645 120mm macro ,why not a 67 equivalent?

[thomas_janik]

I am curious as to why the design used in the 645 120mm macro is not

used in a lens for the 67. If anyone has any thoughts, I'd

appreciate hearing them. I know weight might be an issue, but anyone

willing to haul around the 67 and tele lenses shouldn't have a

problem with that. Thanks in advance

[steve_rasmussen]

I think what you are asking is, why is there not a 150mm macro for the 6x7?

 

The 100 macro has a pretty close working distance and I was surprised they made it. The 135 is much more versatile for my work but I still prefer my 90-180 zoom set at 150 or 180 for most close up work these days.

 

Pentax has not been addressing its customers' needs very well in my opinion. We have long needed a 35mm rectilinear lens for the 67. I even sent them a prelim design for an aspherical version some time ago with no response from them. We have four 75mm lenses (if you count the 55-100). Maybe the emphasis should have been on a 150mm macro with f/45?

[thomas_janik]

Steve:

 

My question was one of curiosity, not implied criticism of Pentax (I have K1000, an LX, 2 645?s and 67, how loyal can a customer be?) The design of the 645 120mm allows very good performance from infinity to life-size without any tubes or additional items. The design is clearly different from the 135mm and, I assume, the 100mm in the 67 system.

Is there some optical reason Pentax did not use the design of this lens in a 67 equivalent?

 

Regards,

 

Tom

[thomas_janik]

Steve:

 

If my reply is confusing, my apologies, I misread you response: "Pentax has not been addressing its customers' needs very well in my opinion". I missed the "not".

[steve_rasmussen]

Have not seen the cross section of the 120mm. Pentax has moved away from its 135mm design(Dynar) in the 67 when they made the 100 macro. The 100 used a Double Gauss type as I recall. There is a good chance the 645 uses a similar design. Let me know if you have a site that shows the cross section or if you have a description of it.

[thomas_janik]

I don't have access to the design, but I can tell you the following: the 645 120mm consists of 9 elements in 7 groups (695 g); the 67 135mm, 5 elements in 3 groups (620 g); 67 100mm, 6 elements in 4 groups (600 g). My question is why hasn't Pentax used the 120mm design in a 67 lens, since it performs so well.

[steve_rasmussen]

Pentax has not put out the cross section for the 120 macro yet but I did look up the 100 for the 67. It is a 6 element Double Gauss with a three element, APO life size adapter(making a total of 9 elements). I believe the newer 120 macro has consolidated the life size adapter into the design without it being separate. The 120 is a 9 elements design. It is my guess that the 120 uses the same design as the 100 but with the added 3 elements. I feel that the 100 and 120 would have been the same design if they were both designed when the 120 was. The 100 is at least 11 years old.