[Steve Verrall]

Hi all,

I purchased 4 Pentax MF lenses (645 and 67) used from Japan (all classified as "Mint") and the corresponding 2 Fotodiox TLT ROKR tilt/shift adapters. I am using the lenses on a 45MP Nikon Z7 body. The reason for getting this equipment is to make quick and easy shifted panoramas, with the ability to add some tilt for depth of field.

The 67 lenses in particular have quite a large image circle and the TLT ROKR adapters seem to shift 15mm in each direction extending my 36mm wide sensor to an effective 66 mm wide, yielding panoramas that are around 15K by 5K in the classic 3:1 aspect.

Some questions I had were:

a) how do the lenses compare to a modern Nikon S line lens (the 24-70 f/4 in this case)
b) how well do the lenses hold up at their edges when fully shifted
c) is the 67 version of the 55mm f/4 better than the 6X7 version of the same lens

d) how well does the 45mm f/4 hold up when compared to the 55mm f/4 i.e. is it somewhat inferior


I have answered all these questions to my satisfaction and will present sample crops in this thread.

The shooting setup was the aforementioned lenses and body mounted on a big RRS tripod with geared head, manual focus, manual exposure, f/11 in all cases, electronic shutter, 2 second timer and ISO64 (base for this body). I shot two subjects - the end of a jetty about 400 metres away and an apartment building about a kilometre away. I compared each lens against the Nikon zoom at the same focal length.

I will post all the crops in subsequent posts in this thread, hopefully over the next 24 hours.

Spoiler Alert: If you are interested in my conclusions, here they are:

a) All of the Pentax lenses are as good as, or better than, the Nikon in the centre of the frame
b) The SMC PENTAX-A 645 35mm f/3.5 is unacceptable at the edge of the fully shifted frame. The 67 lenses are good enough at the extremities.

c) My 55mm f/4 67 lens is noticeably better than the 6X7 version of the same lens and;
d) The 45mm f/4 67 lens is not as good as the 55 but is still quite good and I would be happy using it for my intended purpose. It also has the benefit of being quite light, relative to the 55 67 (which itself is very slightly heavier than the 55mm 6X7.


A bonus observation is that a comparable panorama made via the rotation (not shift) method, when using the highly regarded Nikon S 24-70mm f/2.8 lens trumps even the 55mm 67 lens, which is of course to be expected. I don't have crops of the latter use case to show you, because I didn't have that lens on the same day. And when shooting those panoramas in portrait orientation I can get a comfortable 24K by 8K in the final file.


I hope that all this is of interest to those of you planning to adapt your Pentax MF lenses.

Cheers,
Steve.

[tuco]

This Pentax 6x7 Lens Guide is a good source for information on 6x7 lenses. It list the different generation of the lenses and if there was an optical update as well as a rating of the lens compared to other Pentax 6x7 lenses. You will see, for example, the 67 generation of the 55mm received an optical update over the 6x7 generation and a higher rating base on user experience.

I'd also note old MF film lenses, in general, didn't have to have as high a MTF as small format. Often you'll see the larger the format the lower the MTF of the lenses.

[Steve Verrall]

In all these cases I should also point out that I shot the subject at the centre, then fully shifted the lens AND rotated the camera about its vertical axis (yaw in aviation terms) to reposition the subject at the edge of the frame, then shot it again. I noticed some vignetting, purple fringing, distortion, loss of sharpness and contrast - none of which was unexpected. I was interested in how much each lens suffered at the edge.

This is the Pentax at the centre of the frame, on my two different subjects.

[Steve Verrall]

And here is the Nikon lens on the same subjects from the centre of the frame. On the Nikon lens I used autofocus with single point AF area mode.

Attached Images

   

[Steve Verrall]

Here are the edges of the 35, fully shifted.

---------- Post added 09-24-20 at 06:05 PM ----------

Hi Tuco,

Thank you. Yes, I looked through that before purchasing the lenses. I had read elsewhere that there was no real difference between the 6X7 55mm and the 67 55mm so I got them both and did my own testing. The 67 is clearly better. And I was also keen to see for myself how much 'worse' the 45mm was to the 55mm. Not much was my assessment.

The (fully shifted) edges of the 67 lenses hold up well, as I expected. The 35mm 645 not so much. With at least 3 versions of that lens I was also keen to start with the A, but given the results I have obtained I will not pursue that line of enquiry any longer.

I take your point about MTF needs in the film days and of course with modern optics design and coatings I would expect that current day lenses would be superior. Yet I found that, in the centre at least, the Pentax MF lenses were generally better than the Nikon S 24-70 f/4. I may shoot them again, but this time against the Nikon S 24-70 f/2.8, which is an excellent lens in every respect.


Lots to learn for me. Of course I have a very specific use case in respect of these lenses and I am looking at only a very specific aspect of the lenses capabilities.

Cheers,
Steve.

[Steve Verrall]

Pentax 45mm centre.

[Steve Verrall]

Nikon centre at 45mm

Attached Images

 

[Steve Verrall]

Pentax edges at full shift

[Steve Verrall]

Pentax in the centre

[Steve Verrall]

Nikon in the centre at 55mm

[Steve Verrall]

The edges of the Pentax, fully shifted.

[Steve Verrall]

Finally the King of the heap in terms of my expectations - the 67 version of the 55mm f/4. The Nikon at 55mm can be seen in the previous post.


Pentax in the centre.

[Steve Verrall]

The edges, fully shifted

[Steve Verrall]

Here is the same section in the far distance from the matching shots of each lens. Both were shot with identical settings and focused in the same place. The 67 is clearly better.

[Steve Verrall]

Last example. Again the 6X7 is quite poor. Perhaps the aperture Manual/Auto lock clicked out of Manual back to Auto and I didn't notice? Would that have made the shot at f/4 instead of the f/11 I had set on the aperture ring?

Perhaps I'd better shoot these two lenses again, just to be sure.

---------- Post added 09-24-20 at 08:22 PM ----------

I should point out that for the extreme edge fully shifted shots I refocused on the subject in all cases above. Perhaps the 6X7 version has much greater field curvature compared to the 67 version?