0.7x reducer for the Fra500

In my opinion, it takes far to long to adjust spacing on reducers to get correct backfocus.   Rarely is the stated backfocus correct (enough).  In this case, I would likely buy a Redcat or smaller Askar to increase FOV, than a reducer, just my general opinion.   Cameras are so refined now, that a great deal of cropping can be done while keeping the pixels hidden on most displays if the FOV is too large.    Just my experience.
Hope this helps,
Dave

David Payne:
In my opinion, it takes far to long to adjust spacing on reducers to get correct backfocus.   Rarely is the stated backfocus correct (enough).  In this case, I would likely buy a Redcat or smaller Askar to increase FOV, than a reducer, just my general opinion.   Cameras are so refined now, that a great deal of cropping can be done while keeping the pixels hidden on most displays if the FOV is too large.    Just my experience.
Hope this helps,
Dave

It’s super easy to get the 55mm back focus from the reducer. Just use the ccd spacers supplied by ZWO. Happy to assist, Dave. My only issue with the reducer paired with Asi2600 is images are slightly undersampled but that can be corrected in  post-processing.

Andy:

David Payne:
In my opinion, it takes far to long to adjust spacing on reducers to get correct backfocus.   Rarely is the stated backfocus correct (enough).  In this case, I would likely buy a Redcat or smaller Askar to increase FOV, than a reducer, just my general opinion.   Cameras are so refined now, that a great deal of cropping can be done while keeping the pixels hidden on most displays if the FOV is too large.    Just my experience.
Hope this helps,
Dave

It’s super easy to get the 55mm back focus from the reducer. Just use the ccd spacers supplied by ZWO. Happy to assist, Dave. My only issue with the reducer paired with Asi2600 is images are slightly undersampled but that can be corrected in  post-processing.

That's great for you, and you will likely get good results with an APS-C camera.   However, in my experience the backfocus of reducers is rarely within 1mm of the advertised value and this will be much more apparent with a full frame sensor.  So I think it depends on your situation.

If you are travelling, and you want the minimize the equipment you travel with, then a reducer may be a good solution so that you can change your field of view with one telescope.   If you are a back-yard imager and may want to switch between APSC and full frame, keep the glass down, don't want to also fiddle with spacers w/wout filter wheels, off-axis guiders, and associated spacers needed to get exact back-focus then it is just a headache to me.    If you plan to use mono/OSC and APS-C/full frame and OAG/guidescope and there are a lot of combinations of spacers to keep track of.

I like Petzval telescopes because I don't have to worry too much about backfocus when changing my imaging train.  Putting a reducer on it might be a convenience when travelling, but it kind of defeats the purpose of a Petzval.   You might as well use an APO triplet.

Having said that, one you do get the backfocus dialed in (as I eventually did for my wide-field corrector on my Televue), they can work extremely well.   I didn't mean to offend.   I have two Askars (the 500 as you do, and the 151phq) and I love them both.  I just don't have the reducers for them.   Why do I have the Askar 500 as well as the Televue despite similar focal lenghts? - simply because the Televue is a big heavy for my HEM27 mount.   If I want a larger FOV, I turn to the RedCat.

Bottom line is that with your 2600MC, the reducer will likely work well for you and if you try a full-frame may you will be lucky and the stars will be perfect corner to corner at the stated 55mm backfocus.

Hi Andy,
I do but I can't say that I am totally satisfied with the results. I imagined the rig would be a widefield comet or dust imaging rig using an OSC camera when I purchased it. The reducer definitely introduces some CA that is not there at my scope's native configuration. Also, I do not use the conical adapter with the reducer as pictured above. Mine had a supplied adapter specifically for connecting the reducer to the back of the scope with none of the conical adapter parts used. I still needed an additional 1.2mm spacer(s) for the best stars using a full frame sensor. They are sill not perfect but that 56.2mm distance gave the best result for me. The CA issue is there even using smaller sensors so I know it is being introduced by the reducer in my case. This is actually the first scope I have owned that would be considered consumer grade, mass produced, or whatever you like to call it. I think it does a wonderful job for the cost especially in it's F5.6 configuration. The vignetting with full frame is minimal using mine at F3.9. Results with an APS-C mono sensor at F3.9 are very good although I don't have any completed images in that configuration to share. I have only premium refractors to compare my use to so I may be a bit too picky on the stars issue. My last image (NGC7000) with it at F3.9 using the full frame 410C sensor is on my page if you would like to see the results. I can't complain too loudly because it did earn a Top Pick nomination that really surprised me. 
CS,
Jeff

Jeff Reitzel:
Hi Andy,
I do but I can't say that I am totally satisfied with the results. I imagined the rig would be a widefield comet or dust imaging rig using an OSC camera when I purchased it. The reducer definitely introduces some CA that is not there at my scope's native configuration. Also, I do not use the conical adapter with the reducer as pictured above. Mine had a supplied adapter specifically for connecting the reducer to the back of the scope with none of the conical adapter parts used. I still needed an additional 1.2mm spacer(s) for the best stars using a full frame sensor. They are sill not perfect but that 56.2mm distance gave the best result for me. The CA issue is there even using smaller sensors so I know it is being introduced by the reducer in my case. This is actually the first scope I have owned that would be considered consumer grade, mass produced, or whatever you like to call it. I think it does a wonderful job for the cost especially in it's F5.6 configuration. The vignetting with full frame is minimal using mine at F3.9. Results with an APS-C mono sensor at F3.9 are very good although I don't have any completed images in that configuration to share. I have only premium refractors to compare my use to so I may be a bit too picky on the stars issue. My last image (NGC7000) with it at F3.9 using the full frame 410C sensor is on my page if you would like to see the results. I can't complain too loudly because it did earn a Top Pick nomination that really surprised me. 
CS,
Jeff

That's a great image! What is your backyard Bortle scale?

Jeff Reitzel:
Hi Andy,
I do but I can't say that I am totally satisfied with the results. I imagined the rig would be a widefield comet or dust imaging rig using an OSC camera when I purchased it. The reducer definitely introduces some CA that is not there at my scope's native configuration. Also, I do not use the conical adapter with the reducer as pictured above. Mine had a supplied adapter specifically for connecting the reducer to the back of the scope with none of the conical adapter parts used. I still needed an additional 1.2mm spacer(s) for the best stars using a full frame sensor. They are sill not perfect but that 56.2mm distance gave the best result for me. The CA issue is there even using smaller sensors so I know it is being introduced by the reducer in my case. This is actually the first scope I have owned that would be considered consumer grade, mass produced, or whatever you like to call it. I think it does a wonderful job for the cost especially in it's F5.6 configuration. The vignetting with full frame is minimal using mine at F3.9. Results with an APS-C mono sensor at F3.9 are very good although I don't have any completed images in that configuration to share. I have only premium refractors to compare my use to so I may be a bit too picky on the stars issue. My last image (NGC7000) with it at F3.9 using the full frame 410C sensor is on my page if you would like to see the results. I can't complain too loudly because it did earn a Top Pick nomination that really surprised me. 
CS,
Jeff

Great insights, Jeff. I just integrate the reducer with my 2600mm for the first time. My target to analyze is Sh2-157/lobster claw nebula. I’m at 56mm backfocus given that I have 2” filters, I needed to add 1mm to the standard 55mm backfocus distance. I’ve already collected enough data of the same target at the native 500mm/ f5.6. I’ll process that data soon to compare with th results from the reducer. Like you, I find the native focal length of the Fra500 to be the sweet spot on this scope. I feel reducer negatively impacts the sharpness of the scope and while integration time is cut in half by using the reducer, It’s not that big of a difference to me as I still expose at 300s. And image throughout the night while I’m asleep. Stay tuned.