Coverage of Protar VII Convertable 485-600?

[Hugo Zhang]

I need help from those who have experience with Protar convertables. I am looking at this lens made by Bausch & Lomb. It is a Protar VII with the front cell of 485mm and back cell of 600mm. I want to know if this lens covers my 10x20 camera. I have searched the internet and numbers are all over the place, from 11x14 to 20x24. I have some experience with Dagors and Artars, but have not used Protar lenses. Image quality? Fair price I should be paying if it covers? Thanks.

[N Dhananjay]

The usual coverage figure quoted for Protar VIIs is about 75 degrees for the combined lens. If I remember correctly, 19" and 24" elements combine to yield a focal length of about 12". A 12" lens with a 75 degree coverage angle would yield an image circle of somewhere in the 18" range. Your 10 X 20 camera has a diagonal of about 22" - so, I'd say the lens would fall short of covering. The single cells have much smaller coverage angles. The 24" may just about cover but I doubt the 19" would. I'd suggest you look for longer focal lengths - I know there was a 16" or so focal length made by combining two 28" elements, which would do the trick, although using the 28" single cells requires a pretty long bellows (well in the 30" + range).

As a comparison to your Dagors and Artars, Protar VIIs are quite similar to Dagors but have somewhat lower coverage. The single cells of Protars tend to perform better than single cells of Dagors because the individual cells of Protars are corrected for coma. The performance of Protars is pretty good when used unconverted (i.e., with both front and rear elements) - single element performance is not as good
(as you would expect since removing one cell upsets some of the corrections) but is surprisingly good, especially if used with a strongly monochromatic filter and stopped down. Usual rules of convertibles - when used combined, the longer focal length element goes in front. When used singly, the single element goes behind the stop (but expect your bellows extension to be somewhat longer than the focal length).

The Protars on the used market were pretty expensive for what they did, although I don't know what the prices would be. Once you are into large formats, I don't know if the weight savings are that attractive. If you do not have the bellows to use the 28" single elements, you would only be using the lens in its combined form. At that point, you may well decide that Dagors and Artars, if they are cheaper (which seems to be a bog 'if' looking at recent prices), are a better bet.

Cheers, DJ

[Jim Galli]

I have one. It's marginal but useable on 11X14 but it won't make it around your 10X20. I'd expect to pay 600-800 for a later post WWII coated version.

[Hugo Zhang]

Thanks. I think I will pass this one and use my 19" and 24" RD Artars. One more question: I might get my hands on a Protar 27cm f/18 lens which would make a very nice ultra wide angle lens for my 10x20. But I will have to pay very dearly for it. In that length, the only other one is probably Computar, which will cost an arm and leg too. Any of your ULF users have ideas for 240-300mm lenses I should look at?

[clay harmon]

The 240/9 Zeiss Dagor will just miss covering the far corners of a 14x17 negative when stopped down to f/45. It would probably cover 10x20 with very little movement.

[Hugo Zhang]

Clay- Nice to hear that Carl Zeiss Dagor 24cm might cover. I have a 18cm one for my Deardorff and just love it. I would say Carl Zeiss Dagor 24cm f/9 is very hard to find and more expensive than Computar.

[Hugo Zhang]

Clay- Your mention of Carl Zeiss Dagor 240mm f/9 has just triggered something in my mind! I have a Dagor 270mm f/7.7 and I was told it would cover 12x16 at f45 back a few years ago. I was shooting 8x10 then and didn't think much of this. Now if the 240mm f/9 Dagor covers 8x20 and possibly 10x20 with little or no movement as you said, my 270mm f/7.7 Dagor might do the same thing. I will use f64 when taking pictures. It seems nobody has mentioned this lens as a superwide for ULF. I can't wait to try it out when I get my film holders in three months!

[clay harmon]

I had a 270 dagor that covered my 7x17 just fine. William Whitaker has it now. It was a fine lens.


Clay- Your mention of Carl Zeiss Dagor 240mm f/9 has just triggered something in my mind! I have a Dagor 270mm f/7.7 and I was told it would cover 12x16 at f45 back a few years ago. I was shooting 8x10 then and didn't think much of this. Now if the 240mm f/9 Dagor covers 8x20 and possibly 10x20 with little or no movement as you said, my 270mm f/7.7 Dagor might do the same thing. I will use f64 when taking pictures. It seems nobody has mentioned this lens as a superwide for ULF. I can't wait to try it out when I get my film holders in three months!

[Hugo Zhang]

Clay- Is your Dagor 270 a f/6.8 or f/7.7? I see claims that Dagor 300mm f/6.8 covers 12x20. Being a f/7.7, my 270 dagor is wider and might cover my 10x20 at f64. Thanks.

[clay harmon]

It was a 6.8 if my memory is correct. I think it would be worth trying out on your 10x20. If nothing else, experiment around with hyperfocal focusing to make it work. I can make my 183mm protar V cover 7x17 by using some hyperfocal tricks. And yes, some 300 dagors will just cover 12x20. The older ones seem to be more likely to cover.


Clay- Is your Dagor 270 a f/6.8 or f/7.7? I see claims that Dagor 300mm f/6.8 covers 12x20. Being a f/7.7, my 270 dagor is wider and might cover my 10x20 at f64. Thanks.

[Hugo Zhang]

experiment around with hyperfocal focusing to make it work...

Clay, please educate this new comer to ULF.

[Michael Mutmansky]

Hugo,

Clay is referring to the fact that a lens that is stopped down to a small aperture does not need to be focused to infinity to be sharp at infinity.

In fact, no lens HAS to be focused at infinity to be sharp at infinty, but in many cases, the depth of field of the lens at a given aperture is small enough that it is effectively focused at infinity anyway.

However, when using a lens on a ULF camera, they are often used at very small apertures to provide sufficient sharpness in the corners. This has the added benefit of increasing the depth of field considerably.

The hyperfocal distance is a calculation of the distance away from the camera that the lens can be focused to provide a given depth of field from a point about 1/2 of the depth of the focus point to infinity at a specified sharpness and aperture. There are calculator programs out there to do the calculations for you, so do a search for that.

For LF lenses, using the hyperfocal distance will increase the image circle that the lens throws, and if you are close to hitting the corners at infinity, it may be enough to get the corners fully covered.

Most people use the hyperfocal distance for the other benefit; it effectively maximizes the depth of field of the image. A lens that is focused at a point in space effective has a distance nearer to the camera in focus and also further from the focus point as well. This range is the depth of field, and is dependant on the aperture of the lens. If you focus at infinith, the DOF goes from some point nearer to the camera to infinity, and the continues past infinity. That range of DOF beyond infinity is essentially 'wasted' DOF. By using the hyperfocal approach, you can pull the focus point closer to the camera, which brings the near end of the DOF closer, and as long as you don't take it too far, you will still have sharpness at infinity.

This approach is the only way that I can get my 210 Computar to cover 7x17 with reasonable sharpness, for example. As it is, it's not a lens that I prefer for that format because it just doesn't have quite enough coverage. The 240 Computar is a much better lens because it has room for moderate movements before the corners are hit, but I doubt it will hit the corners of 10x20. 8x20 probably, and 10x20 maybe with hyperfocal help. a 270 Computar will probably cover the format OK.

---Michael

[clay harmon]

You know how depth of field increases as you stop down the lens? The trick to hyperfocal focusing is to focus at a distance that will allow infinity to just become clearly focused. There are tables available on the internet that have these focus distances listed. For example, one source has the hyperfocal distance for a 300mm lens at f/32 listed as 78meters. So in theory, you could focus on an object at that distance, stop down to f/32, and objects at infinity would meet your resolution needs. By focusing on something closer than infinity, your bellows will extended further, and a given angle of illumination by the lens will be able to cover more film than if the bellows are racked in and focused at infinity.

In practice, what I do is extend the bellows out until the corners of the ground glass are just covered by the lens. I then stop the lens down to the shooting aperture and use a loupe to determine if objects at various distances in the frame are acceptably sharp. This is perhaps not as technically precise, but is a quick and dirty way to get to the same point. In some borderline cases, I will decide to go ahead and take the picture anyway, even if distant objects are not completely sharp, because psychologically, the viewer can accept the fact the distant objects may not be as sharp as closer ones.

here is a link to one of the tables:

http://www.angelfire.com/yt/jmyers/info/hyptable.htm


experiment around with hyperfocal focusing to make it work...

Clay, please educate this new comer to ULF.

[Hugo Zhang]

Thanks, Michael and Clay! Nice thing about LF and ULF is there are so many new discoveries each day. This afternoon, I put on my 270mm f/7.7 Dagor, 12" f/6.8 Dagor and 14" Trigor on the camera. The 12" and 14" seemed to cover the ground glass wide open and the 270mm did not. When I close the aperture all the way to the f64, it was too dark to see. On the 10x20 ground glass, there is not a big visual difference from 270mm to 300mm. So my wide angle lens for this banquet camera might start at 12" or even 14". I will do some testing when I get my film holders.