Enlarger focusing problem

[jlpape]

I am in the process of setting up a Beseler 23C II for 35mm and 6x6 printing. I recently purchased a 80mm Rodagon f/4 lens on eBay and received it today. I did the procedure in the manual for leveling out the enlarger and installed the lens and a negative. What I see when at full aperture is the image in focus (or close to it) in the center of the image but very out of focus off center. Talking about noticeably out of focus 1/4 way from center out to the edge. Stopping down improves matters, but is there something that I am doing wrong here? I cannot believe that this would be typical performance for this lens wide open.
Thanks in advance,
Jim

 

[keithwms]

So you radial loss of sharpness? It's not sharper toward one side than the other?

 

[jlpape]

So you radial loss of sharpness? It's not sharper toward one side than the other?

Nope, I was looking for that. It's radial. Also, I cannot focus the outer sections, they go from blurry to blurrier.

 

[keithwms]

If it's radial blur then chances are that it is indeed a lens issue and you'll need to stop down or get another lens. Unless your work surface or paper is concave or convex

 

[Arvee]

For leveling the 23CII, there are several adjustments. At the negative stage, use the plastic adjustment bolt/nut at the bottom of the enlarger head, below the lens/bellows. This will adjust fore/aft at the negative stage. Side/side has a small amount of adjustment by loosening the two hex screws that fasten the head support bracket to the carriage. This is all you have for the neg stage.

The lens stage is adjusted with the knurled screw just above the plastic bolt mentioned above. The side/side adjustment is accomplished by loosening the knurled screw and rocking the lens stage adjusting for balanced focus at each side of the enlarged image.

The other axis (top/bottom) of the neg can be adjusted but not easily. You have to remove the back of the little box that the knurled screw goes into (it just pops off with a screwdriver) and remove the locking screw threaded into the back of the knurled screw. NOTE the position and order of the washers as they are assembled on the threaded portion of the knurled screw. Adjustment is accomplished by shimming the 'washer pack' between the box and the articulating side/side lens adjustment bracket.

Hope this helps,

Fred

PS. I was typing when the other posts came in. Perhaps someone has taken the lens apart and re-assembled it improperly. The convex surfaces of each element face outward from the iris in most conventional six element designs.

 

[RobC]

is that a condenser enlarger because if it is then you must make sure you have correct condensers and they are fitted the right way round. There may be one or two condenser lenses. And are they the right condensers for 6x6 or 6x7 or are they the condensers for 35mm?

 

[keithwms]

Fred's comment reminded me of the possibility that your neg stage and lens stage are not parallel. When you say that the loss of sharpness is radial, is it really symmetric? Try tilting one stage to see if you see any improvement at all.

 

[Arvee]

Good point, Rob! The condenser system in the 23CII uses two different condensers. The round surfaces face each other but one is flat and one is slightly convex. The slight convex is the bottom one. The flat one goes into the top of the condenser pack.

Also, be sure the knob next to the top of the head is set to whatever size neg you will be using.

Fred

 

[jlpape]

Thanks for all of the responses. Yes, it does appear to be radial. Tilting the stage does not help. Trying to focus the off-center part of the neg is impossible. I did a full check from the top down of the enlarger. The condenser is set to 35mm, I believe it is in the right way, impossible to set any other way (but would this impact focus anyway?). The negative stage and lens board are parallel to the baseboard in both the x and y directions, at least to the precision of a fairly good level. I also checked the flatness of the negative carrier, and that seems to be fine as well. Negative is sitting flat in the carrier, emulsion side down. Nothing in the path of the light between lamp and condenser, condenser to neg and neg to lens.
Regards,
Jim

 

[jlpape]

Good point, Rob! The condenser system in the 23CII uses two different condensers. The round surfaces face each other but one is flat and one is slightly convex. The slight convex is the bottom one. The flat one goes into the top of the condenser pack.

Also, be sure the knob next to the top of the head is set to whatever size neg you will be using.

Fred

Hi Fred,
Condensers are oriented as you state.

 

[Arvee]

jlp,

Do you have another lens to use to determine if the problem is enlarger or lens?

If you don't have another enlarging lens, you might be able to hold a 50mm camera lens to the lens board and quickly see if it has uniform focus. A camera lens isn't perfect but certainly would be flat enough to make a determination.

BTW, the condenser pack should be set to 2 1/4 x 2 1/4 or 2 3/4 for an 80mm lens.
Fred

 

[jlpape]

So, now that it is darker in the house (darkroom under construction) I see that at f8 or so the image appears to be sharp, but wider apertures, IQ suffers. Am I right in assuming that the image should still be in focus corner to corner even wide open? Not to be confused with optimal IQ when stopped down a bit from wide open. In my case f4.0 and 5.6 would be unusable.

This is not a cheap lens, new, so I believe I should expect better.

Jim

 

[Lee L]

The condensers will have an effect on evenness of illumination, but won't affect focus.

I'd agree with an earlier poster that it's a lens problem, either badly reassembled or perhaps missing an element or perhaps more. IIRC, this is a double-Gauss type lens, and they're often in separate front and rear cells that screw together inside a barrel with aperture, each cell holding a set of three elements. One of these cells (most likely the rear) may be missing. Is the aperture behind three glass elements when viewed from the negative side, or is it exposed?

Lee

 

[RobC]

your 80mm lens is for 6x6 and possibly 6x7 so condensers should be set for 6x6 or 6x7 and not 35mm.

You should be using a 50mm lens for 35mm or thereabouts.

 

[Arvee]

That lens should be quite good at f4. You can close down the aperture and stand under a bright light and look into the lens and count the reflections viewing into each end of the lens. You should see 3 reflections from each side if the lens is intact but doesn't guarantee that it is assembled correctly.

Fred

 

[keithwms]

I agree that the lens should be acceptable at f/4... sounds like it's not. But frankly... I don't know when I'd ever print at f/4, that's pretty damn bright! Even when I use a grain focuser I work at f/8 or so just to spare my eyes. If you print at f/4 you won't even have time to pick your nose.

As mentioned, the condenser pieces should only affect the falloff, not the focus.

Let me suggest making yourself an inexpensive corner test target by inkjetting some concentric circular patterns onto some overhead transparency material. This high contrast focus target will allow you to check sharpness at fairly small apertures. This technique is better than trying to move around with a grian focuser because these (at least the ones I've used) don't allow you to easily get right over to the edges where misfocus is most obvious.

 

[jlpape]

jlp,

Do you have another lens to use to determine if the problem is enlarger or lens?

If you don't have another enlarging lens, you might be able to hold a 50mm camera lens to the lens board and quickly see if it has uniform focus. A camera lens isn't perfect but certainly would be flat enough to make a determination.

BTW, the condenser pack should be set to 2 1/4 x 2 1/4 or 2 3/4 for an 80mm lens.
Fred

Hi Fred, tried the 50mm camera lens test that you mentioned (do not have another enlarger lens)... had to hand hold the lens, but I was able to get great focus corner to corner. Even the center looked much, much better.

Also thanks for the condenser direction I was wondering if it should match the lens or the negative.

So, I am going to assume that the lens is bad. The seller has a 100% rating (300+ sales) and has a 14 day return policy, so I do not think that there will be a problem returning it.

Someone suggested looking to see if all the elements were there... As far as I can tell yes, three reflections in the front and three in the back.

Thank you all for your help.

Best Regards,
Jim

 

[jlpape]

I agree that the lens should be acceptable at f/4... sounds like it's not. But frankly... I don't know when I'd ever print at f/4, that's pretty damn bright! Even when I use a grain focuser I work at f/8 or so just to spare my eyes. If you print at f/4 you won't even have time to pick your nose.

As mentioned, the condenser pieces should only affect the falloff, not the focus.

Let me suggest making yourself an inexpensive corner test target by inkjetting some concentric circular patterns onto some overhead transparency material. This high contrast focus target will allow you to check sharpness at fairly small apertures. This technique is better than trying to move around with a grian focuser because these (at least the ones I've used) don't allow you to easily get right over to the edges where misfocus is most obvious.

Hi Keith,I agree that I would not use it at f/4, however, I think if there is an issue wide open, then that will translate to sub-optimal performance at smaller apertures.
Best regards.
Jim

 

[Lee L]

Someone suggested looking to see if all the elements were there... As far as I can tell yes, three reflections in the front and three in the back.

I should also have mentioned that missing half the elements in a double Gauss design would noticeably lengthen (very approximately double) the focal length of the lens.

Lee

 

[RobC]

well I would suggest you put a medium format neg in the enlarger and then test again because using a 35mm neg and 80mm lens will not perform optimally on a condenser enlarger as far as I'm aware.

Furthermore, an 80mm Rodagon has an optimal enlargement factor of X6 with maximum of X10 so if you were using a 35mm neg and moved enlarger head high up, then you would likely be way past the optimum enlargement for that lens. So test again using a medium format negative and I think you will get better results because you won't need to enlarge so much.

Alternatively, test using 35mm neg and 35mm condensers but aim for print size of at or below 9x6in and see if that gives you a good image because the enlargement factor will be optimum for 80mm lens at that print size from a 35mm neg.
For a 6x6cm neg optimum enalrgement will be at or below 13 1/2 x 13 1/2 ins. Any bigger and lens performance will start to drop off.

 

[Nicholas Lindan]

80mm Rodagon f/4 lens on eBay ... the image in focus (or close to it) in the center of the image but very out of focus off center.

I would suspect someone has taken the lens apart and put it back together again with an element reversed. If it seems like its focal length is much other than 80mm an element may be missing.

Are there any scratch marks on the lens's lens retaining rings? That's usually a give-away: someone who would put it together backwards is also likely to have used a pair of scissor points or crossed screwdrivers to unscrew the rings.

 

[jlpape]

well I would suggest you put a medium format neg in the enlarger and then test again because using a 35mm neg and 80mm lens will not perform optimally on a condenser enlarger as far as I'm aware.

Hi Rob, Happens at all enlargements.