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Telecentric lenses and microlens arrays


bencoyote

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So now that more photos of the SL have been posted and people have digested the initial reviews and specs for the SL it appears like it is finally starting to sink in that the SL body isn't really that big in comparison to other FF bodies and is only slightly bigger than the A7 II a portion of which could be considered to be due to the weather sealing and dual card slots and bigger batteries. Whatever.

 

The big difference appears to be the lenses which were allowed to be as large as their full frame DSLR counterparts. As opposed to the rangefinder lenses which must be optimized for size to avoid blocking the rangefinder and to maintain the rangefinder concept of a small camera. Reading this forum and others, it seems that the reason that they are so big is that they are a telecentric design. As far as I can tell, the reason for this is so that Leica can achieve nearly prime lens quality at every focal distance within the range of their zoom lens. 

 

We know that the M8 existed because the engineers had not yet figured out how to handle the angle of incidence of the light rays from the tiny rangefinder lenses on a digital sensor. The M9 was a breakthrough product because they solved that problem with a microlens array. It is the lack of the microlenses that causes some M lenses to not work as well on cameras like the A7.

 

It seems like the short distance between the sensor and the back of the lens causes problems for everybody. The fact that you ADD an adapter to M lenses to get them to work on the L-mount indicates that there is more distance between the sensor and the back of the lens on the M than on the T and SL. I don't know the actual distances.

 

Does the fact that Leica chose to use telecentric lenses for the native lenses indicate that the SL doesn't have a microlens array? What would that mean for M lenses on the SL? In a hypothetical SL2 could they add a microlens array and then make the lenses smaller?

 

If it does have a microlens array to improve performance of M lenses, then are their other lens design tricks which could be employed to reduce the size of the lenses without sacrificing quality much like they do for the rangefinder lenses.

 

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We know that the M8 existed because the engineers had not yet figured out how to handle the angle of incidence of the light rays from the tiny rangefinder lenses on a digital sensor. The M9 was a breakthrough product because they solved that problem with a microlens array. It is the lack of the microlenses that causes some M lenses to not work as well on cameras like the A7.

Actually the sensor of the M8 has microlenses, as have the Alpha 7 and its successors. It is not an issue of having microlenses or not; it is the position and shape of the individual microlenses that matters.

 

With the M9 Leica used microlens shifting to accommodate large incident angles towards the corners – near the center of the sensor the microlenses are centered on the photosites beneath whereas microlenses further out are shifted towards the center.

 

With the M (Typ 240) Leica switched to a different approach. There is no microlens shifting but the focal length of the microlenses and the gap between microlens and sensor is reduced. This renders the pixels less sensitive to varying incident angles, the advantage being that the sensor isn’t optimised for M lenses specifically but can als be used with more telecentric R lenses.

 

It seems like the short distance between the sensor and the back of the lens causes problems for everybody.

The back focus length doesn’t create issues; it is the distance between the exit pupil and the sensor that is critical.

 

The fact that you ADD an adapter to M lenses to get them to work on the L-mount indicates that there is more distance between the sensor and the back of the lens on the M than on the T and SL.

It only implies that the flange distance of the M system is larger – 27.8 mm vs. about 20 mm for the L mount. The adapter accounts for the difference in the flange distance so the lens keeps the same distance to the sensor as it would on an M.

 

Does the fact that Leica chose to use telecentric lenses for the native lenses indicate that the SL doesn't have a microlens array?

No, it doesn’t.

Edited by mjh
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Thank you, Michael.

 

With the M-T adapter, will the SL sensor still need to deal with that very shallow angle of incidence on the edge of the sensor with M wides?  And do you know if the SL sensor has the same "shallow buckets" the M(240) sensor has, or the micro lenses the Kodak sensor on the M9 had?

 

The performance of this sensor with M wides is going to be make or break, I suspect ...

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Hello John,

 

Wide Angle lens use will probably not be as important an aspect of 601 use as it is with the .68X range/viewfinder of the digital M family.

 

Don't forget M3 users have always been comfortable with 135mm lenses because of that range/viewfinder's .91X.

 

Leitz Leicaflex & R Camera users have no problems incorporating 180mm & longer lenses in their mind's eye.

 

It would appear that 601 users might well be in that latter category with "M" users still preferring shorter focal lengths.

 

Best Regards,

 

Michael

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Hi Michael,

 

This is less about what you see in the viewfinder than about what you see in the photo once it's taken - smeary edges and colour shift!

 

At least with the EVF I would know exactly where the corners of the image lie and I would see the whole frame clearly, just not the lovely window view of what is going on around it.  Such are the compromises in life.

 

Cheers

John

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With the M-T adapter, will the SL sensor still need to deal with that very shallow angle of incidence on the edge of the sensor with M wides?

Yes, the adapter doesn’t change anything. The lens is designed to be in a certain distance to the sensor and the adapter makes sure that it is. That is the lightrays are following the exact same paths in the SL and M.

 

And do you know if the SL sensor has the same "shallow buckets" the M(240) sensor has

I don’t know, but in any case the sensor was designed to cope with all kinds of lenses, both telecentric lenses and lenses where the exit pupil is close to the rear lens.

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Hello Again John,

 

Also: Probably less "smeary edges and colour shift" with longer lenses than there would be with wider angled lenses. Another reason to encourage people to explore longer focal lengths.

 

Best Regards,

 

Michael

 

Yes, Michael, that's very true.  However, it is the wides that are the problem, and it would be good to know how the problematic ones perform.

 

My experience with the A7r is that it was not just a factor of how wide the lens is.  My 21 Summilux performed okay on that camera, whereas the 28 Summicron performed worse than the Zeiss Distagon 15/2.8 ZM.  Similarly, the WATE also seems to perform okay on that camera.

 

I'd very much like to know how Leica's various, otherwise excellent, M wides perform on the SL - they are problematic.  Long lenses, not so much.

 

Cheers

John

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 A bit better than on other EVILs i guess but i would not expect sharp corners below f/8. 

 

exactly what Sean Reid's latest comparison review shows ...... as expected really. 

 

none of the M wides are ever going to work well on other cameras unless the sensor is specifically designed to allow for their particular optical properties 

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exactly what Sean Reid's latest comparison review shows ...... as expected really. 

 

none of the M wides are ever going to work well on other cameras unless the sensor is specifically designed to allow for their particular optical properties 

 

That's not quite accurate, though is it?  Neither Sean's review nor Jono's say the M wides do not work well on the SL.  What they both say is that the M lenses generally perform better on an M camera - that's hardly news.  What they also say is that while the SL does not handle M lenses as well as M cameras, it's miles ahead of the A7 cameras.

 

The way I read the reviews, we're dancing on the head of a pin.  Sean's review also shows that in the centre, the SL performs better in the centre with the M lenses he chose than the M(240) - go and have a look at the review.

 

The issue for me is that I don't know if I have challenging M lenses or not - "compact and wide".  I'm guessing that means the 28 Summicron, as it was very difficult on the A7.  Sadly, neither Sean nor Jono appear to have a 28 Summicron to test with (not such a huge issue if my 28 Summilux ever arrives).  The 21 Summilux is hardly compact; nor is the 15 Distagon but it will almost certainly have colour shift (but I can fix that in post).

 

I do think this issue needs to be kept  in perspective - 100% crop, side by side comparison is not really the way I choose to view my photos.  What I do need to know is if there's a problem (of A7 proportions).  I haven't seen one, and neither Sean nor Jono have identified one.  Yes, your M lenses work best on M cameras; but, M lenses on the SL are not far behind (which we've been told pretty conclusively).

 

Cheers

John

Edited by IkarusJohn
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exactly what Sean Reid's latest comparison review shows ...... as expected really. 

Haven't read reviews about this yet but there is no free lunch as some of us did say before the SL release. To get the most out of the SL better choose L or R lenses or accept some softness in corners with M wides as we're used to with other EVILs already. 

Edited by lct
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Haven't read reviews about this yet but there is no free lunch as some of us did say before the SL release. To get the most out of the SL better choose L or R lenses or accept some softness in corners with M wides as we're used with other EVILs already. 

 

Might be an idea to read the reviews to get an idea of how much softness we can expect - it's still an open issue, but I've seen nothing which supports the comment "none of the M wides are ever going to work well on other cameras."  Similarly, I don't know how you define "getting the most" - sure, we accept some softness, but again "as we're used to with other EVILs already"? Where does this come from if you haven't read the reviews?

 

There are degrees of softness - you can dance on the head of a pin all you like, but everything I've read so far says that the SL is nowhere near in the same league as the A7 cameras.  Or am I jumping to conclusions that these are the "other" cameras?

 

To be honest, I look at these comparisons and most of the time I think, stuff it.  I'm comparing 100% enlargements of two images looking for differences - provided there is nothing fatal (Sony level), who cares.  I don't think I do.  If it's critical, I have no shortage of M cameras to use instead, as will most M lens owners ...

Edited by IkarusJohn
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[...] I don't know how you define "getting the most" - sure, we accept some softness, but again "as we're used to with other EVILs already"? Where does this come from if you haven't read the reviews? [...]

 

Well getting the most is getting what we get out of the M i guess. This is out of reach with any mirrorless camera besides Leica Ms and the Ricoh GXR A12 perhaps. I have nothing against reviewers of course but i don't feel the need to read reviews to know that. My modest experience with R lenses on Canon bodies and M lenses on Leica, Epson, Fuji and Ricoh bodies has taught me that there is no free lunch in this matter. YMMV. 

Edited by lct
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Free lunch and Leica don't belong in the same sentence!

 

Opinions are useful, and we have yours (without the benefit of having used the SL) and we have Jono's (he has) - Jono's experience (just posted on another thread) is pretty unequivocal, I'd say.

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Well with respect towards everyone i stand by what i said above: To get the most out of the SL better choose L or R lenses or accept some softness in corners with M wides. Time will tell if i'm right or wrong. :)

 

Actually, probably not the way these things go.  There will be those who go ahead and buy the camera, and they will say they are happy (e.g., K-H and his Sonys); there will be those who buy and find they don't like the camera and sell it for whatever reason (me with my A7r); and there will be those who say there is a problem with soft corners, don't buy the camera and say with their dying breath it was a good call on their part.

 

I don't think time will actually tell ...

 

PS - Sorry, LCT I meant to quote Jono:

 

 

Whilst it's certainly true that corners at infinity are better with the M240 than with the SL . . . they aren't much better, and certainly not a problem on the SL.

 

It's difficult to get the balance right with this kind of stuff . . .from my point of view using M lenses on the SL is a great alternative - I'll keep on using an M when I  want to use a rangefinder (which is often), but I've no scruples using M lenses on the SL, whereas I found it a frustrating experience on a Sony A7 . . .

Edited by IkarusJohn
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Confucius said "Life is very simple, but we insist on making it complicated" I said: Photography should be the same. To much science is not good, although all points of this discussion are valid, why to be so extremely technical? It will help us decide if we want the camera or not? I understand, they are not pennies but if a camera make you feel good, inspired, you like the results coming out of it, it adds something yo can't achieve under your current equipment? who cares?

 

On a personal note...I will have the opportunity to try the camera this Friday and decide if i want it or not. Expensive...yes, Can I justify the cost once I bill my customers inside my budget and depreciation of equipment?...Perhaps, If I can attached non Leica Lenses like I do with the Sony, Canon, etc, and perform well...It will give me a final push to decide. So far when I found that my TS-E canon lenses perform better on the Sony a7r than my own Canon 5DMIII I decide to get it (didn't care about the technical part if the distance between sensor and lens bias the metabones adapter make it better or not)...I happy, customer happy, wallet happy and must important kids and wife happy.

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[...] There will be those who go ahead and buy the camera, and they will say they are happy (e.g., K-H and his Sonys); there will be those who buy and find they don't like the camera and sell it for whatever reason (me with my A7r); and there will be those who say there is a problem with soft corners, don't buy the camera and say with their dying breath it was a good call on their part. [...]

 

Seems like you forgot an endangered specie, those (or he) who say(s) what i say and will buy the camera... perhaps. :D

More seriously, knowing Sean Reid a bit i suspect that he will show some soft coins or vegetables out of the SL610 if he did not do it already.

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