Astro modded focus

[Simon Pepper]

Hi all,

 

I recently had my camera Astro modded IR filter removed and I immediately noticed that when attaching my Samyang 14mm the infinity focus was way off. I’m lucky to have two Canons so on the non modded camera the infinity mark works a treat (I am aware some Samyang lenses have poor quality control but mine works fine on non mod). I kind of want to understand if this is expected behaviour after modification? Would the in focus mark be completely different? I used live view in order to make Jupiter as small as possible and captured the attached. I think this was a 4 or 5 minute single exposure. I guess what I want to ask the community is is this in proper focus and also is the purple glow expected cab this be corrected with white balance any advise would be appreciated. Thanks 

[Stuart1971]

After the Astro mod, if you did not pay the extra and have a clear filter fitted in its place, or have the sensor shimmed, then yes the focus will be off, and if you use autofocus that won’t work either... 👍

[Simon Pepper]

17 minutes ago, Stuart1971 said:

After the Astro mod, if you did not pay the extra and have a clear filter fitted in its place, or have the sensor shimmed, then yes the focus will be off, and if you use autofocus that won’t work either... 👍

Thanks it cost £75 I think so I assume I only paid for the filter to be removed. I was not fussed about autofocus either. Just on the image then any feedback you can give on whether I have perfect focus that will be appreciated. I think it looks ok, but I know some peoples eye is better than mine. Also is this colour expected upon IR removal. The North American nebula again looks as expected I think. Thanks 🙏 

[almcl]

It's hard to be sure about focus as you have star trailing along the RA direction (bottom left towards top right or approximately the line from Sadir to Vega) and the star shapes are a little strange:

 

I've never used a lens with that wide an angle but you might be able to make a suitable Bahtinov mask and use that to check the focus?

The colour (enhanced red from the extra IR) is not unusual - post processing can usually deal with this.

[Stuart1971]

26 minutes ago, Simon Pepper said:

Thanks it cost £75 I think so I assume I only paid for the filter to be removed. I was not fussed about autofocus either. Just on the image then any feedback you can give on whether I have perfect focus that will be appreciated. I think it looks ok, but I know some peoples eye is better than mine. Also is this colour expected upon IR removal. The North American nebula again looks as expected I think. Thanks 🙏 

The colour is normal with Astro mod, it will show more red (Ha) than before, also the odd shaped stars in the corners are also normal with a lens, unless you pay thousands of pounds for it...but for any lens that costs just a few hundred or less, coma and other aberrations will be ever present, as you will never have a flat field, it’s why we use field flattens on scopes.... 👍😀

Edited October 4, 2020 by Stuart1971

[Simon Pepper]

7 minutes ago, almcl said:

It's hard to be sure about focus as you have star trailing along the RA direction (bottom left towards top right or approximately the line from Sadir to Vega) and the star shapes are a little strange:

 

I've never used a lens with that wide an angle but you might be able to make a suitable Bahtinov mask and use that to check the focus?

The colour (enhanced red from the extra IR) is not unusual - post processing can usually deal with this.

Thanks for feedback I will drop the exposure time to see if I can correct for the trailing. Bahtinov is not possible as I have the annoying petal hood thing on the Samyang. Also will play with WB and temp in LR! Thanks all!

[michael8554]

After the #LPF-2 filter removal with no correction to Autofocus, the only way to get correct focus is with LiveView - the viewfinder image will be wrong too.

Michael