using a 135mm lens to enlarge 6x7??

[Ian Grant]

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.

Times will change because the bellows distance increases as well as the height of the enlarger when you use a longer focal length lens, it's the inverse square law.

It also depends on the enlargers light source, a condenser enlarger needs the right condenser set for each focal lenght lens.

In practice there's no benefits of using a longer lens unless you're making small prints, or even reductions.

Ian

[fschifano]

All good advice here. Truth be told, I have an 80 mm. Schneider Componon-S that I use for 6x6 and 6x7 negatives. It's not officially rated for the 6x7 negatives, but it works well at up to 8x magnification, and that will get you a print greater than 16 x 20 from a 6x7 negative. At f/8 or f/11, it's clean all the way out to the edges. I don't see any difference between prints made using that lens or those made with a 135 mm. EL-Nikkor at that level of magnification. Using the longer lens does come in handy when making small prints from medium format negatives because of the extra working distance it affords. It's a lot easier to get a soft penumbra with a dodging tool when it's not smack up against the paper.

[ic-racer]

In practice there's no benefits of using a longer lens unless you're making small prints, or even reductions.

Ian

Actually it is high magnification that taxes a "standard" lens. This is the cool trick where an enlarging lens with a focal length longer than the film diagonal can be a cheap substitute for an APO-HM (High Mag) enlarging lens. This trick may only be applicable to those with 8x10 enlargers, though (because of the column height needed).

[ic-racer]

Just so everyone is on the same page, Trouble areas are as follows:
1) At a large magnification, the lens gets much closer to the film. The cosine effects are more pronounced so more light falloff compared to a longer lens.
2) If the lens has good flatness of field at low mag (far from the negative) it is unlikely the same lens will have good flatness of field when close to the negative (high mag).
3) The corners of the negative will be very close to the image circle at high mag. Centering will be crucial.
4) The lenses angle of view of a typical diffusion light source opening will be such that the opening appears smaller, and may not be big enough for the film format. Forcing the paradox of going to the bigger light box (when you really wanted to use that smaller, brighter, one for your massive full-frame enlargement!)

Typical 'normal focal length' High Mag enlarging lenses solve some of these problems, but just using a cheap 'standard magnification' lens of longer focal length can be even better (as it also helps with #4 and #1 above, where the 'normal focal length' HM lens won't help those two because of physics).

[RobertV]

I have an 80 mm. Schneider Componon-S that I use for 6x6 and 6x7 negatives. It's not officially rated for the 6x7 negatives, but it works well at up to 8x magnification,

Interesting because it's competitor, Rodenstock Rodagon 4,0/80mm is specified till 6x7cm.
It's the lens I use for my 6x7cm negatives.

[fschifano]

Yeah, I think Schneider is being extra conservative with their recommendation. The reason I added the 8x limitation to my post is because that's how far I've pushed it. It would likely be fine for more than that, but I'm not equipped to handle a 20+ inch print.