[marktomaras]

Does anyone know of a database that shows the sizes of the image circles for the various pentax 645 (and possibly 67) lenses?

thanks!

[Adam]

For 645 lenses, A, FA, and D FA lenses cover the film 645 format, whereas DA lenses are designed to only cover the reduced 44x33mm format.

[Alex645]

For 645 lenses, A, FA, and D FA lenses cover the film 645 format, whereas DA lenses are designed to only cover the reduced 44x33mm format.

And the 645 film format is not actually 60mm x 45mm but 56mm x 41.5mm. The DA or digital medium format uses the 44x33mm that Adam is referring to.

So according to basic geometry, the diagonal of the 645 image is 81.12mm, so that would be the minimum diameter of the image circle for a wide angle lens like a 35mm. Keep in mind the image circle increases with the focal length, but due to the focal plane gate, itʻs always cropped unless you have a non-rectilinear fisheye.

Would be curious to see the actual data base for the image circles.

[marktomaras]

Exactly. Adam, you are both correct but that is not the whole story. Yes, the circles cover that film size, but that does not mean that the circle is that size precisely. In fact, many medium format lenses, by virtue of their design, cover more than the film size. These lenses are particularly well suited for shift adapters. So my real purpose is to analyze which lenses have the largest circles, and perhaps, the best performance at the edges on a shift adapter.

thanks, and I look for any more responses!

[Digitalis]

For this purpose Pentax 67 or 6X6 format lenses would be a better choice.

[wombat2go]

For this purpose Pentax 67

I am using:
Takumars 6x7 1:4.5/75mm and 1:3.5 55mm
on the Graflex 4x5 with RH/8 back which is a larger frame than the Pentax 6x7.
There are some movements available but I have not determined the extent.
https://app.box.com/s/zz9woy21e7vmfydsc3ux

[angerdan]

1. And the 645 film format is not actually 60mm x 45mm but 56mm x 41.5mm.
2. So according to basic geometry, the diagonal of the 645 image is 81.12mm...
3. Keep in mind the image circle increases with the focal length...

1. yes
2. no, the diagonal of 56mm x 41.5mm is 69,7mm
3. do you have proof for this claim?

[Alex645]

[*]do you have proof for this claim?[/LIST]

This "claim" that the image circle created by a lens increases in diameter with the increase in the focal length of the lens?

The Pentax 10-17mm Fisheye with a 180 degree angle of view at 10mm has an image circle so small, you can see the image circle created on the sensor. Change that focal length to 17mm and the image circle increases beyond the sensor and the outer areas of the image begin to be cropped and decreases the angle of view.

I understand this would be counter intuitive if thinking about projected light such as from an enlarger or any light projection, which has the opposite effect.

[johnha]

This "claim" that the image circle created by a lens increases in diameter with the increase in the focal length of the lens?

The Pentax 10-17mm Fisheye with a 180 degree angle of view at 10mm has an image circle so small, you can see the image circle created on the sensor. Change that focal length to 17mm and the image circle increases beyond the sensor and the outer areas of the image begin to be cropped and decreases the angle of view.

I understand this would be counter intuitive if thinking about projected light such as from an enlarger or any light projection, which has the opposite effect.

The DA 10-17 FE is a fish-eye at 10mm on APS-C becoming less fishy as the focal length increases. It is also a fish-eye on FF at 17mm (almost identical to a SMC-K 17mm FE), vignetting more as the focal length is reduced. A projector takes a small image and enlarges it, a lens takes a large image and reduces it.

From what I've seen, most people interested in shift/tilt want wide-angles. Medium format lenses are not really wide-enough for that on smaller formats, the widest sensible 645 lens is 35mm and for 6x7 it's 45mm (both of these are compromised by what is practical to achieve in wide lenses with these image circles). These lenses generally drop off quite markedly (IQ and illumination) towards the edges but make up for it to some degree in the centre - fine if the centre is centred, not so fine if the centre is shifted towards one side or the other (the drop-off then becomes lopsided). Also these lenses were designed for film where purple fringing was never a problem.

[angerdan]

1. This "claim" that the image circle created by a lens increases in diameter with the increase in the focal length of the lens?
2. The Pentax 10-17mm Fisheye with a 180 degree angle of view at 10mm has an image circle so small, you can see the image circle created on the sensor.
3. Change that focal length to 17mm and the image circle increases beyond the sensor and the outer areas of the image begin to be cropped and decreases the angle of view.

1. yes, like i quoted you and numbered questions/answers.
2. Fisheye lenses are special lenses and aren't representive for non-fisheye lenses.
3. That's no argument. Many zoom lenses are vignetting on their lower end and are less vignetting on their longer end.

[RICHARD L.]

The diameter of the illuminated field of P67 lenses is at least 90 mm. Concerning 645 digital cameras, the diagonal of the sensor is 55 mm and all the "vintage" A and FA 645 lenses cover more than this (Square root of (56 squared + 41 squared)) = 70 mm approximately.