Hi everyone,
after months of study and evaluation I finally took courage and tackled a complete upgrade of my equipment, following this forum's advices. I kept my trusty modified Canon 90D and first of all I changed my mount, switching to the EQ6-R Pro (actually a notable leap forward compared to the GTI).
I then finally decided to move on a refractor, purchasing a TS-Optics AP 115/800 ED Photoline. Using a 0.79x flattener and after an update of the guidescope (now a 240mm) everything is fine and works perfectly: focusing, guiding, field, no aberrations. Great!
On the other hand, if I use the 115/800 without the 0.79x flattener I notice a lot of aberration moving away from the center of the image, with the stars progressively getting longer in a noticeable way (never seen such an effect with my old Sigma 600mm, not even multiplied 2x). Okay, so far not bad: flattener, a few micro adjustments on backfocus with a couple of very thin rings and everything is ok.
Now I'm carrying out some tests with a Barlow 3x suitable for photographic use: without a flattener (in my head it makes no sense to put a reducer in front of a Barlow, or not?) the result is the one here attached.
To center the focus perfectly I used an adequate extension (8cm!), but the farer I'm from the image center, the longer the stars get and I have a lot of aberration.
Is this a backfocus issue and/or do I need to use a flattener (1.0x) with the Barlow? And if it's a backfocus problem, considering that I use a Canon 90D reflex, how do I calculate the correct one?
Am I completely lost and as usual doing something gross wrong?
Thank you!
after months of study and evaluation I finally took courage and tackled a complete upgrade of my equipment, following this forum's advices. I kept my trusty modified Canon 90D and first of all I changed my mount, switching to the EQ6-R Pro (actually a notable leap forward compared to the GTI).
I then finally decided to move on a refractor, purchasing a TS-Optics AP 115/800 ED Photoline. Using a 0.79x flattener and after an update of the guidescope (now a 240mm) everything is fine and works perfectly: focusing, guiding, field, no aberrations. Great!
On the other hand, if I use the 115/800 without the 0.79x flattener I notice a lot of aberration moving away from the center of the image, with the stars progressively getting longer in a noticeable way (never seen such an effect with my old Sigma 600mm, not even multiplied 2x). Okay, so far not bad: flattener, a few micro adjustments on backfocus with a couple of very thin rings and everything is ok.
Now I'm carrying out some tests with a Barlow 3x suitable for photographic use: without a flattener (in my head it makes no sense to put a reducer in front of a Barlow, or not?) the result is the one here attached.
To center the focus perfectly I used an adequate extension (8cm!), but the farer I'm from the image center, the longer the stars get and I have a lot of aberration.
Is this a backfocus issue and/or do I need to use a flattener (1.0x) with the Barlow? And if it's a backfocus problem, considering that I use a Canon 90D reflex, how do I calculate the correct one?
Am I completely lost and as usual doing something gross wrong?
Thank you!
