Home
SearchSearch MemberlistMemberlist RegisterRegister ProfileProfile Log in to check your private messagesLog in to check your private messages Log inLog in

Mamiya Sekor 55mm f1.8
View previous topic :: View next topic  


PostPosted: Thu Mar 07, 2019 9:27 pm    Post subject: Reply with quote

DCS wrote:
papasito - from oldhand's photographs above, can you say what is the configuration of his lens?

Can you explain more about reflections with aperture-open vs aperture closed?

Thanks.

I can understand the theoretical basis of your comments on this thread, but I still do not understand the practical application.

Maybe it will help if you use his example/

Thanks! I appreciate it.


Oldhand's lens is the same as my own one.
IT's the 6/4 formula.

Aperture close let you see only the front or rear elements. Not both at the same time.

practical application?
Seeing the reflections you can know how much elements and grupos has your lens, and then know which version is it


PostPosted: Fri Mar 08, 2019 11:02 am    Post subject: Reply with quote

I find it hard to determine the elements/groups based on the reflections but so for some standard lenses it seems correct. The kitted surfaces can still throw two reflections but they are close to one another and more faint.

Images shown;

From left to right with aperture closed:

Canon FD SSC 55mm 1.2 = 8/6 3/2:
Mamiya Sekor SX 55mm 1.8 = 6/5 3/3:
Topcor RE 58mm 1.8 serno99etc = 6/5 3/3:
Olympus OM G-Z 50mm 1.4 = 7/6 3/3:
Yashica ML 50mm 2.0 = 6/4 3/2:

3/2: number of elements/groups in front of aperture





PostPosted: Fri Mar 08, 2019 1:16 pm    Post subject: Reply with quote

Ernst Dinkla wrote:
I find it hard to determine the elements/groups based on the reflections but so for some standard lenses it seems correct. The kitted surfaces can still throw two reflections but they are close to one another and more faint.

Images shown;

From left to right with aperture closed:

Canon FD SSC 55mm 1.2 = 8/6 3/2:
Mamiya Sekor SX 55mm 1.8 = 6/5 3/3:
Topcor RE 58mm 1.8 serno99etc = 6/5 3/3:
Olympus OM G-Z 50mm 1.4 = 7/6 3/3:
Yashica ML 50mm 2.0 = 6/4 3/2:

3/2: number of elements/groups in front of aperture





That was used by Leica's collectors.

I have learned seeing them.

WIth practice it should be very easy and fast to do.

And if you use only one lamp, it will be faster


PostPosted: Fri Mar 08, 2019 1:43 pm    Post subject: Reply with quote

Well it is one fluorescent tube lamp. Here at another angle:

Last edited by Ernst Dinkla on Fri Mar 08, 2019 1:47 pm; edited 1 time in total


PostPosted: Fri Mar 08, 2019 1:47 pm    Post subject: Reply with quote

Idea

One of this


PostPosted: Fri Mar 08, 2019 2:28 pm    Post subject: Reply with quote

Give me a good reason for that choice ... I do not see it


PostPosted: Fri Mar 08, 2019 3:40 pm    Post subject: Reply with quote

Well.

If you want, do it.

You will find the reason by yourself.

Think, man. It's logic.


PostPosted: Fri Mar 08, 2019 4:38 pm    Post subject: Reply with quote

Point source, continuous spectrum, doesn't make a difference in this case. The separation of the kitted surfaces is already visible with the fluorescent tube.


PostPosted: Sat Mar 09, 2019 12:28 am    Post subject: Reply with quote

Ernst's photo of SX 55/1.8 helped me understand. Thanks for posting those images.

I also read some other info online.

A lens will return a reflection from each air-glass interface.
Sometimes the innermost reflection is weaker or different color.

A lens will also return a reflection from the glass-glass interface between 2 cemented elements,
but it is almost always a very weak reflection, and usually a different color.

The SX lens is 6/5, with 3/3 in front and 3/2 behind aperture.
Therefore the front will show 6 reflections with aperture closed. Thanks Ernst!

My TL/DTL chrome-nose 55/1.8 looks like oldhand's lens. I get 4 strong reflections and 1 week reflection. Ergo 3/2 in front, ergo 6/4 lens.

Oldhand's photos only show 3 bright reflections in front of closed aperture. What I observed on my (same) lens is that the very front reflection (the reflection off the outer surface of the front element) is very large and bright. It is necessary to turn the lens away from the eye or camera slightly to move this large reflection out of view so that you can see or photograph the inner 3 bright reflections. Oldhand's photos are good because the camera-to-subject angle is set so that the front reflection does not obscure the others. But it also is not shown in the photos.

I believe the grey-blue reflection in oldhand's photos is the weak reflection from the union of two elements.

So if oldhand's photos included the very front reflection, we would see 4 bright reflections and 1 weak one = 3/2 in front of aperture.

FYI, I also have the chrome-nose TL/DTL 55/1.4.
With aperture closed,
it has 4strong+1weak in front = 3/2 front,
and 4strongyellow+1strongblue+1weakpurple in back = 4/3 back,
= 7/5 total.

To sum up, papasito is correct about counting reflections, but the matter was confusing to a new person because the discussion did not match oldhand's photos because his photos did not show the very front reflection.

****************************************************

I wonder if anyone has a photograph of a TL/DTL 55/1.8 with aperture closed with 6 reflections like what is seen in Ernst's SX image? Do we have proof that this lens was made in both 6/4 and 6/5 configuration?

What about Mamiya literature that designates chrome-nose lenses as TL only and black as DTL only?

Thanks!


PostPosted: Sat Mar 09, 2019 8:18 am    Post subject: Reply with quote

DCS wrote:
Ernst's photo of SX 55/1.8 helped me understand. Thanks for posting those images.

I also read some other info online.

A lens will return a reflection from each air-glass interface.
Sometimes the innermost reflection is weaker or different color.

A lens will also return a reflection from the glass-glass interface between 2 cemented elements,
but it is almost always a very weak reflection, and usually a different color.

The SX lens is 6/5, with 3/3 in front and 3/2 behind aperture.
Therefore the front will show 6 reflections with aperture closed. Thanks Ernst!

My TL/DTL chrome-nose 55/1.8 looks like oldhand's lens. I get 4 strong reflections and 1 week reflection. Ergo 3/2 in front, ergo 6/4 lens.

Oldhand's photos only show 3 bright reflections in front of closed aperture. What I observed on my (same) lens is that the very front reflection (the reflection off the outer surface of the front element) is very large and bright. It is necessary to turn the lens away from the eye or camera slightly to move this large reflection out of view so that you can see or photograph the inner 3 bright reflections. Oldhand's photos are good because the camera-to-subject angle is set so that the front reflection does not obscure the others. But it also is not shown in the photos.

I believe the grey-blue reflection in oldhand's photos is the weak reflection from the union of two elements.

So if oldhand's photos included the very front reflection, we would see 4 bright reflections and 1 weak one = 3/2 in front of aperture.

FYI, I also have the chrome-nose TL/DTL 55/1.4.
With aperture closed,
it has 4strong+1weak in front = 3/2 front,
and 4strongyellow+1strongblue+1weakpurple in back = 4/3 back,
= 7/5 total.

To sum up, papasito is correct about counting reflections, but the matter was confusing to a new person because the discussion did not match oldhand's photos because his photos did not show the very front reflection.

****************************************************

I wonder if anyone has a photograph of a TL/DTL 55/1.8 with aperture closed with 6 reflections like what is seen in Ernst's SX image? Do we have proof that this lens was made in both 6/4 and 6/5 configuration?

What about Mamiya literature that designates chrome-nose lenses as TL only and black as DTL only?

Thanks!


BTW, the bayonet ES version of the 55mm1.8 has the same optical design the SX has. So 3 elements up front.


PostPosted: Sat Mar 09, 2019 2:14 pm    Post subject: Reply with quote

I personally saw the dtl 55/1,8 with 6/5 formula.

Some 6/5 normal lenses have 3/3 in the rear grupos (summicron M 50/2 v.4, among others).
The mamiya 55/1,8 has 3/3 in the front.

The pale green reflection generally come from the exterior face of the first lens of the escond group, not from the union.


PostPosted: Sat Apr 20, 2019 11:57 am    Post subject: Reply with quote

Anybody knows image differences taken with the tl/dtl and the SX version?