Help needed with an enlarging sharp images

[Stephen Willard]

My intent is how to improve the sharpness of an enlarged photograph at the edges when making big enlargements of 40 inches or greater along one side.

I currently have one of the latest EL Nikkor 210mm lenses for enlarging photographs using 4x10 color negatives. The lens cover the format and the negatives are sharp from edge to edge. Four years ago I benched marked this lens against a new Schneider and Rodenstock enlarging lens of comparable focal length and found the Nikkor lens produced the sharpest image at the edges when making big enlargements. All of the lenses were very sharp near the center of the image, but after a side of the print reached 40 inches in length, the edges became noticeably softer for all lenses. Please note, I have not had any customer complaints yet about this problem, but I still find the soft edges unacceptable.

I suspect that part of the problem arises because I am using faster-wider aperture settings (f8, f11) to keep the exposure times reasonable short or under 30 seconds. I am also trying to use the least dense CC adjustments as possible to further reduce the exposure times. My color head uses 2000 watts consisting of eight 250W halogen lamps. Long exposures can burn out lamps in my color head real quick. I have resorted to using two shorter exposures with some cool down time between each exposure instead of one long exposure. This seem to help cut down on lamp burning out.

I am also considering buying a 300mm enlarging lens. I am hoping because of the greater coverage of this lens, this means the edges of the 4x10 negative will now be closer to the center of the lens and there will be less blurring at the edges. Can anyone speak about this approach of using a larger focal length lens to get greater sharpness at the edges of big enlargements? Is my logic plausible?

[Bob Salomon]

Did you try this with a 150mm Apo Rodagon-N or a 120mm Rodagon WA lens? You also need a glass carrier and a critically aligned enlarger and be using the optimal aperture of the lens and be within the optimazation range of the lens.

You don't mention any of these very critical requirements for a high quality very large print. The longer the focal length the less the lens is corrected for larger magnification. You need a lens of the correct focal length corrected for the amount of magnification that you want.

[Ari]

Bob is exactly right.
I just wanted to add, from my own experience, that simply changing focal lengths will not improve your coverage; that depends on how much your particular lens will cover. Some shorter focal lengths cover more than longer focal lengths, to wit, some of the lenses Bob listed
And if you're interested in keeping your exposure times down, stay with a shorter focal length lens, as that will reduce your lens-to-paper distance.
Good luck.

[Dave Dawson]

"And if you're interested in keeping your exposure times down, stay with a shorter focal length lens, as that will reduce your lens-to-paper distance."

But it won't increase the illumination level:eek:

Same amount of light spread over the same area...Same level of light.

Cheers Dave

[Drew Wiley]

I routinely do 30x40 prints with 305 and 360 Apo-Nikkors, which are very sharp from f/11 down. When I need more speed I use a 360 El Nikkor at f/8. This is with
8x10 film of course.

[Arthur Nichols]

I cannot address the lens sharpness concerns that is left to more knowledgeable people than I, but I also have a 2000 Watt Devere color head that I use regularly for VC b&w printing. I purchased long life bulbs for my color head and have never had any problems with lamps burning out, even when leaving the enlarger on for long exposures. I assume that you have a fan powered cooling system for the head. I cannot imagine a 2000 watt head without one. Some further investigations into why lamps are buring out may be in order. Possibly there is a problem with insufficient air movement.

[ic-racer]

That lens does not cover the format at f11 at that magnification; and you know it because you just told us its blurry at the edges at that aperture and magnification. ;)

Just like a view camera lens covers better at closeup range, an enlarger lens covers better at small enlargements.

Doing a big enlargement is like going to infinity on your view camera, so coverage will get worse.

[Stephen Willard]

In response to some of the thoughtful considerations noted:


I use a negative glass carrier.

The 210mm lens is the shortest focal length lens I can use to cover a 4x10 negative. A 150mm lens will not cover the 4x10 negative.

All of the longer focal length lenses have considerably greater coverage than my 210mm lens.

I have aligned my enlarger with my own laser alignment tool.

All of the prints are razor sharp in the middle and soft on both edges 40 inches or greater.

All of the lenses I have tested range from 210mm to 240mm show the same characteristics of being sharp in the middle and soft at the edges. The Nikkor lens was the sharpest at the edges, but it to was still soft.

[Bob Salomon]

In response to some of the thoughtful considerations noted:


I use a negative glass carrier.

The 210mm lens is the shortest focal length lens I can use to cover a 4x10 negative. A 150mm lens will not cover the 4x10 negative.

All of the longer focal length lenses have considerably greater coverage than my 210mm lens.

I have aligned my enlarger with my own laser alignment tool.

All of the prints are razor sharp in the middle and soft on both edges 40 inches or greater.

All of the lenses I have tested range from 210mm to 240mm show the same characteristics of being sharp in the middle and soft at the edges. The Nikkor lens was the sharpest at the edges, but it to was still soft.


After selling enlarging lenses to professional, high end labs, for over 20 years and not having had youir complaints I would have to question your technique or your testing. Just what is your alignment system?

And you need a lens equal to the diagonal. That would be something like a 300mm Rodagon since you have a diagonal over 12" long on 4 x 10".

[Stephen Willard]

After selling enlarging lenses to professional, high end labs, for over 20 years and not having had youir complaints I would have to question your technique or your testing. Just what is your alignment system?


I use the Parallel by Versalab laser alignment tool to align my 10x10 Fotar enlarger. The enlarger has lots of adjustments that can be made to facilitate alignment. A 16x40 print enlarged from a 4x10 negative is will be very sharp in the middle, but both sides of the print will be soft. Either the lens is soft at the edges or the enlarger becomes noticeably out of alignment at the 40 inch length or 20 inches from the center. Here is a test I could do that just occurred to me:


If I am able to use my 10x focusing loupe and bring either end of the projected 16x40 image into focus by raising or lowering the colorhead then the problem is an alignment problem.

If I cannot bring either edge of the projected 16x40 image into focus then the problem is not an alignment problem, but rather an inherent shortcoming of the enlarger lens.




And you need a lens equal to the diagonal. That would be something like a 300mm Rodagon since you have a diagonal over 12" long on 4 x 10".
From my calculations the digaonal of a 4x10 negative is 10.77" or 273.558mm which is barely within the 270mm coverage of the lens. Perhaps I should consider getting a 240mm lens just to make sure!

Thanks Bob for your persistence. I will get back to you about the results of my little test outlined above. In any case, please recommend 240mm lens that would allow at least a 8x enlargement or greater. I want to get the best lens possible.

[ic-racer]

I think Bob knows his stuff. Even a 240 may only cover (ie sharp at edges) when stopped down more than f11. I'd use a 300mm. If you can't use that focal length and you can't stop down, then maybe consider horizontal projection. This may not be an easy problem to solve given the constraints.

If it were me, I'd give that head and power supply a good look over. Check for burned sockets, dirty diffusers, dirty filters, appropriate bulb voltage from the power supply, etc.

[Arthur Nichols]

Try using a 240 G Claron. I use this lens for enlarging 8x10 up to 30x40 and never noticed any loss of sharpness. It is definitely sharper under my peak magnifier than my 180 Componon.

[Nathan Potter]

Stephen as you suggested, try doing a critical focus at the extremity of your 30 X 40 inch enlarged image using a focusing aid. If you can establish maximum sharpness do an exposure and development on a piece of your paper to see if the sharpness is equivalent to the center region. Corner sharpness will be hard to judge using a grain focuser so you may want to use a loupe at an angle on a very smooth white surface.

If you are fanatical, a glass plate resolution mask will certainly give you a high contrast image that is flat. Possibly still available from Edmund Scientific. If only a small size is available just support it on a piece of flat glass over the corner to be evaluated. I use this to great advantage for enlarger alignment.

Nate Potter, Austin TX.

[Bob Salomon]

[LIST]

Thanks Bob for your persistence. I will get back to you about the results of my little test outlined above. In any case, please recommend 240mm lens that would allow at least a 8x enlargement or greater. I want to get the best lens possible.

The Rodagon 240mm 5.6 was corrected for 2 to 8X and the highest quality at that magnification and negative would be with the 300mm 5.6 Rodagon G (the 240 G did not cover 8x10). The 300 G was corrected for 8 to 30X magnification. So at 8X either lens will be about equal but above 8X the G wins hands down. These are big lenses. The 300G has a 90mm flange diameter and the 240mm was 72mm. So these will not fit most enlargers used at home.

[percepts]

please recommend 240mm lens that would allow at least a 8x enlargement or greater. I want to get the best lens possible.

Can you clarify whether you are talking about 8 times linear or 8 times area enlargement. I ask because 8 times linear is an 80x32 inch print which is pretty big by anyones standards. If you are talking 8 times area then you only need a lens with 4X magnification which means a rodagon-G is not the lens you want.

[Stephen Willard]

The Rodagon 240mm 5.6 was corrected for 2 to 8X and the highest quality at that magnification and negative would be with the 300mm 5.6 Rodagon G (the 240 G did not cover 8x10). The 300 G was corrected for 8 to 30X magnification. So at 8X either lens will be about equal but above 8X the G wins hands down. These are big lenses. The 300G has a 90mm flange diameter and the 240mm was 72mm. So these will not fit most enlargers used at home.

Bob, I have found some one selling the 240mm 5.6 Rodagon-G and claiming it will cover an 8x10 negative. The specification sheet I have on EL Nikkor lenses states its 240mm lens covers 8x10. In fact it has always been my belief that the 240mm lens was a wide angle lens for 8x10 much like the 135mm is a wide angle lens for 4x5.

The specs published by the seller of the 240mm 5.6 Rodagon-G says that it is corrected for enlargements of 8x-30x which is consistent with your statement. Does this mean that the lens will not work with smaller enlargements than 8x?

Currently I am moving toward doing big prints because that is what is selling well in todays market for me. The 240mm 5.6 Rodagon-G would be a great lens for my 4x10 and 5x7 negs I hope since the 4x10 has a digaonal of 273mm (correct me if I am wrong about this). However, I would not want to preclude having the ability of enlarging 8x10 negatives.

Bob, your comments are always appreciated.

[Stephen Willard]

Can you clarify whether you are talking about 8 times linear or 8 times area enlargement. I ask because 8 times linear is an 80x32 inch print which is pretty big by anyones standards. If you are talking 8 times area then you only need a lens with 4X magnification which means a rodagon-G is not the lens you want.

Percepts, I am finding out that big prints are selling well in todays depressed market. People who have money and are not effected by the recession have big homes and want big prints. Currently, I am using 4x10 and 5x7 negs and the largest size prints I can produce in my home color lab are 20x50s from my 4x10 negs and 30x40s from my 5x7. Both enlargements are less than 8x. However, there is a very good chance I will be opening a gallery in the next three years, and I intend to be targeting really big prints for big homes, hotels, and corporations. Those markets appear to be more resilient in economic down turns. I have two 10x10 horizontal enlargers in storage and having a lens that can handle enlargements greater then 8x would be a good long term investment.

[Stephen Willard]

Bob Salomon, I was just on the Rodenstock website and could not find specifications for both the 240mm 5.6 Rodagon-G lens and the 300mm 5.6 Rodagon-G lens. Could you post the specifications for these lenses? Are they multicoated lens?

Thanks, Stephen

[Oren Grad]

Stephen -

Pending Bob's response, I'm pretty sure the Rodagon-G series has been discontinued for a while. But there's an old Russian (distributor?) page with specifications here:

http://www.prograf.ru/rodenstock/enlarging_en.html#table1

The longest one - 480mm, optimized for 20x enlargement from formats up to 10x12" - boggles the mind.

[Drew Wiley]

Rodagon G was more for mural-size enlargements and probably not what you need anyway. A regular Rodagon would seem to be more appropriate for this degree of
magnification.

[Stephen Willard]

Stephen -

Pending Bob's response, I'm pretty sure the Rodagon-G series has been discontinued for a while. But there's an old Russian (distributor?) page with specifications here:

http://www.prograf.ru/rodenstock/enlarging_en.html#table1

The longest one - 480mm, optimized for 20x enlargement from formats up to 10x12" - boggles the mind.

Thanks Oreb. Unfortunately, the chart does not include the diameter of the images/coverage circle of the lenses. The diagonal of an 8x10 is 12.8" or 326mm. The diagonal of 4x10 is 10.77" or 273mm. At a minimum I need the lens to be able to cover 273mm for my 4x10 or 326mm should I decide to shoot 8x10. I also would like it to be the smallest focal length possible to minimize my colorhead heights. With a horizontal enlarger, space would not be as big of an issue.

[Oren Grad]

Well, you have to go to the 300 for the recommended format to reach 8x10, which is pretty much telling you the same thing. The only enlarging lenses for which I can recall seeing image circle specifications, as opposed to recommended formats, are my EL-Nikkors, which include them in the information sheets packed in the boxes with the lenses.

[Stephen Willard]

Stephen -

Pending Bob's response, I'm pretty sure the Rodagon-G series has been discontinued for a while. But there's an old Russian (distributor?) page with specifications here:

http://www.prograf.ru/rodenstock/enlarging_en.html#table1

The longest one - 480mm, optimized for 20x enlargement from formats up to 10x12" - boggles the mind.

Thanks Oreb. Unfortunately, the chart does not include the diameter of the images/coverage circle of the lenses. The diagonal of an 8x10 is 12.8" or 326mm. The diagonal of 4x10 is 10.77" or 273mm. At a minimum I need the lens to be able to cover 273mm for my 4x10 or 326mm should I decide to shoot 8x10. I also would like it to be the smallest focal length possible to minimize my colorhead heights. With a horizontal enlarger, space would not be as big of an issue.

[Bob Salomon]

Bob Salomon, I was just on the Rodenstock website and could not find specifications for both the 240mm 5.6 Rodagon-G lens and the 300mm 5.6 Rodagon-G lens. Could you post the specifications for these lenses? Are they multicoated lens?

Thanks, Stephen

Neither of these are in current production. Currently the 150mm Rodagon is the longest enlarging lens that Rodenstock currently makes. Both of these lenses would only be available on the used market.
Te half diagonal of the 300 G was 154.4mm and the 240 Rodagon was 153.8 so they both covered about the same full circle.

[Bob Salomon]

Bob, I have found some one selling the 240mm 5.6 Rodagon-G and claiming it will cover an 8x10 negative. The specification sheet I have on EL Nikkor lenses states its 240mm lens covers 8x10. In fact it has always been my belief that the 240mm lens was a wide angle lens for 8x10 much like the 135mm is a wide angle lens for 4x5.

The specs published by the seller of the 240mm 5.6 Rodagon-G says that it is corrected for enlargements of 8x-30x which is consistent with your statement. Does this mean that the lens will not work with smaller enlargements than 8x?

Currently I am moving toward doing big prints because that is what is selling well in todays market for me. The 240mm 5.6 Rodagon-G would be a great lens for my 4x10 and 5x7 negs I hope since the 4x10 has a digaonal of 273mm (correct me if I am wrong about this). However, I would not want to preclude having the ability of enlarging 8x10 negatives.

Bob, your comments are always appreciated.

He is wrong.

[percepts]

34991

The above pdf is the old rodenstock lens chart. They are not all available now.

From that chart you can see that the Rodagon 5.6 240 will cover 8x10 and would be good for your 40inch print. The 210 does not cover 8x10

But for your 8 X print the Rodagon-G 300 is required as the Rodagon 240 would be right at its limit as the optimum for the 240 is 4 X enlargement whereas its 20 X for the Rodagon-G. You might get away with Rodagon 240 or you might not. If your neg is less than perfect then that would be exagerated by using the 240 at 8 times.
A Rodagon 240 should be be cheap to find second hand so I would suggest you get one of those and see how you go. You can trial it at 8 times enlargement and see if its good enough and if not then get a Rodagon-G 300.
Neither of these lenses are current.

Unfortunately Nikon and Schneider never published this sort of data for their lenses so I don't know the comparisons for those lenses which leaves you needing to buy to try those lenses to see if they are better or not.

p.s. the Rodagon 300 would also do it for you and being less of a wide angle lens I would suspect it would perform better than the the Rodagon 240.