Back Focus Frustration

I have been imaging from the back of the image train using the Starizona SCT and the Askar OAG. The Celestron reducer may not be the best option for the C8. I have the 533 MC Pro and 2600 MC Pro. I also use the Hyperstar for Nebula season which makes the focal length 390mm and f2 aperture.

My suggestion would be to contact Steve or Scott at Starizona and they can help you make sure you have everything you need to image from the back of the image train and also look into the Hyperstar if that is of interest to you.

Olaf Fritsche:
I sometimes have similar problems with the ZWO EAF on a Celestron EdgeHD 9.25. The focus point with/without reducer is at completely opposite ends. Occasionally it happens that I can't focus properly because the EAF has reached its limit, although the mirror could go further. 

The following solution has helped me: 
1. go as far as you can with the EAF. 
2. tap on the symbol for the EAF in the ASIair app. 
3. in the EAF settings there is an information for the current position (should be “0” or “60000”). 
4. you can overwrite this position. Enter a value there that offers enough distance to focus. (Simply try it out, starting with “10000” or “50000”).
5. exit the EAF settings and try to focus again. 

I hope this helps!

Olaf Fritsche:
I sometimes have similar problems with the ZWO EAF on a Celestron EdgeHD 9.25. The focus point with/without reducer is at completely opposite ends. Occasionally it happens that I can't focus properly because the EAF has reached its limit, although the mirror could go further. 

The following solution has helped me: 
1. go as far as you can with the EAF. 
2. tap on the symbol for the EAF in the ASIair app. 
3. in the EAF settings there is an information for the current position (should be “0” or “60000”). 
4. you can overwrite this position. Enter a value there that offers enough distance to focus. (Simply try it out, starting with “10000” or “50000”).
5. exit the EAF settings and try to focus again. 

I hope this helps!

Great information, thank you. Do you know if there is any risk of damage to the EAF or the scope if the EAF is trying to actuate even if the mirror has reached its travel limit?

I am trying to stitch over my ASI533MC Pro with ASI Filter Drawer and the required 16.5mm spacer for that party of the image train to reach a back focus of 55mm. I know that is solid because I have used it for years on my refractors. I am finally trying to get my C8 with an EAF set up for some DSO targets now that I have 2 AM5 mounts. I have the Celestron.63 focal reducer installed correctly then add the Celestron T Adaptor (50mm) make the threaded connection and measure with calipers and a story stick and bingo 105mm. 

No matter what I do I can't get distant focus.  I use a benchmark house that is about a mile away and I just can't bring it into focus before the EAF zeros out. I can focus very well on tree limbs that are 100 yards or so but other than that I am stuck. I got so frustrated I tore the entire set up back down and put it back on a 72mm refractor (minus the T Adaptor) and it focused perfectly.  Now my C8 sits on my desk with a visual back in it waiting for Planets. I need to get it in the game for DSOs. Any suggestions? I suspect that somehow the EAF isn't allowing full travel of the mirror but have no idea how to proceed.

As a secondary question, I was planning to look into a Starizona reducer once I was up and running. Are they worth the investment? 

Thanks in advance.

John Hayes:

I am trying to stitch over my ASI533MC Pro with ASI Filter Drawer and the required 16.5mm spacer for that party of the image train to reach a back focus of 55mm. I know that is solid because I have used it for years on my refractors. I am finally trying to get my C8 with an EAF set up for some DSO targets now that I have 2 AM5 mounts. I have the Celestron.63 focal reducer installed correctly then add the Celestron T Adaptor (50mm) make the threaded connection and measure with calipers and a story stick and bingo 105mm. 

No matter what I do I can't get distant focus.  I use a benchmark house that is about a mile away and I just can't bring it into focus before the EAF zeros out. I can focus very well on tree limbs that are 100 yards or so but other than that I am stuck. I got so frustrated I tore the entire set up back down and put it back on a 72mm refractor (minus the T Adaptor) and it focused perfectly.  Now my C8 sits on my desk with a visual back in it waiting for Planets. I need to get it in the game for DSOs. Any suggestions? I suspect that somehow the EAF isn't allowing full travel of the mirror but have no idea how to proceed.

As a secondary question, I was planning to look into a Starizona reducer once I was up and running. Are they worth the investment? 

Thanks in advance.

You have to design the system for the correct BWD with the reducer, which won’t be 105 mm.  As I recall, the C8 native BWD is 105 mm.  When you add the reducer, that distance will be smaller.  So, you need to know what the correct BWD is WITH the reducer.

John