Filter removal and infinity focus

[Starflyer]

Hi knowledgeable folks,

I'm thinking of a full spectrum mod, both filters removed, on a canon 1100D.  I understand I won't achieve infinity focus with camera lenses, this is the intended use btw, if I added an IDAS clip filter would it then focus with camera lenses?  And if so is this filter UV/IR blocking?

I'll need a LP filter and I'm trying to get the mod done and retain infinity focus.

 

Cheers

Ian

[Adam J]

no it will not be sufficiently thick to allow you to focus. You need a astronomic clear glass filter to be placed within the camera.

[Starflyer]

1 hour ago, Adam J said:

no it will not be sufficiently thick to allow you to focus. You need a astronomic clear glass filter to be placed within the camera.

Thanks for the reply.

 

Cheers

Ian

[Adam J]

1 hour ago, Starflyer said:

Thanks for the reply.

 

Cheers

Ian

No problem,

Its this one BTW.

https://www.astronomik.com/en/photographic-filters/mc-glass-for-dslr-astromodification/astronomik-mc-klarglas-for-canon-eos-1100d-1200d.html

[Starflyer]

Thanks Adam. Is there an IR/UV blocking version? If I go with a replacement filter I may leave the IDAS filter until a later date.

[Adam J]

5 minutes ago, Starflyer said:

Thanks Adam. Is there an IR/UV blocking version? If I go with a replacement filter I may leave the IDAS filter until a later date.

Baader do a replacement filter along the same lines with UV/IR blocking but I would not recommend it as it results in refelctions.

Adam

[michael8554]

3 hours ago, Starflyer said:

Is there an IR/UV blocking version?

If you need this filter, consider leaving the LPF#1 filter in place which blocks IR, rather than the whole Full Spectrum Mod ?

And you could retain Infinity Focus with correct shimming of the sensor, Full Spectrum may be too much to correct unless clear glass is added.

Michael

 

[Merlin66]

The attached images show the affect of the FULL mod on the Canon 1000D

The first image shows the spectrum recorded with the FULL mod

The second the spectrum through the front (#1 filter on the graph) anti-alias/ dust shake mirror. You'll see it's an effective UV/IR filter.

The #1 filter assembly as removed and the transmission graphs for both filters.

 

Edited July 1, 2020 by Merlin66

[Adam J]

1 hour ago, michael8554 said:

If you need this filter, consider leaving the LPF#1 filter in place which blocks IR, rather than the whole Full Spectrum Mod ?

And you could retain Infinity Focus with correct shimming of the sensor, Full Spectrum may be too much to correct unless clear glass is added.

Michael

 

never like shimming as a solution as I alwasy worried about interducing tilt so if keeping LPF1 I would still go with the clear glass filter.

[Starflyer]

Just come back to a load of replies, thanks all!

Lots to consider 😀

I may well get Juan to do the full spectrum mod for me, as part of this he adjusts the sensor to retain infinity focus. This way I can use it with the IDAS filter from home and 'naked' from dark sites. The clear glass filter isn't much cheaper than getting Juan to remove both filters and adjust the sensor.

[michael8554]

18 hours ago, Adam J said:

never like shimming as a solution as I alwasy worried about interducing tilt

If you reduced all three shims by the same amount how would you get tilt?

Michael

[Adam J]

1 hour ago, michael8554 said:

If you reduced all three shims by the same amount how would you get tilt?

Michael

Well if your reducing them you are going in the wrong direction. But that aside it's very critical. 

[Starflyer]

32 minutes ago, Adam J said:

Well if your reducing them you are going in the wrong direction. But that aside it's very critical. 

Agreed and something I wouldn't want to attempt. I don't have the patience to tweak and take test images over and over.

[michael8554]

2 hours ago, Adam J said:

Well if your reducing them you are going in the wrong direction. But that aside it's very critical. 

Michael

I'm afraid you're wrong.

The filters in front of the sensor move the focal point further away from the subject, towards the back of the camera, by refraction.

To compensate for removal of either or both filters the sensor has to be moved towards the front of the camera,  by putting thinner shims in.

I've modified 5 cameras over the years, all preserving Autofocus.

Don't take my word for it, read Gary Honis's procedure for replacing both filters with thinner glass, which is under compensating, or similar to removing only one filter:

• Original Canon LPF#1 and LPF#2 combined thickness: 1.40mm
• Replacement Astronomik MC clear glass thickness: 0.97mm
• Difference is .43mm
• The out of focus distance = (n-1)/n X Difference where n is the refractive index (1.517 for glass).
• The out of focus distance = (1.517-1)/1.517 X .43mm = .147mm
• So the out of focus distance of .147mm is the distance the CMOS imaging chip needs to be moved toward the lens.

This can be done by reducing the .35mm shims by .147mm.

Michael

[R26 oldtimer]

I have full-spectrum modified a Canon 500d and a 600d. I have found that I needed to screw the three torx screws all the way in, in order to achieve infinity focus with the kit lens at 18mm.

Also, even with the same zoom lens, the focusing point is different at each focal length, and this of course is the case with different lenses. If you wish to maintain autofocus, this can be adjusted with a particular lens and only at a certain focal length. Best practice with a full spectrum mod is to manually focus using liveview.

[michael8554]

1 hour ago, R26 oldtimer said:

I have full-spectrum modified a Canon 500d and a 600d. I have found that I needed to screw the three torx screws all the way in,

Same here, half a turn.

Michael