Canon EOS 600D Full Spectrum Mod Query

[Mark_C]

Hi everyone,

Hope you have all had a great Christmas!

I have bought a second hand 600D at a decent price and wish to perform a full spectrum modification on it so will be removing both the LPF#1 and #2 filters. I wish to use this camera both for astrophotography with a CLS-CCD filter that I currently own and for daytime and IR photography use (also using relevant clip in filters.) From what I understand, autofocus will be an issue if I do not buy something like the Astronomik MC glass in place of where the LPF#1 Filter/Piezoelectric assembly sits.

My question is whether this glass is actually a requirement to retain accurate autofocus? Or can I modify the sensor spacing for autofocus to work without any glass in the way whatsoever? Has anyone tried to do this and if so have you been successful?

I have been reading the modification guide by Gary Honis for this camera thoroughly and it still looks as though slight sensor adjustment is required even with the MC glass in place due to its thickness.

Any input on this is most welcome!

 

Thanks,

Mark. 

[michael8554]

Hi Mark

You have to compensate for the removal of both filters, the clear glass won't be enough, but may be with the CLS as well.

The imager can be moved closer to the shutter with the 3 spring-loaded mounting screws, but who knows by how much to accurately compensate?

[Jannis]

Is there any reason why auto focus would be any issue on a 600D if just simply using "live mode" AF? The focus should then be read by the sensor, and any change in the optical train should be ignored. Naturally it's much slower, but...

[Merlin66]

I have a FULL full (both filters removed) 1000D.

To allow the use of standard lenses I use a clip-in CLS filter, this allows full auto focus etc.

I’m not sure using the “live view”would be effective - the issue is with the lens and it’s positioning, I’d think the live view would still be out of focus.

 

[Mark_C]

Thanks for the response guys. I have yet to mod the camera but am considering doing so later today. I just wasn't sure whether to wait and order the Astronomik MC glass, however if it's not needed then I'd rather save the £60. Ideally I'd like phase AF to work as it's much faster than Live AF.

@Merlin66 - So did you find the Astronomik MC glass unnecessary in the end? Everywhere I read seems to indicate that the glass is required or else autofocus will never work regardless of sensor adjustment or clip in filters. There seems to be a lot of conflicting information about this and it's getting very confusing. Did you have to adjust the sensor positioning screws after reassembling the sensor? Lastly, has dust been an issue with there being no glass in the sensor path? (Other than the clip in filter.)

[Jannis]

Phase af will be off with filter removed, but by how much i dont know. Fast optics will naturally suffer more.

If you decide to skip the replacement filter, could you please perform some before and after tests and share? Focus both near and far, and with both slow and fast optics. Would be interesting to see. :-) 

Edit: a clip in filter wont correct phase af in any way as its mounted before the mirror. Only way to correct focus is adjusting the sensor or add glass between mirror and sensor (out of view for the phase af sensor). Adjusting the sensor is in general not recommended as far as i know (very easy to mess up, near impossible to correct due to the small adjustments).

[Merlin66]

Mark,

I didn't want any filters in the camera - I was looking for maximum spectral coverage for spectroscopy. 

The only reason I added the clear clip in filter was to allow the use of the standard camera lens for the occasional "objective grating" imaging. The lenses would not come to a infinite focus would the filter.

I don't know why you're so concerned with AF focusing of a modded camera?? 99% of the time you'll need to focus manually....or the modded body will be used on a telescope.

I've had no issues with dust etc etc. I just does the job, no issues, no drama.

 

[Mark_C]

Hi Merlin,

The reason I want AF to work is because I want to be able to use the camera for everyday use with an OWB filter as well as for astrophotography. 

 

Jannis,

I'd be happy to do this but unfortunately (and ironically) I have no Canon lenses to try at the moment, I was thinking of buying a cheap 50mm 1.8 lens soon though so if the camera isn't modded beforehand then I will certainly try this out!

 

Happy new year!

Mark.

 

[Merlin66]

I think there lies the issue......

A modded camera is uniquely an astronomical instrument...to try to use it for both "family snaps" and astronomy is difficult. Easier to find a good s/h second camera for the day to day shots.

just my 2c

 

[StuartJPP]

As mentioned, live view focus (contrast, not phase/quick) will still work. It would be much easier to use a tripod to focus in live view or use one of those loupe/eyepieces that attach to the rear LCD and use it that way with contrast based live view focusing during the day.

I doubt that you would be able to get (phase) focus spot on by removing and adding  various filters...Gary mentions 1/8th of a turn or something similar for certain modifications but I am not sure how accurate that would be...and it would be a fair bit of trial and error getting it all correct and square as well....

Personally I'd forgo the auto-focus and make sure the sensor is replaced exactly where it was give or take a bit on EACH shim.

However there will be a position that the sensor will be in where phase AF will work...so technically it would be possible.

[Mark_C]

I decided to go ahead and perform the mod and remove both filters, put it all back together and the camera seems to be working just fine, I've no way of testing yet as the weather is awful outside.

I "think" I've wound the screws near enough back to the original position for the sensor but I'm not sure whether they're 100% in the same place as before. I marked the screws position but stupidly most of the markings had rubbed off. I did measure the height of the black pins by cutting up an old credit card and drawing a line across, so I used this as a guide. If the screws are slightly off, will this affect the image in any way? Of course I have to accept that autofocus will probably not work again on this camera, but I bought the camera cheaply so it's no big issue.

I think Merlin does have a point about having a second camera rather than a do it all in one solution. I do actually have a Panasonic GH5 for everyday use but I thought it'd be nice to have a backup body with some nice Canon lenses which I could also use on my GH5 with a Metabones adapter.

[Jannis]

Yes. If the screws are off it can be a huge problem, which i why i mentioned its not recommended to touch them at all.

Say that one screw is just a bit off, then that corner of the sensor will never be in focus with the rest as the sensor is no longer flat. 

Naturally it depends how far off it is, and how fast your optics are. For example, it might look ok at f 5, but using an f 1.4 lens for example might not be possible anymore.

Only way to know for sure is to give it a try and see how it looks i guess. :-) 

[Mark_C]

Oh dear, that's not good! Unfortunately no way of checking focus consistency across the frame as I have no lenses and it's pouring down outside. Frustrating as I really want to know if this was a success.

If I do mod another camera, this will learn me to use a permanent marker that doesn't rub away so easily.

Given the location of the screws, if there is indeed sensor misalignment then it looks like its going to be a nightmare to correct with all of the ribbon cables situated where they are.  ?

[Merlin66]

Hmmmmm......

Guys,

Have any of you actually tried to use the AF on a modded camera?????

The reason I ask, is with my FULL full modded 1000D fitted with the Astronomik clear clip in filter, the AF works 100%...

I've just taken a few images close-up and distance using AF and the results are not too bad.

So, fitting a clip in filter seems to compensate very well.

(Edit - I’ll download the images and have a good look at them and post samples. See later posts for corrections!)

[Mark_C]

2 hours ago, Merlin66 said:

Hmmmmm......

Guys,

Have any of you actually tried to use the AF on a modded camera?????

The reason I ask, is with my FULL full modded 1000D fitted with the Astronomik clear clip in filter, the AF works 100%...

I've just taken a few images close-up and distance using AF and the results are excellent.

So, fitting a clip in filter seems to compensate very well.

(Edit - I’ll download the images and have a good look at them and post samples)

I will have to try this when I get hold of a Canon lens, this is interesting! If an OWB filter does indeed act in part to allow autofocus to work then this reinforces the viewpoint that the MC Glass is just not worth the time and money to install.

On a sidenote, I have managed to get the scope out quickly tonight, took a few unguided subs at orions nebula under heavy moonlight and stacked in DSS, there doesn't seem to be any focus issues that I can see, not bad! Can't believe what a difference a modded camera makes.

 

[Merlin66]

That looks pretty good!!!

The attached image was taken with a 85mm prime, AF on the modded 1000D

 

[Jannis]

That looks great! If there really is any difference on the sensor, it does not show up on your final image as far as i can see at least, so i would be very happy with that.

Merlin66, I don't have a modded camera myself, so i have nothing to test with, but it's not technically possible for a clip-in filter (or any other filter mounted in front of the mirror) to compensate for missing glass in front of the sensor. The phase AF system only "reads" the optics until right before the sensor, it does not include the sensor mounted filters. The phase AF is simply calibrated at the factory with these filters in place.
What they meant by "still able to use AF" with clip in filters was not that it corrects for removed filters (if this was the case, any none-modded DSLR with a clip in filter would be out of focus), but that it still allows the lens to be electrically connected to the camera.

Nr. 7 is the phase AF sensor.

But like i said though, i don't know how much it actually affects the focus as i haven't modded my camera. If you say it still works fine after removing the filter that sounds great, but what optics did you test with? A "stock" ~F/3.5 lens, or a faster F/1.2-1.4 lens, and wide angle or long FL? I would be very interested in seeing some images at full res if you have.

[Jannis]

3 minutes ago, Merlin66 said:

That looks pretty good!!!

The attached image was taken with a 85mm prime, AF on the modded 1000D

That's a very small image, and it honestly looks out of focus to me. Naturally this could be if the lens is very "soft" wide open, but where is the AF point? I would assume center, but the center is for sure out of focus.

A full res image, or a 100% cropped section of there the AF point would be more useful for checking focus. Preferable also if you could take 2 images with center point as AF point (only the center phase AF point of the 1000D is a cross-type) - one with phase AF, and one with contrast AF.

[Merlin66]

Jannis,

If the distance to the AF sensors and the viewfinder (as per the diagram) are set to allow for effect of the thickness of the filters on the imaging sensor, then I would have thought the removal of these filters would effectively change the focus distance from the lens.

If a compensating filter element is placed behind the lens (just above position marked 5) then the optical length to the imaging sensor is maintained and hence the optical paths to the other AF sensors and viewfinder??????

[Merlin66]

I focused on the wing root....it's a 85mm f1.8 lens and I think you're seeing the depth of field???

 

[Jannis]

34 minutes ago, Merlin66 said:

If the distance to the AF sensors and the viewfinder (as per the diagram) are set to allow for effect of the thickness of the filters on the imaging sensor, then I would have thought the removal of these filters would effectively change the focus distance from the lens.

This is in fact exactly what you are doing, you're changing the backfocus every so slightly. The viewfinder will still show perfect focus with a removed sensor filter, but the sensor will no longer have the same focus as seen in the viewfinder or by the phase AF sensor.

34 minutes ago, Merlin66 said:

If a compensating filter element is placed behind the lens (just above position marked 5) then the optical length to the imaging sensor is maintained and hence the optical paths to the other AF sensors and viewfinder??????

No, because the only thing the phase AF can see is the optical system in front of the phase AF mirror (right behind the primary mirror that reflects light to the viewfinder). If you place a filter (or even a 100 filters) anywhere in front of the mirror, the phase AF will still work fine as it will see the added class and compensate for it. It does however not see what's mounted on the sensor itself, unlike the contrast based AF does as it's a reading from the sensor itself.

32 minutes ago, Merlin66 said:

I focused on the wing root....it's a 85mm f1.8 lens and I think you're seeing the depth of field???

It's hard to tell. If you mean the tip of the right wing then it surely looks better then the center, but it still looks very soft (this could be the lens though, 1.8 lenses are usually not very sharp wide open and off center). Best way to test is to for example take a pic of text hanging flat on a wall with both phase AF and with contrast AF to compare, then you'll know right away if it's off or not.

I must say it either way looks less "off" then i would have expected considering all the warnings of "AF no longer working with filter removed", but a small image like this does not tell the whole story.

Edit: My bad, you said wing root, meaning where the wing is attached to the body, right? That part looks out of focus to me.

[michael8554]

I agree, can't  see that any part of the plane image is in focus.

Michael 

[Merlin66]

Jannis, Mark,

OK,OK, my eyes are obviously no good for this......

For the run of the mill they looked OK, but on detailed analysis the out of focus shows up.

The solution is to manually focus, check the saved image, adjust focus until success.....

Sorry for the confusion.......

 

[Jannis]

Thank you for the two comparing images. I see clearly now that the focus is in fact rather far off, and not just soft optics, so it's safe to say phase AF is not an option anymore. Well, at least not with fast optics.
You say you had to do test shots and manually adjust, but did you test with contrast based AF (live view AF)?

Also, if you stop down the lens a bit, say to F/3.5-4, is the focus still much off? I'm thinking for daytime imaging that stepping down the lens might just be enough to still use phase AF with an acceptable accuracy. F/1.8 @ 85mm is not normally used for "everyday photos" anyway, but F/3.5-5.6 is more normal.

[Mark_C]

Depending on the Canon camera you have, for manual focus it may be possible to install Magic Lantern and use focus peaking to find the desired focus?

Also, has anyone found contrast autofocus to be rather slow and clumsy on Canon cameras? I haven't tried the newer ones so am not sure whether this is still the case but I remember from when I owned a 60D and owned a 50mm lens, it wasn't a patch on my GH5 (which I believe also uses CBAF).