Hello
I am the happy owner of an Askar 71F that I bought to send to Starfront observatories together with my old AM5, a ZWO off axis guider, filter wheel and 2600 MM Pro. I also ordered a ZWO CAA but I don't know when I will receive it due to the massive delays they seem to have with this equipment. So I will probably end up sending my rig in its current configuration and send the CAA later to Sarfront as soon as I receive it. My question is as follows: my current setup is around 55 mm back focus but when I will add the CAA, it will bring it to over 70 mm. I have enough travel space on the focuser to reach focus, but could it degrade the quality of the images ? I know it is a Petzval design, but the reviews I saw were all performed at around 55 mm. Did any of you ever tested it well beyond the 55 mm classical sweet spot ?
Best
Damien
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If the focus point is at 55mm then that will not change will it, all that will happen is your focus tube will not come out as far, the space between the internal flattener and the sensor will be exactly the same as it was before at focus…
the sweet spot as you call it. Is really just the focus point, the point at which the scopes reaches focus, that will never change no matter what you add
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The problem will be if you have enough inward focus travel, so if you are adding a device that is 20mm thick, then can you afford to move the focus tube in 20mm or is it not out that far to start with…??
Just deduct what you are adding off the focus tube distance that it protrudes, and you will know what you can fit in
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The tube is out by 37 mm so if I add 16.5 mm to the light path, there will be around 20 mm left, so this will not be a problem.
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Damien Galanaud:
The tube is out by 37 mm so if I add 16.5 mm to the light path, there will be around 20 mm left, so this will not be a problem. There you go, problem solved, the focus point will not change it will always be at 55mm if that’s where it focuses, the more kit you add the less the tube will come out…
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