600mm and 750mm APO Germinar - Actual Coverage?

I'd also like to call on the collective wisdom of this group regarding the actual usable coverage of the 600mm and 750mm APO Germinars. Thanks to Arne and his excellent articles on these lenses I know what the official specs are. I know that based on these specs the 600mm will cover 7x17 with some left over for movements, but just miss the corners of 8x20 and that the 750mm should cover 12x20 with about an inch or so left over for front rise/shift. However, it has been my experience with other lenses originally targeted at the demanding reprographics industry (APO Artars, APO Ronars, G Clarons, etc.) that the official specs are often very conservative. Those using these lenses for pictorial use (usually involving some type of contact printing) often find they cover considerably more than the official spec would indicate.

So, if anyone has any first hand knowledge of the actual usable coverage of the 600mm and 750mm APO Germinars, please share your experiences here.

Thanks,
Kerry

I use a 600mm apo-germinar for 11x14. The circle of coverage is way beyond that. The angle is listed as 46 degrees, with a circle of coverage of 520mm at infinity: http://medfmt.8k.com/mf/droptic.html. My real world experience is that I have to put a big front tilt on to run out of coverage. The sharpness is pretty even over the whole circle, until near the edges. I had a 750mm also, but the thing was so giant that I had no use for it, and decided just to keep the 600. Sadly, I never got to use it. Not necessarily the sharpest lens ever, but I am also not the sharpest photographer ever.

Kerry, in addition to the official 46° coverage specs (calculates to 510mm diameter for the 600mm lens, 636mm for the 750mm lens, and 850mm for the 1000mm lens, all at infinity) there are the mysterious "infinity" circles published in a single typed page by Docter: 585mm for the 600mm lens (52°), 715mm for the 750mm lens (51°), 895mm for the 1000mm one (48°) - this is supposedly all for the barrel versions wide open (!) at f/9. Stopped down, the coverage increases a little further to values up to 57°.

Disclaimer: I have not tested these values, these are values from an old Docter leaflet.

Arne,

Thanks for providing this additional information. I was not aware of the published infinity coverage specs for the longer APO Germinars. These numbers, if accurate, would indicate that:

The 600mm APO Germinar can cover 8x20 with some left over for movements and just hit the corners of 12x20 wide open.

The 750mm APO Germinar can cover 16x20 with movements wide open.

Even with the most conservative specs (46 degree coverage) the 1000mm APO Germinar can cover in excess of 20x24 wide open at infinity.

If the 57 degree number for coverage "stopped down" is realistic, that would yield image circle of 651mm, 814mm and 1085mm for the three lenses. This theoretical data would certainly indicate that these lenses are capable of covering very large formats for general pictorial use.

Additional Disclaimer: Again, as Arne stated above, these calculated image circle values are based on the coverage specs published by Docter Optics and have not been verified by me experimentally.

However, this data is also consistent with the limited feedback I have received directly from users who have actually checked the coverage of these lenses. One user reported that with even with maximum combined front rise and shift on his 12x20 Phillips he could not exceed the coverage of the 750mm APO Germinar. Another report indicated an image circle in excess of 600mm with no mechanical vignetting (at which point his camera ran out of movements) for the 600mm APO Germinar.

So, the only remaining questions are just how far do you need to stop down to get the full 57 degree coverage and what is the optical performance at the outer most edges of the image circle. At some point this becomes entirely academic as most people shooting such large formats are used to stopping down quite far for depth of field issues and most likely contact printing.

Kerry

Kerry, you can find these numbers on page 51 of my Docter article as part of the text, not in the tables. The basis for these numbers is a photocopy of a hand-typed sheet that came from Docter with some other Docter information, and that is why I put some caveats in the text there. They have never shown up in any other Docter literature. The statement that the numbers are for wide open lenses is my deduction since that list shows higher values for the shuttered versions, where the size 3 shutter limits the open aperture to a smaller value. The 57° is for the 600mm at f/11.5 (650mm), it is 56° for the 750mm at f/14.5 (795mm), and 53° for the 1000mm at f/19.5 (995mm circle). I would take them with a grain of salt, as the same table lists 61° for the smaller focal length (240-450mm), which is quite high for an Artar type.

I am taking mine out this weekend, and will attempt to measure the coverage of the 600mm. I'll post my results here.

Craig,

which one are you going to test ? .. barrel or shutter version ?

Best

Joerg

600mm, barrel version. Wide open and focused on some trees on the horizon, a 38 degree front tilt put the end of the light circle in the middle of the ground glass, meaning that the lens "put light out" to a whopping 76 degrees! From what I could tell on the ground glass, the outer 4 inches or so of the circle of coverage where not focused with the rest of the image at wide open (f/9). Stopping down to f/22 brought it (the area of good focus) to 2 inches or so from the end of the image circle. This is just observing on the ground glass, I did not make an exposure. I estimate a useable image circle of 830mm at f/22, much more than docter optics claimed, with light being put out to around 940mm.

Craig,

Do you still have the 600 mm lens and is it now a favorite? Any pictures?

Asher