semispot/spot options with great results.
Well, we have transformed an CANON DSLR camera in Manual Focus DSLR with Minolta MC/MD mount !
There are still doubts about the possibility to mount Minolta MC/MD Rokkor lens on a DSLR like a CANON EOS ? I hope not.