Enlarging Lens Question

[Travis Nunn]

I'm a little unclear on this....
I'm making small enlargements from 6x4.5 and 6x7 negatives using an 80mm lens. The problem I have is that the lens is too close to the easel. Would using a 135mm or a 150mm lens give me some extra space between the lens and the easel?

Seems simple but I'd rather know for sure before buying another lens.

 

[Sirius Glass]

Yes. 135mm should do it. 150mm will do more. Time to buy the enlarging lens and a Large Format camera to go with it.

Can you borrow or rent a lens to try it?

Steve

 

[Travis Nunn]

Thanks, Steve. I thought it would do the trick, but there's always that little bit of doubt. I don't know of a place where I can borrow or rent one. Richmond kinda sucks as far as the photographic community is concerned unless you're strictly digital. They aren't too expensive so I'll just pick one up off ebay.

 

[dentkimterry]

I needed a 135mm to make 5x5's comfortably from my Hasselblad negatives. It worked very well

Terry

 

[fotch]

Travis, do you already have an extra lens board? Be sure to get the right size lens mount for what ever board you will be using. Also, the retaining ring.

 

[srs5694]

When pondering these sorts of questions, I sometimes find it useful to imagine a camera sitting behind the bellows, rather than a negative carrier. What happens to the field of view projected on the film when I swap in a longer lens? It gets smaller. To view the same size (say, a 4x6-inch area on the baseboard), I'd need to move the camera further away (raise the head). It works the same way with a regular enlarger setup, of course; it's just that the light is travelling (predominantly) in the other direction.

 

[Travis Nunn]

When pondering these sorts of questions, I sometimes find it useful to imagine a camera sitting behind the bellows, rather than a negative carrier. What happens to the field of view projected on the film when I swap in a longer lens? It gets smaller. To view the same size (say, a 4x6-inch area on the baseboard), I'd need to move the camera further away (raise the head). It works the same way with a regular enlarger setup, of course; it's just that the light is travelling (predominantly) in the other direction.

Makes sense Sometimes I just need to reassure myself that my thinking is correct.

Fotch, I do have an extra lensboard already so I'm good with that. Thanks!

 

[Travis Nunn]

So just an update... a fellow APUGer sent me a pm with some potential issues I may run in to; one being "the long lens will draw considerably more bellows than the regular lens. Depending on the enlarger, you might not have enough bellows to focus onto a small print."

Well, he was right on the money. I found a really cheap 135mm lens and gave it a try. I don't have enough bellows to make the prints as small as I want (3x3.5, 2x4, etc...). I'm only out $10 so it's not really that big of a deal.

Lesson learned, though.

 

[ic-racer]

You did not mention the enlarger brand or type, but many brands have extended lensboards or lensmounts to help solve that problem (ie Omega, Durst, others I'm sure).

 

[Rick A]

I suspect a lens in the range of 90-105mm will help you out. Personally, I would look for the 105mm, I dont think you would have any problem with focus.

 

[srs5694]

You could also get some extension tubes. If nothing else, some Russian/FSU sellers on eBay may have them for old M39 Zenits, but if your enlarger uses a standard 39mm lens mount, those should work fine with your enlarger.

 

[Travis Nunn]

Rick, I believe you're right. That was my next step, look for a 90mm-105mm lens and if I can find one cheap enough, give it a try

 

[Travis Nunn]

You could also get some extension tubes. If nothing else, some Russian/FSU sellers on eBay may have them for old M39 Zenits, but if your enlarger uses a standard 39mm lens mount, those should work fine with your enlarger.

I have a Chromega c760 so yeah, it's the standard 39mm mount.

 

[michaelbsc]

When pondering these sorts of questions, I sometimes find it useful to imagine a camera sitting behind the bellows, rather than a negative carrier. What happens to the field of view projected on the film when I swap in a longer lens? It gets smaller. To view the same size (say, a 4x6-inch area on the baseboard), I'd need to move the camera further away (raise the head). It works the same way with a regular enlarger setup, of course; it's just that the light is travelling (predominantly) in the other direction.

This is how I visualize it as well. Makes it intuitive instead of rote.

 

[ic-racer]

When pondering these sorts of questions, I sometimes find it useful to imagine a camera sitting behind the bellows, rather than a negative carrier. What happens to the field of view projected on the film when I swap in a longer lens? It gets smaller. To view the same size (say, a 4x6-inch area on the baseboard), I'd need to move the camera further away (raise the head). It works the same way with a regular enlarger setup, of course; it's just that the light is travelling (predominantly) in the other direction.

Actually the better analogy, which is really not an analogy but an equivalent, is to just think of the bellows going from the lensboard to the paper. The enlarger is exactly the same as a large fromat camera doing macro work. The optical formulas for macro photography, bellows extension, field of view, diffraction, lens coverage, depth of field etc. are the same.

 

[Ian C]

Limit Imposed by the Bellows When Making a Small Print

As pointed out, some enlargers can be fitted with recessed boards to allow placing the lens close enough to the negative to achieve focus on machines that otherwise couldn’t get the lens close enough.

Good examples are some models by Durst, Beseler, DeVere, Elwood, and some Omega models. Other enlargers can’t use recessed boards due to the small cross section of the bellows that taper down to a lens receiver just big enough for the lens and its mount.

You can measure the maximum bellows extension your enlarger allows and calculate the magnification m you’ll use determined by the negative and print size wanted to determine what focal lengths will give you what you need and still fit the enlarger.

You mentioned the use of 6 x 7cm negatives and possibly wanting 2” x 4” prints. That provides an example to see how it works.

Suppose that with your bellows fully extended the distance from the negative to the approximate position of the diaphragm of a typical enlarging lens is 135mm. That’s the limit imposed by your bellows if you can’t use a recessed board. You need to project the image of the negative big enough to fully cover the 4” length of the print to make a borderless print. Suppose that the 70mm dimension of the negative must be projected to 4.3” = 109mm.

Then m = print dimension/corresponding negative dimension = 109/70 = 1.6

The lenses that fully cover the 6 x 7cm negative at all conventional print sizes are: 60mm (e.g. Rodagon WA), 80mm, 90mm, and longer.

The distance from negative to diaphragm is

p = (1 + m)f/m

The distance from the diaphragm to the print is

i = pf/(p-f)

for a 60mm WA lens p = (1 + 1.6)*60mm/1.6 = 97.5mm diaphragm to print

and i = 97.5*60/(97.5 – 60) = 156mm negative to diaphragm.

In the form: focal length/negative-to-diaphragm/diaphragm-to-print, we have

60/97.5/156

80/130/208

90/146/235

But 146mm exceeds the 135mm limit we measured, so a 90mm lens is too long for this enlarger.

These are not necessarily exact, but the calculated values give us approximations that are close enough for most practical purposes.

 

[tlitody]

As pointed out, some enlargers can be fitted with recessed boards to allow placing the lens close enough to the negative to achieve focus on machines that otherwise couldn’t get the lens close enough.

He would need the opposite, i.e. a top hat extender to get lens further from negative. Lens has a longer focal length.

But since required magnification is less than 2X I would suggest looking for a 105 process lens if such a thing exists because most enalrging lenses are not optimised for less than 2X enlargement. Process lenses are designed for 1:1 upto maybe 1:2 or or 1:3 enalrgments or reductions. There is a currently produced APO Rodagon D 120 lens and with a top hat extender that would be perfect but pricey.

 

[fotch]

Maybe time to get a 4x5 enlarger. Probably cheaper in the long run.

 

[Ian C]

Yes, I should have said "Extended Lens Board."

 

[Travis Nunn]

Ian, thanks for such a detailed response. It's only a minor hassle so I think my 80mm lens will be just fine.

Fotch, I agree and I would love to have a 4x5 enlarger. In fact I had one, but had to give it away, it was just entirely too big for my darkroom, which is a converted bathroom.

 

[tac]

I think the 105 is where I would look first, And don't forget the retaining ring if your enlarger needs one, or just switch out the one you already have.

And an aside - Isn't APUG a great place!