Agfa apotar 85mm allways focused on infinity - frozen

[artur2000]

Hello forum members!

I've got an agfa isolette II folding camera with agfa apotar 85mm f4.5 lens.
I look for someone, who knows, how the lens agfa apotar 85mm is supposed to focus.

I attach my drawing for this lens here. Looking from the right side, you can see the two lenses which form the front facing tubus.

Now my question - how is the lenses focus adjustment supposed to work:
1) by variation of the distance between the first and second lens within the front tubus?
2) by variation of the distance between the front tubus and the third/rear lens?

I am able to screw in and out the entire front tubus from the shutter casing.
But I am not able to rotate the parts of the front tubus itself - is this what is known as "frozen apotar lens"?

Artur

 

[dxqcanada]

Three elements in two groups. The focus adjustment is performed by the front group of two elements ... they both move as one.

 

[dxqcanada]

Pronto, pronto … Prontor.

Ok, so I got an Agfa Isolette with the bunch of folders from Goodwill. This camera was really cheap … so this has now become a test subject … or should I say an experience building proj…

oldcam.wordpress.com

 

[Nicholas Lindan]

#1.

The focusing helical is between the front and middle elements.

The lens should extend ~2mm focusing from close-up to infinity.

There are lots of posts and articles on fixing a frozen focusing helical on Agfa Cameras. Google for "agfa frozen focus" for a slew of remedies - pick the one that seems the least evil to you.

The steps are:

1. Scribe a line between the focusing scale and the front element surround.
2. Remove the setscrews around the focusing scale.
3. Unscrew the front lens capsule from the shutter.
4. Scribe a line between the front and back halves of the capsule.
5. Separate the lens capsule halves, if you can. People have found heat and solvents work to unfreeze the halves.
6. Remove as much of the green goo/glue as possible with a toothpick, Q-Tip and some lighter fluid (white gas/Coleman fuel/naptha).
7. Relube the helical threads with a synthetic grease (the synthetic stuff doesn't throw off oil or outgas) or 'vacuum grease'.
8. Put the two halves back together - check that the scribe marks line up. Note there are three or more ways the halves can screw into each other.
9. Screw the capsule back into the shutter and tighten well.
10. Slip the focusing scale back over the front half of the capsule, again line up the scribe marks, and tighten the setscrews.
11. Stretch some 'magic' Scotch tape across the film gate in lieu of a ground glass and confirm the lens focuses correctly.

 

[Pioneer]

If I had a dollar for every post from someone trying to figure out how to fix the frozen focus on an Agfa folder I would be quite a rich man.

I love my Agfa folders but those cameras were never intended to last for a long time, certainly not for this long. Their only purpose for existing was to sell Agfa film.

 

[Alex Varas]

Take out both front elemets, use a hairdryer to heat the set, then the front lens will be easly removed but beware of the heat metal.

 

[albada]

#1.

The focusing helical is between the front and middle elements.

The lens should extend ~2mm focusing from close-up to infinity.

There are lots of posts and articles on fixing a frozen focusing helical on Agfa Cameras. Google for "agfa frozen focus" for a slew of remedies - pick the one that seems the least evil to you.

The steps are:

1. Scribe a line between the focusing scale and the front element surround.
2. Remove the setscrews around the focusing scale.
3. Unscrew the front lens capsule from the shutter.
4. Scribe a line between the front and back halves of the capsule.
5. Separate the lens capsule halves, if you can. People have found heat and solvents work to unfreeze the halves.
6. Remove as much of the green goo/glue as possible with a toothpick, Q-Tip and some lighter fluid (white gas/Coleman fuel/naptha).
7. Relube the helical threads with a synthetic grease (the synthetic stuff doesn't throw off oil or outgas) or 'vacuum grease'.
8. Put the two halves back together - check that the scribe marks line up. Note there are three or more ways the halves can screw into each other.
9. Screw the capsule back into the shutter and tighten well.
10. Slip the focusing scale back over the front half of the capsule, again line up the scribe marks, and tighten the setscrews.
11. Stretch some 'magic' Scotch tape across the film gate in lieu of a ground glass and confirm the lens focuses correctly.

+1.

I'll add that for step 5, I remove the front and/or rear elements of the pair if they're secured with retaining rings. Then I heat the assembly in the oven at, say, 100 C (212 F). That softens the green gluey grease enough that the helical will unscrew.

Mark

 

[artur2000]

Thank You everyone for the quick answers!

I managed to fix the issue really easy at the end.
First I made simmulation for a lens arrangement like the apotar here phydemo.app/ray-optics/simulator/.
This way I figured out, that the distance between first and second lens must be varied to focus, so now I know, that the front tubus consist of two two elements, which are suposed to move relative to each other. I am am not able to move them, so this must be the "frozen" state

1) I just removed the aluminium ring with focus distance markings by loosening the three tiny screws at the side of the ring - without making any markings - I will collimate the lens at the end
2) I unscrewed the front element of the lens (two lenses) from the shutter
3) I unscrewed the rear cap on this element and removed the shutter facing second lens
4) I put the rest of the front element with one lens into isopropyl alcohol overnight
5) Next day the rear outer ring and the front inner tubus moved freely, so I unscrewed them apart
6) Now I put all elements again into isopropyl alcohol bath for an hour to get rid of the old lubricant with a toothbrush afterwards
7) I cleanded the lenses with isopropyl alcohol and put everything together again
8) I screwed the loosened outer ring with the second lens into the shutter again using a spanner tool
9) Now I screwed the front tubus with the first lens into the outer ring using some grease between - going back and forth now moves the focus

Now I collimated the lens to adjust the focus

1) I covered a thin 6x7 piece of polycarbonate sheet with scotch tape, the matt variery. I scratched a cross in the middle onto the taped surface
2) I put the camera on a tripod. Opened the camera back, fastened this focus screen into the film plane and put enough light on this focus screen on the back of the camera
3) I set the shutter into "B", opened the aperture fully (4.5) and opened the shutter - it stays open in "B" locked (by tape or with the long exposure lock feature)
4) I got another SLR camera with 85 mm lens, focused it to infinity and looked with this second camera through the front of the apotar lens at the focus screen looking for the cross
5) I focused the agfa apotar to see this cross clealry through the second SLR camera
6) Now the agfa apotar is focused at infinity. I put the aluminium ring back, aligned infinity mark with black diamond and fastened the three tiny screwed again.

Work done. Camnera is focusing correctly and is clean again. Time for photographs

 

[artur2000]

#1.

The focusing helical is between the front and middle elements.

The lens should extend ~2mm focusing from close-up to infinity.

There are lots of posts and articles on fixing a frozen focusing helical on Agfa Cameras. Google for "agfa frozen focus" for a slew of remedies - pick the one that seems the least evil to you.

The steps are:

1. Scribe a line between the focusing scale and the front element surround.
2. Remove the setscrews around the focusing scale.
3. Unscrew the front lens capsule from the shutter.
4. Scribe a line between the front and back halves of the capsule.
5. Separate the lens capsule halves, if you can. People have found heat and solvents work to unfreeze the halves.
6. Remove as much of the green goo/glue as possible with a toothpick, Q-Tip and some lighter fluid (white gas/Coleman fuel/naptha).
7. Relube the helical threads with a synthetic grease (the synthetic stuff doesn't throw off oil or outgas) or 'vacuum grease'.
8. Put the two halves back together - check that the scribe marks line up. Note there are three or more ways the halves can screw into each other.
9. Screw the capsule back into the shutter and tighten well.
10. Slip the focusing scale back over the front half of the capsule, again line up the scribe marks, and tighten the setscrews.
11. Stretch some 'magic' Scotch tape across the film gate in lieu of a ground glass and confirm the lens focuses correctly.

Thank you! This is what I found out in the mean time. Focusing helical is between the front (first) and the middle (second) lens.
Isopropyl alcohol bath worked great to dissolve old grease, which I removed with a tooth brush completely.
Thank you for the tip with the type of grease to use. Nice to know because this thrown off oil is a problem in a nikkor 50 mm f1.2 I own. This oil penetrates into the aperture blades which ruins the exposure, so I need to clean it every few months/years.