Autofocus Mirror/Cat Lens with Adapter: Worth Trying?

Started 3 months ago | Discussions
xaprb Forum Member • Posts: 78
Autofocus Mirror/Cat Lens with Adapter: Worth Trying?

I’m curious if anyone has stacked a manual-focus mirror/catadioptric/reflex lens onto an autofocus adapter like one of the Leica M-mount to Sony E-mount adapters, and how it works.

Theoretically, I think a lot of the cat lenses need to focus by moving elements relative to each other, but in practice I wonder how well it’d work to move the whole lens.

The other thing I’m curious about is focusing near infinity. That’s where it seems to get really difficult with the cat lenses, because the adjustments need to be so delicate. Do these autofocus adapters have the precision required for that?

Speaking of that, I think the close-focus range is often quite a range of movement; maybe the adapters don’t have the travel required for that. Can they be set to limit to focus from, say, 50m to infinity? Then you could set the lens to inifinity and let the adapter twitch back and forth a tiny bit.

I don’t have one of these adapters, so this is all theoretical for me, but something I’m interested in. If it seems promising, or if someone has experience or could test this, I’d love to know how it works. I could also get one of those adapters and try it myself if that doesn’t seem like a fool’s errand.

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ProfHankD
ProfHankD Veteran Member • Posts: 7,861
Yes.

xaprb wrote:

I’m curious if anyone has stacked a manual-focus mirror/catadioptric/reflex lens onto an autofocus adapter like one of the Leica M-mount to Sony E-mount adapters, and how it works.

Yup. Both Samyang 500mm f/6.3 and Spiratone 300mm f/5.6.

They work great, but you're just auto-tweaking manual focus. 4mm of movement is nothing for long mirror lenses.

Theoretically, I think a lot of the cat lenses need to focus by moving elements relative to each other, but in practice I wonder how well it’d work to move the whole lens.

Works fine, and would no matter what for such long focal length lenses because 4mm movement is so small.

The other thing I’m curious about is focusing near infinity. That’s where it seems to get really difficult with the cat lenses, because the adjustments need to be so delicate. Do these autofocus adapters have the precision required for that?

Yup. At least the TechArt Pro LM-EA7 does on my A7RII.

Speaking of that, I think the close-focus range is often quite a range of movement; maybe the adapters don’t have the travel required for that. Can they be set to limit to focus from, say, 50m to infinity? Then you could set the lens to inifinity and let the adapter twitch back and forth a tiny bit.

Again, just 4mm AF movement range. That's just a tiny tweak on manual focus.

I don’t have one of these adapters, so this is all theoretical for me, but something I’m interested in. If it seems promising, or if someone has experience or could test this, I’d love to know how it works. I could also get one of those adapters and try it myself if that doesn’t seem like a fool’s errand.

As described, they work well. However, the only truly autofocus mirror lens is the Minolta/Sony 500mm f/8 AF Reflex, and it really does autofocus on an LA-EA4 on my A7RII. You really only get the center AF point in the SLT adapter with the AF reflex lens, but it's pretty quick and accurate too. Major disadvantage is that the AF reflex lens doesn't focus very close, while the Samyang gets near macro range. I'm still not sure if the IQ of the Minolta or Samyang is better; the Minolta seems better when manually focusing the Samyang, but using the LM-EA7 to tweak focus, it's a pretty close race.

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OP xaprb Forum Member • Posts: 78
Re: Yes.

Great, thanks! I have Fuji and Olympus M4/3 bodies. Maybe I’ll try the FotodioX Pronto Pro and see if it’s up to the task!

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markintosh13
markintosh13 Veteran Member • Posts: 4,811
Re: Autofocus Mirror/Cat Lens with Adapter: Worth Trying?
1

I use a Minolta AF 500 F8 Reflex with a Monster Adapter LA-EA4r (a modified Sony LA-EA4 - with a customized circuit board and no SLT mirror) and a Sony A7iii.

It gives me more than the previous single AF point, though it isn't quite as fast as on a native A-mount camera like my A99.

But it does work quite well, and with lock on tracking, face and eye AF - that's quite nice.

OP xaprb Forum Member • Posts: 78
Re: Autofocus Mirror/Cat Lens with Adapter: Worth Trying?

I bought a FotodioX Pro Pronto adapter for Leica M to Fuji X. Upon mounting it on an X-T4 and putting a Tokina 400mm f8 reflex lens on it, it attempted to focus but didn't even come close. (Sometimes it indicated focus success but it wasn't remotely focused.) I helped it by getting the lens nearly focused, and the adapter just defocused it more.

I gave it a couple dozen attempts and then, on reading the manual again, deduced that its mode is controlled by the camera-set aperture. I had it at f/1.0 with AF-S as instructed; then out of curiosity I decided to try switching to MF mode and set the aperture to f/32. This should activate "close focus mode" which I guessed meant that it would extend the helicoid all the way like a macro extension tube. It didn't do anything.

I switched it back to f/1.0 and AF-C mode; nothing happened. I turned the camera off and on, took it off and let it sit for a while, tried again; nothing. Normally when you turn the camera on and off it activates the helicoid. It doesn't do that anymore. It appears to have stopped working. I'll be sending it back.

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petrochemist Veteran Member • Posts: 3,061
Re: Autofocus Mirror/Cat Lens with Adapter: Worth Trying?

Most mirror lenses are above the maximum weight of the techart pro, I have used one that was unusually light so that the lens (with the adapter to LM) slipped in just under the maximum recommended weight. The combination worked OK at an airshow but the lack of aperture control made shutter priority (my preferred mode for propeller aircraft) unsuitable.

As others have said the 4mm movement of this adapter means it's just perfecting a nearly focused lens. Fine for airshows where the subject is always several hundred meters away, but less useful for birding.

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OP xaprb Forum Member • Posts: 78
Re: Autofocus Mirror/Cat Lens with Adapter: Worth Trying?

I checked the weight before using... the Tokina 400/8 is about 2/3 the max recommended weight for the FotodioX Pronto Pro. (355g versus 600g recommended).

I agree about the circumstances in which this can be useful. I was hoping the Pronto Pro could fine-tune focus once I got it reasonably close. I can focus the mirror lenses pretty well with focus magnification, but I'm slow. If it were quick and accurate to fine-tune the last little bit of focusing, that'd make the lenses easier for me to use in a lot of situations.

It sounds to me like the FotodioX Pronto Pro and the Techart Pro are not in the same league as far as quality and capability. I have read that a lot of people find the TAP to be a great adapter.

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