Canon-EOS-Protokoll

[kisa]

Astrophotography requires focusing everytime you take a photo.

Imperfections in the scope, slight movements in the focuser grearing, atmospheric changes, changes in colour filters, can all cause changes in the focal point especially under large magnification. e.g. one of my telescopes acts as a 1200mm len and at times I use a x5 barlow, making it a 6000mm lens.

Hence my want for autofocus. Autofocus would increase my evening imaging by x10

 

[Nightshot]

For using AF on a virtually 6000m telescope you need at least a 75cm mirror. Do you have such a monster? Before doing all this work you should test if the AF is capable of focusing this telescope. You need one of this AF confirm chips. This will activate the AF module without lens and when the telescope is in focus the green AF lamp in the camera will flash up for focus confirm. If you won't see this focus confirm your project is dead anyway.
If you don't have such an AF confirm chip you can connect the camera pins to a lens externally and switch the lens to MF.

 

[drei]

I have nor expertise in astrophotography, but a quick search found:

http://www.spike-a.com/

Isn't a diffractive mask like this a much more precise way to achieve correct focus?

 

[kisa]

@NightShot: I'm not sure how you came up with that value as I hadn’t mentioned my focal ratio. But if my mirror was 75cm I'd have a focal length of 22500mm with the x5 barlow.

The telescope focal length is derived from the multiplication of the aperture and focal ratio. My larger telescope has an aperture of 200mm and a focal ratio of 6, giving me a focal length of 1200mm.

http://www.astro.shoregalaxy.com/index_010.htm

Using my x5 barlow simple multiplies that by 5 again, making a focal length of 6000mm.

http://en.wikipedia.org/wiki/Barlow_lens

@drei: I have tried the masks and they are ok but still tedious as they still require the manual focus and need to be manually attached and removed.

Thanks for your suggestions. I have been imaging for some time now and believe I have a reasonable understanding of the process and its difficulties. My visit to this forum was not to be given alternates to astrophotography but to pursue a hobby of mine to make my telescope auto focus.
If you could please help me with that, that would be great.

Thanks,

Markus

 

[Nightshot]

For a working AF you need a f-number of at least 5,6. With a telescope is it a bit different because the capture mirror in the center blocks light and this part isn't used for AF anyway. So with a telescope AF works up to a f-number of 8.

Your telescope plus 5x barlow has 6000mm and a 200mm capture mirror so you get a f-ratio of 30! Not a single photon will hit the AF module and it will be totally blind.

 

[drei]

I have been imaging for some time now and believe I have a reasonable understanding of the process and its difficulties.

Are you sure that you are aware of the requirements and limits of phase detection AF?

Although you expressed that you won't take any other advice I strongly suggest that you try some alternative like the following focusing software:

http://www.dslrfocus.com/

 

[kisa]

@NightShot: I didn't think AF purely worked on F stops. I've seen Nikon lens that has a minimum of F/32 and the camera still uses AF. I believe it would relate more to the intensity of light from the image being photographed. For example if I aimed my telescope (configured to 6000mm) at the Sun to photograph a Sun spot, I believe it would still AF due to the light intensity. In actual fact it would probably ignite the camera (literally) .

@drei: I was unaware of phase detection before coming to this forum, hence all my questions. I have tried DSLRFocus and a number of other recommended focusing methods for astrophotography, including mean averaging values, etc. All require the user to take individual photos, upload them onto your PC (high resolution images take some time), analyse the image, then adjust the focuser and recapture another image, and so on. This is long and tedious and is what I was referring to when I said it can take up to an hour to get it perfect.

Is there any reason you guys are avoiding sharing the information regarding the Canon protocol? It looks like you're putting more effort into just trying to discredit me. I’m not trying to prove a point or argue with you guys, I’m just an engineer who is an astronomy enthusiast who wants to experiment with some ideas.

 

[pspilot]

It looks like you're putting more effort into just trying to discredit me.

Right! That's why everyone in a German board tries to speak English for the last 3 pages just for you ... Jeez, obviously you got some things wrong about the Canon system and some guys are trying to tell you.

 

[Dande]

@NightShot: I didn't think AF purely worked on F stops. I've seen Nikon lens that has a minimum of F/32 and the camera still uses AF. I believe it would relate more to the intensity of light from the image being photographed. For example if I aimed my telescope (configured to 6000mm) at the Sun to photograph a Sun spot, I believe it would still AF due to the light intensity. In actual fact it would probably ignite the camera (literally) .

For phase detection AF there is an f-stop limit. For consumer cameras it is f/5.6 (as far as I know for all brands) and for pro models they use some enhanced phase detection modules that can be used up to f/8. That's were the electronic blocks the usage of the phase detection AF module. In truth that number is not a hard break but the phase detection AF gets worse after that. So you might get some good result with f/8 on comsumer DSLRs and f/11 on pro models. But at f/32 you will not see a working phase detection AF on any DSLR.
Contrast detection AF is something complete different. With contrast detection AF the only thing you have to worry about is light intensity.

About helping you: The guys here are really trying to help you. But do you really think Nightshot has the time to write you 30 or 40 pages of information about the protocoll. It took him a lot of time to figure all of that out and he is earning some money with that information. So he is the guy that can help you and he did. He told you why it won't work with your configuration and how you can get it working after you changed your configuration.

 

[kisa]

Thank you for the detailed explanation regarding the F stop limit. I now have a better understanding of the limitations, and I will do some more research into the exact operation of AF and its specific limitations, so I get an even better understanding.

I never asked for or expected 30-40 pages of information and I'm not trying to rob someone of their royalty. I just asked for help in getting a basic understanding of the communication sequence between the camera and lens. I ask this because I would like to reverse engineering the protocol if it is viable and would prefer not to re-invent the wheel if I don't have to. Sharing information is normally what forums are for, so that's why I'm here asking questions.

@pspilot: I am very appreciative that I am getting responses in English, it certainly makes it a lot easier for me to follow. So thanks to all that have. But please note that most of the three pages you mentioned have been more trying to defend my pursuit and hobby than anything else.

From what you have told me, interpreting the responses I’ve received as evasive is incorrect. If that is the case I apologise. I will keep my questions short to try and minimise any future misunderstanding.

My f/30 now seems to be the reason not to pursue my hobby of an AF telescope.

What if I used my 1200mm f/6 or my 600mm f/5 telescope, to image things like Orion, can I then use the Canon AF capability?

 

[drei]

What if I used my 1200mm f/6 or my 600mm f/5 telescope, to image things like Orion, can I then use the Canon AF capability?

Question: Is there any chance to use a setup where an original Canon lens is just part of the optical system?

Remark 1: You still might have the problem that the light intensity is below the operating limits of the AF system. There are several limits to the camera system. Apparently you have initially overlooked the f-number requirements of the AF system. You should also check other applicable parameters. These should be documented in the Canon product literature.

Remark 2: You should check what others have done. There is a tremendous chance that everything possible has already been tried by other hobby astronomers.

 

[Nightshot]

What if I used my 1200mm f/6 or my 600mm f/5 telescope, to image things like Orion, can I then use the Canon AF capability?

Yes, this would work. I'm using the EF protocol on a 2,5m class telescope but not with phase AF (still not accurate enough). I use some kind of contrast AF. The image is captured with a photon multiplier camera, the PSF analyzed and the focus and telescope adjusted corresponding to the result.

 

[kisa]

@drei: I don't think adding a lens as part of the optical system would work. There would be no way to adjust the focus point of the telescope which would far exceed anything the lens could compensate for. Also adding a lens to a telescope would degrade the amount of light collected and the quality of the image.
I agree there may be other factors that could affect the ability to AF on a telescope and I have been looking more into things that may make AF impossible (since the f problem was raised). I have not found anything else yet but I will keep looking.
I have been looking at how to improve the telescope focusing procedure for quite a while (about 3 years), including searching forums and attending astronomy camps and have not yet from anything that would compete with being able to AF. I have also not found any other forums that have come as this one to resolving the canon protocol.
I have used FWHM and HFD values for focusing. They are both accurate most of the time (but not all the time). But both still required taking a photo, analysing it, and then adjust the focus, then repeat many times..., so it's very slow. If I had a Canon 450D with live view that would probably work well, but unfortunately I don't.

@NightShot: 2,5m scope is huge, what is the f of that? I'm not familiar with photon multiplier cameras, but they certainly sound out of my price range
Will the canon phase AF be accurate enough for imaging on my f6 and f5 telescopes?

 

[drei]

The image is captured with a photon multiplier camera, ...

Was ist eine Photomultiplier-Kamera?

Ich bin da kein Fachmann und habe nie eine gesehen, aber soweit ich das verstehe, muss so eine Kamera Millionen kosten und liegt damit nicht mehr ganz im typischen Amateur-Budget.

 

[MasterFX]

Was ist eine Photomultiplier-Kamera?

Vermutlich eine Kamera aus Photomultipliern: http://www.astroteilchenphysik.de/grafik/camera.htm

 

[Nightshot]

Will the canon phase AF be accurate enough for imaging on my f6 and f5 telescopes?

Do my quick test from post 342 and you will know.

Was ist eine Photomultiplier-Kamera?

Das fällt unter Restlichtverstärkung wie es auch in Nachtsichtgeräten Anwendung findet. Wird aber jetzt durch eine Electron Multiplying CCD ersetzt, da das alte System kaputt geht, wenn eine so helle Quelle wie Jupiter durch das Bildfeld läuft.

Ich bin da kein Fachmann und habe nie eine gesehen, aber soweit ich das verstehe, muss so eine Kamera Millionen kosten und liegt damit nicht mehr ganz im typischen Amateur-Budget.

Das Teleskop liegt im zweistelligen Mio. Bereich, da spielt die Kamera keine Rolle mehr, die bekommst aber schon für ein paar Tausend Euro.

 

[kisa]

@NightShot: Sorry I completely missed the test you suggested:-

You need one of this AF confirm chips. This will activate the AF module without lens and when the telescope is in focus the green AF lamp in the camera will flash up for focus confirm. If you won't see this focus confirm your project is dead anyway.
If you don't have such an AF confirm chip you can connect the camera pins to a lens externally and switch the lens to MF.

I will buy an AF confirm chip and do the test, thanks for that. Just looked them up on ebay, amazing, have never seen one before.

Are they all the same (does it matter which one I buy)?

Can the communication between the AF confirm chip and the camera be analysed to help work out some of the canon protocol?

Is the green light you are referring too just the standard green circle seen in the view finder when focus is achieved?

Thanks again.

 

[Nightshot]

Are they all the same (does it matter which one I buy)?

The better ones can adjust the AF if your optic needs a calibration offset.

Can the communication between the AF confirm chip and the camera be analysed to help work out some of the canon protocol?

I have looked into the communication and there are plenty of wrong answers from the chip but sufficient correct that the camera doesn't deactivate the AF module.

Is the green light you are referring too just the standard green circle seen in the view finder when focus is achieved?

Yes it is.

 

[kisa]

Thanks again

 

[kisa]

I've ordered an AF Confirm Chip that has adjustable aperture and focal length.

Do these values acutally make any difference to the way the canon camera does AF?

My understanding was that the camera just checked the focus on it's sensors, if not in focus, it moves the lens in or out and rechecks, then moves again if required (ignoring the fact the amount the lens is moved, is also calculated using the phase values).

Is my understanding correct or does the aperture and focal length also somehow get involved? Or am I completely misunderstanding the AF process?