using a 135mm lens to enlarge 6x7??

[stradibarrius]

I trypically use a 90mm enlargeing lens for my 6x7 negs but wondered how a 135mm would work? Will that improve edge sharpness?

[3e8]

In theory, yes. The edges of the lens are less "sharp" than the center. With a 135mm lens on a 6x7 neg, you would not be using the edges of the lens. I put sharp in quotes because with a good quality lens, it's unlikely that you will be able to tell the difference, unless at very high magnifications.

The image will be smaller on the baseboard with a 135mm, so you have to raise the head, resulting in longer printing times.

With most quality enlarging lenses, you likely won't see a difference. I do this for my med format negs just because my enlarger is mounted on an enlarging box such that it's more convenient to have the easel lower.

Cheers,
Bryan

[awldune]

Before you buy a 135mm lens, be sure your enlarger can focus that lens. Beseler 23C for example does not have enough bellows draw.

[Ronald Moravec]

You will also need to raise the head 30+% more for the same size print.

If you were to use a modernish enlarging lens, you will not see an improvement. If you have some cheap 90 mm, just buy a decent one .

This whole idea was started by Ansel Adams back when lenses were not so good. It is no longer valid for decent lenses.

If you have soft edges, the first thing I would improve is getting a flat negative and properly aligning the enlarger which if you do not accomplish, a perfect enlarging will not be adequate.

Generally a flat neg is obtained from a double glass negative carrier.

A neg is not flat in an open carrier and heat from the bulb can cause it to bow upward even more. When this happens, the center can be focused, but not the edges. A quick check can be made if you focus on the center with a grain magnifier and then can refocus on the corners getting them sharp. Unless you have a dog of a lens or an alignment problem, this will tell you the neg is not flat enough.

[polyglot]

Theoretically more sharp yes... but your 90mm lens should give you grain-sharpness all the way to the corners if it's any good. No point resolving more than the grain.

I don't think your printing times will increase for a given enlargement as long as the 135 is used at the same f-stop as the 80. Of course if it's a slower lens, printing will be slower.

[ic-racer]

It also depends on how much magnification you are using. If the magnification is low (that is small prints) you are only using the center of your 90 anyway. That is one reason 'cheap' lenses can be OK for small prints.

The paradox is that for big enlargements (where your 90 may be stressed at the edges) using the 135 will be difficult because of the column height required.

[Anscojohn]

I trypically use a 90mm enlargeing lens for my 6x7 negs but wondered how a 135mm would work? Will that improve edge sharpness?

******
It should. Probably more even lighting, as well. At least that's what the old lab rats told me, although that might be more than "one size over." I use either a 100 or 105 for 6x7.

[David A. Goldfarb]

If you've got both lenses in hand, then test and report back. I don't think you can predict which will be better theoretically, since the additional column height in any given case may introduce greater column vibration, which, could reduce sharpness. How solid is your darkroom floor? While the longer lens may have a sharper sweet spot in the middle, the right-sized lens may be sharper in general, because it doesn't need to cover as large a neg.

[MattKing]

stradibarrius:

If you decide to join us in the Postcard Exchange, you will appreciate the 135mm lens. I used a 150mm Rodagon for my last batch (from a 6x7 negative).

Which is just another way of saying that for smaller enlargements, there is an advantage when using a good quality longer lens, as compared to using a good quality shorter lens.

If one lens is of better quality, in most cases that will be the one to use.

Don't forget, as well, to consider other factors, like the benefits to be enjoyed as a result of features like illuminated f/stop indicators, and larger maximum apertures (for focussing).

[Ronald Moravec]

Times do not change. F8 is F8 reguardless off focal length.

I sometime use a longer lens for small prints because I want the increaded print to neg distance. Over 8x10 things get very unweildy. I do not see increased edge resolution. Repeat, do not see.