Astro Modded Canon DSLR focusing trouble

[LoveFromGallifrey]

Hi! I'm looking for advice with my Canon 700D. It's H-alpha astro modded. I was specifically told by the last owner that it is not fill spectrum modded, and he showed me daytime photos with a custom white balance. I've only ever used it with a telescope, but now I'm looking to photograph landscapes during the day, as well the milky way at night etc with a regular lens. I've set my custom white balance to one the previous owner already made for daytime photography. I've also brought a 2nd hand Tokina 11-16mm lens. Its the 2nd version with autofocus. 

 

Now, I prefer manual focus for astro. But for quick shots while travelling on holiday, I love autofocus. But the autofocus on this lens is not working. I brought it from a reputable 2nd hand dealer, in "like new" condition. Manually, the lens seems to focus well. But auto? It's just constantly adjusting, never settles at all, and I have to switch to viewfinder before I can actually get the camera to take a photo because in love view the camera won't focus enough for an image to be captured. 

Manual focusing seems to work fine, although I haven't tried focusing to infinity yet. It's just too wide a lens for me to be constantly faffing around with focus for daytime photography  

 

Before I return the lens and look for something else, does anyone know if it's the H-alpha mod or something that's stopping the autofocus from working? I feel really silly for not knowing this

 

Thanks!

[AustenM]

The Canon 700D has two mechanisms for autofocus. One uses the imaging sensor (live view) and the other uses separate point sensors in the prism (normal). I presume you are using the viewfinder mode for your daytime autofocus experiments. I'd suggest trying the live view mode - button to the right of the viewfinder will activate the mirror and the image will appear on the screen - focus as usual by half-pressing the shutter. In theory this mode is more likely to be affected by the modifications, but it's worth a try.

[LoveFromGallifrey]

Hi! Thanks for the quick reply. I normally use live view for everything since its what I use for astro haha. 

In live view, the lens will not focus at all. The autofocus is constantly adjusting, never settling, and when I attempt to just take a single image, it won't even focus enough for that. I press the shutter release and it just continues trying to focus. 

In viewfinder mode, it still doesn't autofocus but it will activate the shutter release. 

[Elp]

It depends highly on how the mod was done. Some people just remove the glass that has to do with IR blocking and leave it at that, others do it properly and add in clear glass or shim the stack forward to compensate for the glass which was removed and then recalibrate the camera to auto focus. My modded 600D didn't have this issue, I could use auto focus lenses fine in normal use. Something you could try, add a UV/IR cut filter on the front of the lens, this has the effect of pushing the focus plane back a bit and kind of compensates for the "missing glass", my Samyang lenses don't focus to infinity but when I do this they do even if they are manual lenses (can't do the infinity adjustment on my lenses which is sometimes an option with manual lenses).

See here:

https://www.cloudynights.com/topic/837845-auto-focus-and-manual-focus-with-modified-canon-t5i/

[LoveFromGallifrey]

If there is no replacement glass/shimmed stack, that's a full spectrum mod, right? 

I can't find it now, but I'm sure there was a piece of paper with the camera from the guy who did the mod (a very well respected guy, has been recommended for modded cameras many times on here) saying its not full spectrum. Hence why I thought I'd be fine with the autofocus. I'll have to take it out in a bit and see if I can manually focus to infinity, since that seems to be another issue. 

This is the only lens I've tried, it'd be frustrating if I can't use it without a telescope since I did buy it for both day and night photography. 

[michael8554]

"If there is no replacement glass/shimmed stack, that's a full spectrum mod, right? "

No, that does not make it a Full Spectrum mod, those are just focus-compensation methods.

You should read up on astro mods and what is removed and added in the various types.

For an Ha only mod the #LPF-2 filter is removed, leaving the #LPF-1 to filter UV/IR.

The filter removal leaves the Autofocusing incorrect and the lens unable to infinity focus.

To correct this, a replacement glass, or adjustment of the spring-loaded sensor (the models after the 450D don't have shims), corrects the autofocus, but leaves the eyelevel finder wrong, as that light path hasn't been corrected.

Focus with Liveview will be correct.

Michael

[LoveFromGallifrey]

6 hours ago, michael8554 said:

"If there is no replacement glass/shimmed stack, that's a full spectrum mod, right? "

No, that does not make it a Full Spectrum mod, those are just focus-compensation methods.

You should read up on astro mods and what is removed and added in the various types.

For an Ha only mod the #LPF-2 filter is removed, leaving the #LPF-1 to filter UV/IR.

The filter removal leaves the Autofocusing incorrect and the lens unable to infinity focus.

To correct this, a replacement glass, or adjustment of the spring-loaded sensor (the models after the 450D don't have shims), corrects the autofocus, but leaves the eyelevel finder wrong, as that light path hasn't been corrected.

Focus with Liveview will be correct.

Michael

OK! Thanks. Sorry for the misunderstanding. I'm not very technical, brought the camera, it works for what I wanted it do. Never bothered researching more, though I probably should have.

I checked earlier and I can manually focus to infinity just fine in live view, and manual focus for everything else is spot on, but autofocus just does not work. In live view it won't even let me take a photo; in viewfinder it will, but out of focus. 

I'll return the lens anyways, I have a Nikon already with a similar lens. Just fancied seeing what difference the astro mod could make on milky way shots mainly. 

Edited February 17 by LoveFromGallifrey

[Elp]

I think in terms of milky way, they'd be little difference from an unmodded one as it's broadband signal. The difference will be the pick up of red hydrogen alpha emission of all the emission nebulae within.