Please ask for information regarding lens adapters!

Beef · 2009-01-07T18:43:25+00:00

Hi Leute, ich fotografiere immer mit einer Revue AC3s (angeblich baugleich der Chinon CP-5...finde ich aber nicht unbedingt). Die Kamera hat den Pentax-K...

Beef

Hi everyone, I always take photos with a Revue AC3s (supposedly identical in construction to the Chinon CP-5... though I don’t necessarily agree). The camera has a Pentax K-mount. I’ve just gone and bought a more modern camera, a ‘Canon EOS 3000’ (analogue), to go with it. I do have a good autofocus zoom lens for it, but I’d also like to continue using one or two of my Revue lenses with it... I’ve got over 10 of them, after all. However, I now have a few questions... The Pentax mechanism is designed so that the aperture is ALWAYS fully open (so you can see through it clearly)... the set aperture is communicated to the camera via mechanical links and only closes when the shutter is released. Here are a few adapters in various price ranges: Pentax to Canon adapters 1. It says that the aperture setting is adjusted manually on the lens (which is obvious)... but is the aperture setting also communicated to the camera? 2. Is the aperture always open when using the adapter and only closes to the set value when the shutter is released? (After all, you can see a bit of the mechanics of the adapters in the pictures) 3. If ‘1.’ or ‘2.’ is not the case: Can the Canon really determine the exposure time based SOLELY on the incoming light (without knowing what aperture is set)??? Actually, I’ve always heard good things about these adapters. But I can’t quite picture how the camera’s exposure metering is supposed to work properly. I’d be grateful for any information or tips... Regards Andi

Tandemfahren

Hi everyone, I always take photos with a Revue AC3s (supposedly identical in construction to the Chinon CP-5... though I don’t necessarily agree). The camera has a Pentax K-mount. I’ve just gone and bought a more modern camera, a ‘Canon EOS 3000’ (analogue), to go with it. I do have a good autofocus zoom lens for it, but I’d also like to continue using one or two of my Revue lenses with it... I’ve got over 10 of them, after all. However, I now have a few questions... The Pentax mechanism is designed so that the aperture is ALWAYS fully open (so you can see through it clearly)... the set aperture is communicated to the camera via mechanical links and only closes when the shutter is released. Here are a few adapters in various price ranges: Pentax to Canon adapters 1. It says that the aperture setting is adjusted manually on the lens (which is obvious)... but is the aperture setting also communicated to the camera? 2. Is the aperture always open when using the adapter and only closes to the set value when the shutter is released? (after all, you can see a bit of the mechanics on the adapters in the pictures) 3. If “1.” or “2.” is not the case: Can the Canon really determine the exposure time based SOLELY on the incoming light (without knowing what aperture is set)??? Actually, I’ve always heard good things about these adapters. But I can’t quite picture how the camera’s exposure metering is supposed to work properly. I’d be grateful for any information or tips... Regards, Andi

Tandemfahren

Hi everyone, I always take photos with a Revue AC3s (supposedly identical in construction to the Chinon CP-5... though I don’t necessarily agree). The camera has a Pentax K-mount. I’ve just gone and bought a more modern camera, a ‘Canon EOS 3000’ (analogue), to go with it. I do have a good autofocus zoom lens for it, but I’d also like to continue using one or two of my Revue lenses with it... I’ve got over 10 of them, after all. However, I now have a few questions... The Pentax mechanism is designed so that the aperture is ALWAYS fully open (so you can see through it clearly)... the set aperture is communicated to the camera via mechanical links and only closes when the shutter is released. Here are a few adapters in various price ranges: Pentax to Canon adapter 1. It states that the aperture is set manually on the lens (which is obvious)... but is the aperture setting also communicated to the camera? 2. Is the aperture always open when using the adapter and only closes to the set value when the shutter is released? (After all, you can see a bit of the mechanism on the adapters in the pictures) 3. If “1.” or “2.” is not the case: Can the Canon really determine the exposure time based SOLELY on the incoming light (without knowing what aperture is set)??? Hello Andi, Question 1: no. The adapter merely creates a light-tight mechanical connection (apart from the option with the AF chip) Question 2: no. That’s called “aperture priority” and doesn’t work via the adapter. Metering at the actual aperture is required. Question 3: yes and no. My experience with two Zeiss lenses on the EOS 50 tells me that the metering is “almost” correct at only two aperture settings – that is to say, identical to an external light meter or a Canon lens. In *my* case, for example, 1.4 and 5.6. Sounds odd, but that’s how it is. Deviations are around one stop. I don’t know if this is the same for all EOS models, but I’ve tried the EOS 50 and 300 myself. So, for reasonably high accuracy requirements (which everyone should really have...), the only option is to use a manual aperture ring or, with a tried-and-tested reliable aperture, measure, convert and set it manually. Measure in ‘Av’ mode on the EOS, of course. The aperture display stubbornly stays at 00 because the camera isn’t even aware that a lens is attached at all. That’s no good at all. So, technically, you can get away with it, but you’re sacrificing the convenience and speed that the original lens offers – personally, I’m currently returning to my Canon 50mm with some regret. If I want to make things complicated, I’ll just pack the RB... Regards Frank

Tandemfahren

Man, how did I end up here again? Button-pushing isn't for me, I realise that now. I should stick with RB; they only have one...

Beef

Hi Frank, Thanks for your reply. But if I set it to Av and f/00 is displayed, then the camera assumes that f/00 is (theoretically) set... so doesn’t the accuracy of the exposure depend on the build quality of the lenses?... In other words, how closely does the aperture scale match the actual optical aperture? I’ve actually noticed in the past that exposure times vary slightly from lens to lens, even though the same aperture is set :) Unfortunately, I haven’t got the camera yet and can’t try it out. Also, I’ve just read on a website that this one metal pin in the Pentax mechanism protrudes too far into the camera and is even said to hit the mirror...so it needs to be filed down (which I definitely don’t want to do). Do you know anything about this? Or do your Zeiss lenses also have a Pentax K-mount? EDIT: I’ve just read the following in an adapter description: “Note: Due to its design, this adapter is not suitable for cameras with a full-frame sensor (e.g. Canon EOS 5D), as the rear end of the lens collides with the swing mirror." So I reckon there won’t be a collision with the EOS 3000, will there? :) Regards Andi

Gerd

But if I set it to Av and the aperture reads 00, then the camera assumes that the aperture is (theoretically) set to 00... so doesn’t the accuracy of the exposure depend on the build quality of the lenses?... In other words, how closely does the aperture scale match the actual optical aperture? I’ve actually noticed in the past that exposure times vary slightly from lens to lens, even though the same aperture is set :)

In that case, the camera simply ignores the aperture you’ve set. It measures the light and suggests a suitable exposure time. So it operates on the basis of working aperture metering. If you’ve got an EF lens fitted, it does exactly the same. After taking the reading, it simply cross-checks the result against the set and transmitted aperture. (Technically speaking, it will do the same in your case, but the additional calculation doesn’t change the result because the relevant parameter is simply 0.) I can’t replicate the issue of incorrect metering with non-EF lenses on the EOS 30. Gerd

Beef

Hi Gerd, OK, I think I’ve got one thing sorted now: the aperture doesn’t matter; the camera just checks the brightness through the lens and sets a suitable shutter speed for the selected ISO value. Right? But what I haven’t quite got yet is this: if I’ve got an EF lens on it, does it do anything different? I mean, I don’t have the camera or the lens here yet...but as I understand it from what you’ve said, the EOS always measures through the lens -> so the aperture is always as wide open (before the shot) as you’ve set it?! I can’t even imagine that... you’d be practically blind if you were looking through it at, say, f/22 :) And with the Pentax lens, you didn’t have to saw off the pin at the back, did you? Oh, and what would you recommend... the stainless steel adapters or the chrome-plated brass ones? :) Regards Andi

Gerd

Hi Gerd, OK, I think I’ve got the hang of it now: the aperture doesn’t matter; the camera just checks the brightness through the lens and sets a suitable shutter speed for the selected ISO value. Right?

Exactly.

But what I haven’t quite got yet: if I’ve got an EF lens on it, does it do anything different? I don’t have the camera and lens here yet... but as I understand it from what you’ve said, the EOS always measures through the lens -> so the aperture is always as wide open (before the shot) as you’ve set it?!

As I’ve already written. The camera meters through the open lens (open-aperture metering) and calculates the result based on the set aperture (an EOS lens informs the camera of the set aperture) Gerd

Tandemfahren

Hi Gerd, OK, I think I’ve got one thing sorted now: the aperture doesn’t matter; the camera just checks the brightness through the lens and sets a suitable shutter speed for the selected ISO value. Right? But what I haven’t quite got yet is this: if I’ve got an EF lens on it, does it do anything different? I mean, I don’t have the camera or the lens here yet...but as I understand it from what you’ve said, the EOS always measures through the lens -> so the aperture is always as wide open (before the shot) as you’ve set it?! I can’t imagine that at all... you’re practically blind if you’re looking through it at, say, f/22 :) Hi Andi, That’s right. Just as blind. With the lens on the adapter, that is – not with the EF, of course. That’s what makes this way of taking photos so tedious and slow. You have to meter and focus with the aperture wide open, convert the settings, adjust them manually, then shoot. Unless your EOS meters better than my two cameras. One more thing: you can also memorise the exposure deviation for *every* aperture and compensate for it with exposure compensation for each shot – that’s how I did it. Yes, it’s as daft as it sounds, but it works. @ Gerd: I can’t make sense of the incorrect readings either, that’s just how it is. Does the 30 measure correctly? Have you tried it? Maybe there’s someone out there who understands it and can explain? There are probably slight differences between different lenses, perhaps for the very same reason that accounts for the inconsistent readings on my Zeiss lenses? – at close-up and infinity, wide open on a 2.8 lens is different from on a 1.4 lens... Oh, and regarding the mirror issue: reputable adapter suppliers can tell you all about it in detail – certainly not the Chinese ones... just drop a few an emails. Good night Frank

Tandemfahren

Oh Andi, I almost forgot: My Zeiss lenses have a Contax bayonet mount. And the main difference between stainless steel and chrome-plated brass is that the chrome surface is harder and smoother – provided it’s been properly polished, that is. The steel scratches more easily with frequent changing. Ultimately, though, it’s a bit of an academic point. So, now you should be in the know! Best regards, Frank