#### rdeloe

##### Well-known member

It's120 degrees, wow, not sure how you managed to calculate this but it sounds pretty &%€#"! mind-blowing!!

**mm**, not degrees -- so 120mm. That's still a big image circle though for a lens at that focal length. I won't be surprised if Pentax made it a bit bigger to help the edges be decent when shifted to the maximum on a Pentax 67 camera.

You can estimate the size of the image circle with the help of our old pal Pythagoras. The size of the image circle needed to cover a sensor (or film) is the diagonal of the rectangle. The imaged area on a piece of 6x7 film is around 58mm x 68mm. Therefore, the diagonal of that rectangle is 89.4mm (I rounded up to 90mm). If you imagine a long, skinny rectangle that is the original 58mm x 68mm plus 20mm on either side (so a rectangle that is 58mm tall and 108mm wide -- which is what you get by shifting 20mm left and 20mm right), then the diagonal of that is 122.6mm. I came up with 120mm by sketching it in PowerPoint and eyeballing the circle needed to cover -- but the math way is more accurate.

Remember these angles of view are for the native "sensor": 6x7 film.Thanks for this very useful answer. With the help of these great diagrams together with the detailed explanation, even I can understand this.

LIke many others I am finding that being stuck at home in these unusual times is a good opportunity to look into the technical aspects of photography with the hope that some day it will be possible to get back out in the big world beyond the back fence and appy what I have learned.

Meanwhile, I have ordered a TLT ROKR to try out with an old 55mm Super Takumar bazouka I have in my dry cabinet to see how stitching with that on my fullframe Sony mirrorless looks, and "if" that works will further consider piggybacking the shift adapter with a shift lens.

When I look here at the specs for the SMC-Pentax-67-75mm-F4.5-Lens it says:

Field of View (Diag. / Horiz.)

61 ° / 50 °

Whereas the wider angle SMC-Pentax-Takumar-6x7-55mm-F3.5 has:

Field of View (Diag. / Horiz.)

78 ° / 65 °

I'm going to take a stab at the math here. Hopefully someone actually math-competent can check my work.Given this, I am uncertain but would like to know how much difference in the "field of view" I could expect to see in a stitched panorama with a full frame mirrorless camera between (a) "120°" of the SHIFTED P67 75mm lens + TLT ROKR vs (b) X° of the UNshifted P67 55mm lens + TLT ROKR.

No doubt the best way to find out what this may look like is by trying it out and see what happens, but not if the difference in look and coverage of (a) vs (b) is not likely to be telling enough to be worth investing in more gear.

If you put a 75mm lens on your full frame camera and shift it 20mm left, then 20mm right (like you could with the P67 shift lens), you end up with a rectangle that is 76mm long and 24mm high. The angle of view across that 76mm long edge is 53.7 degrees*. A 35mm lens on full frame, long edge with no shift, has an angle of view of 54.4 degrees. So in terms of angle of view, a 75mm lens shifted 20mm left and 20mm right to create a long skinny panorama on full frame has an angle of view about the same as a 35mm lens on full frame unshifted.

This gives you an idea for what you can do with the Pentax 67 75mm shift lens -- all assuming that there's no mechanical vignetting and the image quality isn't crap because of the extreme angle of the beam. Those are big "ifs".

If you put a 55mm lens on a full frame camera, the angle of view for the long edge, unshifted, is 36.2 degrees. Remember that it doesn't matter what format the lens was designed for -- 55mm is 55mm. I believe that P67 to Sony E FotoDiox TILT-ROKR adapter can only shift 10mm. If you shift your P67 55mm lens 10mm left and 10mm right on full frame, you'll get a rectangle that is 56mm wide. The angle of view on the long edge of this rectangle would be 54 degrees -- again, about the same angle of view as a 35mm lens on full frame with no shift.

Once you get your adapter and start playing around with it, keep in mind that among the P67 55mm lenses, you have the worst of the bunch. Don't judge what is possible with P67 lenses with that one. The third generation P67 55mm lens was completely redesigned, and is much better. I've used it on a GFX camera and closed down a couple stops it keeps up with the Fuji lenses.

One last thought on lens choices: if you get the P67 75/4.5 shift lens, I seriously doubt you'll be able to take advantage of all the shift capacity it provides on the Tilt-ROKR adapter. There's a reason Fotodiox limited their adapter to 10mm. What you would get is shift independent from the direction of tilt; now that's actually quite handy if you start using tilt. You could also start doing things like shifting the adapter up, and then using the shift lens to do the shifting; that would allow you to flat stitch rows of panorams together to create larger files.

* If you have Excel, the formula is as follows: =DEGREES(2*ATAN(Edge/(2*FocalLength)))