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Wide angles that focus as far as possible past infinity?
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PostPosted: Sun Oct 18, 2020 11:55 pm    Post subject: Wide angles that focus as far as possible past infinity? Reply with quote

I got a full spectrum converted camera for experimentation (Canon EOS 1100D), but the conversion screwed with it's ability to focus (apparently this is normal) and now I have to focus further than you usually would. 50mm+ mostly have little issue focusing far enough past infinity to nail focus, but the one 35mm vintage prime I own - Porst Macro Weitwinkel f/2.8 35mm, it's pretty low quality and there's something screwy with it, it's never sharp on this camera no matter how far I stop down, I don't know either. It can be okay on my other camera which is an EOS 77D. Do you guys have any idea if there are any 35mm (or better even wider) lenses that can focus a significant amount past infinity? Thanks.


PostPosted: Mon Oct 19, 2020 1:48 am    Post subject: Reply with quote

Use a thicker lens adapter


PostPosted: Mon Oct 19, 2020 3:22 am    Post subject: Reply with quote

Wouldn't a thicker lens adapter make the problem worse? The lens needs to be closer to the sensor to focus past infinity, not farther away. Though please correct me if I misunderstood what you were saying.

I'm not sure I can offer a great deal of advice, but I've been looking into a mod for my 1000D for astrophotography, likely using tutorials from Gary Honis. I know there are often shims on screws near the sensor that are very sensitive to changes. Was a replacement (clear) piece of glass used in the conversion that matched the thickness of the filters removed? I'm leaning away from FS and just removing a single filter for increased Ha sensitivity.

I'm fairly new to camera lenses but I did just pick up a Mir-1V 37mm F2.8. It needs a bit of work but should be a fine lens for my purposes and it wasn't expensive. I had to change the shim ring out because it wasn't quite hitting infinity. Totally removing the shim would allow it to focus far past infinity, and maybe even be too much in your case. To really nail infinity during a CLA on my vintage primes I've been making shims of various thickness and checking infinity focus using a Bahtinov mask and a bright star (or Mars or Jupiter this time of year). It's a bit of trial and error but doesn't take too long and gives pretty good results thus far.

The Mir-1V should be fine on a Canon APS-C like your 1100D but the protruding rear housing doesn't play nicely with some FF Canon cameras. This could be worse when adjusting the lens to focus past infinity, since it will move the housing even closer to the mirror.


PostPosted: Mon Oct 19, 2020 5:08 am    Post subject: Reply with quote

I don't think the solution is needing a lens that focuses past infinity.

I converted an old EOS 1d mkII N by removing the hot mirror and it still focuses exactly as it did before with both AF and manual lenses.


PostPosted: Mon Oct 19, 2020 8:21 am    Post subject: Reply with quote

visualopsins wrote:
Use a thicker lens adapter


THINNER you certainly meant to say to focus PAST INFINITY


PostPosted: Mon Oct 19, 2020 12:01 pm    Post subject: Reply with quote

kds315* wrote:
visualopsins wrote:
Use a thicker lens adapter


THINNER you certainly meant to say to focus PAST INFINITY


Embarassed


PostPosted: Mon Oct 19, 2020 12:38 pm    Post subject: Reply with quote

If you take an adapter for Nikon F (see photo below), remove the auxiliary lens and attach it to the adapter for your camera, there is a good chance that you reclaim the focus to infinity.



PostPosted: Mon Oct 19, 2020 1:57 pm    Post subject: Reply with quote

Gerald wrote:
If you take an adapter for Nikon F (see photo below), remove the auxiliary lens and attach it to the adapter for your camera, there is a good chance that you reclaim the focus to infinity.



wouldn't work. A Nikon Adapter puts the lens even further away from infinity (the Nikon distance) If you take out the corrective element you will take it even further from infinity (more close up) because m42 is to far away from the sensor on Nikon in the first place. The rear element needs to be closer to the sensor (possibly causing mirror conflicts on a Canon dslr)


PostPosted: Mon Oct 19, 2020 2:50 pm    Post subject: Reply with quote

D1N0 wrote:
Gerald wrote:
If you take an adapter for Nikon F (see photo below), remove the auxiliary lens and attach it to the adapter for your camera, there is a good chance that you reclaim the focus to infinity.



wouldn't work. A Nikon Adapter puts the lens even further away from infinity (the Nikon distance) If you take out the corrective element you will take it even further from infinity (more close up) because m42 is to far away from the sensor on Nikon in the first place. The rear element needs to be closer to the sensor (possibly causing mirror conflicts on a Canon dslr)




Sorry, but I have to disagree. If the lens cannot focus to infinity, it means the back focal length (BFL) is too short. What is needed to get focus to infinity is to increase the effective BFL, but without increasing the physical distance from lens to sensor. That is exactly what the a Nikon F adapter does!


The lens in a Nikon F adapter has negative power, so it works like a Barlow lens:


from https://upload.wikimedia.org/wikipedia/commons/thumb/3/37/Barlow_lens.svg/1200px-Barlow_lens.svg.png

The green rays show that the effective BFL has increased, but the original lens has not changed position. To get focus to infinity, just move the lens forward enough, using the focusing helicoid.


PostPosted: Mon Oct 19, 2020 4:00 pm    Post subject: Reply with quote

I am talking about the flange focal distance a lens needs for infinity focussing. When this is too long a lens will not reach infinity. You were not being clear about whether you were going to use the Nikon lens or the Nikon adapter to achieve infinity.


PostPosted: Mon Oct 19, 2020 4:09 pm    Post subject: Reply with quote

A barlow lens would work fine (I use them to attach a DSLR to a big Dobsonian telescope), but introducing more surface to air transitions isn't going to do the image any favors.

You could adjust the infinity stop in your lenses like I mentioned. You'd have to do this for every lens though and you'd lose some close focus distance. You could also take a cheap M42 adapter and shave down material off the face so the lens mounts closer to the body. These are both options for achieving infinity with M39 Zenit style lenses and an M42 adapter, which also don't quite hit infinity due to the focal flange difference between the two (44.20 versus 44.46mm). But that depends on how far off infinity is on your modded 1100D versus an OEM EF mount. 'Z39' to M42 as an example is only 0.26mm.

Another option is having the camera serviced and the sensor shims corrected for proper infinity focus. This would be expensive and not worth it IMO. You could attempt it yourself (seems like adding shims would do it), but it's easy to screw it up and make it worse. Personally I'd cut down an M42 adapter and make absolutely sure I wasn't going to deal with mirror contact by moving the lens closer. That way your lenses stay properly adjusted for use on other cameras.


PostPosted: Mon Oct 19, 2020 5:14 pm    Post subject: Reply with quote

Er... I am stunned about all this blather here... The first thing to consider should be: How can the infinity focus of the lens be adjusted?

With most vintage lenses this is possible without problems. Sometimes it's easy, sometimes fiddly - you just either have to get proper information how to do it yourself or let an expert do it (which of course would cost something).


PostPosted: Mon Oct 19, 2020 5:56 pm    Post subject: Reply with quote

Gerald wrote:
D1N0 wrote:
Gerald wrote:
If you take an adapter for Nikon F (see photo below), remove the auxiliary lens and attach it to the adapter for your camera, there is a good chance that you reclaim the focus to infinity.



wouldn't work. A Nikon Adapter puts the lens even further away from infinity (the Nikon distance) If you take out the corrective element you will take it even further from infinity (more close up) because m42 is to far away from the sensor on Nikon in the first place. The rear element needs to be closer to the sensor (possibly causing mirror conflicts on a Canon dslr)




Sorry, but I have to disagree. If the lens cannot focus to infinity, it means the back focal length (BFL) is too short. What is needed to get focus to infinity is to increase the effective BFL, but without increasing the physical distance from lens to sensor. That is exactly what the a Nikon F adapter does!


The lens in a Nikon F adapter has negative power, so it works like a Barlow lens:


from https://upload.wikimedia.org/wikipedia/commons/thumb/3/37/Barlow_lens.svg/1200px-Barlow_lens.svg.png

The green rays show that the effective BFL has increased, but the original lens has not changed position. To get focus to infinity, just move the lens forward enough, using the focusing helicoid.


But you said to remove the auxiliary lens, in which case all you have done is to move the lens further from the sensor. With the negative lens in place it would certainly focus past infinity, but that means finding a way to attach a non-Nikon F mount lens to the Nikon F adapter. Any adapting ring thicker than about 2.5mm puts you right back where you were, plus you have a cheap piece of glass in the light path that trashes the image quality.


PostPosted: Mon Oct 19, 2020 6:10 pm    Post subject: Reply with quote

hasenbein wrote:
Er... I am stunned about all this blather here... The first thing to consider should be: How can the infinity focus of the lens be adjusted?

With most vintage lenses this is possible without problems. Sometimes it's easy, sometimes fiddly - you just either have to get proper information how to do it yourself or let an expert do it (which of course would cost something).


Hardly easy. You would need to cut the rear mount down, and most vintage lenses have mechanisms immediately behind the mount. Even if you have a solid metal ring behind the mount, shaving off one millimeter of metal will be difficult and compromise the structural integrity of the lens. One common solution would be to move the rear element group further towards the front of the lens, but that might not work with wide, depending on the optical formula, and in any case would certainly increase aberrations.

On top of this most wide lenses have the rear element as far back as possible without hitting the mirror. Any milling or an adapter thinner than normal would stand a good chance of putting the rear group in the path of the mirror.


PostPosted: Mon Oct 19, 2020 6:38 pm    Post subject: Reply with quote

kymarto wrote:

But you said to remove the auxiliary lens, in which case all you have done is to move the lens further from the sensor. With the negative lens in place it would certainly focus past infinity, but that means finding a way to attach a non-Nikon F mount lens to the Nikon F adapter. Any adapting ring thicker than about 2.5mm puts you right back where you were, plus you have a cheap piece of glass in the light path that trashes the image quality.


I suppose the Porst Macro Weitwinkel f/2.8 35mm lens has an M42 mount (but I'm not sure).

What I suggested was to take out the negative power lens that comes with a Nikon F adapter and see if it is possible to somehow put that lens on an M42 to Canon adapter (the camera is a Canon EOS 1100D). Obviously the Nikon adapter would be discarded.


PostPosted: Mon Oct 19, 2020 6:44 pm    Post subject: Reply with quote

Gerald wrote:



Sorry, but I have to disagree. If the lens cannot focus to infinity, it means the back focal length (BFL) is too short. What is needed to get focus to infinity is to increase the effective BFL, but without increasing the physical distance from lens to sensor. That is exactly what the a Nikon F adapter does!


The lens in a Nikon F adapter has negative power, so it works like a Barlow lens:


from https://upload.wikimedia.org/wikipedia/commons/thumb/3/37/Barlow_lens.svg/1200px-Barlow_lens.svg.png

The green rays show that the effective BFL has increased, but the original lens has not changed position. To get focus to infinity, just move the lens forward enough, using the focusing helicoid.


The BFL is increased with the extra optical elements in this adapter to make up for the adapter being too long for infinity focus. (Nikon F having a longer BFL than M42) Moving a lens further from the film/sensor brings the point of focus closer (the reason extension tubes work for macro).

If focus shift from shooting IR is making it necessary to focus beyond infinity a shorter adapter would be needed. However I think most of my lenses need to be focused closer to cater for the IR shift. This is something that varies considerably with lens design.

The only legacy lens I have handy with an IR mark is a Miranda 24mm/2.8 macro where the IR focus needs the lens focused slightly closer than it does for visual light. (My example is in PKA mount) For the record the shift with this lens is fairly small f/4 giving about enough DOF to make up for the shift.


PostPosted: Mon Oct 19, 2020 8:05 pm    Post subject: Reply with quote

I would consider adjusting the camera mount itself so that all lenses reach infinity as they are designed. Depending on how much closer the lens needs to be to the sensor maybe removing mounting flange screws and shaving off a bit of the metal on the back of the mount on the camera?


PostPosted: Tue Oct 20, 2020 4:35 am    Post subject: Reply with quote

Gerald wrote:
kymarto wrote:

But you said to remove the auxiliary lens, in which case all you have done is to move the lens further from the sensor. With the negative lens in place it would certainly focus past infinity, but that means finding a way to attach a non-Nikon F mount lens to the Nikon F adapter. Any adapting ring thicker than about 2.5mm puts you right back where you were, plus you have a cheap piece of glass in the light path that trashes the image quality.


I suppose the Porst Macro Weitwinkel f/2.8 35mm lens has an M42 mount (but I'm not sure).

What I suggested was to take out the negative power lens that comes with a Nikon F adapter and see if it is possible to somehow put that lens on an M42 to Canon adapter (the camera is a Canon EOS 1100D). Obviously the Nikon adapter would be discarded.


Aha. I didn't get that. The distance has som effect, and if it were too far from the rear element of the lens it would degrade the optical quality even more than it is with the Nikon adapter, which is already considerable.


PostPosted: Tue Oct 20, 2020 5:06 am    Post subject: Reply with quote

No! No! No!

What's up here?

Lenses have screws (in different locations, and you have to do different things to reach these screws) with which it can be adjusted at which point the focus ring hits infinity.

There doesn't need anything to be shimmed or shaved off! It's just necessary to find a guide how to do the adjustment on this particular lens!


PostPosted: Tue Oct 20, 2020 7:16 am    Post subject: Reply with quote

hasenbein wrote:
No! No! No!

What's up here?

Lenses have screws (in different locations, and you have to do different things to reach these screws) with which it can be adjusted at which point the focus ring hits infinity.

There doesn't need anything to be shimmed or shaved off! It's just necessary to find a guide how to do the adjustment on this particular lens!

I think this lens is the Enna München 35mm 3.5 plastic mold. Infinity probably baked in. Just get another lens.


PostPosted: Tue Oct 20, 2020 6:49 pm    Post subject: Reply with quote

I don't have this lens but its reputation is not great. So if it just this lens, I agree. Get another lens. But my understanding is that the issue is secondary to the camera being modded and that has changed the flange distance. so the issue may crop up with other wide angle lenses as well.


PostPosted: Tue Oct 20, 2020 7:11 pm    Post subject: Reply with quote

The easiest I guess and one which could solve that problem would be:
1) a suitabe negative diopter built into a lens to camera adapter
2) a suitable negative diopter in a filter frame to be used in front of the taking lens

Have done both....


PostPosted: Wed Oct 21, 2020 7:27 am    Post subject: Reply with quote

Klaus,
the negative diopter adapter I have for M42 to Nikon F seriously degrades the image quality. Perhaps there are better ones, but I don't think any single element negative is going to be able to control the CA.


PostPosted: Wed Oct 21, 2020 8:13 am    Post subject: Reply with quote

kymarto wrote:
Klaus,
the negative diopter adapter I have for M42 to Nikon F seriously degrades the image quality. Perhaps there are better ones, but I don't think any single element negative is going to be able to control the CA.


Then a single element negative diopter isn't 'suitable'
Achromats are available in negative diopters, but sadly they're not easy to track down in suitable mounts.