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Can't reach focus with camera lens on Canon T5i

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#1 Scott Mitchell

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Posted 26 May 2019 - 11:56 PM

Howdy everyone, I just ran into an interesting, well frustrating really, issue. I have a couple of classic Leica lens that I have used in the past on my old camera with pretty good success (here's one example). However, tonight I tried these lenses on my modified Canon T5i and they can't reach focus.

 

Does the removal of the lpf2 filter cause the focal plane to move? Could it cause regular lenses not to come to focus at infinity?

 

I use an adapter to mount the Leica lens to the Canon body. Surely I wouldn't need a different adapter when moving from my old XSi to the T5i, right?

 

Assuming that the focal plane has, in fact, moved and hence I need to conceptually go past infinity to reach focus, does that mean I'd need to the the lens closer to the body or farther away? Closer seems like a non-starter, but I guess it might be possible to get some sort of spacer to get it moved farther away.

 

Any insights are appreciated!



#2 james7ca

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Posted 27 May 2019 - 12:13 AM

If your Canon body has been modified it may not reach focus when used with a lens that only provides the standard flange distance for infinity focus. Normally if a filter is removed from the sensor you need to install a clear filter or glass cover that restores the original optical spacing. Since the filter was removed you need to move the lens closer to the sensor, which may not be possible (unless you can find a thinner adapter).


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#3 Scott Mitchell

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Posted 27 May 2019 - 12:17 AM

Thanks James, not sure I'll be able to find another, thinner adapter. As I recall, there were pretty slim pickings when I looked for a Leica/Canon adapter the first time around. 

 

Would adding a filter to the mix tweak the focal plane in the right direction? Maybe this one?



#4 james7ca

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Posted 27 May 2019 - 12:33 AM

A replacement filter would have to have the same optical thickness (or greater) than whatever was removed and I don't know whether a clip-in filter would provide that same thickness (depends both on the physical thickness of the filter and the refractive index of the glass).

 

As I said earlier, normally when a camera is modified whatever is removed is replaced with a filter of the correct optical thickness to correct for the shift in the focal point.



#5 D_talley

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Posted 27 May 2019 - 12:49 AM

If your modified Canon T5i had a Full Spectrum mod, (all filters removed, none added)  then it will not focus with camera lens.  That is a known side affect.  It will only work with telescopes.  If you replace the removed filters with a replacement filter that corrects the light path, then the camera will work with lens.  I did full on my camera since I don't need to use it with camera lens. 



#6 Scott Mitchell

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Posted 27 May 2019 - 01:05 AM

If your modified Canon T5i had a Full Spectrum mod, (all filters removed, none added)  then it will not focus with camera lens.  That is a known side affect.  It will only work with telescopes.  If you replace the removed filters with a replacement filter that corrects the light path, then the camera will work with lens.  I did full on my camera since I don't need to use it with camera lens. 

Hi Dwight, the mod that was performed was just the removal of the lpf2 filter not a full spectrum mod. However, I could see how that might change the focal point somewhat as there wasn't replacement glass put in its place.


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#7 mistateo

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Posted 27 May 2019 - 01:31 AM

Hi Dwight, the mod that was performed was just the removal of the lpf2 filter not a full spectrum mod. However, I could see how that might change the focal point somewhat as there wasn't replacement glass put in its place.

Even if this were the case, you would be talking 1mm of change in the focal plane, max (if lpf2 filter was 3mm thick).  Is the focus CLOSE, just a hair off, or a bit more?  This could help determine if any extra filter may help or not.



#8 Scott Mitchell

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Posted 27 May 2019 - 11:37 AM

Even if this were the case, you would be talking 1mm of change in the focal plane, max (if lpf2 filter was 3mm thick). Is the focus CLOSE, just a hair off, or a bit more? This could help determine if any extra filter may help or not.


I didn't think to take an image of how things looked when the focus mask was on, but I'd say it was about like example second from the left in this image:
4977f4ba4daba629e91804c3d1aa6e99.jpg


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#9 bridgman

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Posted 27 May 2019 - 11:42 AM

Try borrowing a clip-in filter... that is usually enough. Depending on the mod you might want a clip-in UV/IR cut filter anyways.



#10 nofxrx

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Posted 27 May 2019 - 12:00 PM

Like mentioned, removing a filter changes the back focus distance. 

Did you modify the camera yourself or did you have it done professionally? I ask because they should be liable to fix this issue since most of us claim that AF (backfocus) is accurate after the mod. 

If you did it yourself then it's a fairly easy fix. You would simply move each of the three sensor screws 1/4 turn CW and then reassemble and test. Make more adjustments until it is dead on. It's best to test this with a fast prime lens (nifty fifty is great as it's very cheap) and at very close distances.

If you are interested in trying this yourself send me a PM and I can help a bit more in depth.

 

I dont think adding a clip in filter will change the back focus distance enough, but I could be wrong as I've never tested this..

 

Good luck. 



#11 Scott Mitchell

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Posted 27 May 2019 - 02:06 PM

Like mentioned, removing a filter changes the back focus distance.
Did you modify the camera yourself or did you have it done professionally? I ask because they should be liable to fix this issue since most of us claim that AF (backfocus) is accurate after the mod.
If you did it yourself then it's a fairly easy fix. You would simply move each of the three sensor screws 1/4 turn CW and then reassemble and test. Make more adjustments until it is dead on. It's best to test this with a fast prime lens (nifty fifty is great as it's very cheap) and at very close distances.
If you are interested in trying this yourself send me a PM and I can help a bit more in depth.

I dont think adding a clip in filter will change the back focus distance enough, but I could be wrong as I've never tested this..

Good luck.


Thanks for the suggestion Brent. I didn't do it myself. I bought it from a vendor here on CN. I am going to try to do some more testing tomorrow night. I'll try the stock kit lens that comes with the Canon cameras. I'll also try all the lenses with a clip in CLS filter that I own to see what impact that has.

Stay tuned!


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#12 nofxrx

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Posted 27 May 2019 - 06:15 PM

Hmmm. Well if the vendor specified it is an "astro only" camera then that implies AF (backfocus) will not be accurate. But if they implied in any way that AF will be accurate then I would have them fix this issue even if a slight inconvenience to yourself. They may not know that what they're doing is wrong so this would be a good lesson for them.
AF functionality is critical to anyone who will use their modified cameras for daytime or for astro with any camera lenses. Infinity focus is pretty necessary lol
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#13 Scott Mitchell

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Posted 29 May 2019 - 09:28 PM

OK, so I think this is gonna work! I put my CLS filter in tonight to perform an experiment. I just setup on a tripod so not rocket science, but I showed that, with the filter in place, I reach focus just a bit *before* infinity now. I've attached a crop of a 1 second exposure that is near focus. I didn't bother trying to get things perfect because it was pretty janky with it on the tripod instead of my regular mount. Main thing I confirmed is that at infinity it was out of focus, and bringing it back from there improved focus and taken far enough it started getting worse again. 

 

So! All I need to do is, yet again, spend a little more money and get the Astronomik L-2 UV-IR Block Clip-Filter. Anyone happen it have on laying around that they don't need anymore? wink.gif

 

Thanks to all that chimed in!

focus.jpg


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#14 Scott Mitchell

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Posted 29 May 2019 - 09:50 PM

Man, that image does just about zero justice to what I was seeing on screen. Just trust me it looks good!


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#15 bridgman

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Posted 02 June 2019 - 12:16 AM

Man, that image does just about zero justice to what I was seeing on screen. Just trust me it looks good!

Oh good... I looked at the image and wondered if I should be feeling guilty for contributing to that solution :D


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#16 Scott Mitchell

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Posted 14 June 2019 - 08:52 PM

Finally got a clear night to do a quick test of the new filter. It works!! Blazing, full moon and an early start to the day tomorrow so didn't set everything up. I just threw the camera on a regular tripod again and messed around with focus. Got Vega this time so had a bright enough star to show much better spikes. This focus isn't perfect, but I can clearly go past focus now before reaching "infinity" on the lens. So, I'm all set to give it a try next time there are clear, dark skies available! This is a huge relief. 

PREVIEW_20190614-21h42m10s773ms (2).JPG


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