Rodagon 80mm + Omega C700 = pincushion?

[nisander]

Hi, all,
I've just recently acquired an Omega C700 enlarger and Rodagon 80mm f4 enlarging lens and had a question concerning some distortion I'm seeing. Upon assembling and testing everything last night I've noticed a bit of pincushion distortion with the set up. Unfortunately it's my only lens so I won't be able to tell if it is a problem with the lens or the head, but I was curious if anyone has experienced this problem before. Would this be an alignment issue perhaps?

This is my first enlarger so sorry to bore you all with a novice's question but I appreciate any and all help.

 

[emerson531]

Hi, all,
I've just recently acquired an Omega C700 enlarger and Rodagon 80mm f4 enlarging lens and had a question concerning some distortion I'm seeing. Upon assembling and testing everything last night I've noticed a bit of pincushion distortion with the set up. Unfortunately it's my only lens so I won't be able to tell if it is a problem with the lens or the head, but I was curious if anyone has experienced this problem before. Would this be an alignment issue perhaps?

This is my first enlarger so sorry to bore you all with a novice's question but I appreciate any and all help.

What are you using for your test negatives? Could the distortion be due to the camera lens? I would be surprised if either your enlarger or the rodagon was the cause ....good luck with the investigation Emerson

 

[Kevin Caulfield]

So, the actual edges of the image on the neg are curved inwards towards the middle? Sounds odd. I'd agree with the previous poster and question your test neg.

 

[Ed Sukach]

That has to be something wong with the lens. I have the Rodagon 80mm f/4 and it is a **fine*"* performer, with no trace of "pincushion" distortion, at any aperture.

I would suspect that at some point, the lens was disassembled, probably for cleaning, and reassembled incorrectly, by leaving out an element spacing shim or using the wrong one, reversing (front to back) an element (possible, at times), or something similar.

Many Rodenstock lenses carry lifetime gurantees. Contact them.

 

[nisander]

Thanks, Emerson. All of my photos are taken with a 50 or 80mm Hasselblad lens, which if anything display a bit of barrel distortion (so in some ways maybe the pincushion effect corrects this and I needn't worry).

Here is an example of the barrel effect with a photo taken at f4 with the 80mm from a scanned negative:

Yet there is still an inward curving of the square image projected out of the enlarger at all apertures even when there isn't a negative in the carrier. I'm REALLY hoping there isn't something out of alignment with the two condensor glass things because I wouldn't know where to begin as far as correcting them, supposing there is a way to do this in the first place. At the end of the day I'm sure a cropped image will work just fine but I thought I'd try to get to the root of this slight aberration regardless.

Thanks again.

 

[emerson531]

Given you still get the pin distortion with just the empty negative carrier it must be a damaged enlarging lens. The condensor lenses above the carrier should NOT be a problem. If you were in Ottawa Canada I would lend you my rodagons to check..rgds Emerson

 

[nisander]

Thank you all for your help!

 

[Ed Sukach]

I did not see "barrel" distortion. What Is there is what is commonly called "Wide-Angle" distortion - remember that a 50mm lens used with medium format is "wide angle". Back up and make another image. This apparent distortion will lessen.

It would be rare indeed for anything NOT between the lens, film, or focal plane to cause distortion of any kind - and that is where the "condensing lenses" are located. They are, properly, collimating lenses, and serve the purpose of providing EVEN illumination across the film.

 

[PHOTOTONE]

The enlarger (no matter what brand and model) will absolutely NOT cause pincushion or barrel distortion. If the enlarger is mis-aligned, the only flaw you might see is lack of even sharpness across the width and height of the image area. If a Rodagon lens exhibits distortion, then it probably has been dis-assembled and re-assembled wrong. It has to be the lens, but the Rodagons do not exhibit significant (or any) distortion when used for their intended formats.