Problem w/ focusing new 135mm lens

[gphoto120]

I just bought a a used, however, Mint in appearance Nikkor 135mm enlarging lens to use w/ my Omega D2 enlarger and fitted w/ an Ilford 500 head. I 'm not able to focus a neg. period! I first tried a 4x5 neg. with the 2.75" cone, then without the cone on just a flat lens board same thing. (I did put the correct 4x5 diffuser in the head). There is a very small perceptible difference if I stop down completely to f45 from 5.6 but nowhere near being "in focus"
Then I tried it using a 6x6 neg (w/ proper size diffuser box for 6x6) and it still won't focus. I tried the 6x6 w/my 80mm lens to check and make sure something wasn't messed up with some other component and I can focus fine w/ the 80mm. Does anyone have an idea on what could be the problem....can it be the lens? If so, what could be the problem w/lens? This lens looks brand new and was described as being in excellent condition, which I think it is. My next step is to borrow another 135mm and try it out to see if there is any difference.
Thanks for any suggestions!
GP

 

[Neal]

Dear gphoto120,

My EL-Nikkor 135mm is mounted on a 2-3/4" cone and focuses properly.

I hope you resolve your issue,

Neal Wydra

 

[elekm]

Are the rollers of the assembly on the correct rail in the column? Also, when I bought my D3 years ago, my 135mm Wollensack was on a 4 1/4-inch cone.

 

[ic-racer]

That 2.75" cone should be the correct cone for a 135mm lens.
Does the 80mm lens focus using the flat plate?

 

[gphoto120]

That 2.75" cone should be the correct cone for a 135mm lens.
Does the 80mm lens focus using the flat plate?

Yes, both my 80mm and 50mm lenses work fine on the flat board, which is why I tried the 135mm on both the flat board and 2.75" cone. I haven't changed anything other than trying out the new lens and changing the mixing box to 4x5. I also double check that to make sure I put the box in properly.

 

[ic-racer]

Yes, both my 80mm and 50mm lenses work fine on the flat board, which is why I tried the 135mm on both the flat board and 2.75" cone. I haven't changed anything other than trying out the new lens and changing the mixing box to 4x5. I also double check that to make sure I put the box in properly.

Hmmm. Maybe an odd-ball thing, like the front and rear lens group of the lens are not from the 135mm. Can you hold the lens under the bellows and get it to focus any inage?

 

[Nicholas Lindan]

What are the minimum and maximum distances from the center of the lens to the negative carrier? The maximum should be 270mm (10 3/4 ") for 1:1 prints and the minimum 165mm (6 1/2") or less for a 5x or greater magnification.

 

[Marcus K]

It sounds like you're using the right sized cone which is required for a 135mm lens on the D2 enlarger (because the bellows won't extend far enough down). Going off what Nicholas said, you may need to raise the head of the enlarger higher up to be able to focus properly. If the head is not high enough, you won't be able to focus any image even if you are using the correct cone and lens.

 

[Ian C]

Estimating Lens Position for a given

It’s unlikely that there is anything wrong with your lens. It will do what it is supposed to if you place it at the correct position relative to the negative.

Here’s how you can use a metric scale and figure it out.

The Thin Lens Formula is:

1/f = 1/p + 1/i

where f = focal length of the lens, p = distance from the object to the center of the lens, and i = the distance from the image to the center of the lens.

So

1/i = 1/f -1/p = (p-f)/fp

Then

i = fp/(p-f)

Let’s suppose that you’ve placed the lens with its diagram 400mm from the print. Then p = 400 and f = 135. So

i = 135*400/(400-135) = 203mm.

So the diaphragm must be about 203mm (roughly 8 inches) from the negative.



If the diaphragm is 700mm from the print, then p = 700 and f =135. Then

i = 135*700/(700-135) = 167.3mm (about 6.6 inches).

You can use the equation to estimate where the diaphragm of the lens must be positioned to focus for a given diaphragm to print distance.

 

[gphoto120]

Thank you folks for your help and suggestions. As it turned out....it was "user error" This was the first time I have used a lens cone and 4x5 as well.......I had mounted the lens board on the OUTSIDE of the cone. After going over every step including taking the lens apart etc. I realized the only other variable I overlooked was in mounting the lens board on the cone. I just mounted the board on the inside of the cone, and...IT WORKS PERFECTLY!!
I feel like such a dummy! So thanks again to everyone who responded to my post !

 

[Jon Shiu]

Glad you got it working, but I have always mounted the lensboard on the outside of the cone. Regardless, the 1/4" or so difference should not matter, because you have ample focus travel.

Jon