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Esprit 100 & Starizona 0.65 Reducer

Sky-Watcher Esprit 100ED Reducer Coma
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Christian Schulbert avatar
Christian Schulbert avatar
Hi,
I got a Starizona 0.65 Reducer for my 100 ED. The nominal backfocus distance should be 58 mm. I tested a lot, but I got always elongated stars in the corners, which indicates, the camera (APS-C-IMX571) is too close. I am now at 59.5 mm and still get elongated stars. Has anyone found a working distance with this combo?

Clear skies,
Chris
Andreas Kenda avatar
Andreas Kenda avatar
Hi Chris,

I am using the same combo and started by accident at 60mm backfocus. I did not like that BFL as I got tangentially deformed stars. I am now at 58.5-59mm which is the nominal 58mm + 0.7mm to account for the 2mm thick filter. I think it is working better in terms of getting small stars round. However, bright stars produce violent bursts: https://www.astrobin.com/full/fq0wcd/0/
Do you see the same effect?

CS, Andy
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Jan Erik Vallestad avatar
Jan Erik Vallestad avatar
Following this as I have been keen to add a smaller FL option, but a working reducer could also be an option. I've always been a bit skeptical towards the Starizona though as I haven't really seen any compelling results or a general consensus considering backfocus.
Don avatar
Don avatar
Following this as I have been keen to add a smaller FL option, but a working reducer could also be an option. I've always been a bit skeptical I use towards the Starizona though as I haven't really seen any compelling results or a general consensus considering backfocus.

I use the 3” Explore Scientific .7x. It works really well on multiple scopes
Christian Schulbert avatar
Christian Schulbert avatar
Andreas Kenda:
Hi Chris,

I am using the same combo and started by accident at 60mm backfocus. I did not like that BFL as I got tangentially deformed stars. I am now at 58.5-59mm which is the nominal 58mm + 0.7mm to account for the 2mm thick filter. I think it is working better in terms of getting small stars round. However, bright stars produce violent bursts: https://www.astrobin.com/full/fq0wcd/0/
Do you see the same effect?

CS, Andy

Hi Andy,

due to the bad weather, I could not make any progress on my experiments with the backfocus. But I think, 58+0.7 could be really the sweet spot. I can also confirm those burst on bright stars like here: https://www.astrobin.com/full/8mya6n/0/

I wouldn't bother me a lot, but BlurXterminator doesn't seem to handle those bursts nicely. Especially, if those bright stars a in the corners. BlurX corrects for the shape of the star, but not for the burst halo. That is surely because, it wasn't trained with images from the Apex-L reducer.

Clear skies,
Chris
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